Biol. Rev. (2016), pp. 000–000. 1
doi: 10.1111/brv.12295
A review of the ecosystem functions in oil
palm plantations, using forests as a reference
system
Claudia Dislich1,2,†, Alexander C. Keyel1, Jan Salecker1, Yael Kisel1, Katrin M. Meyer1,
Mark Auliya3, Andrew D. Barnes4, Marife D. Corre5, Kevin Darras6, Heiko Faust7,
Bastian Hess1, Stephan Klasen8, Alexander Knohl9, Holger Kreft10, Ana Meijide9,
Fuad Nurdiansyah1,6, Fenna Otten7, Guy Pe’er3,11, Stefanie Steinebach12,
Suria Tarigan13, Merja H. To¨lle9,14, Teja Tscharntke6 and Kerstin Wiegand1,∗
1Department of Ecosystem Modelling, Faculty of Forest Sciences and Forest Ecology, University of Go¨ttingen, 37077 Go¨ttingen, Germany
2Department of Ecological Modelling, Helmholtz Centre for Environmental Research - UFZ, 04318 Leipzig, Germany
3Department of Conservation Biology, Helmholtz Centre for Environmental Research - UFZ, 04318 Leipzig, Germany
4Department of Systemic Conservation Biology, Faculty of Biology and Psychology, University of Go¨ttingen, 37073 Go¨ttingen, Germany
5Department of Soil Science of Tropical and Subtropical Ecosystems, Faculty of Forest Sciences and Forest Ecology, University of Go¨ttingen,
37077 Go¨ttingen, Germany
6Department of Crop Sciences, Faculty of Agricultural Sciences, University of Go¨ttingen, 37077 Go¨ttingen, Germany
7Department of Human Geography, Faculty of Geoscience and Geography, University of Go¨ttingen, 37077 Go¨ttingen, Germany
8Department of Development Economics, Faculty of Economic Science, University of Go¨ttingen, 37073 Go¨ttingen, Germany
9Department of Bioclimatology, Faculty of Forest Sciences and Forest Ecology, University of Go¨ttingen, 37077 Go¨ttingen, Germany
10Department of Biodiversity, Macroecology & Conservation Biogeography, Faculty of Forest Sciences and Forest Ecology, University of Go¨ttingen,
37077 Go¨ttingen, Germany
11German Centre for Integrative Biodiversity Research (iDiv), 04103 Leipzig, Germany
12Institute of Social and Cultural Anthropology, Faculty of Social Sciences, University of Go¨ttingen, 37073 Go¨ttingen, Germany
13Department of Soil Sciences and Land Resources Management, Bogor Agriculture University, Bogor, Indonesia
14Institute for Geography, University of Giessen, 35390 Giessen, Germany
ABSTRACT
Oil palm plantations have expanded rapidly in recent decades. This large-scale land-use change has had great ecological,
economic, and social impacts on both the areas converted to oil palm and their surroundings. However, research on
the impacts of oil palm cultivation is scattered and patchy, and no clear overview exists. We address this gap through
a systematic and comprehensive literature review of all ecosystem functions in oil palm plantations, including several
(genetic, medicinal and ornamental resources, information functions) not included in previous systematic reviews. We
compare ecosystem functions in oil palm plantations to those in forests, as the conversion of forest to oil palm is
prevalent in the tropics. We find that oil palm plantations generally have reduced ecosystem functioning compared
to forests: 11 out of 14 ecosystem functions show a net decrease in level of function. Some functions show decreases
with potentially irreversible global impacts (e.g. reductions in gas and climate regulation, habitat and nursery functions,
genetic resources, medicinal resources, and information functions). The most serious impacts occur when forest is
cleared to establish new plantations, and immediately afterwards, especially on peat soils. To variable degrees, specific
plantation management measures can prevent or reduce losses of some ecosystem functions (e.g. avoid illegal land
clearing via fire, avoid draining of peat, use of integrated pest management, use of cover crops, mulch, and compost) and
we highlight synergistic mitigation measures that can improve multiple ecosystem functions simultaneously. The only
* Address for correspondence (Tel: +49 (0)551 39-10121; E-mail: mail@Kerstin-Wiegand.de)
† Present address: Helmholtz Interdisciplinary Graduate School of Environmental Research, Helmholtz Centre for Environmental
Research - UFZ, 04318 Leipzig, Germany.
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium,
provided the original work is properly cited and is not used for commercial purposes.
2 C. Dislich and others
ecosystem function which increases in oil palm plantations is, unsurprisingly, the production of marketable goods.
Our review highlights numerous research gaps. In particular, there are significant gaps with respect to socio-cultural
information functions. Further, there is a need for more empirical data on the importance of spatial and temporal scales,
such as differences among plantations in different environments, of different sizes, and of different ages, as our review
has identified examples where ecosystem functions vary spatially and temporally. Finally, more research is needed
on developing management practices that can offset the losses of ecosystem functions. Our findings should stimulate
research to address the identified gaps, and provide a foundation for more systematic research and discussion on ways
to minimize the negative impacts and maximize the positive impacts of oil palm cultivation.
Key words: ecosystem functions, ecosystem services, biodiversity, oil palm, land-use change, Elaeis guineensis.
CONTENTS
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
(1) Scope and overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
(2) Oil palm cultivation and oil production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
(3) Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
II. Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
III. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
(1) Gas & climate regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
(a) Greenhouse gas fluxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
(b) Air quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
(c) Local climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
(d ) Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
(e) Research gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
(2) Water regulation & supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
(a) Water storage and supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
(b) Water quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
(c) Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
(d ) Research gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
(3) Moderation of extreme events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
(a) Landslides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
(b) Wildfires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
(c) Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
(d ) Research gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
(4) Erosion prevention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
(a) Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
(b) Research gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
(5) Soil fertility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
(a) Nutrient losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
(b) Nutrient inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
(c) Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
(d ) Research gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
(6) Waste treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
(a) Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
(b) Research gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
(7) Pollination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
(a) Native pollinators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
(b) Pollination by Elaeidobius weevils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
(c) Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
(d ) Research gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
(8) Biological control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
(a) Biological control within oil palm plantations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
(b) Biological control in surrounding areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
(c) Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
(d ) Research gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
(9) Refugium & nursery functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
(a) Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
Ecosystem functions of oil palm versus forest 3
(b) Research gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
(10) Food & raw materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
(a) Foods and materials from oil palm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
(b) Loss of forest foods and materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
(c) Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
(d ) Research gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
(11) Genetic resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
(a) Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
(b) Research gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
(12) Medicinal resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
(a) Medicinal benefits of oil palm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
(b) Mitigation and research gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
(13) Ornamental resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
(a) Mitigation and research gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
(14) Information functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
(a) Information functions associated with oil palm and palm oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
(b) Information functions lost with forest conversion to oil palm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
(c) Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
(d ) Research gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
IV. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
(1) Impacts of oil palm plantations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
(2) Options for mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
(3) Major research gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
(4) Considerations of scale: spatial, temporal, and management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
(5) Policy considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
V. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
VI. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
VII. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
VIII. Supporting Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
I. INTRODUCTION
(1) Scope and overview
Over the past few decades, oil palm plantations have
expanded dramatically, especially in Southeast Asia (e.g.
Koh, 2011; see online Appendix S1). As the production
of palm oil is highly cost- and area-effective compared to
other oil crops (e.g. Zimmer, 2010), this trend is projected
to continue in Southeast Asia and other tropical regions
(Fitzherbert et al., 2008). During the past few years, the
scientific community has given increasing attention to oil
palm expansion and its consequences for ecosystems and
people. However, research on the environmental impacts of
oil palm cultivation has been fragmented by discipline. While
natural scientists have mostly focused on the contributions of
oil palm expansion to the loss of rainforest, biodiversity, and
soil carbon as well as greenhouse gas emissions (e.g. Fargione
et al., 2008; Barnes et al., 2014; van Straaten et al., 2015),
economists have discussed costs and benefits associated with
development (Corley, 2009). Social scientists have drawn
attention to large-scale oil palm cultivation in relation to
land grabbing (Hall, 2011; Borras & Franco, 2012) and
land-use conflicts between local communities and oil palm
companies (Afiff & Lowe, 2007; Potter, 2009; Colchester
et al., 2011; Steinebach, 2013). The impact of agro-industrial
oil palm cultivation on local social structures, e.g. plantation
workers who interact or conflict with indigenous communities
(Dove, 2005; van Klinken, 2008), has been investigated as
well as how gender relationships are influenced by new
labour requirements (Li, 2014). The interaction of large-scale
oil palm cultivation and social transformation still requires
further scientific investigation and is beyond the scope of our
review.
Here we present an interdisciplinary, comprehensive
overview of the environmental consequences of oil palm
expansion. We first summarize the process of oil palm
cultivation (Section I.2), and its direct effects on biodiversity
(Section I.3). We then use ecosystem functions as a unifying
framework to synthesize research results from natural
sciences, economics, and social sciences. Ecosystem functions
are defined as ‘the capacity of natural processes and
components to provide goods and services that satisfy human
needs, directly or indirectly’, and consequently are a subset
of ecological processes and ecosystem structures (de Groot,
Wilson & Boumans, 2002). While ecosystem functions are
related to ecosystem services, an ecosystem function is the
ecosystem’s capacity to provide a given service, regardless
of whether the service is actually utilized (e.g. an ecosystem
may be able to treat more organic waste than is present).
Ecosystem functions are grouped into four main categories:
regulation, habitat, production, and information. Regulation
functions maintain biogeochemical cycles, e.g. carbon
sequestration, and water and nutrient cycling. Habitat
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
4 C. Dislich and others
functions support biological diversity. Production functions
provide natural resources for human use. Finally, information
functions are the cultural, aesthetic, and educational values
of ecosystems (de Groot et al., 2002).
We reviewed these ecosystem functions systematically
(Section II) to assess the change in ecosystem function
in oil palm plantations relative to forest (the dominant
ecosystem replaced by oil palm; Koh & Wilcove, 2008),
summarize mitigation actions that can be taken to maintain
ecosystem functions, assess which ecosystem functions are
understudied, and highlight important research gaps for
each ecosystem function (Sections III.1–14 and IV.2–4).
Where data are available, we also consider the spatial,
temporal, and management (smallholder versus large-scale
plantations) scales at which changes in ecosystem functions
occur (Section IV.4; Rodríguez et al., 2006).
(2) Oil palm cultivation and oil production
Elaeis guineensis Jacq., the species most broadly used
for palm oil production, is native to tropical Africa,
with its native range extending from Guinea to Angola
(Corley & Tinker, 2003). Easy establishment, low costs,
and high output make oil palm a highly profitable
tropical cash crop and economically the most efficient
(Mg ha−1) oil crop in the world (Wahid, Abdullah &
Henson, 2005). Oil palms are now grown throughout the
humid tropical lowlands (18.1 million ha in 43 countries),
with Indonesia (7.1 million ha) and Malaysia (4.6 million ha)
together accounting for about 85% of global crude palm oil
production (see online Appendix S1, data to 2013; FAO,
2015). Oil palms grow on a range of soil types, including soils
where few other crops grow successfully (Corley & Tinker,
2003). The costs of palm oil production are low because oil
palms require relatively low fertilizer inputs per Mg of oil
produced (but still may require large absolute amounts of
fertilizer). Also, they are affected by few pests and diseases
and palm oil mills can be powered by waste biomass from
plantations (Basiron, 2007; Zimmer, 2010).
The establishment of an oil palm plantation begins
with clearing the land, either mechanically or with fire.
Mechanical clearing often requires heavy machinery in
the case of large-scale plantations, which can lead to
soil compaction (Lal, 1996) among other soil physical
degradations. Clearing through slashing and burning
removes aboveground biomass, understorey vegetation, and
ground litter and thus results in high environmental costs
(e.g. Schrier-Uijl et al., 2013, more details below). Despite
laws prohibiting the clearing of land with fire, (i.e. since the
1990s in Malaysia and Indonesia), it remains the common
practice (Murdiyarso et al., 2004; DeFries et al., 2008). If a
plantation is being established in peat lands, the next step
is drainage, as oil palms cannot grow on waterlogged peat
soils. This results in even higher carbon losses than from
plantation establishment alone (Fargione et al., 2008). Next,
roads/tracks are built, along with drainage ditches and, in
some cases, terraces. Oil palm seedlings are then planted
at densities of about 110–150 palms per hectare (Sheil
et al., 2009). After 2–3 years, the palms mature and fruits
can be harvested. Oil palm production peaks at 9–18 years
(USDA FAS, 2012), but palms are left on the field for up
to 25–30 years until they become too tall for fruit harvest
(Basiron, 2007; Sheil et al., 2009). At this point, the palms are
usually cut down and new seedlings are planted (see Fig. 1 for
oil palm plantations at different stages of growth). After oil
palm fruit bunches are harvested, they need to be processed
in a local mill within 48 h to prevent fruit deterioration
(Vermeulen & Goad, 2006). First, the stalks are separated
from the fruits, leaving empty fruit bunches as a by-product.
The fruits are then pressed, producing a press liquor that
is separated into crude palm oil and palm oil mill effluent
(POME). The crude palm oil is refined and separated into
solid and liquid fractions (Sheil et al., 2009). The press cake
left over from pressing contains fibres, shells, and kernels
(the seeds of the palm fruit); the kernels are ground, heated,
and treated with a solvent to extract palm kernel oil (Poku,
2002). Most crude palm oil is used in food, while most palm
kernel oil is used to produce detergents, cosmetics, plastics,
and chemicals (Wahid et al., 2005). Empty fruit bunches and
POME, a waste product that consists of an acidic mix of
crushed shells, water, and fat residues, are the main organic
wastes produced.
Oil palm plantations usually occur either as large-scale
plantations (3000–20000 ha; Sheil et al., 2009) or as
family-based smallholder plantations (defined as <50 ha,
most around 2 ha; Vermeulen & Goad, 2006). Large-scale
plantations usually include a processing mill, and are
mainly owned by private companies, with a minority being
state-owned (Central Bureau of Statistics Indonesia, 2014, p.
xx). Smallholder plantations make up about 40% of the land
under oil palm cultivation in Indonesia and 13% in Malaysia
(Malaysian Palm Oil Board 2012, cited by Azhar et al., 2014;
Central Bureau of Statistics Indonesia, 2014).
Smallholders either work independently or as supported
smallholders. Independent smallholders are self-financed,
manage their own farms, and may deal directly with
the local mill operators of their choice or even process
their own palm oil using their own or community-owned
manual palm oil presses (Zoological Society London, 2015).
Supported smallholders are linked to large-scale plantations
and receive support on material inputs, training, and
plantation preparation (Sheil et al., 2009). In return for this
assistance, supported smallholders commit to selling their
crops to a large-scale company at a set price to be processed
at the company’s nearby mill, with a proportion of any
loans received deducted from the revenue. For example,
under the nucleus estate scheme of the 1990s (Fearnside,
1997; Budidarsono, Susanti & Zoomers, 2013) utilized in
the villages of Jambi province (Indonesia), the large-scale
plantations allocated 30% of their land for their core oil palm
plantation while 70% was available for use by participating
smallholders. In the last decade, the partnership model has
arisen, where the core estate retains up to 80% of its land
and makes only the remaining share of the land available to
smallholders (McCarthy, 2010).
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
Ecosystem functions of oil palm versus forest 5
Fig. 1. Examples of oil palm plantations (Jambi, Indonesia) in different stages of establishment: (A, B) initial establishment, (C) a
young plantation, and (D, E) a mature oil palm plantation. Photo credits: A, C, D, Oliver van Straaten, 2010; B, Suria Tarigan,
2014; E, Ana Meijide, 2015.
(3) Biodiversity
Biodiversity is a multifaceted concept that includes the
diversity of life on different levels of organization from
genes, to species, to entire ecosystems. Biodiversity as such
is not an ecosystem function but is important to many
ecosystem functions. Conversion of forest to oil palm clearly
represents a major threat to biodiversity (see reviews by
Fitzherbert et al., 2008; Danielsen et al., 2009; Yule, 2010;
Foster et al., 2011; Savilaakso et al., 2014; Drescher et al.,
2016). Most studies on oil palm have investigated species
richness in small sampling plots. Almost all organisms studied
so far have lower species richness in oil palm plantations
than in forests, including wood-inhabiting fungi, plants,
litter invertebrates, dung beetles, ants, amphibians, lizards,
birds, and mammals (Gillison & Liswanti, 1999; Aratrakorn,
Thunhikorn & Donald, 2006; Maddox et al., 2007; Danielsen
et al., 2009; Fayle et al., 2010; Azhar et al., 2011; Foster et al.,
2011; Gillespie et al., 2012; Hattori, Yamashita & Lee, 2012;
Jambari et al., 2012; Barnett et al., 2013; Faruk et al., 2013;
Barnes et al., 2014; Drescher et al., 2016). Not only is species
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6 C. Dislich and others
richness lower, the species that are present are more likely
to be common, generalist species (Yule, 2010) while forest
species tend to be absent. Fitzherbert et al. (2008) found
that only 15% of primary forest species also occur in oil
palm plantations when averaging across all taxa, while
Danielsen et al. (2009) found that only 23% of vertebrates
and 31% of invertebrates overlapped between forest and
oil palm plantations (also cf . Yaap et al., 2010). Functional
diversity of dung beetles and birds has also been found to be
reduced in oil palm plantations (Edwards et al., 2013, 2014a),
although more studies on functional diversity are needed
(but see Senior et al., 2013; Mumme et al., 2015). Abundances
are lower in oil palm plantations for many taxa, including
ants, beetles, moths, mosquitoes, birds, small mammals, and
primates (Foster et al., 2011), although some taxa, while still
less diverse, may have higher abundances (i.e. dung beetles,
isopods, lizards, and bats; Foster et al., 2011; and some species
of birds, ants, and beetles, Senior et al., 2013). The loss of
biodiversity in oil palm plantations is due to loss of habitat (see
Section III.9), altered habitat characteristics (e.g. vegetation
structure and microclimate; Drescher et al., 2016), increased
access to species of food or commercial interest (e.g. access for
hunting; Meijaard et al., 2005), and direct removal of species
considered to be pests (including orangutans, elephants, and
tigers; Brown & Jacobson, 2005).
II. METHODS
We based our review on the list of 23 ecosystem functions
from de Groot et al. (2002). We combined strongly related
functions, resulting in a working list of 14 ecosystem functions
(Table 1, Fig. 2). To improve accuracy, some functions were
updated based on de Groot et al. (2010). We based our review
on a structured literature search, but did not conduct a
formal meta-analysis, as too few studies reported suitable
effect sizes for comparison. For each of these functions we
developed a list of search terms (see online Appendix S2).
We then used the search terms in combination with ‘oil
palm’, ‘palm oil’, or ‘elaeis guineensis’ to search Web of
Knowledge for publications between 1970 and mid-February
2015. Our searches returned many off-topic articles, as
evidenced by their titles and abstracts, and these were
removed from further consideration. The remaining studies,
plus additional relevant articles and reports that were found
during the preparation of this review, were organized as a
JabRef literature database (see online Appendix S3; JabRef
Development Team, 2015). Each ecosystem function was
assigned to two or more section authors, who used the
literature database and their knowledge of the topic to write
the narrative portion of this review. Where available, the
section authors used recent reviews as a starting point (e.g.
Foster et al., 2011; Comte et al., 2012). Due to the large
number of publications for some ecosystem functions, we
cannot give an exhaustive overview of all studies. Instead,
we report the findings that to our judgment are the most
important and novel. The results from each narrative were
Table 1. Summary of the number of relevant studies found
in the literature search. The categories Regulation, Habitat,
Production, and Information functions are indicated by R, H,
P, and I, respectively. Gas & climate regulation and Refugium
& nursery functions were the most studied ecosystem functions,
while Ornamental resources was the least studied. See online
Appendix S3 for a complete list of references
Ecosystem functiona Studies
1. (R) Gas & climate regulation 204
2. (R) Water regulation & supply 89
3. (R) Moderation of extreme events 54
4. (R) Erosion preventionb 60
5. (R) Soil fertilityb 103
6. (R) Waste treatment 38
7. (R) Pollination 36
8. (R) Biological control 109
9. (H) Refugium & nursery functions 217
10. (P) Food & raw materials 140
11. (P) Genetic resources 47
12. (P) Medicinal resources 80
13. (P) Ornamental resources 14
14. (I) Information functions 30
Totalc 955
aThe following ecosystem functions from de Groot et al. (2002) were
combined: gas regulation and climate regulation; water regulation
and water supply; nutrient regulation and soil formation; refugium
function and nursery function; food and raw materials; and aesthetic
information, recreation, cultural & artistic information, spiritual &
historic information, and science and education. This resulted in
14 instead of 23 ecosystem functions.
bSoil retention was updated to erosion prevention and nutrient
regulation was updated to soil fertility for increased clarity (de
Groot et al., 2010).
cNote that a study may be included in more than one category,
hence the sum of the studies in the 14 functions exceeds the total
number of studies.
then synthesized based on expert opinion to arrive at a net
effect for each ecosystem function. We acknowledge that
different experts could arrive at different conclusions, but
present the rationale for each decision in online Appendix S4.
We focus our review on ecosystem functions in
monocultures. In their native range, oil palms are often
grown in mixed-species agroforestry systems (Poku, 2002),
which we expect to differ in ecosystem functioning. However,
such farms make up only a tiny fraction of the world’s oil
palm production. We focus on ecosystem functions that arise
within and immediately surrounding oil palm plantations
rather than downstream effects of palm oil use or indirect
effects of the oil palm industry. These indirect impacts have
been treated elsewhere (e.g. Sheil et al., 2009; Achten &
Verchot, 2011).
We use forests as a reference point because they are
the potential natural vegetation in most areas where oil
palm plantations are established. We do not distinguish
between primary and secondary forests because differences
between them in ecosystem functions are expected to be
small compared to the differences between either type of
tropical forest and oil palm plantations (e.g. Edwards et al.,
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Ecosystem functions of oil palm versus forest 7
Fig. 2. Oil palm plantations have a predominantly negative net effect on ecosystem functions when compared to primary and
secondary rainforest. Net effects do not imply that all effects on a given ecosystem function are positive or negative, but that the
majority or most-dominant effects are in the given direction. See Table 2 for additional details. Estimates of net effect direction and
correlation are qualitative and are based on the summary presented herein.
2011). We exclude studies which exclusively compare oil
palm to non-forest land-use types. We are aware that oil
palm plantations sometimes replace degraded or previously
cultivated land rather than forest (Wicke et al., 2008).
However, large swathes of forest have been and are still
being cleared for oil palm (e.g. Koh & Wilcove, 2008; Sheil
et al., 2009), and this comparison therefore provides a useful
upper bound for possible changes in ecosystem function.
III. RESULTS
In total, we found 955 studies and reports dealing with
ecosystem functions in oil palm plantations (Table 1, see
online Appendix S3), with an increase in publication rate
over time. Studies were not evenly distributed among
ecosystem functions, with some functions (e.g. Gas & climate
regulation and Refugium & nursery functions) receiving a
disproportionate share of attention, while others are relatively
understudied (e.g. Pollination and Ornamental resources,
Table 1). Overall, oil palm had a predominantly negative
effect on 11 of the 14 ecosystem functions relative to native
rainforest (Table 2, Fig. 2). However, for many ecosystem
functions, oil palm had both positive and negative effects
(Table 2).
(1) Gas & climate regulation
Gas and climate regulation refers to biotic and
abiotic processes of terrestrial ecosystems influencing the
atmosphere. It includes biogeochemical cycles associated
with greenhouse gas (GHG) emission and air quality, as
well as biophysical processes which regulate climate through
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8 C. Dislich and others
Table 2. Changes in ecosystem functions with conversion of forest to oil palm plantations (−, decrease; +, increase). The change in
ecosystem function relative to intact forest is given for deforested land (e.g. Fig. 1A, B), young plantations (e.g. Fig. 1C), and mature
plantations (e.g. Fig. 1D, E). Plantations on peat soils have additional negative effects on ecosystem function not captured in this
table. ++ or − − indicates qualitatively larger effects (based on expert opinion); = indicates no detectable changes; ? indicates
absent or insufficient data, thus highlighting important research gaps. In some cases where no studies have been conducted, existing
research suggests an expected direction or outcome. These instances are indicated with the expected direction and a footnote (6) to
clarify that the direction is hypothesized, but not confirmed
Ecosystem sub–functiona Deforested land Young plantation Mature plantation
(1) Soil carbon storage − − − −
(1) Biomass carbon storage − − − − −
(1) N2O balanceb − − − − −/+/=
(1) CH4 balancec ? ? −
(1) Air quality − − ? −
(1) Volatile organic compound balanceb − − ? −
(2) Water storage − − − − −
(2) Water yields ++ + ?
(1, 2) Actual evapotranspiration − − ? =
(2) Infiltration rate − −d −d
(2) Regularity of supply (baseflow) − − ?
(2) Regulation of peak flows − − − ?
(2, 4) Water quality: low sediment loads − − − −e
(2, 6) Water quality: low pollution − −e −e
(2, 3) Flood prevention −/− − −/− −e −/− −e
(2, 3) Drought prevention − −e −e
(3) Landslide prevention − −f − −f −f
(3) Wildfire prevention − − −e −e
(4) Erosion prevention − − − −
(5) Organic nutrient retention − − − −e −e
(5) Nutrient inputs ? ++e ++e
(6) Treatment of organic waste −f −f −f
(6) Treatment of inorganic waste ? ? +
(6) Decomposition rate ? =e =e
(6) Noise abatement ? ? ?
(7) Pollination: plantations − −f ? ?
(7) Pollination: surrounding areas −f ? ?
(8) Biological control: plantation ?g −/+e, g −/+e, g
(8) Biological control: surrounding area ?g ?g ?g
(9) Species richness: plantation − − − − − −
(9) Species richness: surrounding area − − − −e − −e
(9) Species’ abundance: plantation − − − −/++e − −/++e
(9) Species’ abundance: surrounding area ? ? ?
(9) Dispersal functions − −f − −f − −
(10) Food/raw materials: quantity − − ? ++
(10) Food/raw materials: diversity − − − −e − −e
(11) Genetic resources − − − −e, f − −e, f
(12) Medicinal resources − − − −e, f − −e, f
(13) Ornamental resources − − −e −e
(14) Aesthetic appeal − − − −/+e, f − −/+e, f
(14) Cultural and artistic, spiritual and historic value −/+ −/+e −/+e
(14) Recreational potential − − − −e − −e
(14) Science and education − − −e, f −e, f
aSub-functions refer to components of the main ecosystem functions, which may change independently of one another. Numbers in
parentheses correspond to main functions listed in Table 1.
b− indicates increased emissions (negative effect on ecosystem function), + indicates decreased emissions (positive effect on ecosystem
function).
c− corresponds to decreased soil uptake.
dStrongly dependent on location and soil type: very high infiltration under frond piles and on sandy soils (Banabas et al., 2008).
ePlantation age not specified in the research study.
f Prediction based on reasoning, but no direct data to support this.
gBiological control function largely unclear, because highly context-dependent and dependent on spread of pest species.
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
Ecosystem functions of oil palm versus forest 9
energy and momentum fluxes, albedo and water-regulating
mechanisms (Bonan, 2008). Gas and climate regulation
is one of the most studied ecosystem functions in the
context of oil palm expansion (Table 1). Most available
studies focused on emissions of GHGs and volatile organic
compounds (VOCs), a precursor to tropospheric ozone,
from oil palm plantations. The replacement of forest by
oil palm plantations represents a large loss in gas and
climate regulation function (see below). Typically, the
carbon sequestered by oil palms does not balance out the
GHGs emitted as a result of land-clearing fires and GHG
emission from fallow land and plantation establishment
(Fargione et al., 2008). Also, VOC emissions from oil palms
are higher than for forests and can lead to reduced air
quality (Fowler et al., 2011). Land-clearing fires for oil palm
cultivation create severe air pollution episodes (Langmann
et al., 2009; Marlier et al., 2013), colloquially referred to as
haze. These air-pollution episodes are particularly strong
during El-Nin˜o Southern Oscillation (ENSO) events, when
drier conditions prevail. During fire periods, VOC emissions
increase (Muraleedharan et al., 2000), as well as GHGs and
aerosol particles, resulting in direct and indirect modifications
of solar irradiation (Langmann et al., 2009). Additionally, the
different structure of oil palm plantations compared to forest
leads to different local microclimatic conditions resulting in
higher air and soil temperature and lower air humidity in oil
palm plantations compared to forest (Hardwick et al., 2015;
Drescher et al., 2016).
(a) Greenhouse gas fluxes
Net GHG fluxes depend on the balance between GHG
uptake and release as a result of processes taking place
above and below ground. Quantifying the overall effect of
land-use changes from forest to oil palm plantation requires
integrating across all stages of the land-use change including
land clearing, peat drainage (if applicable), and young oil
palm stages and typically results in lower carbon stored and
a negative GHG balance compared to forests (Fargione et al.,
2008). Carbon dioxide (CO2) is the main GHG contributing
to the GHG budget of oil palm plantations, while nitrous
oxide (N2O) and methane (CH4) emissions are modest in
comparison to CO2 (Ishizuka et al., 2005; Melling, Hatano
& Goh, 2005a,b, 2007; Hooijer et al., 2010), despite their
greater global warming potentials (298 and 25 CO2eq per
molecule of N2O and CH4, respectively; IPCC, 2007).
Land-clearing fires lead to large releases of CO2, both
from vegetation and soil (Fargione et al., 2008). Land needs
to be cleared to establish oil palm plantations, and fires
are the main form of land clearing in Indonesia (Kim
et al., 2015). While a small fraction of the carbon in
burned vegetation is stored long-term as biochar/charcoal,
most is released. The conversion of forest on mineral
soil to oil palm plantation results in mean carbon losses
of 702 ± 183 (S.D.) Mg CO2 ha−1 over 30 years (Fargione
et al., 2008), while conversions on peatlands lead to carbon
losses of 1486 ± 183 (S.E.M.) Mg CO2 ha−1 over 25 years
(Murdiyarso, Hergoualc’h & Verchot, 2010) to 3452 ± 1294
(S.D.) Mg CO2 ha−1 over 30 years (Fargione et al., 2008).
CO2 emissions from burning soils are particularly large on
peat. The emissions from peat fires for Indonesia during the
fire events of 1997 have been estimated to be 0.81–2.57 Pg C
(Page et al., 2002). Fires can also indirectly increase emissions
by exposing organic-rich soil layers to rapid decomposition
(Ali, Taylor & Inubushi, 2006) and producing ash, which
speeds up peat decomposition (Murayama & Bakar, 1996).
Large amounts of CO2 are released when peat
soils are drained to establish plantations and thus are
allowed to oxidize and decompose: estimates range from
26 to 146 Mg CO2 ha−1 year−1 (Schrier-Uijl et al., 2013).
These estimates vary because the rate of CO2 emissions
depends on drainage depth and changes with time since
drainage. Each additional 10 cm of drainage increases
CO2 emissions by approximately 9 Mg CO2 ha−1 year−1
(Couwenberg, Dommain & Joosten, 2010; Hooijer et al.,
2010). The rate of CO2 release from peat oxidation peaks
immediately after drainage. The initial rate may be as high
as 178 Mg CO2 ha−1 year−1 in the first 5 years (Hooijer
et al., 2012) and then decreases with time. Considering
all these variables, the most robust currently available
empirical estimate for CO2 emissions from peat drainage
is 86 Mg CO2 ha−1 year−1, calculated for a typical drainage
depth of 60–85 cm, annualized over 50 years, and including
the initial emission peak just after drainage (Page et al.,
2011a). In addition, dissolved organic matter is flushed out
of peat soils when they are drained, which then decomposes
and releases additional CO2 (Schrier-Uijl et al., 2013). This
additional carbon loss is estimated to increase total carbon
losses by up to 22% (Moore et al., 2013).
Oil palm plantations usually store less carbon in the soil
than forests (Aweto, 1995; Sommer, Denich & Vlek, 2000;
Ishizuka et al., 2005) even if some studies have reported
similar carbon stocks in both land-use systems (Tanaka et al.,
2009; Fraza˜o et al., 2013). The generally observed lower soil
carbon storage in oil palm plantations results from increased
decomposition in young plantations as a consequence of
increased soil disturbance and temperatures (Aweto, 1995;
Sommer et al., 2000), decreased leaf litter input (Lamade
& Boillet, 2005), and increased soil respiration (Ishizuka
et al., 2005; Lamade & Boillet, 2005; Melling et al., 2005b).
However, the extent of soil carbon loss seems to depend
on initial levels, with little loss in soils that are already
carbon-poor (Smith et al., 2012). The difference between
forests and oil palm plantations also decreases in the first
decade or so after plantation establishment as organic matter
is added to the soil by leaf litter and roots (Haron et al., 1998;
Smith et al., 2012), but even when soil carbon reaches an
equilibrium, it is only 55–65% of forest soil carbon levels
(Lamade & Boillet, 2005).
Oil palm plantations, like any vegetation, assimilate CO2
from the atmosphere, acting as a carbon sink. Overall,
oil palm plantations assimilate more CO2 and produce
more biomass per hectare each year than forests due
to very high fruit production (Lamade & Boillet, 2005;
Kotowska et al., 2015). This high productivity is often used as
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
10 C. Dislich and others
an argument in favour of oil palm cultivation. However,
unless very long timescales are considered, this higher
rate of carbon uptake does not make up for the carbon
released when forests are cleared for oil palm cultivation, as
forests have more aboveground and belowground biomass
than oil palm plantations (Germer & Sauerborn, 2008;
Kotowska et al., 2015); while tropical rainforests typically
store 145 ± 53 Mg C ha−1 (Pan et al., 2013), estimations for
the time-averaged carbon stock of oil palm plantations range
between 36 and 91 Mg C ha−1 (Tomich et al., 2002; Henson,
2003, cited in Bruun et al., 2009).
Oil palm plantations also release more N2O into the
atmosphere than forests, mainly due to nitrogen (N) fertilizer
use (Murdiyarso et al., 2002; Melling et al., 2007; Fowler
et al., 2011; Schrier-Uijl et al., 2013). How N2O emissions
increase after fertilizer application in relation to increases
in CO2 uptake remains unclear (Murdiyarso et al., 2010).
Additionally, high spatial variability in N2O emissions
is observed due to fertilization usually being applied
directly around the palms and not homogeneously over
the plantations (Fowler et al., 2011). Soil texture plays an
important role for N2O emission as well (Sakata et al., 2015).
Methane emissions from oil palm plantations and their
controlling factors are highly variable depending on their
establishment on mineral soils or on peatlands. The
conversion of peatland primary forest to oil palm plantation
could promote CH4 oxidation and thus CH4 uptake (Melling
et al., 2005a), while on mineral soils this conversion has been
shown to reduce CH4 uptake (Hassler et al., 2015). CH4
emissions from tropical peat soils depend on water table,
temperature and litter characteristics and are generally low
compared to temperate peat soils (Couwenberg et al., 2010).
They make up less than 10% in terms of CO2eq of the total
GHG emissions (Page et al., 2011a). On mineral soils, Fowler
et al. (2011) and Ishizuka et al. (2005) found only small fluxes
of CH4 both in forest and oil palm plantations.
(b) Air quality
Oil palm plantations affect local and regional air quality
mainly in two ways: air pollution from land-clearing fires,
and increased emissions of VOCs. Land-clearing fires can
lead to severe smoke and haze pollution, especially in dry
years. For example, during the El Nin˜o episodes in 1994
and 1997, fires in Southeast Asia led to tremendous air
pollution with severe negative impacts on human health
(Murdiyarso et al., 2002; Glover & Jessup, 2006). Forest fires
release carcinogens and toxic gases such as CO, O3, NO2 and
particulate matter, decreasing air quality (Reddington et al.,
2014) and causing immediate respiratory problems (Mott
et al., 2005) as well as long-term health problems (Ostermann
& Brauer, 2001; Kamphuis et al., 2010; Schrier-Uijl et al.,
2013) and increased mortality (Johnston et al., 2012). In
addition, fires add black carbon to the atmosphere, which
might enforce global warming (Fargione, Plevin & Hill,
2010).
Oil palms are a major emitter of the VOC isoprene
(Misztal et al., 2011), and in general produce more VOCs than
forests (Fowler et al., 2011). While the relationships between
VOC concentrations, atmospheric chemistry, and climate
are still poorly understood (Wilkinson et al., 2006), isoprene
and other VOC emissions from oil palm plantations are
generally expected to decrease surrounding air quality (Royal
Society, 2008; Pyle et al., 2011). This is because isoprene
can lead to the production of aerosols/haze and ozone,
especially in areas where nitric oxide (NOx) concentrations
are high as well (e.g. where traffic volume is high; Sheil
et al., 2009; Fowler et al., 2011; Pyle et al., 2011). Studies have
measured similar ozone concentrations in the boundary
layers of forests and oil palm plantations (Hewitt et al., 2009,
2011). However, future increases in NOx concentrations due
to fertilization and industrialization might lead to critical
increases of ozone concentration in oil palm plantations
(Hewitt et al., 2009, 2011) and negative impacts on human
health, crop yields, and global climate (Royal Society, 2008).
Thereby, the emission of VOCs from oil palm plantations
indirectly affects regional and global climate (Misztal et al.,
2011).
(c) Local climate
Oil palm plantations are expected to affect global climate
through GHG emissions, but they also have a direct effect
on local microclimates. Oil palm plantations have lower,
less dense canopies and a lower leaf area index than forests,
and as a result are warmer, drier, and allow more light
penetration. A recent study in Borneo found that mean
maximum air temperatures were up to 6.5◦C warmer in
oil palm plantations than in primary forests, and up to 4◦C
warmer in oil palm plantations than in logged forests, with
large differences in air moisture content and soil temperature
as well (Hardwick et al., 2015). This effect is more pronounced
in young (compared to mature) oil palm plantations (Luskin
& Potts, 2011), because of their lower canopy cover and
lower leaf area index.
(d ) Mitigation
The most effective possible action to reduce GHG emissions
related to oil palm cultivation is to limit oil palm expansion to
areas with moderate or low carbon stocks. Specifically, this
would require stopping the development of new plantations
on peat land as peat oxidation and peat fires are the
largest oil palm-related GHG sources, and extending and
enforcing the current moratorium on new concessions in
primary forests (Austin et al., 2015). Rehabilitation and
restoration of converted peatlands is also an option (Table 3).
On mineral soils, limiting flooding may prevent increased
CH4 emissions (Schrier-Uijl et al., 2013). Reducing nitrogen
fertilizer use can reduce nitrogen-based emissions (N2O,
NOx, see Table 3). Negative microclimatic effects associated
with clear-cutting senescent plantations can be mitigated
by sequential replanting that leaves a range of palm
ages and maintains canopy cover (Luskin & Potts, 2011).
Finally, considering that land-clearing fires continue to be
used despite being outlawed in Malaysia and Indonesia,
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
Ecosystem functions of oil palm versus forest 11
Table 3. Potential mitigation options for retaining and improving ecosystem functions in oil palm plantations
Mitigation options Ecosystem functions improveda Source(s)
Protect high-carbon and high-biodiversity areas
No new concessions in primary forest; no
development of plantations on peat land
GC, MEE, P, RN, MR,
GR, OR
Yule (2010) and Austin et al. (2015)
Enhance enforcement of burning prohibitions
and forest moratorium policy
GC, MEE, RN Environment Conservation Department (2002)
Rehabilitate developed peatlands
Keep water table as high as possible and rewet soil GC, MEE Hooijer et al. (2010), Couwenberg et al. (2010) and Othman
et al. (2011)
Maintain ground cover on peat to reduce soil
temperature and decrease decomposition rates
GC, WT Hooijer et al. (2012) and Jauhiainen et al. (2012)
Maintain a hydrological buffer zone around
plantations to protect neighbouring peatlands
GC, MEE Page, Rieley & Banks (2011b)
Compact peat soil to reduce oxidation and
decomposition prior to planting (but planting
on peat soil should be avoided)
GC Schrier-Uijl et al. (2013)
Improve fertilization practices
Plant a leguminous ground cover GC, WRS, SF e.g. Agamuthu & Broughton (1985)
Use composted plantation and mill waste as fertilizer GC, WRS, SF, WT Griffiths & Fairhurst (2003) and Comte et al. (2012)
Use slow-release coated fertilizers GC, SF sensu Akiyama, Yan & Yagi (2010)
Nutrient models, guidelines, and foliar sampling
to maximize efficiency of fertilizers
GC, WRS, SF Comte et al. (2012)
Careful application of fertilizer, accounting for
soil type, slope, landform, and weather to
minimize nutrient leaching losses
GC, WRS, SF Goh, Ha¨rdter & Fairhurst (2003)
Improve hydrological practices, soil conservation practices and protection of microclimate
Plant herbaceous ground cover to slow run-off
and increase infiltration, and reduce erosion
WRS, MEE, SE, SF, WT Department of Irrigation & Drainage (1989), Fairhurst
(1996) and Banabas et al. (2008)
Use mulch from plantation wastes (e.g. empty
fruit bunches, palm fronds) to slow run-off,
increase infiltration, and reduce erosion
WRS, MEE, SE, WT e.g. Maene et al. (1979), Department of Irrigation &
Drainage (1989), Fairhurst (1996), Banabas et al. (2008)
and Stichnothe & Schuchardt (2010)
Maintain hydrological buffers around streams
and use silt-pits and foothill drains to prevent
sediment and pollution from entering streams
WRS, WT, SE, SF Haag & Kaupenjohann (2001), Pennock & Corre (2001),
Environment Conservation Department (2002) and
Comte et al. (2012)
Avoid establishment in flood plains and areas
prone to flooding
WRS, MEE, RN Abram et al. (2014)
Limit flooding on mineral soils GC Schrier-Uijl et al. (2013)
Leave areas with slopes >25% with natural
forest cover intact and use terracing to
reduce soil erosion when applicable
MEE, SE Dorren & Rey (2004), Murtilaksono et al. (2011),
Walsh et al. (2011) and de Ble´court et al. (2014)
Minimize the amount of time that soil is bare WRS, SE Environment Conservation Department (2002)
Replant plantations sequentially to protect
microclimatic conditions
GC Luskin & Potts (2011)
Improve biodiversity practices
Use integrated pest management and replace
pesticides with biological pest control and
herbicides with manual weeding when possible
WRS, P, BC, GR Caudwell & Orrell (1997), Ponnamma (2001),
Environment Conservation Department (2002) and
Yusoff & Hansen (2007)
Increase diversity and structural complexity of
vegetation and include areas of native
vegetation cover to increase diversity and
abundance of species (e.g. decomposers,
pollinators, and biological control agents)
WT, P, BC, RN, GR,
MR, OR
Caniago & Siebert (1998), Chung et al. (2000), Mayfield
(2005), Aratrakorn et al. (2006), Bhagwat & Willis
(2008), Koh (2008a), Koh et al. (2009), Foster et al.
(2011) and Azhar et al. (2013)
Maintain epiphyte coverage RN, GR Koh (2008b) and Prescott et al. (2015)
Include buffer areas between plantations and forests RN, GR Environment Conservation Department (2002) and Koh
et al. (2009)
Plant polyculture plantations to grow multiple
forest products and enhance structural
complexity and biodiversity
RN, FRM, GR, MR Koh et al. (2009); but see Azhar et al. (2014)
Controlled breeding of oil palms to maintain
genetic diversity and local adaptation
GR Corley & Tinker (2003)
Protect areas and species of spiritual, cultural,
or historic importance
IF Colchester et al. (2011)
Require that sufficient habitat remains for
endemic species and genotypes
RN, GR, IF Yule (2010)
Improve waste management
Treat organic wastes from oil palm plantations
(e.g. to produce other products or energy)
WT e.g. Stichnothe & Schuchardt (2010)
aBC, biological control; FRM, food & raw materials; GC, gas & climate regulation; GR, genetic resources; IF, information functions; MEE, Moderation of
extreme events; MR, medicinal resources; OR, ornamental resources; P, pollination; RN, refugium & nursery functions; SE, (soil) erosion prevention; SF,
soil fertility; WRS, water regulation & supply; WT, waste treatment.
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
12 C. Dislich and others
enforcement needs to be enhanced. It is unclear whether such
fires could be eliminated entirely, but at the very least, limiting
the area that is burned daily would help in reducing the air
pollution impacts (Environment Conservation Department,
2002).
(e) Research gaps
The best available estimates of gas fluxes from oil
palm plantations are based on only a few measurements
from short-term studies using techniques which are not
always representative of the whole ecosystem (i.e. chamber
measurements which only consider soil GHG fluxes but not
whole-ecosystem fluxes, and with insufficient replicates to
cover soil heterogeneity). In addition, more data are needed
on soil carbon, the role of ground-cover plants, emissions
from drainage canals and ponds in plantations, and on CH4
and N2O emissions (Lamade & Boillet, 2005; Schrier-Uijl
et al., 2013). Locally, the biophysical changes (e.g. albedo,
surface energy fluxes, microclimate) associated with changes
in land use are important drivers of climate change, but have
received little attention.
(2) Water regulation & supply
Water regulation and supply refers to the amount, timing,
and quality of water stored in and flowing through and out
of an ecosystem (Millennium Ecosystem Assessment, 2005).
The conversion of forest to oil palm plantation generally
leads to a decrease in water storage, an increase in annual
water yield (the total amount of water flowing out), and a
decrease in water quality, but these changes tend to become
less extreme as plantations mature (Comte et al., 2012) and
can be reduced to some extent with management (Yusop,
Chan & Katimon, 2007). Oil palms have been found to be
susceptible to drought, and irrigation can be used to increase
their productivity during dry periods by improving the sex
ratio (female/total inflorescence production) and reducing
the abortion of immature inflorescences (Carr, 2011). Drip
irrigation and micro-sprinklers are considered to be suitable
methods for irrigating oil palm and the best estimates on yield
increase are 20–25 kg fresh fruit bunches ha−1 mm−1 even if
these effects on yield are only seen after 3 years (Carr, 2011).
However, irrigation may also contribute to the depletion of
aquifers and increase water scarcity (Famiglietti, 2014).
(a) Water storage and supply
Water storage in oil palm plantations may be reduced in
two ways: through peatland drainage and decreased water
infiltration (Merten et al., 2016). This decrease in storage
increases the risk of both floods and droughts (see below).
Peatlands, like giant sponges, hold large quantities of water.
Drained peat is inevitably lost, either quickly to fire or slowly
to oxidation, permanently reducing the area’s water storage
capacity (Andriesse, 1988). In addition, soil subsidence due to
peat oxidation or burning can lower the soil surface enough
that the water table can rise above it during periods of
high rainfall, leading to floods (Page et al., 2009). Infiltration
rates are reduced through soil compaction, e.g. due to
land clearing, heavy machinery, or traffic (Bruijnzeel, 2004;
Rieley, 2007; Banabas et al., 2008). Reduced infiltration
rates lead to surface run-off and reduced groundwater
recharge, resulting in an amplified catchment response to
rainfall events, e.g. increased peak discharge and decreased
time-to-peak (Department of Irrigation & Drainage, 1989;
Bruijnzeel, 2004).
This increases the risk of floods (Rieley & Page,
1997; Bruijnzeel, 2004; Bradshaw et al., 2007; Rieley,
2007), although the magnitude of the difference before
and after plantation establishment depends on the
hydraulic conductivity before land conversion. Plantation
establishment will cause the greatest difference in cases where
the previous landscape was very effective at preventing floods
(i.e. peat soils; Clark et al., 2002; Rieley, 2007; Tan et al.,
2009). Young oil palm plantations also have much higher
annual water yields than forests and the difference can be
extreme (e.g. 270–420% increase in Malaysia; Department
of Irrigation & Drainage, 1989). Water yield is increased
through a decrease in evapotranspiration (Rieley, 2007;
Ellison, Futter & Bishop, 2012) and reduced infiltration rates.
There are few comparable studies on evapotranspiration of
oil palm plantations of different ages but studies on mature oil
palm plantations found evapotranspiration rates to be similar
to those of forested catchments (1000–1300 mm year−1 for
oil palms versus 1000–1800 mm year−1 for lowland forests;
Bruijnzeel, 2004; Comte et al., 2012).
While overall water yield is increased, baseflow (streamflow
coming from groundwater) is decreased, leading to greater
variability in water yields (Bruijnzeel, 2004). For example,
baseflow accounted for 54% of streamflow in oil palm
plantations (Yusop et al., 2007) but 70% of streamflow in
forests (Abdul Rahim & Harding, 1992). This means that,
even though total annual streamflow coming from oil palm
plantations is usually greater, streamflow in dry seasons,
when groundwater is the main water source, is likely to
be lower (Bruijnzeel, 2004; Adnan & Atkinson, 2011). The
decreased dry-season flow increases the risk of drought, and
on peat soils this risk is amplified by the loss of water storage
due to peat drainage (Clark et al., 2002; Rieley, 2007; Tan
et al., 2009).
(b) Water quality
Sediment run-off is one of the largest water quality problems
in and around oil palm plantations, as it is greatly
increased by the decreased ground cover and increased
surface run-off in plantations. For example, in one study,
sediment loads increased from below 50 Mg km−2 year−1 in
forest to 400 Mg km−2 year−1 immediately after clearance
(Department of Irrigation & Drainage, 1989). The
establishment of ground cover decreases this impact but
sediment loads in water bodies remain higher than in forest:
in the Department of Irrigation & Drainage (1989) study,
sediment loads dropped only to 100 Mg km−2 year−1 after
legume cover was established. This soil loss can be a severe
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
Ecosystem functions of oil palm versus forest 13
threat to aquatic ecosystems (Edinger et al., 1998; Bilotta &
Brazier, 2008; Buschman et al., 2012).
Drainage of peat soils for plantation establishment also
has consequences for water quality. Some peat soils occur
above acid sulphate soils. As the drained peat subsides or is
lost to oxidation, these lower layers are exposed to oxygen.
As they oxidize, they increase soil acidity, which may affect
water quality in the surrounding area (Wo¨sten, Ismail & Van
Wijk, 1997). In addition, peat drainage reduces the ability of
peatlands to act as a freshwater buffer, allowing salt water to
intrude (Silvius & Giesen, 1992, cited by Silvius, Oneka &
Verhagen, 2000).
Finally, there is the impact of oil palm production itself.
Fertilizers, pesticides, and herbicides are inevitably washed
away, contributing to eutrophication of water bodies and
negatively affecting water quality and aquatic organisms
(Bilotta & Brazier, 2008; Kemp et al., 2011; Gharibreza et al.,
2013). In addition, streams and rivers near oil palm mills are
often contaminated with palm oil mill effluent (POME) due
to leaks (Ahmad, Ismail & Bhatia, 2003). POME has also
been shown to have negative effects on aquatic ecosystems
(e.g. due to high biochemical oxygen demand; Khalid &
Mustafa, 1992).
(c) Mitigation
The negative impacts of peatland drainage are likely to
be irreversible (Comte et al., 2012). In existing plantations,
management practices can help improve water regulation
and supply (Table 3). Improved hydrological practices
help to slow run-off, increase infiltration, and increase
groundwater recharge (Table 3). Improved fertilization
practices, reduction of pesticides, and reduction of
herbicides have the potential to reduce eutrophification and
contamination of streams, groundwater, and water bodies
(Table 3).
(d ) Research gaps
There is a need for studies identifying actual water
management practices in plantations (Comte et al., 2012),
investigating the impact of pesticides in water bodies (Comte
et al., 2012), and assessing whether nutrient leaching is still
a problem when organic fertilizers are used (Okwute &
Isu, 2007). Comparisons of water dynamics of oil palm
plantations at different plantation ages also are lacking
(Comte et al., 2012). Further study of water dynamics in
mature oil palm plantations is needed, as it is unknown
if they show the same differences from forest as young
plantations (Comte et al., 2012). Another research priority
is to determine methods of restoring dry-season water flow
(Bruijnzeel, 2004).
(3) Moderation of extreme events
The term ‘moderation of extreme events’ is equivalent to
the term ‘disturbance prevention’ used by de Groot et al.
(2002), but the terminology change acknowledges that some
disturbances may be necessary for some ecosystems and their
functioning. It is defined as the ability of an ecosystem to
prevent and mitigate disruptive natural events (de Groot
et al., 2002, 2010). Most of the studies we found examined
the moderation capacity of agricultural areas in general
and not oil palm plantations in particular. The majority of
studies investigated floods, droughts and landslides; only a
few studies addressed wildfires. Risks of flooding, drought,
landslides, and wildfires are all higher in oil palm plantations
and surrounding areas than in forests and their surroundings.
Flooding and drought were discussed in Section III.2a.
(a) Landslides
The establishment of oil palm plantations is likely to
increase the probability of shallow landslides, whereas large,
deep landslides (>3 m soil depth) are mostly influenced by
geological, topographic, and climatic factors and should not
be affected by land use (Ramsay, 1987a,b; Bruijnzeel, 2004).
It is known that forests reduce the probability of shallow
landslides by stabilizing the top metres of soil with their
roots (Starkel, 1972; O’Loughlin, 1984), while deforestation
increases the risk of landslides on steep terrain (Imaizumi,
Sidle & Kamei, 2008; Walsh et al., 2011). In addition, soil
stability is generally lower in plantations and agricultural land
because there is less ground cover and soil structure than in
forests (Sidle et al., 2006). Thus, the risk of shallow landslides
should increase in oil palm plantations, particularly young
plantations. However, we found no direct data to confirm or
reject this hypothesis.
(b) Wildfires
The establishment of oil palm plantations increases the
risk and frequency of wildfires in surrounding areas in
many ways (Hope, Chokkalingam & Anwar, 2005; Naidoo,
Malcolm & Tomasek, 2009). First, fires used for vegetation
clearing greatly increase the risk of accidentally starting
wildfires. Second, peat that has been drained for plantation
establishment is very flammable due to its high content
of organic matter and flammable resins (Mackie, 1984).
Peat fires can burn underground, making them difficult
to extinguish. Third, oil palm plantations are in general
more flammable than forests, which usually can burn only
during times of moisture stress (Cochrane, 2003). This is
because oil palm plantations are drier and more open than
forests (e.g. Mackie, 1984; Hardwick et al., 2015). Finally,
the establishment of oil palm plantations tends to lead to
degradation of surrounding forests. Oil palm plantations
may fragment forests. As tree mortality is elevated at forest
edges and in small forest fragments, this may increase fuel
loads and thus the vulnerability of forests to canopy fires
(Mesquita, Delamoˆnica & Laurance, 1999; Laurance et al.,
2002; Morton et al., 2013). Fragmentation may also allow an
increase in human activities that can start wildfires (Sheil et al.,
2009), while roads can facilitate fire igniting and spreading
as well (Mackie, 1984).
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
14 C. Dislich and others
(c) Mitigation
The strategies for reducing the risk of extreme events in
and around oil palm plantations are quite straightforward.
Measures to increase infiltration and groundwater recharge
will help prevent floods and droughts (Table 3). Avoiding
draining peatlands, or draining them as shallowly as possible,
helps reduce the risks of floods, droughts, and fires. The
establishment of oil palms in flood plains and other areas
prone to flooding should also be avoided as oil palm is
intolerant to inundation (Mantel, Wosten & Verhagen, 2007;
Abram et al., 2014). To prevent landslides, Walsh et al. (2011)
suggest leaving areas with slopes >25% with their natural
forest cover intact. Finally, the enforcement of laws against
the use of fire to clear land should be improved.
(d ) Research gaps
We did not find any studies directly addressing the risks of
landslides or wildfires in or around oil palm plantations.
Drought risks due to meso-climatic effects of land-use
conversion need to be studied in the context of oil palms
as well.
(4) Erosion prevention
The soil erosion process involves four phases: detachment,
breakdown of aggregates, transport/redistribution, and
sedimentation. These four phases depend strongly on land
cover/land use, parent material, soil texture, landscape
position/landform shape, and climate. Sufficient vegetation
cover and land use-associated management practices
which improve cover and water infiltration can reduce
surface run-off and consequently soil erosion (Kosmas,
Gerontidis & Marathianou, 2000). Parent material and its
position in the landscape influence transport-limited and
detachment-limited erosion, and hence the spatial patterns
of soil redistribution (Schoorl, Veldkamp & Bouma, 2002).
Soil texture affects transport and redistribution of soil, as clay
fractions are more easily removed and redistributed over
the landscape than the heavier silt and sand fractions (Lal,
2003). Landscape position and landform shape influence
transfer of water within and between landscapes which, in
turn, controls soil redistribution and sediment deposition
(Swanson et al., 1988). Lastly, precipitation intensity as an
agent of these four phases of erosion strongly influences
transport and sedimentation processes.
One of the drawbacks of loss of sufficient vegetation cover
through forest conversion to oil palm (Fig. 1A–C) is increased
soil erosion (Guillaume, Damris & Kuzyakov, 2015). When
soil erosion and sedimentation alter the biological process of
soil organic carbon (SOC) mineralization, vegetation growth,
and water and nutrient availability, they can in turn affect
redistribution of SOC within the landscape and its net loss
from the landscape (Corre et al., 2015). In a recent pan-tropic
study, lowland forest conversion to smallholder oil palm
plantations caused the loss of, on average, 40% of stored
SOC in the original forest soils in the top 0.1-m depth during
the first 10 years of conversion, whereafter a steady-state
condition of SOC stocks was attained (van Straaten et al.,
2015). Moreover, SOC losses from forest conversion to
smallholder oil palm plantations were detected even down
to 0.5-m depth.
Based on estimates from erosion models, one can expect
soil loss from oil palm plantations to be about 50 times
greater than in natural forests, which usually have very
low annual sediment losses (<1–2 Mg ha−1; Hartemink,
2006; Buschman et al., 2012). Several other soil erosion
studies in oil palm catchments in Malaysia have found
similar results (e.g. see Hartemink, 2006). Most soil losses
occur during plantation establishment (Fig. 1A, B), when
the land is bare and maximally exposed to wind and water
erosion (e.g. Bruijnzeel, 2004; Hartemink, 2005). In addition,
land-clearing fires can cause soil to become water repellent
(water repellency reviewed in DeBano, 2000), increasing
surface run-off and the potential for soil erosion (Sidle
et al., 2006). Rates of soil erosion should then decrease
with plantation age, as the oil palm canopy closes and
the root network develops (Fig. 1D, E), although even in
mature plantations the canopy is broken by roads and other
infrastructure (Fig. 1D; Hartemink, 2005).
(a) Mitigation
Soil erosion can be minimized by soil conservation practices
(Table 3) and by good planning before and during plantation
establishment, so that soils are left bare for as little time
as possible (Environment Conservation Department, 2002).
Maene et al. (1979) found a threefold reduction in soil loss in
a plantation with mulched paths compared to a plantation
with uncovered paths. Terracing is a commonly employed
management practice, especially in areas with steep slopes,
which has been shown to reduce soil erosion and SOC
losses in converted landscapes (de Ble´court et al., 2014). For
terracing to be effective, it must be well planned, correctly
constructed, and properly maintained (Dorren & Rey, 2004).
Terraces should be adapted to local conditions and be
combined with additional soil conservation practices (see
Table 3).
(b) Research gaps
Soil erosion and sedimentation model predictions [e.g.
landscape process modelling at multi dimensions and scales
(LAPSUS); Schoorl, Sonneveld & Veldkamp, 2000; Schoorl
& Veldkamp, 2001; Schoorl et al., 2002] could be tested in
the field, with emphasis on landscape positions, landforms,
and management practices. For example, LAPSUS-based
estimates of soil erosion and sedimentation have been
successfully used for landscape-scale estimates of net SOC
losses in a converted landscape (e.g. Corre et al., 2015). Such
tools can be used to inform policies and methodologies,
e.g. REDD+ (reducing emissions from deforestation and
forest degradation + conservation, sustainable management
of forests, and enhancement of forest carbon stocks).
Improved methodologies for the estimation of soil loss and
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
Ecosystem functions of oil palm versus forest 15
SOC redistribution at the landscape level can reduce costs,
e.g. in the implementation and monitoring of the REDD+
program, and increase accuracy of accounting for the benefit
of stakeholders (de Koning et al., 2011).
(5) Soil fertility
Soil fertility refers to the provision of sufficient soil nutrients
essential for plant growth and the upkeep of nutrient cycles
between vegetation and soil. In tropical forest ecosystems,
prior to their conversion to oil palm plantations, their
high ecosystem productivity is sustained even on highly
weathered, nutrient-poor soils because of efficient cycling
of rock-derived nutrients [phosphorus (P) and base cations]
between vegetation and soil as well as their inherently high
biological nitrogen (N) fixation (Hedin et al., 2009). This
efficient cycling of nutrients between plants and soil is altered
when tropical forests are converted to agricultural land-use
systems, resulting in a decrease in soil fertility (Ngoze et al.,
2008). The large amounts of nutrients previously bound in
the vegetation and soil organic matter are released in a
pulse from burning of slashed vegetation. The subsequent
release of nutrients via decomposition and mineralization is
susceptible to losses through leaching and gaseous emissions,
because the magnitude of uptake from the newly established
crops is still relatively low (Mackensen et al., 1996; Dechert,
Veldkamp & Brumme, 2005). Nutrient losses are especially
high in the earlier years of crop establishment and decrease
with time (Klinge et al., 2004), and the magnitude of decrease
in soil fertility and SOC depends on the initial soil fertility
of the original forest (Dechert, Veldkamp & Anas, 2004;
Allen et al., 2015; van Straaten et al., 2015). Additionally,
in fertilized land-use systems like oil palm plantations, the
eventual decline in soil fertility with age of conversion is
abated although nutrient leaching losses are sustained (Allen
et al., 2015; Kurniawan, 2016).
(a) Nutrient losses
Large amounts of nutrients are lost during plantation
establishment as a result of forest clearing and the increased
soil leaching that follows (Department of Irrigation &
Drainage, 1989; Brouwer & Riezebos, 1998). Large amounts
are also lost from established plantations through harvest and
removal of palm biomass (Hartemink, 2005) and leaching
(Goh & Ha¨rdter, 2003). For example, drainage leaching
fluxes increased for oil palm plantations compared to the
original forests (for ammonium, nitrate, dissolved organic
carbon, sodium, calcium, magnesium, and total aluminium
measured at 1.5 m soil depth at a site near Jambi, Sumatra,
Indonesia; Kurniawan, 2016). These increased leaching
losses resulted in a 55% decrease in N retention efficiency
(defined as 1 − N leaching losses ÷ soil N availability) and a
70% decrease in base cation retention efficiency (defined as
1 − base cation leaching losses ÷ soil exchangeable bases) in
the soil under mature oil palm plantations compared to the
same soil type under the original lowland forest. This suggests
detrimental effects on water quality (see also Section III.2b).
(b) Nutrient inputs
The main nutrient inputs in oil palm plantations are
fertilizers, lime, nitrogen-fixing ground cover, and com-
post/mulch. Large quantities of mineral fertilizers are used
in oil palm plantations (Sheil et al., 2009). Fertilization rates
in smallholder oil palm plantations are typically very varied
depending on available monetary capital and distance to fer-
tilizer suppliers. For example, in Jambi province (Sumatra,
Indonesia), smallholders apply 330–550 kg NPK-complete
fertilizer ha−1 year−1, equivalent to 48–88 kg N ha−1 year−1,
21–38 kg P ha−1 year−1 and 40–73 kg K ha−1 year−1, and
occasionally lime (200 kg dolomite ha−1 year−1). Addi-
tional sources of N (138 kg urea-N ha−1 year−1) and K
(157 kg K-KCl ha−1 year−1) are also applied (Allen et al.,
2015). Increased fertilization levels lead to increased nutri-
ent leaching losses (e.g. on loam Acrisol soils relative to
clay Acrisol soils; Kurniawan, 2016). Leguminous plants
are commonly planted during plantation establishment as a
cover and can contribute 239 kg N ha−1 year−1 (Agamuthu
& Broughton, 1985). However, this ground cover dies off
when the canopy closes, releasing a large quantity of N
that is vulnerable to leaching (Campiglia et al., 2011). Empty
fruit bunches, palm oil mill effluent, male inflorescences,
and fronds can all be used for mulch or compost, which
gradually breaks down and releases nutrients into the soil
(Comte et al., 2012). One study found that oil palms in a plan-
tation in Sumatra produced 10 Mg ha−1 year−1 of dry palm
fronds containing 125 kg N, 10 kg P, 147 kg K, and 15 kg Mg
(Fairhurst, 1996).
(c) Mitigation
Improved fertilization practices may improve soil nutrient
balances and minimize risk of nutrient losses through
leaching (Table 3). Unlike pulse rates of applications
of mineral fertilizers, leguminous cover crops and
mulch/compost release nutrients slowly and may have
minimal risk of nutrient loss to drainage leaching or run-off.
Maintaining riparian buffers may also help recover leached
nutrients, as such areas are characterized by high content of
organic matter and soil nutrients as well as strong retention
of nutrients (Table 3; e.g. Haag & Kaupenjohann, 2001;
Pennock & Corre, 2001).
(d ) Research gaps
More empirical data are needed on nutrient-retention
and nutrient-use efficiencies in oil palm plantations. In
general, studies are needed to test management trials on-site
for screening management practices (e.g. mulching with
compost, organic fertilization, various rates of chemical
fertilization, weed control) that will yield optimum benefits
(e.g. yield and profit) with maximum nutrient-retention
efficiency (or less nutrient losses) in the soil. Economic
evaluation should also be conducted on such management
trials to select for the optimal N, P, and base cation input
requirements for achieving and sustaining profitable crop
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
16 C. Dislich and others
production while preventing degradation in soil fertility. In
particular, field studies on decomposition rates and nutrient
release from frond stacks (piles of senesced fronds spread over
the whole plantation area or put on inter-rows to facilitate
harvest and maintenance works) are lacking, even though
such is common practice in both smallholder and large-scale
plantations. On-going studies are directly comparing soil
nutrient levels and leaching losses in forest and oil palm
plantations using a space-for-time substitution approach
(M.D. Corre, personal observations).
(6) Waste treatment
Waste treatment refers to the ability of an ecosystem to
remove or recycle organic or inorganic waste, or to abate
noise. Palm oil production results in large amounts of organic
waste, in particular empty fruit bunches and palm oil mill
effluent (Stichnothe & Schuchardt, 2010). While there are
many studies on the technical aspects of waste treatment, we
did not include these in the database. Instead, we focus on
those studies relating to the ecosystem functioning aspects
of waste treatment. As discussed in Section III.2b, oil palm
plantations may act as net sources of organic waste to the
surrounding environment, although organic wastes from oil
palms can also be used to treat a variety of pollutants,
including heavy metal pollution (e.g. Ahmad et al., 2011;
Vakili et al., 2014). Foster et al. (2011) found no difference in
litter decomposition rates (organic waste treatment) between
oil palm plantations and forests. Hypothetically, the rate of
decomposition of organic matter may differ between forests
and oil palm plantations as oil palm plantations are on
average warmer and drier than forests (Hardwick et al., 2015),
and have lower biodiversity, biomass, and energy uptake of
decomposer organisms (Barnes et al., 2014). However, the
direction of expected change is unclear, as drier conditions
should slow decomposition (Lamade & Boillet, 2005), while
warmer conditions should speed decomposition (Aweto,
1995; Sommer et al., 2000).
(a) Mitigation
Organic wastes from palm oil production can be recycled
in oil palm plantations into mulch and compost or can
be treated separately with the potential for additional
bioenergy production (e.g. Stichnothe & Schuchardt, 2010).
Understorey vegetation can help maintain the abundance
and species richness of understorey beetles in oil palm
plantations (Chung et al., 2000) and therefore may improve
decomposition rates of organic matter in oil palm plantations.
Riparian buffers may reduce surface water pollution
(Table 3).
(b) Research gaps
There is a clear need for studies of overall waste treatment
in oil palm plantations and differences from forests,
including comparison of net production (or removal) of
organic and inorganic wastes at the plantation and in the
surrounding environment. Decomposition is influenced by
leaf composition (e.g. Palm & Sanchez, 1990), and the degree
to which oil palm plantations result in a systematic change
in nutrient composition, lignin content, and polyphenolic
concentrations requires additional study. Additionally, the
capacity of oil palms relative to forest to abate anthropogenic
noise has not been studied.
(7) Pollination
The ecosystem function pollination refers to the pollination
of crops and wild plants (Klein et al., 2007; Ollerton, Winfree
& Tarrant, 2011). We found only 36 papers on pollination
functions provided by oil palm plantations (Table 1 and see
online Appendix S3). We note that there are many more
papers on oil palms as beneficiaries of pollination, which
will only be discussed briefly below. The data available are
too incomplete to come to any explicit conclusions about
major differences in pollination between forests and oil palm
plantations.
(a) Native pollinators
Compared to forests, oil palm plantations generally support
lower species richness and abundances of invertebrate
pollinators (Sodhi et al., 2010). Liow, Sodhi & Elmqvist
(2001) found lower abundances, but a greater diversity of
pollinating bees. However, the data of Liow et al. (2001)
come from observations along transects of only the lower
canopy and shrub layers, which may differ considerably
from higher canopy layers. The weedy vegetation in oil palm
plantations (and in cropland in general) is predominantly
independent of cross-pollination (due to autogamy, and
apomixis, as well as wind pollination, mainly in grasses),
which makes them independent of pollinator availability
(Gabriel & Tscharntke, 2007). Overall status of pollinators
and pollination functions within the remaining natural
ecosystems, i.e. in forest habitats, may be reduced in the
future due to habitat loss, fragmentation, and isolation of
habitats (Potts et al., 2010). Further losses of pollinators can
be anticipated due to pollution from large-scale fires.
(b) Pollination by Elaeidobius weevils
In their native range, oil palms are pollinated mainly by
Elaeidobius weevils (Vaknin, 2012). Because oil palm yields
are dramatically lower without these weevils (Greathead,
1983), Elaeidobius kamerunicus has been introduced into South
America and Southeast Asia (Vaknin, 2012). Dhileepan
(1994) found that in India populations of E. kamerunicus
decline during the dry season, but without compromising
pollinating efficiency. In the absence of any pollinating
insects, wind plays an important role in oil palm pollination
(Dhileepan, 1994). Elaeidobius weevils also pollinate other
palm species such as betelnut (Areca catechu) and coconut
(Cocos nucifera) and so, in theory, oil palm plantations
may provide pollination functions to neighbouring
crops.
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
Ecosystem functions of oil palm versus forest 17
(c) Mitigation
The oil palm industry’s reliance in most regions on a single
pollinator species, Elaeidobius kamerunicus, is risky. One way
to address this would be to introduce additional Elaeidobius
species, but this carries the usual risks of exotic species
introduction (Foster et al., 2011). Alternatively, plantation
managers could implement measures to increase insect diver-
sity in oil palm plantations (see Table 3). This should improve
pollination rates for both oil palms and insect-pollinated
native plants (Mayfield, 2005; Foster et al., 2011).
(d ) Research gaps
Direct comparisons of pollination success rates in oil palm
plantations and forest would be helpful in theory, but difficult
to carry out in practice because of the drastically different
plant communities and pollination systems. The highest
priority, then, should be additional surveys of pollinator
abundance and diversity (including insects, birds, and bats) in
oil palm plantations and neighbouring forests. The impact of
deforestation and forest fragmentation and isolation, as well
as the use of fire for clearing, needs to be assessed in terms of
its local and landscape-scale effects on native pollinators and
pollination. The potential for oil palm plantations to decrease
the pollination function in surrounding native habitat patches
(e.g. isolated forest fragments) also needs attention. It would
also be useful to test whether oil palm plantations improve
pollination of other neighbouring palm crops, as predicted,
or whether pollination is diminished due to loss of native
pollinator diversity. The potential importance of native
pollinators for oil palm fruit set and whether fluctuations
of oil palm fruit set and yield are driven by pollination
limitation is still unclear and requires further investigation
(T. Tscharntke, personal observations).
(8) Biological control
The ecosystem function biological control refers to the ability
of ecosystems to prevent organisms from acting as pests or
diseases (e.g. Norris, Caswell-Chen & Kogan, 2003). An
organism becomes an agricultural pest or a disease if it
causes damage to a crop that is above the economic threshold
level (Norris et al., 2010; Peshin & Pimentel, 2014). Globally,
30–40% of potential crop yield is destroyed by pathogens
and pests (Oerke, 2006).
(a) Biological control within oil palm plantations
In oil palm plantations, the main organisms that may act
as pests or diseases can be categorized as trunk borers
(e.g. Oryctes rhinoceros, Rhynchophorus ferrugineus), defoliators (e.g.
Metisa plana, Setora nitens), frugivores (Rattus rattus diardii), plant
suckers (Zophiuma butawengi), and wilt diseases (Ganoderma
boninense; see online Appendix S3). Both trunk borer pests
are usually associated with one another and may reduce
yield by about 12–80% (Liau & Ahmad, 1995; Chung,
Cheah & Ramalingam, 1999). The adult of O. rhinoceros
initially bores into young oil palm spears through petioles
and damages the growing point of the palm. The holes give
access to R. ferrugineus, which further damages the palm.
This in turn produces favourable conditions for O. rhinoceros
larvae to develop inside the stem. M. plana and S. nitens are
common caterpillars and can cause severe defoliation (up to
29–90% yield losses at high infestation levels; Basri, Norman
& Hamdan, 1995; Potineni & Saravanan, 2013). The main
mammalian pests are rats (Rattus tiomanicus, R. rattus diardii,
and R. argentiventer), which can reach densities of 600 ha−1
and reduce yields by 5–10% by consuming the mesocarp
(Wood & Fee, 2003; Fitzherbert et al., 2008). Damage from
the planthopper, Z. butawengi, has not yet been quantified,
but may be substantial. It is characterized by chlorosis of
fronds (Finschhafen disorder) and may kill palms (Woruba
et al., 2014). Finally, G. boninense is a disease of old palms and
can reduce yields by around 50–80% ha−1 by restricting
water absorption (Priwiratama & Susanto, 2014).
Many of these species could be targeted by biological
control. There is limited knowledge of the differences in
biological control between oil palm plantations and forests
(Savilaakso et al., 2014). In general, tropical monoculture tree
plantations are more susceptible to pest outbreaks than native
forests (Nair, 2001). This is likely a result of reduced species
diversity and abundance of native parasitoids and predators
of oil palm pests due to local practices such as pesticide
applications and clearance of the understorey as well as the
simplification of the surrounding landscape (Tscharntke et al.,
2007; Foster et al., 2011). The simplification of the biological
and physiological environment creates unsuitable conditions
for most biocontrol agents in the plantation because of a
significant decrease in food and habitat resources (Chung
et al., 2000; Donald, 2004; Koh, 2008a; Bateman et al., 2009;
Koh, Levang & Ghazoul, 2009). For instance, insectivorous
birds and bats, known as major biocontrol agents for a
number of pests (Maas, Clough & Tscharntke, 2013), have
difficulty adapting to oil palm plantations, resulting in higher
pest attacks, and potentially reduced crop yield (Aratrakorn
et al., 2006; Koh, 2008a,b). Compared to forests, the majority
of birds and bats are lost in oil palm (Aratrakorn et al.,
2006; Shafie et al., 2011). Low population size and diversity
of predatory beetles might explain the high density of
chrysomelid pests in oil palm plantations (Chung et al., 2000).
However, biological control in oil palm plantations is
managed directly by plantation owners, who introduce and
manage species that combat oil palm pests and diseases
(Wood, 2002; Corley & Tinker, 2003). These include fungi
and entomopathogenic viruses to control the rhinoceros
beetle Oryctes monoceros (Huger, 2005; Murphy, 2007) and
other trunk borers and lepidopteran pests, parasitoids to
control planthoppers (Gitau et al., 2011; Guerrieri et al., 2011),
the fungus Trichoderma harzianum and endophyte bacteria to
control the Ganoderma fungus which causes basal stem rot
(Susanto, Sudharto & Purba, 2005; Sundram et al., 2008,
2011; Suryanto et al., 2012), barn owls and snakes to control
rats (Sheil et al., 2009), and assassin bugs to control a variety
of herbivorous insects (Turner & Gillbanks, 2003, cited in
Foster et al., 2011).
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
18 C. Dislich and others
(b) Biological control in surrounding areas
The overall effect of oil palm plantations on biological
control in surrounding areas is unclear. Because some oil
palm pests also affect other crops, surrounding areas may
benefit from the release of control agents of these pests in oil
palm plantations. For instance, rhinoceros beetles and plan-
thoppers are also pests of coconut (Huger, 2005; Gitau et al.,
2011; Guerrieri et al., 2011) and basal stem rot also affects
the timber tree Acacia mangium (Eyles et al., 2008). In addition,
oil palm products can be used for pest control: empty fruit
bunches can be used to combat rhinoceros beetles in coconut
(Allou et al., 2006) and wet rot in okra (Siddiqui et al., 2008),
endophytic bacteria isolated from oil palm roots can be used
against Fusarium rot in Berangan banana (Fishal, Meon &
Yun, 2010), and palm oil reduces beetle incidence in maize,
sorghum, and wheat grains (Kumar & Okonronkwo, 1991).
However, oil palm plantations can also foster the spread of
pests into surrounding areas. For example, one study showed
that soil disturbance caused by wild pigs feeding in oil palm
plantations correlated with the invasion of the exotic shrub
Clidemia hirta into forest (Fujinuma & Harrison, 2012).
(c) Mitigation
By definition, the use of integrated pest management
practices instead of chemical pesticides alone increases the
provisioning of biological control in oil palm plantations.
Management practices that increase diversity (especially of
arthropods and birds) in oil palm plantations (see Table 3, but
see also Teuscher et al., 2015, for a cost–benefit analysis) may
also increase the provisioning of biological control – native
insectivorous birds, for instance, could reduce herbivory on
oil palms (Aratrakorn et al., 2006; Koh, 2008a).
(d ) Research gaps
While much research has focused specifically on oil palm
pests and diseases and methods for combatting them, little
is known about the contribution of native biodiversity to
biological control in oil palm plantations. It is necessary to
study the habitat requirements of biological control agents
and the potential for incorporating the necessary habitat
features into oil palm plantations to maintain robust bio-
logical control agent populations. There is a need for basic
surveys of biodiversity in oil palm plantations and forests that
identify naturally occurring pest control agents and measure
their abundances. Further studies are needed on biocontrol,
both in forests and oil palm plantations, in a range of condi-
tions – similar to the approach taken by Koh (2008a). More
research is needed on methods to maintain biological control
agents in the landscape, such as the role of riparian buffers
in the plantation, patches of semi-natural habitat within or
surrounding plantations, and growing flowering plants in the
understorey, as flowering plants may provide supplemental
food resources when prey are scarce (e.g. Basri et al., 1995).
Spillover from crop fields to adjacent natural habitat or
crops has been little studied, as most studies on spillover
across habitat boundaries focus on effects of natural habitats
on cropland (e.g. Blitzer et al., 2012; Lucey et al., 2014).
(9) Refugium & nursery functions
These functions refer to the ability of an ecosystem to
provide habitats that meet species’ needs and thus allow
them to survive and reproduce. These functions are crucial
for the maintenance of biodiversity and associated services
(Tscharntke et al., 2012a; see also Section I.3). Oil palm plan-
tations have a simpler structure than forests: their canopy is
much lower, the upper canopy comprises only one species,
and other plant growth forms such as lianas are completely
absent or reduced (Danielsen et al., 2009; Foster et al., 2011;
Luskin & Potts, 2011). Furthermore, the understorey of oil
palm plantations is hotter, drier, and receives more light
than the forest understorey (Hardwick et al., 2015; Drescher
et al., 2016). As a result, oil palm plantations are lacking the
specific environmental conditions required by many forest
species. Furthermore, due to high levels of disturbance
and propagule pressure, oil palm plantations contain more
weedy and exotic species than forests, and are exposed
to more agrochemicals, further reducing the chances of
survival for many species (Foster et al., 2011).
The establishment of oil palm plantations also has
negative effects on the habitat functions and biodiversity
of surrounding contiguous forests and forest fragments
(e.g. Edwards et al., 2010) in two important ways. First,
plantation development usually increases access to forest
areas, leading to increased utilization and higher likelihood
of forest degradation and loss (Meijaard et al., 2005; Sheil
et al., 2009). Second, plantation establishment often results in
forest fragmentation, leading to edge effects, spillover effects,
increased invasion of non-native species, reduced species
movement, greater population isolation, and greater risks
of local and global extinction (Campbell-Smith et al., 2011;
Fujinuma & Harrison, 2012).
The ability of oil palm plantations to provide habitat
depends on plantation age (Luskin & Potts, 2011) and
management intensity (Teuscher et al., 2015). Habitat quality
should increase with plantation age, as the canopy closes
and structural complexity increases (Luskin & Potts, 2011),
although the trend is not so clear for birds (Azhar et al.,
2011). Management practices in oil palm plantations, with
respect to available riparian and terrestrial habitats, mainly
determine anuran species composition in oil palm plantations
(Faruk et al., 2013; Norhayati, Ehwan & Okuda, 2014). In
addition, there is some evidence that biodiversity is higher in
smallholder than in large-scale plantations, at least for birds
(Azhar et al., 2011). Within smallholder plantations, Teuscher
et al. (2015) have shown that the density of native trees has a
positive effect on bird diversity and abundance.
(a) Mitigation
The habitat functions of oil palm plantations can be
improved by changing management practices in planted
areas and by maximizing unplanted areas maintaining
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
Ecosystem functions of oil palm versus forest 19
native vegetation (see Table 3, but see also Edwards et al.,
2010). In planted areas, management for biodiversity hinges
on increasing the diversity and structural complexity of
vegetation – through increasing the height, coverage, and
diversity of ground-cover plants, planting tree species, and
letting epiphytes thrive (Koh, 2008b; Koh et al., 2009).
Management practices that harm biodiversity (e.g. epiphyte
removal) may result in costs with no benefit to yield (Prescott,
Edwards & Foster, 2015). Unplanted areas can also act as a
buffer zone to reduce impacts on adjoining forest areas.
(b) Research gaps
Refugium and nursery functions are still underappreciated in
biodiversity research. They require a landscape perspective
that includes assessments of edge effects, landscape
configuration, and species’ patch size requirements (Zurita
et al., 2012). More research into the role of increasing
dissimilarity of community composition with distance is
needed as well, considering that small patches over a
large distance may harbour many more species than one,
spatially restricted large patch (Tscharntke et al., 2012b; but
see Edwards et al., 2010). Further, the role of adding habitat
patches as refuges to increase functional biodiversity has
not yet been quantified. Similarly, the influence of adjacent
habitat type (e.g. jungle rubber, scrubland, rubber plantations
or secondary forest) on community composition and
ecological functioning inside oil palm plantations has been
neglected so far (but see Edwards et al., 2014b). Smoke from
land-clearing fires has been shown to cause serious human
health problems (Aiken, 2004), and impacts of smoke-related
pollution on wildlife habitat need to be addressed. Finally, the
links between the Refugium & nursery functions and other
functions and services must be explored within a multi-scale
context and in consideration of the long-term effects of
gradual degradation of remaining forest habitats.
(10) Food & raw materials
This function refers to the ability of an ecosystem to
produce food and raw materials for human use. As oil palm
plantations are managed specifically for palm oil production,
this function is increased in oil palm plantations compared
to forests. However, forests produce a wider variety of foods
and raw materials. Oil palm may also contribute to local
food insecurity when land is taken from rural or indigenous
communities for commercial oil palm production (Nesadurai,
2013) or when palm oil is used for biofuels instead of food
(Ewing & Msangi, 2009).
(a) Foods and materials from oil palm
Oil palm outperforms other oil crops such as rapeseed and soy
by 3–8 times in production per hectare (Sheil et al., 2009). Oil
palm plantations produce an average of 3–4 Mg ha−1 year−1
of oil, with some commercial plantations producing around
7 Mg ha−1 year−1, and improved varieties and management
could result in yields over 10 Mg ha−1 year–1 (Wahid et al.,
2005). Palm oil is the main output of oil palm plantations,
with crude palm oil mainly being used in food and palm
kernel oil in the production of detergents, cosmetics, plastics,
and chemicals (Wahid et al., 2005). Palm kernel meal and
POME can be used for animal feed. Livestock can graze in
oil palm plantations and intercropped plantations can also
produce a range of other food crops (Corley & Tinker, 2003,
pp. 265–269). However, these practices generally take place
before plantations reach full maturity. In Africa, oil palm
sap is extracted, fermented, and distilled into palm wine
(Corley & Tinker, 2003). Oil palm trunks can be made into
furniture (e.g. Suhaily et al., 2012), and other waste products
(empty fruit bunches, leaves, fruit shells, and fibres) can be
used to make a variety of products (e.g. paper, activated
carbon, and fish food; Ahmad, Loh & Aziz, 2007; Bahurmiz
& Ng, 2007; Wanrosli et al., 2007). Oil palm products can
also be used as fuels (e.g. Harsono et al., 2012), POME can be
fermented to produce methane/biogas (Yacob et al., 2006),
and oil palm waste products can be burned directly (Yusoff,
2006). Finally, pigs, snakes, and rats, often considered as
pests, may be hunted in oil palm plantations for food (Luskin
et al., 2014; K. Darras, personal observations).
(b) Loss of forest foods and materials
Forests support many species that oil palm plantations do not,
including many species used for food and raw materials (e.g.
construction materials, fuelwood, resins; Shackleton, Delang
& Angelsen, 2011). Such timber and non-timber forest
products are especially important during times of crop failure
(Sheil et al., 2006; Shackleton et al., 2011). In addition, forests
in many regions are used for the cultivation of rattan and
jungle rubber, and for swidden/slash and burn agriculture
(Sheil et al., 2006; van Noordwijk et al., 2008). The loss of
these forest products and forest agriculture due to conversion
to oil palm has negatively impacted many forest-dependent
societies (Belcher et al., 2004; Sheil et al., 2006).
(c) Mitigation
Some forest plants could potentially be cultivated in oil
palm plantations to prevent the loss of some forest products.
However, many forest products will be entirely absent from
harvestable oil palm plantations.
(d ) Research gaps
This is a well-researched ecosystem function for oil palm
plantations and our database only reflects a fraction of
the research on this topic because the scope of our
study only included local production (i.e. direct products
from the plantation and not downstream production). A
summary of active research topics is given by Corley
& Tinker (2003, p. 479). Additionally, the full range of
forest species that can be used for food and raw materials
is doubtless unknown and additional ethnological surveys
of forest-dependent communities are needed – including
monetary and non-monetary valuation of forest resources.
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20 C. Dislich and others
(11) Genetic resources
Genetic resources refer to the genetic material of organisms
present in an ecosystem including the potential for future
evolution (modified from de Groot et al., 2002). The
importance of genetic resources for ‘food security, public
health, biodiversity conservation, and the mitigation of and
adaptation to climate change’ is internationally recognized
(Nagoya Protocol, 2011). In general, oil palm agriculture
can impact genetic resources in two important ways.
First, as conversion of forest to oil palm plantations
greatly reduces species richness and species’ abundances
for most taxa (see Section I.3), genetic resources at the
assemblage level are most likely greatly reduced in oil
palm plantations. Consequently, the long-term viability
of forest plant and animal populations is expected to
be negatively affected in oil palm landscapes due to the
extinction of rare alleles and reduced gene flow between
isolated forest fragments (Vellend, 2003), as recently shown
for Malaysian ants (Bickel et al., 2006) and bats (Struebig
et al., 2011). Second, genetic resources are further reduced
because the oil palms themselves are derived from genetically
limited sources (Thomas, Watson & Hardon, 1969; Corley
& Tinker, 2003). With clonal propagation of oil palms,
genetic variation is expected to decrease even further due
to the planting of high-yield clones (Corley & Tinker,
2003). However, genetic variability in oil palms has
attracted considerable research (e.g. Cochard et al., 2009),
and natural genetic variation exists. Several organizations,
such as the Malaysian Palm Oil Board, maintain oil palms
of a variety of genetic origins (Hayati et al., 2004). In
sum, genetic resources are critical to maintaining global
biodiversity and to maintaining high yields from oil palm
plantations.
(a) Mitigation
Much of the loss of genetic resources due to the loss of species
and decreases in species abundances cannot be mitigated.
Mitigation measures for biodiversity loss (see Table 3) will
also help to maintain genetic resources. On-going breeding
programs can make conservation of oil palm genetic diversity
a priority (Corley & Tinker, 2003). Breeding can be carried
out selectively to maintain genetic diversity while still
preserving local co-adapted traits (Corley & Tinker, 2003).
In addition, genetic modification has been suggested to have
the potential to increase yield and resistance to disease and
stress (Corley & Tinker, 2003).
(b) Research gaps
Research gaps include quantifying the non-oil palm genetic
resources lost with conversion from forest, as well as
researching the necessary steps to prevent their irreversible
loss. For oil palm, research is needed on the appropriate
balance between selection for uniformly high-yielding strains
and the maintenance of genetic diversity necessary to convey
disease and disturbance resistance.
(12) Medicinal resources
This function refers to medicinal resources derived from the
organisms in an ecosystem. An estimated 52885 flowering
plant species are used today worldwide for medicinal
purposes (Schippmann, Leaman & Cunningham, 2002) and
over 2000 Southeast Asian forest species are used in women’s
healthcare (de Boer & Cotingting, 2014). In Kalimantan,
Indonesian local healers use more than 250 medicinal
plants of which Caniago & Siebert (1998) found the most
in old secondary forest (79 species) and the fewest in logged
areas (18 species), concluding that land degradation and
forest conversion reduce the availability of medicinal plants.
Mathews, Yong & Nurulnahar (2007) surveyed oil palm
plantation ecosystems and identified 48 species of medicinal
value, many of which were common generalist species. Many
of these are considered weeds, and are actively removed
(Sarada, Nair & Reghunath, 2002; Mathews et al., 2007).
However, the conversion of forests to oil palm plantations
leads to an impoverishment of the biotic community
(Danielsen et al., 2009, see Section I.3) and with that to an
overall loss of medicinal resources. Consequently, the expan-
sion of oil palm plantations represents a loss in this function
at local, regional, and global scales compared to forest.
(a) Medicinal benefits of oil palm
Documented uses of palm oil include treating prostate
diseases, use as a component in skin lotion, and as a carrier
for medicinal extracts of other plants (Arsic et al., 2010,
2012; Emmanuel, 2010). Historically, palm oil has been used
for soap production (Henderson & Osborne, 2000) and to
cure colds and bad coughs (Macía, 2004). Traditional use
of leaf extract has led to its study for wound-healing and
antimicrobial properties (Chong et al., 2008; Sasidharan et al.,
2010; Sasidharan, Logeswaran & Latha, 2012), and the role
of its antioxidants in treating disease (e.g. diabetes; Rajavel
et al., 2012). Anecdotally, a variety of uses have been ascribed
to oil palm, including all parts of the plant (Opute, 1975;
Caniago & Siebert, 1998; Chong et al., 2008).
(b) Mitigation and research gaps
Measures to mitigate the loss of medicinal resources will
be difficult as the medicinal properties of many species
remain unknown, especially for species unknown to science.
Both the medicinal uses of oil palm products and the
discovery of new medicinally useful species remain active
fields of research. Research cataloguing the biodiversity of
Southeast Asian forests and its medicinal properties may
allow species of medicinal importance to be conserved and
their medicinal benefits retained. Such studies should be
guided by traditional ecological knowledge and detailed
ethnobotanical research. Studies of medicinal uses of oil
palm products would also benefit from ethnobotanical
studies, and medicinal claims should be backed up by
clinical, double-blind studies published in respected medical
journals.
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Ecosystem functions of oil palm versus forest 21
(13) Ornamental resources
Ornamental resources are the variety of organisms in
ecosystems with potential ornamental use (e.g. as garden
plants, pets, or jewellery; definition modified from de
Groot et al., 2002). This includes organisms collected for
domestic purposes (predominantly bird species; Nash, 1993),
or for international trade (Ng & Tan, 1997; Sodhi et al.,
2004; New, 2005; Nijman, 2010; Phelps & Webb, 2015),
in particular plants (especially orchids), invertebrates (bird
spiders, scorpions, stick insects, rhino beetles, butterflies,
and moths), and vertebrates (fish, amphibians, reptiles,
birds and mammals). Very few studies on this topic were
found (Table 1), as most studies instead focus on the
over-exploitation of species used for ornamental purposes
(e.g. Nijman, 2010), and much of the trade is illegal (e.g.
Phelps & Webb, 2015). Ornamental resources have been
found to decrease in cultivated land relative to forests (Sheil
& Liswanti, 2006). Changes in hydrology due to the drainage
of peat land for the cultivation of oil palm plantations
has led to population decreases of some economically
important ornamental fish species, e.g. Betta spp. and the
arowana, Scleropages formosos, despite these species being bred
commercially (Ng & Tan, 1997; Yule, 2010; Posa, Wijedasa
& Corlett, 2011). A few ground-dwelling python species used
in the pet trade (i.e. Python brongersmai, P. curtus, P. breitensteini)
and several rat snake species (e.g. Ptyas spp.) and cobras
(e.g. Naja sumatrana, N. sputatrix) harvested for their skins and
medicinal purposes, largely benefit from oil palm plantations
(Whitten et al., 1984; Shine et al., 1999; Auliya, 2006) due to
high rodent densities attracted to palm fruit (Buckle et al.,
1997). However the commercial offtake and trade for their
skins and medicinal uses is many times over that of the
pet trade (see CITES, 2015). Keeping caged pet birds is
a common practice and an important part of Indonesian
culture (Jepson & Ladle, 2009), and there is evidence of
bird trapping from oil palm plantations (K. Darras, personal
observations). Based on preliminary results of an ongoing bird
market survey in Jambi city, Indonesia, the majority of birds
are collected from forests (33 species from forest compared
to 15 species in oil palm, only two shared; K. Darras &
T. Tscharntke, personal observations). Despite decreasing
forest cover and decreasing accessibility to forests, oil palm
supplies considerably fewer birds at lower prices than do
forests, representing a decrease in the ornamental resources
ecosystem function.
(a) Mitigation and research gaps
Overall, it appears that the ornamental resources in forests
are greater than in oil palm plantations and irreplaceable
in the case of birds, and this is likely true for many other
taxa as well. More research is needed to understand the
separate and combined effects of the oil palm industry
and the trade in ornamental species on the availability
of ornamental resources, their viability, and long-term
sustainability.
(14) Information functions
Information functions provide ‘opportunities for cognitive
development’ (de Groot et al., 2002), in other words, they
provide the basis for rather intangible benefits that people
derive from an ecosystem. They are subject to individual
perception and valuation and contribute to maintenance of
human health. de Groot et al. (2002) classify information
functions into: (i) aesthetic information, i.e. appealing
landscape elements; (ii) recreation and tourism, constituted
through a variety of such landscapes; (iii) cultural/artistic
inspiration and spiritual/historic information, both inherent
in natural features with respective values; and (iv) scientific
and educational information, i.e. scientific and educational
values in nature. In general, the conversion of forest to oil
palm cultivation leads to a large loss in information functions.
We discuss all information functions together, as we found
only 30 papers relevant to information functions in oil palm
plantations (see online Appendix S3). Most of these papers
address aesthetic, cultural and artistic, spiritual and historic
aspects (23), nine papers treat recreation and tourism, and
only six papers address issues of educational and scientific
relevance. In part, the under-representation of information
functions is due to a focus of research on the socioeconomic
benefits of oil palms (e.g. Rist, Feintrenie & Levang, 2010;
Hector et al., 2011; Cramb & Curry, 2012; Obidzinski et al.,
2012; Lee et al., 2014). Further, few articles address the triad
between oil palms, information functions, and forest – the
loss of information functions during forest conversion is
hardly investigated.
(a) Information functions associated with oil palm and palm oil
In its native range, locations where oil palms are growing
are considered sacred places (Gruca, van Andel & Balslev,
2014). Several parts of the palm, including palm oil, are
integrated into local traditions and customs [e.g. local food
cultures (Atinmo & Bakre, 2003; Gruca et al., 2014), and
in other ritual ceremonies and traditional medicines (Gruca
et al., 2014)]. Outside its native range, oil palms may also
be incorporated into local culture and traditions. In Bahia,
Brazil, agro-ecological cultivation of oil palm in polyculture
has resulted in a local cultural landscape (Watkins, 2015).
In Jambi province, Sumatra, Indonesia, smallholder farmers
were found to perceive small oil palm plantations as clean
and beautiful, in contrast to formerly present agroforests
(Therville, Feintrenie & Levang, 2011). However, large
oil palm monocultures are typically associated with few
information functions (Watkins, 2015).
(b) Information functions lost with forest conversion to oil palm
Unlike oil palm plantations, forests are valued highly for
different reasons (Sheil & Liswanti, 2006; Sheil et al., 2006;
Pfund et al., 2011), e.g. health, cultural, and spiritual purposes
(Meijaard et al., 2013) and recreational potential (Bennett
& Reynolds, 1993; Broadbent et al., 2012; Burke & Resosu-
darmo, 2012; Ratnasingam et al., 2014). With deforestation
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
22 C. Dislich and others
for establishment of oil palm plantations and the related
depletion of resources, these functions and the so-called
‘locality of value’ (Nooteboom & de Jong, 2010) likewise
disappear. A case study conducted in Indonesia recorded
the destruction of the ‘ancestral grave which is located in
forested groves that is of cultural significance to indigenous
people’ (Manik, Leahy & Halog, 2013, p. 1390), but note
that graveyards can also exist in oil palm plantations (Colch-
ester et al., 2011). Land-use conflicts may also lead to the
depletion of information functions (historical and spiritual),
as happened in Kalimantan, Indonesia (Potter, 2009).
A closer look at the recreational potential of ecosystems
reveals that natural forests support a tourist industry while
clearance for oil palm plantations or other land uses reduces
the aesthetic qualities and thus the basis for nature-based
tourism. For example, Bennett & Reynolds (1993) found
a loss of 50% of tourism revenues (3.7 million USD)
when mangroves were cleared for ponds and oil palm.
Further, tourism presents an alternative income source and
is therefore a means to nature conservation (Broadbent et al.,
2012) and long-run green growth (Burke & Resosudarmo,
2012). The difference in the appreciation of information
functions between forest and oil palm is particularly large
for those people who traditionally depend on forests for their
livelihoods (Manik et al., 2013).
(c) Mitigation
Some information functions, such as spiritual and historic
information, are linked to certain species or places.
Consequently, prioritizing the conservation of those species
and forest cover of distinct places could maintain some
information functions. However, oil palm plantations and
forests are qualitatively different environments and we do
not see any way to mitigate the loss of many information
functions resulting from forest conversion to oil palm.
(d ) Research gaps
Not much research on information functions has
been conducted. Consequently, information functions are
proportionally under-represented among all ecosystem
functions (Table 1). Research has focused on socio-economic
benefits, human well-being following land-use change and
land-use conflicts, instead of on information functions
(following de Groot et al., 2002) or transformation of
cultural ecosystem services (see, e.g. Millennium Ecosystem
Assessment, 2005).
IV. DISCUSSION
(1) Impacts of oil palm plantations
With few exceptions, oil palm plantations have reduced
ecosystem functioning compared to forests (Table 2). The
greatest impacts are on gas regulation, water regulation
and supply, habitat functions, and information functions.
Food and raw material production is the only function that
shows a net increase in oil palm plantations. With proper
management, it may be possible to maintain some functions
at forest levels (water regulation, regulation of extreme events,
soil retention, nutrient regulation, and waste treatment).
Evaluating ecosystem functions in oil palm plantations
is often not straightforward. First, many functions are
interrelated – for instance, poorer water regulation in oil
palm plantations can also lead to increased risks of floods
and droughts and greater losses of soil and nutrients. Second,
ecosystem functions change throughout the life cycle of
an oil palm plantation, with greatest losses in functioning
when land is cleared for plantation establishment, and a
gradual restoration of some functions as plantations mature.
Third, ecosystem functions in oil palm plantations depend
heavily on plantation management practices, which vary
greatly. Fourth, some effects on ecosystem functions are
heterogeneous (e.g. N2O balance, Table 2) and may vary
depending on local conditions. Finally, in some cases,
contrasting effects on ecosystem functions can be present
simultaneously. For example, some species abundances
greatly increase while others greatly decrease (Table 2).
(2) Options for mitigation
First, impacts of oil palm cultivation and losses in ecosystem
functions could be greatly reduced by stopping the conversion
of forest (especially peat forest) to oil palm, and establishing
new oil palm plantations only on degraded or existing
agricultural land (Ha¨rdter, Chow & Hock, 1997; Yusoff
& Hansen, 2007; Reijnders & Huijbregts, 2008). However,
debate continues over what land is defined as acceptable
for oil palm (Koh & Wilcove, 2008). This includes indirect
conversion where cultivated land replaces forest, and oil palm
then replaces other cultivated land (i.e. the cascade effect;
Lambin & Meyfroidt, 2011). The loss of some forest-specific
ecosystem functions cannot be mitigated (e.g. loss of forested
areas critical to the persistence of endemic forest-specialist
species; Gibson et al., 2011). In order to maintain certain
ecosystem functions such as medicinal resources, and habitat
and nursery functions, these areas would need to remain
uncleared, and cleared areas would need to be restored.
The negative impacts of oil palm plantations may also
be reduced through improved plantation management (see
Table 3). Many mitigation management practices contribute
to improving multiple ecosystem functions at once (see
Table 3).
(3) Major research gaps
We identified important research gaps for each ecosystem
function. Generally, there is a need for comparative
studies to identify the influences of plantation age, local
environmental conditions, and plantation management on
ecosystem functioning within and surrounding plantations.
Management practices vary greatly among plantations
(Vermeulen & Goad, 2006; Comte et al., 2012), and
these factors have largely been neglected. Studies should
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
Ecosystem functions of oil palm versus forest 23
explicitly consider differences between smallholder and
large-scale plantations (Azhar et al., 2011; Harsono et al.,
2012; Jambari et al., 2012). Most of the studies we reviewed
are based on a small number of observations in a small
number of oil palm plantations and thus give only limited,
coarse-scale information on ecosystem functions. Finally,
capacity building is required to foster studies by local
scientists, who are likely to have the most complete and
up-to-date knowledge (Sheil et al., 2009), as well as better
access to knowledge held by native and indigenous people.
(4) Considerations of scale: spatial, temporal, and
management
Oil palm plantations affect ecosystem functioning at different
spatial scales. At the global scale, food and raw material
production functions are increased with a corresponding
loss of climate regulation, habitat functions, and genetic,
medicinal and ornamental resources. At the regional
scale (countries/islands), air quality, water regulation and
moderation of extreme events functions are decreased. At
the landscape scale (plantation and immediate surroundings),
microclimate, air quality, water regulation, moderation
of extreme events, and erosion prevention are decreased
while soil fertility is changed. Aside from additional
waste production, the effects on local waste treatment are
unclear. The regional and local effects on pollination and
biological control are also unclear. Educational and scientific
information functions are lost at all scales, due to a loss
of species and habitat diversity associated with the loss of
forest (e.g. Foster et al., 2011). Local-scale changes may also
drive larger-scale effects, especially on climate regulation
(droughts) and downstream regions within watersheds (flood
risks, nutrient leaching, soil erosion). The landscape context
and cross-scale impacts of oil palm plantations thus warrant
further research.
Ecosystem functioning also shows strong temporal patterns
(Table 2). Most decreases in ecosystem functioning occur with
the loss of forest or drainage of peat (i.e. GHG emissions,
air quality reduction, water regulation changes, moderation
of extreme events, soil retention, and loss of information
functions). Some recovery of ecosystem functioning occurs
with the establishment of the plantations, including carbon
fixation by oil palms and stabilization of soil with
establishment of ground cover. Production functions are also
dynamic, starting at zero at establishment, reaching a peak at
intermediate plantation age, and then declining as the palms
reach heights that are difficult to harvest (Sheil et al., 2009).
Much of the temporal fluctuation in ecosystem functioning is
mediated by plantation management. For example, nutrient
regulation depends strongly on fertilizer application and
mulching approach (Comte et al., 2012). However, much
knowledge is missing about the processes occurring during
oil palm ageing and during the replacement of old with
new palms. The number of sequential plantings and their
dependence on external inputs (nutrients) remains unknown,
thus impeding evaluations of long-term functioning and
sustainability.
A third scale important to oil palm effects on ecosystem
functions is the scale at which management is carried out.
However, for many ecosystem functions, the difference in
effect on ecosystem functions, if any, between smallholder
and large-scale plantations is unknown (e.g. water regulation,
soil loss, pollination, biological control).
(5) Policy considerations
An accurate assessment of ecosystem functions is essential to
the establishment of comprehensive guidelines for protecting
natural capital. The findings of this review could be used
to assess potential changes in ecosystem functions associated
with oil palm plantations. This comprehensive assessment
could complement on-going efforts to map ecosystem
services (e.g. Barano et al., 2010), and provide a basis for
sustainable development policies in regions where oil palm is
grown. Official governmental policies, certification schemes,
lobbying by industry and non-governmental organizations
and consumer choices (e.g. boycotts) all influence oil palm
production, and hence ecosystem functions in oil palm
plantations. For example, official governmental policy in
Indonesia prohibits the clearing of land through burning,
but laws are not always enforced (Sheil et al., 2009).
Enforcing existing regulations would therefore be a positive
step forward. Government policies in importing countries
may also influence oil palm production, as some countries
have set import standards in response to public pressure
(e.g. with respect to biofuels, European Union Renewable
Energy Directive; United States Renewable Fuel Standard
2; Lim, Biswas & Samyudia, 2015), although corporations
can partially by-pass such restrictions by exporting oil palm
products from sustainably managed plantations to countries
with import standards, while exporting oil palm products
produced unsustainably to other markets (e.g. China and
India; Lim et al., 2015).
In order partly to address the limited compliance with
existing legislation, Indonesia has now introduced the
Indonesia Sustainable Palm Oil (ISPO) certification scheme
(mandatory for large plantations as of 2014, and for
smallholders by 2020). The ISPO requires that oil palm
only be planted on lands for which official legal titles exist,
which excludes recently deforested land and peatlands (see
http://www.ispo-org.or.id/index.php?lang=en). Whether
implementation will indeed proceed as planned is an open
question, particularly as implementation is seen as costly
to producers and might cause particular challenges for
smallholders who often do not have legal titles for their land.
Internationally, oil palm growers can obtain certification
from the Roundtable on Sustainable Palm Oil (RSPO,
which certified 16% of global palm oil production as of
March 2014; Lim et al., 2015) and/or from the International
Sustainability and Carbon Certification (ISCC, which as
of May 2014 only certified a small part of the market;
Lim et al., 2015). The Roundtable on Sustainable Palm Oil
(RSPO) is a well-known international voluntary certification
scheme which has been in operation since 2004 (Nesadurai,
2013). The RSPO is an internationally recognized standard
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
24 C. Dislich and others
that focusses on transparency, compliance with laws and
regulations, long-term viability, environmental and social
responsibility, among other aspects and is attracting an
increasing number of producers (see rspo.org). However,
RSPO has a mixed record in ensuring environmental
sustainability and maintaining biodiversity in oil palm and
more needs to be done to strengthen the standard as well as
improve compliance (e.g. Paoli et al., 2010; Brandi et al., 2012;
Nesadurai, 2013). Finally, public pressure on the oil palm
industry, especially from non-government organizations
(NGOs) such as Greenpeace, the Rainforest Action Network,
and the World Wildlife Fund, has had a strong influence on
public policy relating to oil palm plantations (Lim et al.,
2015). In summary, existing policies have been insufficient
to prevent the loss of many ecosystem functions associated
with the establishment of oil palm plantations (Table 2,
Fig. 2). It appears that this has been largely due to poor
compliance with existing laws, policies, and standards. A
more holistic sustainability assessment framework (Lim et al.,
2015), including the ecosystem functions highlighted herein
and their associated ecosystem services, could serve to correct
for deficiencies and further strengthen the existing standards.
V. CONCLUSIONS
(1) This comprehensive review of ecosystem functions
in oil palm plantations revealed that 11 of 14 ecosystem
functions showed a net decrease in oil palm plantations.
(2) We provide novel reviews of the following ecosystem
functions in oil palm plantations: genetic resources,
medicinal resources, ornamental resources, and information
functions. We highlight that there are critically important
knowledge gaps with respect to these neglected but important
topics.
(3) We identify research gaps, mitigation options, and
highlight mitigation options that improve multiple ecosystem
functions simultaneously. With respect to the gaps, most
results originate from short-term studies that may not be
representative of whole ecosystems. In this respect, we reveal
a great need for more comprehensive and long-term studies,
with more variables measured, comparing a wider range of
environments and management practices.
(4) Ecosystem functions in the regulation, habitat, and
information categories tend to decrease in oil palm
ecosystems compared to forest as a reference land use. Very
large and globally important decreases occur in greenhouse
gas regulation, habitat provision, medicinal, genetic,
and ornamental resources, and recreational potential.
Regionally, water regulation and erosion prevention
functions are decreased. The decreasing trends vary
depending on plant ages, soil types, and spatial scale. On the
other hand, the food and raw materials production function
of oil palm is higher compared to that of forest.
(5) For gas and climate regulation, water regulation,
moderation of extreme events, and habitat and nursery
functions, a key option from an ecosystem function
perspective is to preserve peatlands (i.e. maintaining
upstream hydrology and completely avoiding drainage;
Comte et al., 2012).
(6) By knowing how oil palm affects the degree and the
direction of changes in ecosystem functions for each category,
strategies can be developed to reduce the degradation of
ecosystem functions while maintaining or even increasing
socio-economic functioning.
VI. ACKNOWLEDGEMENTS
This study was financed by the German Research
Foundation (DFG) in the framework of the collaborative
German – Indonesian research project CRC990 ‘EFForTS,
Ecological and Socioeconomic Functions of Tropical
Lowland Rainforest Transformation Systems (Sumatra,
Indonesia)’. We thank Renzoandre de la Pen˜a Lavander,
Frauke Thorade, Nina Heymann, and Alina Maj Kraus
for help with the literature database. We thank Elvira
Ho¨randl for assistance in understanding oil palm understorey
pollination systems, Lisa Denmead and two reviewers for
comments on the manuscript. G.P. acknowledges funding
from the FP7 project EU BON (ref. 308454).
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VIII. SUPPORTING INFORMATION
Additional supporting information may be found in the
online version of this article.
Appendix S1. Oil palm expansion over time.
Appendix S2. Literature search terms.
Appendix S3. JabRef database.
Appendix S4. Rationale for net ecosystem function effects.
(Received 9 September 2015; revised 7 July 2016; accepted 11 July 2016 )
Biological Reviews (2016) 000–000 © 2016 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.