Oil palm plantations have dramatically expanded in tropical Asia over the past decades. Although their establishment has been projected to increase nitrous oxide (N2O) emissions, earlier reports have shown inconsistent results. This study analyzed these previously published data to compare N2O emissions in oil palm plantations to reference forests. A linear mixed-effects model was used to examine the significance of the effect of establishing oil palm plantations on N2O emissions, rather than to calculate mean effect sizes because of limitations in the data structure. The results indicated that N2O emissions were significantly greater from oil palm plantations than from reference forests, as expected. This is the first study to report the effect of oil palm plantations on N2O emissions by synthesizing previously published data. To quantify the size of this effect, additional studies with frequent and long-term monitoring data are needed.
Oil palm (Elaeis guineensis Jacq.) plantations in tropical Asia have expanded dramatically in the past decades and has contributed to a significant decline in natural forests (Gaveau et al. 2016). According to the FAO (FAOSTAT 2021), the harvested area of oil palm fruit increased from 3.6 million ha in 1961 to 28.3 million ha in 2019; approximately 70% was in Indonesia and Malaysia. The rapid and large expansion of oil palm plantations causes loss of species richness and functional diversity (Koh and Wilcove 2008; Edwards et al. 2014).
Expansion of oil palm plantations has attracted global attention, not only due to the loss of biodiversity but also to enhanced nitrous oxide (N2O) emissions (Kaupper et al. 2020; Skiba et al. 2020). N2O is mainly produced by soil microbial processes such as nitrification and denitrification (Davidson et al. 2000). Because nitrogen (N) is the main source of N2O production, increased N input into soils, including the deposition of atmospheric N (Zhang et al. 2008; Wang et al. 2014), nitrogen-rich litter inputs (Arai et al. 2008; Ishizuka et al. 2021a, b), and chemical fertilization (Liu and Greaver 2009), stimulates N2O emissions. Because N fertilization is a common practice for oil palm plantations, the conversion of forests to oil palm plantations is generally projected to increase N2O emissions (Kaupper et al. 2020; Skiba et al. 2020). Several studies have reported greater N2O emissions from oil palm plantations than from forests in the same region (Melling et al. 2007; Hewitt et al. 2009; Drewer et al. 2021). Nitrogen fertilization resulted in greater N2O emissions in multiple oil palm plantations (Aini et al. 2015; Hassler et al. 2017; Oktarita et al. 2017; Rahman et al. 2019), although special (fertilized vs unfertilized areas) and temporal (short vs long period after fertilization) heterogeneity of the effects of fertilization is very large (Fowler et al. 2011; Aini et al. 2015).
However, several studies have reported only slight differences in N2O emissions between oil palm plantations and reference forests (Ishizuka et al. 2005; Swails et al. 2021). Even smaller amounts of N2O emissions have been reported on oil palm plantations (Yashiro et al. 2007). These inconsistent results could be partly due to insufficient monitoring to detect any fertilization effects (Yashiro et al. 2007; Aini et al. 2015). Hassler et al. (2017) discovered that large-scale plantations emit greater levels of N2O than forests, but emissions from smallholder plantations did not differ significantly from forest emissions. Thus, previous results have been inconsistent. A larger-scale analysis synthesizing published data is necessary to evaluate the effects on N2O emissions of tropical forest conversion to oil palm plantations.
Materials and methods
Studies reporting N2O fluxes from oil palm plantations and forests in the same region were collected using the ISI Web of Science database and the following combinations of keywords: [N2O OR “nitrous oxide”] AND [“oil palm”] AND [soil]. The final search was completed on August 23, 2021. Only field-based studies reporting N2O fluxes from both oil palm plantations and reference forests were selected for data extraction; incubation experiments were excluded because the environmental conditions varied substantially. Primary, secondary, or disturbed forests were selected as reference forests. A total of 49 papers were identified through the search, however, only eight met the above criteria. The cumulative or average N2O emissions were extracted. Cumulative N2O emissions were converted into fluxes (µg N m–2 h–1). Vegetation type (oil palm vs reference forest), soil type, mean temperature, and annual precipitation were recorded. Google Scholar was used to complement the literature search, and three additional papers were added to the database. Finally, 69 N2O flux data from 63 study sites in 10 regions were extracted from the 11 papers (Table S1). Two datasets were prepared. The first was a “full dataset” consisting of all data obtained and containing short-term observations such as single-time measurements. The second was a “long-term frequent monitoring dataset,” which consisted of monitoring data with a frequency of every ≤ 2 months and a period of ≥ 1 year.
Previous meta-analyses generally used effect sizes (i.e., log-transformed values of N2O emissions from post land-use change sites divided by those from reference sites) to evaluate the effects of land-use changes on N2O emissions (Hergoualc’h and Verchot, 2014; Van Lent et al. 2015; McDaniel et al. 2019). However, pairwise observations have been uncommon in previous studies (Table S1). In addition, the standard deviation data needed for this approach have been occasionally unavailable. Therefore, in the present study, the effect of establishing an oil palm plantation on N2O emissions was evaluated using a linear mixed-effects model. The model was constructed with vegetation type (oil palm plantation vs. reference forest) as a fixed effect, and the study region and study site (Table S1) as random effects. The N2O flux data were natural log-transformed before analysis. Since a N2O flux datum was smaller than zero, it was replaced with one-half (0.57 µg N2O-N m–2 h–1) of the minimum gas flux in the dataset (1.14 µg N2O-N m–2 h–1) (Mori et al. 2016). Statistical analyses were performed using R, version 4.1.1 (The R Foundation for Statistical Computing, Vienna, Austria) and the lme4 and lmerTest packages (R Core Team 2021).
Results and discussion
Linear mixed-effects model analysis demonstrated that N2O emissions were significantly greater from oil palm plantations than from reference forests (Fig. 1, Table 1), which is in agreement with the commonly accepted view (Kaupper et al. 2020; Skiba et al. 2020). This result was obtained using both the full dataset (Fig. 1a, Table 1) and the frequent long-term monitoring dataset (Fig. 1b, Table 1). As suggested previously, N fertilization is probably the most important contributing factor in these increased N2O emissions (Hassler et al. 2017). Drainage may cause greater N2O emissions from peat soils because denitrification, which reduces N2O to N2 under flooded conditions, may be inhibited by reduced water content (Murdiyarso et al. 2010).
Thus, the present study demonstrated the enhancing effect of establishing oil palm plantations on N2O emissions, but this meta-analysis also has limitations. First, the sample size is insufficiently robust to quantify the effect on N2O emissions and to estimate its impact on global warming (Skiba et al. 2020), although the linear mixed-effects model showed that tropical forest conversion into oil palm plantations elevated ln(N2O emissions) by 0.7 to 0.85 (µg N2O-N m–2 h–1) (Table 1). More long-term and frequent monitoring data are required. The collected dataset included 29 oil palm plantations and 34 reference forests, among which only a third (11 oil palm plantations and 12 reference forests) had data collected via long-term and frequent monitoring (i.e., with a frequency of every ≤ 2 months and a period of ≥ 1 year). These long-term and frequent monitoring-based data are particularly important because rare or short-term gas flux measurements may fail to detect the fertilization-derived hotspots of N2O fluxes (Yashiro et al. 2007; Aini et al. 2015), which would lead to an underestimate of the effect of oil palm plantations on N2O emissions. Secondly, the relative importance of factors contributing the higher N2O emissions in oil palm plantations, (such as N fertilization or drainage of peatlands) were not determined, also due to the insufficient sample size. For constructing models to estimate the impact of oil palm plantations on N2O emissions, additional data are necessary.
Despite these limitations, this paper has shown the enhancing effect of establishing oil palm plantations on N2O emissions by synthesizing previously published data. This meta-analysis provides a data-driven basis for the general projection that tropical forest conversion enhances N2O emissions (Kaupper et al. 2020; Skiba et al. 2020) and underscores a need for oil palm management practices that mitigate N2O emissions.
AiniHergoualc’h FKK, Smith JU, Verchot L (2015) Nitrous oxide emissions along a gradient of tropical forest disturbance on mineral soils in Sumatra. Agric Ecosyst Environ 214:107–117. https://doi.org/10.1016/j.agee.2015.08.022
Arai S, Ishizuka S, Ohta S, Ansori S, Tokuchi N, Tanaka N, Hardjono A (2008) Potential N2O emissions from leguminous tree plantation soils in the humid tropics. Global Biogeochem Cycles 22:GB2028. https://doi.org/10.1029/2007GB002965
Davidson EA, Keller M, Erickson HE, Verchot LV, Veldkamp E (2000) Testing a conceptual model of soil emissions of nitrous and nitric oxides. Bioscience 50:667–680. https://doi.org/10.1641/0006-3568(2000)050[0667:TACMOS]2.0.CO;2
Drewer J, Leduning MM, Griffiths RI, Goodall T, Levy PE, Cowan N, Comynn-Platt E, Hayman G, Sentian J, Majalap N, Skiba UM (2021) Comparison of greenhouse gas fluxes from tropical forests and oil palm plantations on mineral soil. Biogeosciences 18:1559–1575. https://doi.org/10.5194/bg-18-1559-2021
Edwards FA, Edwards DP, Larsen TH, Hsu WW, Benedick S, Chung A, Vun Khen C, Wilcove DS, Hamer KC (2014) Does logging and forest conversion to oil palm agriculture alter functional diversity in a biodiversity hotspot? Anim Conserv 17:163–173. https://doi.org/10.1111/acv.12074
FAOSTAT (2021) http://www.fao.org/faostat/en/#data/QCL. Accessed Aug 2021
Fowler D, Nemitz E, Misztal P, di Marco C, Skiba U, Ryder J, Helfter C, Neil Cape J, Owen S, Dorsey J, Gallagher MW, Coyle M, Phillips G, Davison B, Langford B, MacKenzie R, Muller J, Siong J, Dari-Salisburgo C, di Carlo P, Aruffo E, Giammaria F, Pyle JA, Hewitt CN (2011) Effects of land use on surface-atmosphere exchanges of trace gases and energy in Borneo: comparing fluxes over oil palm plantations and a rainforest. Philos Trans Royal Soc B 366:3196–3209. https://doi.org/10.1098/rstb.2011.0055
Gaveau DLA, Sheil D, Husnayaen SMA, Arjasakusuma S, Ancrenaz M, Pacheco P, Meijaard E (2016) Rapid conversions and avoided deforestation: Examining four decades of industrial plantation expansion in Borneo. Sci Rep 6:1–13. https://doi.org/10.1038/srep32017
Hassler E, Corre MD, Kurniawan S, Veldkamp E (2017) Soil nitrogen oxide fluxes from lowland forests converted to smallholder rubber and oil palm plantations in Sumatra, Indonesia. Biogeosciences 14:2781–2798. https://doi.org/10.5194/bg-14-2781-2017
Hergoualc’h K, Verchot LV (2014) Greenhouse gas emission factors for land use and land-use change in Southeast Asian peatlands. Mitig Adapt Strateg Glob Chang 19:789–807. https://doi.org/10.1007/s11027-013-9511-x
Hewitt CN, MacKenzie AR, Di Carlo P, Di Marco CF, Dorsey JR, Evans M, Fowler D, Gallagher MW, Hopkins JR, Jones CE, Langford B, Lee JD, Lewis AC, Lim SF, McQuaid J, Misztal P, Moller SJ, Monks PS, Nemitz E, Oram DE, Owen SM, Phillips GJ, Pugh TAM, Pyle JA, Reeves CE, Ryder J, Siong J, Skiba U, Stewart DJ (2009) Nitrogen management is essential to prevent tropical oil palm plantations from causing ground-level ozone pollution. Proc Natl Acad Sci USA 106:18447–18451. https://doi.org/10.1073/pnas.0907541106
Ishizuka S, Iswandi A, Nakajima Y, Yonemura S, Sudo S, Tsuruta H, Murdiyarso D (2005) The variation of greenhouse gas emissions from soils of various land-use/cover types in Jambi province, Indonesia. Nutr Cycl Agroecosystems 71:17–32. https://doi.org/10.1007/s10705-004-0382-0
Ishizuka S, Mori T, Nakayama Y, Nakayama Y, Kawabata C, Konda R, Sasaki T, Sawa Y, Hamotani Y, Gobara Y, Kuwashima K, Wicaksono A, Heriyanto J, Hardjono A, Ohta S (2021a) Effects of conversion from leguminous acacia to non-leguminous eucalyptus on soil N2O emissions in tropical monoculture plantations. For Ecol Manage 481:118702. https://doi.org/10.1016/j.foreco.2020.118702
Ishizuka S, Ohta S, Mori T, Konda R, Gobara Y, Hamotani Y, Kawabata C, Wicaksono A, Heriyanto J, Hardjono A (2021b) N2O emissions in Acacia mangium stands with different ages, in Sumatra. Indonesia for Ecol Manage 498:119539. https://doi.org/10.1016/j.foreco.2021.119539
Kaupper T, Hetz S, Kolb S, Yoon S, Horn MA, Ho A (2020) Deforestation for oil palm: impact on microbially mediated methane and nitrous oxide emissions, and soil bacterial communities. Biol Fertil Soils 56:287–298. https://doi.org/10.1007/s00374-019-01421-3
Koh LP, Wilcove DS (2008) Is oil palm agriculture really destroying tropical biodiversity? Conserv Lett 1:60–64. https://doi.org/10.1111/j.1755-263x.2008.00011.x
Liu LL, Greaver TL (2009) A review of nitrogen enrichment effects on three biogenic GHGs: the CO 2 sink may be largely offset by stimulated N2O and CH4 emission. Ecol Lett 12:1103–1117. https://doi.org/10.1111/j.1461-0248.2009.01351.x
McDaniel MD, Saha D, Dumont MG, Hernandez M, Adams MA (2019) The effect of land-use change on soil CH4 and N2O fluxes: a global meta-analysis. Ecosystems 22:1424–1443
Melling L, Hatano R, Goh KJ (2007) Nitrous oxide emissions from three ecosystems in tropical peatland of Sarawak, Malaysia. Soil Sci Plant Nutr 53:792–805. https://doi.org/10.1111/j.1747-0765.2007.00196.x
Mori T, Ishizuka S, Konda R, Wicaksono A, Heriyanto J, Hardjono A, Ohta S (2016) Effects of phosphorus addition on N2O emissions from an Acacia mangium soil in relatively aerobic condition. Tropics 25:117–125. https://doi.org/10.3759/tropics.MS15-15
MurdiyarsoHergoualc’H DK, Verchot L (2010) Opportunities for reducing greenhouse gas emissions in tropical peatlands. Proc Natl Acad Sci USA 107:19655–19660. https://doi.org/10.1073/pnas.0911966107
Oktarita S, Hergoualc’H K, Anwar S, Verchot LV (2017) Substantial N2O emissions from peat decomposition and N fertilization in an oil palm plantation exacerbated by hotspots. Environ Res Lett 12:104007. https://doi.org/10.1088/1748-9326/aa80f1
R Core Team (2021) R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL https://www.R-project.org/. Accessed June 2022
Rahman N, Bruun TB, Giller KE, Magid J, van de Ven GWJ, de Neergaard A (2019) Soil greenhouse gas emissions from inorganic fertilizers and recycled oil palm waste products from Indonesian oil palm plantations. GCB Bioenergy 11:1056–1074. https://doi.org/10.1111/gcbb.12618
SkibaHergoualc’h UK, Drewer J, Meijide A, Knohl A (2020) Oil palm plantations are large sources of nitrous oxide, but where are the data to quantify the impact on global warming? Curr Opin Environ Sustain 47:81–88. https://doi.org/10.1016/j.cosust.2020.08.019
SwailsHergoualc’h EK, Verchot L, Novita N, Lawrence D (2021) Spatio-temporal variability of peat CH4 and N2O fluxes and their contribution to peat GHG budgets in Indonesian forests and oil palm plantations. Front Environ Sci 9:617828. https://doi.org/10.3389/fenvs.2021.617828
Van Lent J, Hergoualc’h K, Verchot LV (2015) Reviews and syntheses: Soil N2O and NO emissions from land use and land-use change in the tropics and subtropics: a meta-analysis. Biogeosciences 12:7299–7313. https://doi.org/10.5194/bg-12-7299-2015
Wang FM, Li J, Wang XL, Zhang W, Zou B, Neher DA, Li ZA (2014) Nitrogen and phosphorus addition impact soil N2O emission in a secondary tropical forest of South China. Sci Rep 4:5615. https://doi.org/10.1038/srep05615
Yashiro Y, Kadir WR, Adachi M, Okuda T, Koizumi H (2007) Emission of nitrous oxide from tropical forest and plantation soils in Peninsular Malaysia. Tropics 17:17–23. https://doi.org/10.3759/tropics.17.17
Zhang W, Mo JM, Yu GR, Fang YT, Li DJ, Lu XK, Wang H (2008) Emissions of nitrous oxide from three tropical forests in Southern China in response to simulated nitrogen deposition. Plant Soil 306:221–236. https://doi.org/10.1007/s11104-008-9575-7
This study was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant No 19H03008.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Project funding: This study was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (Grant Number 19H03008).
The online version is available at http://www.springerlink.com.
Corresponding editor: Zhu Hong.
Below is the link to the electronic supplementary material.
About this article
Cite this article
Mori, T. Effects of tropical forest conversion into oil palm plantations on nitrous oxide emissions: A meta-analysis. J. For. Res. (2022). https://doi.org/10.1007/s11676-022-01493-2
- Nitrogen fertilization
- Nitrous oxide
- Oil palm plantation
- Tropical forest