Kimberly M. Carlson

Committed carbon emissions, deforestation, and community land conversion from oil palm plantation expansion in West Kalimantan, Indonesia.

Industrial agricultural plantations are a rapidly increasing yet largely unmeasured source of tropical land cover change. Here, we evaluate impacts of oil palm plantation development on land cover, carbon flux, and agrarian community lands in West Kalimantan, Indonesian Borneo. With a spatially explicit land change/carbon bookkeeping model, parameterized using high-resolution satellite time series and informed by socioeconomic surveys, we assess previous and project future plantation expansion under five scenarios. Although fire was the primary proximate cause of 1989–2008 deforestation (93%) and net carbon emissions (69%), by 2007–2008, oil palm directly caused 27% of total and 40% of peatland deforestation. Plantation land sources exhibited distinctive temporal dynamics, comprising 81% forests on mineral soils (1994–2001), shifting to 69% peatlands (2008–2011). Plantation leases reveal vast development potential. In 2008, leases spanned ∼65% of the region, including 62% on peatlands and 59% of community-managed lands, yet <10% of lease area was planted. Projecting business as usual (BAU), by 2020 ∼40% of regional and 35% of community lands are cleared for oil palm, generating 26% of net carbon emissions. Intact forest cover declines to 4%, and the proportion of emissions sourced from peatlands increases 38%. Prohibiting intact and logged forest and peatland conversion to oil palm reduces emissions only 4% below BAU, because of continued uncontrolled fire. Protecting logged forests achieves greater carbon emissions reductions (21%) than protecting intact forests alone (9%) and is critical for mitigating carbon emissions. Extensive allocated leases constrain land management options, requiring trade-offs among oil palm production, carbon emissions mitigation, and maintaining community landholdings.

Leverage points for improving global food security and the environment

How to optimize global food production Keeping societies stable and managing Earths resources sustainably depend on doing a good, steady job producing and distributing food. West et al. asked what combinations of crops and regions offer the best chance of progress. Their analysis focused on reducing greenhouse gas emissions, nutrient pollution, water use, and food waste. They identify regions that are likely to yield the best balance between applying fertilizer to increase crop yields versus the resulting environmental impact. Science, this issue p. 325 A limited set of interventions could disproportionately improve crop production and environmental sustainability. Achieving sustainable global food security is one of humanity’s contemporary challenges. Here we present an analysis identifying key “global leverage points” that offer the best opportunities to improve both global food security and environmental sustainability. We find that a relatively small set of places and actions could provide enough new calories to meet the basic needs for more than 3 billion people, address many environmental impacts with global consequences, and focus food waste reduction on the commodities with the greatest impact on food security. These leverage points in the global food system can help guide how nongovernmental organizations, foundations, governments, citizens’ groups, and businesses prioritize actions.

Multiple Pathways of Commodity Crop Expansion in Tropical Forest Landscapes

Commodity crop expansion, for both global and domestic urban markets, follows multiple land change pathways entailing direct and indirect deforestation, and results in various social and environmental impacts. Here we compare six published case studies of rapid commodity crop expansion within forested tropical regions. Across cases, between 1.7% and 89.5% of new commodity cropland was sourced from forestlands. Four main factors controlled pathways of commodity crop expansion: (i) the availability of suitable forestland, which is determined by forest area, agroecological or accessibility constraints, and land use policies, (ii) economic and technical characteristics of agricultural systems, (iii) differences in constraints and strategies between small-scale and large-scale actors, and (iv) variable costs and benefits of forest clearing. When remaining forests were unsuitable for agriculture and/or policies restricted forest encroachment, a larger share of commodity crop expansion occurred by conversion of existing agricultural lands, and land use displacement was smaller. Expansion strategies of large-scale actors emerge from context-specific balances between the search for suitable lands; transaction costs or conflicts associated with expanding into forests or other state-owned lands versus smallholder lands; net benefits of forest clearing; and greater access to infrastructure in already-cleared lands. We propose five hypotheses to be tested in further studies: (i) land availability mediates expansion pathways and the likelihood that land use is displaced to distant, rather than to local places; (ii) use of already-cleared lands is favored when commodity crops require access to infrastructure; (iii) in proportion to total agricultural expansion, large-scale actors generate more clearing of mature forests than smallholders; (iv) property rights and land tenure security influence the actors participating in commodity crop expansion, the form of land use displacement, and livelihood outcomes; (v) intensive commodity crops may fail to spare land when inducing displacement. We conclude that understanding pathways of commodity crop expansion is essential to improve land use governance.

Vegetation-climate interactions among native and invasive species in Hawaiian rainforest

We compiled a time series of Earth Observing-1 Hyperion satellite observations with field measurements to compare the structural, biochemical, and physiological characteristics of an invasive nitrogen-fixing tree Myrica faya and native Metrosideros polymorpha in montane rainforests in Hawai’i. Satellite-based canopy water measurements closely tracked variations in leaf area index, and the remotely sensed photochemical and carotenoid reflectance indices (PRI, CRI) indicated variations in upper-canopy leaf chlorophyll and carotenoid content during a climatological transition. The PRI and CRI were related to differences in light-use efficiency of each species, as indicated by field measurements of leaf electron transport rate. The suite of hyperspectral metrics indicated maximum differences in the structure, biochemistry, and physiology of Myrica and Metrosideros when canopy vapor pressure deficit was high during hotter and drier periods. These satellite data, combined with the Carnegue-Ames-Stanford Approach (CASA) carbon cycle model, suggested that Myrica growth rates were 16–44% higher than Metrosideros, with relative differences between species closely linked to climate conditions. The satellite hyperspectral data identified the basic biological mechanisms favoring the spread of an introduced tree, and provided a more detailed understanding of how vegetation–climate interactions affect the time course of plant growth with respect to the invasion process.

Influence of watershed‐climate interactions on stream temperature, sediment yield, and metabolism along a land use intensity gradient in Indonesian Borneo

Oil palm plantation expansion into tropical forests may alter physical and biogeochemical inputs to streams, thereby changing hydrological function. In West Kalimantan, Indonesia, we assessed streams draining watersheds characterized by five land uses: intact forest, logged forest, mixed agroforest, and young ( 10 years) oil palm plantation. We quantified suspended sediments, stream temperature, and metabolism using high-frequency submersible sonde measurements during month-long intervals between 2009 and 2012. Streams draining oil palm plantations had markedly higher sediment concentrations and yields, and stream temperatures, compared to other streams. Mean sediment concentrations were fourfold to 550-fold greater in young oil palm than in all other streams and remained elevated even under base flow conditions. After controlling for precipitation, the mature oil palm stream exhibited significantly greater sediment yield than other streams. Young and mature oil palm streams were 3.9°C and 3.0°C warmer than the intact forest stream (25°C). Across all streams, base flow periods were significantly warmer than times of stormflow, and these differences were especially large in oil palm catchments. Ecosystem respiration rates were also influenced by low precipitation. During an El Nino–Southern Oscillation-associated drought, the mature oil palm stream consumed a maximum 21 g O2 m−2 d−1 in ecosystem respiration, in contrast with 2.8 ± 3.1 g O2 m−2 d−1 during nondrought sampling. Given that 23% of Kalimantans land area is occupied by watersheds similar to those studied here, our findings inform potential hydrologic outcomes of regional periodic drought coupled with continued oil palm plantation expansion.

Spatially explicit estimates of N2O emissions from croplands suggest climate mitigation opportunities from improved fertilizer management

With increasing nitrogen (N) application to croplands required to support growing food demand, mitigating N2 O emissions from agricultural soils is a global challenge. National greenhouse gas emissions accounting typically estimates N2 O emissions at the country scale by aggregating all crops, under the assumption that N2 O emissions are linearly related to N application. However, field studies and meta-analyses indicate a nonlinear relationship, in which N2 O emissions are relatively greater at higher N application rates. Here, we apply a super-linear emissions response model to crop-specific, spatially explicit synthetic N fertilizer and manure N inputs to provide subnational accounting of global N2 O emissions from croplands. We estimate 0.66 Tg of N2 O-N direct global emissions circa 2000, with 50% of emissions concentrated in 13% of harvested area. Compared to estimates from the IPCC Tier 1 linear model, our updated N2 O emissions range from 20% to 40% lower throughout sub-Saharan Africa and Eastern Europe, to >120% greater in some Western European countries. At low N application rates, the weak nonlinear response of N2 O emissions suggests that relatively large increases in N fertilizer application would generate relatively small increases in N2 O emissions. As aggregated fertilizer data generate underestimation bias in nonlinear models, high-resolution N application data are critical to support accurate N2 O emissions estimates.

Modeling relationships between water table depth and peat soil carbon loss in Southeast Asian plantations

Plantation-associated drainage of Southeast Asian peatlands has accelerated in recent years. Draining exposes the upper peat layer to oxygen, leading to elevated decomposition rates and net soil carbon losses. Empirical studies indicate positive relationships between long-term water table (WT) depth and soil carbon loss rate in peatlands. These correlations potentially enable using WT depth as a proxy for soil carbon losses from peatland plantations. Here, we compile data from published research assessing WT depth and carbon balance in tropical plantations on peat. We model net carbon loss from subsidence studies, as well as soil respiration (heterotrophic and total) from closed chamber studies, as a function of WT depth. WT depth across all 12 studies and 59 sites is 67 ± 20 cm (mean ± standard deviation). Mean WT depth is positively related to net carbon loss, as well as soil respiration rate. Our models explain 45% of net carbon loss variation and 45–63% of soil respiration variation. At a 70 cm WT depth, the subsidence model suggests net carbon loss of 20 tC ha−1 yr−1 (95% confidence interval (CI) 18–22 tC ha−1 yr−1) for plantations drained for >2 yr. Closed chamber-measured total soil respiration at this depth is 20 tC-CO2 ha−1 yr−1 (CI 17–24 tC-CO2 ha−1 yr−1) while heterotrophic respiration is 17 tC-CO2 ha−1 yr−1 (CI 14–20 tC-CO2 ha−1 yr−1), ~82% of total respiration. While land use is not a significant predictor of soil respiration, WT depths are greater at acacia (75 ± 16 cm) than oil palm (59 ± 15 cm) sample sites. Improved spatio-temporal sampling of the full suite of peat soil carbon fluxes—including fluvial carbon export and organic fertilizer inputs—will clarify multiple mechanisms leading to carbon loss and gain, supporting refined assessments of the global warming potential of peatland drainage.

The role of supply-chain initiatives in reducing deforestation

A major reduction in global deforestation is needed to mitigate climate change and biodiversity loss. Recent private sector commitments aim to eliminate deforestation from a company’s operations or supply chain, but they fall short on several fronts. Company pledges vary in the degree to which they include time-bound interventions with clear definitions and criteria to achieve verifiable outcomes. Zero-deforestation policies by companies may be insufficient to achieve broader impact on their own due to leakage, lack of transparency and traceability, selective adoption and smallholder marginalization. Public–private policy mixes are needed to increase the effectiveness of supply-chain initiatives that aim to reduce deforestation. We review current supply-chain initiatives, their effectiveness, and the challenges they face, and go on to identify knowledge gaps for complementary public–private policies.In this Perspective, private company supply-chain initiatives designed to reduce deforestation are assessed. Public–private policy mixes are advocated to increase their efficacy.

Effect of oil palm sustainability certification on deforestation and fire in Indonesia

Significance Demand for agricultural commodities is the leading driver of tropical deforestation. Many corporations have pledged to eliminate forest loss from their supply chains by purchasing only certified “sustainable” products. To evaluate whether certification fulfills such pledges, we applied statistical analyses to satellite-based estimates of tree cover loss to infer the causal impact of a third-party certification system on deforestation and fire within Indonesian oil palm plantations. We found that certification significantly reduced deforestation, but not fire or peatland clearance, among participating plantations. Moreover, certification was mostly adopted in older plantations that contained little remaining forest. Broader adoption by oil palm growers is likely needed for certification to have a large impact on total forest area lost to oil palm expansion. Many major corporations and countries have made commitments to purchase or produce only “sustainable” palm oil, a commodity responsible for substantial tropical forest loss. Sustainability certification is the tool most used to fulfill these procurement policies, and around 20% of global palm oil production was certified by the Roundtable on Sustainable Palm Oil (RSPO) in 2017. However, the effect of certification on deforestation in oil palm plantations remains unclear. Here, we use a comprehensive dataset of RSPO-certified and noncertified oil palm plantations (∼188,000 km2) in Indonesia, the leading producer of palm oil, as well as annual remotely sensed metrics of tree cover loss and fire occurrence, to evaluate the impact of certification on deforestation and fire from 2001 to 2015. While forest loss and fire continued after RSPO certification, certified palm oil was associated with reduced deforestation. Certification lowered deforestation by 33% from a counterfactual of 9.8 to 6.6% y−1. Nevertheless, most plantations contained little residual forest when they received certification. As a result, by 2015, certified areas held less than 1% of forests remaining within Indonesian oil palm plantations. Moreover, certification had no causal impact on forest loss in peatlands or active fire detection rates. Broader adoption of certification in forested regions, strict requirements to avoid all peat, and routine monitoring of clearly defined forest cover loss in certified and RSPO member-held plantations appear necessary if the RSPO is to yield conservation and climate benefits from reductions in tropical deforestation.

Policy perils of ignoring uncertainty in oil palm research

Success of the emerging Low Emissions Development paradigm in Southeast Asia depends on mitigating impacts of oil palm (OP) expansion on carbon-dense ecosystems, especially tropical peatlands. To this end, Koh et al. (1) mapped OP planted before 2002 across Peninsular Malaysia, Sumatra, and Borneo to estimate emissions and biodiversity losses from peatland conversion (≈880,000 ha). Unfortunately, emissions scenarios are oversimplified, remote-sensing (RS) methods are unsuitable for OP monitoring, and recommendations for peatland restoration are overstated.