Conversion of rainforest to oil palm and rubber plantations alters energy channels in soil food webs

In the last decades, lowland tropical rainforest has been converted in large into plantation systems. Despite the evident changes above ground, the effect of rainforest conversion on the channeling of energy in soil food webs was not studied. Here, we investigated community‐level neutral lipid fatty acid profiles in dominant soil fauna to track energy channels in rainforest, rubber, and oil palm plantations in Sumatra, Indonesia. Abundant macrofauna including Araneae, Chilopoda, and Diplopoda contained high amounts of plant and fungal biomarker fatty acids (FAs). Lumbricina had the lowest amount of plant, but the highest amount of animal‐synthesized C20 polyunsaturated FAs as compared to other soil taxa. Mesofauna detritivores (Collembola and Oribatida) contained high amounts of algal biomarker FAs. The differences in FA profiles between taxa were evident if data were analyzed across land‐use systems, suggesting that soil fauna of different size (macro‐ and mesofauna) are associated with different energy channels. Despite that, rainforest conversion changed the biomarker FA composition of soil fauna at the community level. Conversion of rainforest into oil palm plantations enhanced the plant energy channel in soil food webs and reduced the bacterial energy channel; conversion into rubber plantations reduced the AMF‐based energy channel. The changes in energy distribution within soil food webs may have significant implications for the functioning of tropical ecosystems and their response to environmental changes. At present, these responses are hard to predict considering the poor knowledge on structure and functioning of tropical soil food webs.     

Plant roots fuel tropical soil animal communities

Belowground life relies on plant litter, while its linkage to living roots had long been understudied, and remains unknown in the tropics. Here, we analysed the response of 30 soil animal groups to root trenching and litter removal in rainforest and plantations in Sumatra, and found that roots are similarly important to soil fauna as litter. Trenching effects were stronger in soil than in litter, with an overall decrease in animal abundance in rainforest by 42% and in plantations by 30%. Litter removal little affected animals in soil, but decreased the total abundance by 60% in rainforest and rubber plantations but not in oil palm plantations. Litter and root effects on animal group abundances were explained by body size or vertical distribution. Our study quantifies principle carbon pathways in soil food webs under tropical land use, providing the basis for mechanistic modelling and ecosystem-friendly management of tropical soils.     

Rainforest conversion to smallholder cash crops leads to varying declines of beetles (Coleoptera) on Sumatra

Southeast Asian arthropod biodiversity is in rapid decline, but the variability of responses within taxa has received little attention. Using canopy fogging, we collected ~50,000 beetles (Coleoptera) in (1) lowland rainforest, (2) jungle rubber (rubber agroforest), and smallholder monoculture plantations of (3) rubber and (4) oil palm in Sumatra, across two landscapes and seasons. On average, beetle abundance was more than 50%, and biomass over 75%, lower in rubber and oil palm plantations than in rainforest and jungle rubber. This pattern was influenced by landscape and season. Abundance and biomass declines were similar in Chrysomelidae, Elateridae, and Staphylinidae, but differed in Curculionidae, which were most abundant in oil palm due to the introduced oil palm pollinator Elaeidobius kamerunicus. Across beetle families, species richness in monocultures was reduced by at least 70% compared to rainforest, with beetle richness in jungle rubber being similar to rainforest. Community composition in oil palm plantations differed markedly from the other land-use systems for Chrysomelidae and Curculionidae, but less for Elateridae and Staphylinidae. Turnover contributed more to overall beta diversity than nestedness for all families and land-use systems. Likely undersampling of the beetle community in rainforest suggests that declines of beetle density and diversity are much more severe than reported here, especially for beetle families with many concealed species, such as Staphylinidae. This study provides first evidence that negative responses of beetles to tropical land-use change vary among families, and is the first report of its kind from heavily understudied Sumatra.     

Effects of land use on surface-atmosphere exchanges of trace gases and energy in Borneo: comparing fluxes over oil palm plantations and a rainforest

This paper reports measurements of land-atmosphere fluxes of sensible and latent heat, momentum, CO(2), volatile organic compounds (VOCs), NO, NO(2), N(2)O and O(3) over a 30 m high rainforest canopy and a 12 m high oil palm plantation in the same region of Sabah in Borneo between April and July 2008. The daytime maximum CO(2) flux to the two canopies differs by approximately a factor of 2, 1200 mg C m(-2) h(-1) for the oil palm and 700 mg C m(-2) h(-1) for the rainforest, with the oil palm plantation showing a substantially greater quantum efficiency. Total VOC emissions are also larger over the oil palm than over the rainforest by a factor of 3. Emissions of isoprene from the oil palm canopy represented 80 per cent of the VOC emissions and exceeded those over the rainforest in similar light and temperature conditions by on average a factor of 5. Substantial emissions of estragole (1-allyl-4-methoxybenzene) from the oil palm plantation were detected and no trace of this VOC was detected in or above the rainforest. Deposition velocities for O(3) to the rainforest were a factor of 2 larger than over oil palm. Emissions of nitrous oxide were larger from the soils of the oil palm plantation than from the soils of the rainforest by approximately 25 per cent. It is clear from the measurements that the large change in the species composition generated by replacing rainforest with oil palm leads to profound changes in the net exchange of most of the trace gases measured, and thus on the chemical composition of the boundary layer over these surfaces.     

Predation of potential insect pests in oil palm plantations,rubber tree plantations,and fruit orchards

In human‐modified landscapes, important ecological functions such as predation are negatively affected by anthropogenic activities, including the use of pesticides and habitat degradation. Predation of insect pests is an indicator of healthy ecosystem functioning, which provides important ecosystem services, especially for agricultural systems. In this study, we compare predation attempts from arthropods, mammals, and birds on artificial caterpillars in the understory, between three tropical agricultural land‐use types: oil palm plantations, rubber tree plantations, and fruit orchards. We collected a range of local and landscape‐scale data including undergrowth vegetation structure; elevation; proximity to forest; and canopy cover in order to understand how environmental variables can affect predation. In all three land‐use types, our results showed that arthropods and mammals were important predators of artificial caterpillars and there was little predation by birds. We did not find any effect of the environmental variables on predation. There was an interactive effect between land‐use type and predator type. Predation by mammals was considerably higher in fruit orchards and rubber tree than in oil palm plantations, likely due to their ability to support higher abundances of insectivorous mammals. In order to maintain or enhance natural pest control in these common tropical agricultural land‐use types, management practices that benefit insectivorous animals should be introduced, such as the reduction of pesticides, improvement of understory vegetation, and local and landscape heterogeneity.     

Land‐use change shifts and magnifies seasonal variations of the decomposer system in lowland tropical landscapes

Deforestation and agricultural expansion in the tropics affect local and regional climatic conditions, leading to synergistic negative impacts on land ecosystems. Climatic changes manifest in increased inter‐ and intraseasonal variations and frequency of extreme climatic events (i.e., droughts and floods), which have evident consequences for aboveground biodiversity. However, until today, there have been no studies on how land use affects seasonal variations below ground in tropical ecosystems, which may be more buffered against climatic variation. Here, we analyzed seasonal variations in soil parameters, basal respiration, microbial communities, and abundances of soil invertebrates along with microclimatic conditions in rainforest and monocultures of oil palm and rubber in Sumatra, Indonesia. About 75% (20 out of 26) of the measured litter and soil, microbial, and animal parameters varied with season, with seasonal changes in 50% of the parameters depending on land use. Land use affected seasonal variations in microbial indicators associated with carbon availability and cycling rate. The magnitude of seasonal variations in microbial parameters in the soil of monocultures was almost 40% higher than in the soil of rainforest. Measured parameters were associated with short‐term climatic conditions (3‐day period air humidity) in plantations, but not in rainforest, confirming a reduced soil buffering ability in plantations. Overall, our findings suggest that land use temporally shifts and increases the magnitude of seasonal variations of the belowground ecosystem compartment, with microbial communities responding most strongly. The increased seasonal variations in soil biota in plantations likely translate into more pronounced fluctuations in essential ecosystem functions such as nutrient cycling and carbon sequestration, and these ramifications ultimately may compromise the stability of tropical ecosystems in the long term. As the observed seasonal dynamics is likely to increase with both local and global climate change, these shifts need closer attention for the long‐term sustainable management of plantation systems in the tropics.     

Oil palm expansion into rain forest greatly reduces ant biodiversity in canopy,epiphytes and leaf-litter

Oil palm cultivation is expanding rapidly into many of the world's most biodiverse tropical regions. One of the most functionally important and ecologically dominant animal groups in these environments is the ants. Here, we quantify the overall impacts of clear-felling lowland dipterocarp rainforest and conversion into oil palm plantation on ant diversity. At study sites in Sabah, Malaysia we collected ants from three microhabitats: 1 – the canopy, 2 – bird's nest ferns (Asplenium nidus complex, a common epiphyte in forest and oil palm), and 3 – leaf litter. We also measured temperature, humidity and light at collection sites to assess their impacts on ant community composition. Total ant species richness decreased from 309 to 110 (?64%) between forest and oil palm plantation. However, this impact was not the same across all microhabitats, with bird's nest ferns maintaining almost the same number of ant species in oil palm compared to forest (forest-oil palm, ferns: 36–35 (3% loss), canopy: 120–58 (52% loss), leaf litter: 216–56 (74% loss)). Relative abundance distributions remained the same for fern-dwelling ants, but became less even for oil palm ants in both the canopy and the leaf litter. These differences may be due in part to the ability of bird's nest ferns to provide a stable microclimate in hot, dry plantations. We also found that non-native ant species were more abundant in oil palm than in forest, and few forest ant species survived in plantations in any of the microhabitats. Only 59 of the 309 forest species persisted in oil palm plantations, corresponding to an 81% loss of forest species resulting from habitat conversion. Although oil palm supports many more ant species than has been previously reported, converting forest into plantation still leads to a dramatic reduction in species richness. The maintenance of forested areas is therefore vital for the conservation of ant biodiversity.     

Losses of soil carbon by converting tropical forest to plantations: erosion and decomposition estimated by δ13C

Indonesia lost more tropical forest than all of Brazil in 2012, mainly driven by the rubber, oil palm, and timber industries. Nonetheless, the effects of converting forest to oil palm and rubber plantations on soil organic carbon (SOC) stocks remain unclear. We analyzed SOC losses after lowland rainforest conversion to oil palm, intensive rubber, and extensive rubber plantations in Jambi Province on Sumatra Island. The focus was on two processes: (1) erosion and (2) decomposition of soil organic matter. Carbon contents in the Ah horizon under oil palm and rubber plantations were strongly reduced up to 70% and 62%, respectively. The decrease was lower under extensive rubber plantations (41%). On average, converting forest to plantations led to a loss of 10 Mg C ha^?1 after about 15 years of conversion. The C content in the subsoil was similar under the forest and the plantations. We therefore assumed that a shift to higher δ¹³C values in plantation subsoil corresponds to the losses from the upper soil layer by erosion. Erosion was estimated by comparing the δ¹³C profiles in the soils under forest and under plantations. The estimated erosion was the strongest in oil palm (35 ± 8 cm) and rubber (33 ± 10 cm) plantations. The ¹³C enrichment of SOC used as a proxy of its turnover indicates a decrease of SOC decomposition rate in the Ah horizon under oil palm plantations after forest conversion. Nonetheless, based on the lack of C input from litter, we expect further losses of SOC in oil palm plantations, which are a less sustainable land use compared to rubber plantations. We conclude that δ¹³C depth profiles may be a powerful tool to disentangle soil erosion and SOC mineralization after the conversion of natural ecosystems conversion to intensive plantations when soils show gradual increase of δ¹³C values with depth.     

Conversion of rainforest into oil palm and rubber plantations affects the functional composition of litter and soil Collembola

Rainforest conversion and expansion of plantations in tropical regions are associated with changes in animal communities and biodiversity decline. In soil, Collembola are one of the most numerous invertebrate groups that affect the functioning of microbial communities and support arthropod predators. Despite that, information on the impact of changes in land use in the tropics on species and trait composition of Collembola communities is very limited. We investigated the response of Collembola to the conversion of rainforest into rubber agroforestry (“jungle rubber”), rubber, and oil palm plantations in Jambi Province (Sumatra, Indonesia), a region which experienced one of the strongest recent deforestation globally. Collembola were sampled in 2013 and 2016 from the litter and soil layer using heat extraction, and environmental factors were measured (litter C/N ratio, pH, water content, composition of microbial community and predator abundance). In the litter layer, density and species richness in plantation systems were 25%–38% and 30%–40% lower, respectively, than in rainforest. However, in the soil layer, density, species richness, and trait diversity of Collembola were only slightly affected by land‐use change, contrasting the response of many other animal groups. Species and trait composition of Collembola communities in litter and soil differed between each of the land‐use systems. Water content and pH were identified as main factors related to the differences in species and trait composition in both litter and soil, followed by the density of micro‐ and macropredators. Dominant species of Collembola in rainforest and jungle rubber were characterized by small body size, absence of furca, and absence of intense pigmentation, while in plantations, larger species with long furca and diffuse or patterned pigmentation were more abundant. Overall, land‐use change negatively affected Collembola communities in the litter layer, but its impact was lower in the soil layer. Several pantropical genera of Collembola (i.e., Isotomiella, Pseudosinella, and Folsomides) dominated across land‐use systems, reflecting their high environmental adaptability and/or efficient dispersal, calling for studies on their ecology and genetic diversity. The decline in species richness and density of litter‐dwelling Collembola with the conversion of rainforest into plantation systems calls for management practices mitigating negative effects of the deterioration of the litter layer in rubber plantations, but even more in oil palm plantations.     

Conservation value of degraded habitats for forest birds in southern Peninsular Malaysia

Clearance of tropical forest for agricultural purposes is generally assumed to seriously threaten the survival of forest species. In this study, we quantified the conservation value, for forest bird species, of three degraded habitat types in Peninsular Malaysia, namely rubber tree plantations, oil palm plantations, and open areas. We surveyed these degraded habitats using point counts to estimate their forest bird species richness and abundance. We assessed whether richness, abundance, and activities of different avian dietary groups (i.e. insectivores and frugivores) varied among the habitats. We identified the critical habitat elements that accounted for the distribution of forest avifauna in these degraded habitats. Our results showed that these habitats harboured a moderate fraction of forest avifauna (approximately 46–76 species) and their functions were complementary (i.e. rubber tree plantations for moving; open habitats for perching; shrubs in oil palm plantations for foraging). In terms of species richness and abundance, rubber tree plantations were more important than oil palm plantations and open habitats. The relatively high species richness of this agricultural landscape was partly due to the contiguity of our study areas with extensive forest areas. Forecasts of forest-species presence under various canopy cover scenarios suggest that leaving isolated trees among non-arboreal crops could greatly attract relatively tolerant species that require tree canopy. The conservation value of degraded habitats in agricultural landscapes seems to depend on factors such as the type of crops planted and distance to primary forest remnants.     

Oil palm and rubber expansion facilitates earthworm invasion in Indonesia

Deforestation, plantation expansion and other human activities in tropical ecosystems are often associated with biological invasions. These processes have been studied for above-ground organisms, but associated changes below the ground have received little attention. We surveyed rainforest and plantation systems in Jambi province, Sumatra, Indonesia, to investigate effects of land-use change on the diversity and abundance of earthworms—a major group of soil-ecosystem engineers that often is associated with human activities. Density and biomass of earthworms increased 4—30-fold in oil palm and rubber monoculture plantations compared to rainforest. Despite much higher abundance, earthworm communities in plantations were less diverse and dominated by the peregrine morphospecies Pontoscolex corethrurus, often recorded as invasive. Considering the high deforestation rate in Indonesia, invasive earthworms are expected to dominate soil communities across the region in the near future, in lieu of native soil biodiversity. Ecologically-friendly management approaches, increasing structural habitat complexity and plant diversity, may foster beneficial effects of invasive earthworms on plant growth while mitigating negative effects on below-ground biodiversity and the functioning of the native soil animal community.

     

Large Canopy Exchange Fluxes of Inorganic and Organic Nitrogen and Preferential Retention of Nitrogen by Epiphytes in a Tropical Lowland Rainforest

Little is known about how tropical forest canopies interact with atmospheric nitrogen deposition and how this affects the internal nutrient dynamics and the processing of external nutrient inputs. The objectives of this study therefore were (1) to investigate gross and net canopy nitrogen (N) fluxes (retention and leaching) and (2) the effect of canopy components on net canopy N retention. Tracers were applied on detached branches in a tropical wet lowland rainforest, Costa Rica. A novel ¹⁵N pool dilution method showed that gross canopy fluxes (retention and leaching) of NO₃ ^?, NH₄ ⁺, and dissolved organic nitrogen (DON) were remarkably higher than net throughfall fluxes. Gross fluxes of NH₄ ⁺ and NO₃ ^? resulted in a negligible net flux whereas DON showed net uptake by the canopy. The highest quantity of ¹⁵N was recovered in epiphytic bryophytes (16.4%) although the largest biomass fraction was made up of leaves. The study demonstrates that tracer applications allow investigation of the dynamic and complex canopy exchange processes and that epiphytic communities play a major role in solute fluxes in tree canopies and therefore in the nutrient dynamics of tropical rain forests.     

Impacts of logging and conversion of rainforest to oil palm on the functional diversity of birds in Sundaland

Commercial selective logging and the conversion of primary and degraded forests to agriculture are the biggest threats to tropical biodiversity. Our understanding of the impacts of these disturbances and the resulting local extinctions on the functional roles performed by the remaining species is limited. We address this issue by examining functional diversity (FD), which quantifies a range of traits that affect a species' ecological role in a community as a single continuous metric. We calculated FD for birds across a gradient of disturbance from primary forest through intensively logged forest to oil palm plantations on previously forested land in Borneo, Southeast Asia, a hotspot of imperilled biodiversity. Logged rainforest retained similar levels of FD to unlogged rainforest, even after two logging rotations, but the conversion of logged forest to oil palm resulted in dramatic reductions in FD. The few remaining species in oil palm filled a disproportionately wide range of functional roles but showed very little clustering in terms of functional traits, suggesting that any further extinctions from oil palm would reduce FD even further. Determining the extent to which the changes we recorded were due to under‐utilization of resources within oil palm or a reduction in the resources present is an important next step. Nonetheless our study improves our understanding of the stability and resilience of functional diversity in these ecosystems and of the implications of land‐use changes for ecosystem functioning.     

Above and below ground impacts of terrestrial mammals and birds in a tropical forest

Understanding the impact of losing trophic diversity has global significance for managing ecosystems as well as important theoretical implications for community and ecosystem ecology. In several tropical forest ecosystems, habitat fragmentation has resulted in declines and local extinctions of mammalian and avian terrestrial insectivores. To assess the ability of a tropical rainforest community in Ivory Coast to resist perturbation from such loss of trophic diversity, I traced feedbacks in above and below ground communities and measured changes in nutrient levels and herbivory rates in response to an experimental exclosure of avian and mammalian terrestrial insectivores. I present evidence that loss of this functional group may result in increased tree seedling herbivory and altered nutrient regimes through changes in the abundance and guild structure of invertebrates. Exclusion of top predators of the forest floor resulted in increased seedling herbivory rates and macro-invertebrate (>5 mm) densities with strongest effects on herbivorous taxa, spiders and earthworms. Densities of microbivores including Collembola, Acarina and Sciaridae showed the opposite trend as did levels of inorganic phosphorus in the soil. Results were evaluated using path analysis which supported the presence of a top down trophic cascade in the detrital web which ultimately affected turnover of phosphorus, a limiting nutrient in tropical soils. Results illustrate the potential importance of vertebrate predators in both above and belowground food webs despite the biotic diversity and structural heterogeneity of the rainforest floor.     

Effects of Logging and Oil Palm Expansion on Stream Frog Communities on Borneo,Southeast Asia

The conversion of tropical rain forests to oil palm plantations is a major threat to Southeast Asia's rich biodiversity. Fostering forest species communities in secondary forests, agroforestry systems, and plantations is therefore increasingly becoming a conservation focus. This study uses standardized transect‐based sampling to compare species richness, density and community composition of stream anuran assemblages among primary forests, repeatedly logged forests and oil palm plantations in northern Borneo. In primary forest streams, we recorded an average of 19 frog species, compared to 15 species in logged forests and 11 species in oil palm plantation streams. However, the high percentage of canopy cover above the plantation streams mitigated this loss to some extent. This study corroborates numerous studies that oil palm plantations have mainly negative effects on the region's biodiversity. However, our results also demonstrate the high conservation value of logged forests for Bornean stream‐dependent anurans. We conclude that palm plantations have a largely unused potential to promote regional anuran biodiversity.     

Microclimate and habitat heterogeneity through the oil palm lifecycle

The rapid expansion of oil palm cultivation and corresponding deforestation has invoked widespread concern for biodiversity in Southeast Asia and throughout the tropics. However, no study explicitly addresses how habitat characteristics change when (1) forest is converted to oil palm, or (2) through the dynamic 25–30-year oil palm lifecycle. These two questions are fundamental to understanding how biodiversity will be impacted by oil palm development.Our results from a chronosequence study on microclimate and vegetation structure in oil palm plantations surrounding the Pasoh Forest Reserve, Peninsular Malaysia, show dramatic habitat changes when forest is converted to oil palm. However, they also reveal substantial habitat heterogeneity throughout the plantation lifecycle. Oil palm plantations are created by clear-cutting forests and then terracing the land. This reduces the 25 m-tall forest canopy to bare ground with a harsh microclimate. Eight-year-old oil palm plantations had 4 m open-canopies; 22-year-old plantations had 13 m closed-canopies. Old plantations had significantly more buffered microclimates than young plantations. Understory vegetation was twice as tall in young plantations, but leaf litter depth and total epiphyte abundance were double in old plantations. Nonetheless, leaf litter coverage was patchy throughout the oil palm life cycle due to the stacking of all palm fronds. Overall, oil palm plantations were substantially hotter (+2.84 °C) and drier (+0.80 hPa vapor pressure deficit), than forests during diurnal hours. However, there were no nocturnal microclimate differences between forests and plantations. Finally, we describe how the variable retention of old palm trees during crop rotation can retain habitat features and maintain more stable microclimate conditions than clear-cutting senescent plantations. We discuss the implications of habitat changes for biodiversity and introduce three methods to utilize temporal habitat heterogeneity to enhance the quality of the oil palm landscape matrix.     

西双版纳地区热带季节雨林与橡胶林林冠水文效应比较研究

季节雨林和橡胶林是西双版纳热带森林系统中可以代表原始林和大面积种植的人工林两种林型,采用水量平衡法,利用对以上两种林分林冠水文各分量1996～2001年的观测结果,初步分析其林冠水文效应,结果表明：一年内,季节雨林林冠截留量660．6mm,树干径流量80．7mm,穿透降雨量,853．2mm,分别占同期降雨总量的41．43％、5．24％、53．74％;橡胶林林冠截留量393．5mm,树干径流量104．1mm,穿透降雨量1096．8mm,分别占同期降雨总量的24．68％、6．68％、67．85％;两种林分森林水文各分量干、雨季差异显著,在研究中还发现,季节雨林中树干径流量随径级的增大而减小,干季出现密林(季节雨林)的穿透降雨量大于疏林(橡胶林)的反常现象;与我国其他地区相比,季节雨林和橡胶林有较大的林冠截留率及干流率。     

The importance of herbivory by protists in lakes of a tropical floodplain system

Inland aquatic ecosystems play a critical role in the global carbon cycle, processing a great fraction of the organic matter coming from terrestrial ecosystems, and the microbial food web is crucial in this process. Thus, we aimed to evaluate whether the food resource of planktonic protozoa comes mainly from small primary producers or heterotrophic bacteria in tropical shallows lakes, assuming the hypothesis that, in general, picocyanobacteria would be the main food resource for protists. We also expected that the autotrophic fraction would be mainly related to protists at the surface of the environments, while the heterotrophic fraction would be more important at the lower strata of the water column. We performed size-fractionation experiments to evaluate the effects of predation of protists on heterotrophic bacteria and picocyanobacteria. We also sampled planktonic organisms at the subsurface and bottom of 20 lakes in a Neotropical floodplain. We found an herbivory preference of heterotrophic flagellates, while ciliates seem to exert a stronger impact on heterotrophic bacteria. We also found no relationship between heterotrophic bacteria and protists in the field data, whereas positive relationships between picocyanobacteria and protists were observed in environments where there was sunlight. Thus, both heterotrophic bacteria and picocyanobacteria were important components in the food webs of tropical shallow lakes. Moreover, the trophic cascade caused by zooplankton predation suggests that protists are efficient in transferring the energy from the base of microbial food webs to higher trophic levels.     

Quantifying above‐ and belowground biomass carbon loss with forest conversion in tropical lowlands of Sumatra (Indonesia)

Natural forests in South‐East Asia have been extensively converted into other land‐use systems in the past decades and still show high deforestation rates. Historically, lowland forests have been converted into rubber forests, but more recently, the dominant conversion is into oil palm plantations. While it is expected that the large‐scale conversion has strong effects on the carbon cycle, detailed studies quantifying carbon pools and total net primary production (NPP_total) in above‐ and belowground tree biomass in land‐use systems replacing rainforest (incl. oil palm plantations) are rare so far. We measured above‐ and belowground carbon pools in tree biomass together with NPP_total in natural old‐growth forests, ‘jungle rubber’ agroforests under natural tree cover, and rubber and oil palm monocultures in Sumatra. In total, 32 stands (eight plot replicates per land‐use system) were studied in two different regions. Total tree biomass in the natural forest (mean: 384 Mg ha^?1) was more than two times higher than in jungle rubber stands (147 Mg ha^?1) and >four times higher than in monoculture rubber and oil palm plantations (78 and 50 Mg ha^?1). NPP_total was higher in the natural forest (24 Mg ha^?1 yr^?1) than in the rubber systems (20 and 15 Mg ha^?1 yr^?1), but was highest in the oil palm system (33 Mg ha^?1 yr^?1) due to very high fruit production (15–20 Mg ha^?1 yr^?1). NPP_total was dominated in all systems by aboveground production, but belowground productivity was significantly higher in the natural forest and jungle rubber than in plantations. We conclude that conversion of natural lowland forest into different agricultural systems leads to a strong reduction not only in the biomass carbon pool (up to 166 Mg C ha^?1) but also in carbon sequestration as carbon residence time (i.e. biomass‐C:NPP‐C) was 3–10 times higher in the natural forest than in rubber and oil palm plantations.     

Land Use Changes and GHG Emissions from Tropical Forest Conversion by Oil Palm Plantations in Riau Province,Indonesia

Increasing prices and demand for biofuel and cooking oil from importer countries have caused a remarkable expansion of oil palm plantations in Indonesia. In this paper, we attempt to monitor the expansion of oil palm plantations on peat land and in tropical forests. We measure the GHG emissions from the land conversion activities at provincial scale. Using Landsat images from three different periods (1990s, 2000s and 2012), we classified LULC of the Riau Province, which is the largest oil palm producing region in Indonesia. A hybrid method of integration, generated by combining automatic processing and manual analysis, yields the best results. We found that the tropical rainforest cover decreased from ∼63% in the 1990s to ∼37% in the 2000s. By 2012, the remaining tropical rainforest cover was only ∼22%. From the 1990s to the 2000s, conversion of forests and peat lands was the primary source of emissions, total CO₂ emitted to the atmosphere was estimated at ∼26.6 million tCO₂.y^-1, with 40.62% and 59.38% of the emissions from conversion of peat lands and forests, respectively. Between 2000 and 2012, the total CO₂ emitted to the atmosphere was estimated at ∼5.2 million tCO₂. y^-1, with 69.94% and 27.62% of the emissions from converted peat lands and converted forests, respectively. The results show that in the Riau Province, the oil palm industry boomed in the period from 1990 to 2000, with transformation of tropical forest and peat land as the primary source of emissions. The decrease of CO₂ emissions in the period from 2000 to 2012 is possibly due to the enforcement of a moratorium on deforestation.