Impact of progressive and retrogressive land use changes on ecosystem multifunctionality: Implications for land restoration in the Indian Eastern Himalayan region

Impact of land use changes on the storage of soil organic carbon in active and recalcitrant pools in a humid tropical region of India

The increasing global demand for vegetable oils has resulted in a significant increase in the area under oil palm in the tropics during the last couple of decades, and this is projected to increase further. The Roundtable on Sustainable Palm Oil discourages the conversion of peatlands to oil palm and rubber plantations. However, our understanding of the effects on soil organic carbon (SOC) stocks and associated greenhouse gas (GHG) emissions of land use conversion is incomplete, especially for mineral soils under primary forests, secondary forests, rubber and other perennial plantations in the tropics. In this review we synthesised information on SOC stocks and GHG emissions from tropical mineral soils under forest, oil palm and rubber plantations and other agroecosystems across the tropical regions. We found that the largest SOC losses occurred after land use conversion from primary forest to oil palm and rubber plantations. Secondary forest and pasture lands showed lower SOC losses as well as total GHG (CO2, N2O and CH4) emissions when converted to oil palm and rubber plantations. However, due to the limited data available on all three GHG emissions, there remains high uncertainty in GHG emissions estimates, and regional GHG accounting is more reliable. We recommend long-term monitoring of oil palm and other perennial plantations established on tropical mineral soils on different soil types and regions on SOC stock changes and total GHG emissions and evaluate appropriate management practices to optimise production and sustainable economic returns, and minimise environmental impact.

Effects of forest conversion to rubber plantation and of replanting rubber trees on soil organic carbon pools in a tropical moist climate zone

Impacts of land use and biophysical properties on soil carbon stocks in southern Yunnan, China

Effects of past land use on soil organic carbon changes after dam construction

Land use effects on tree species diversity and soil properties of the Awudua Forest, Ghana

Mapping deciduous rubber plantations through integration of PALSAR and multi-temporal Landsat imagery

Intensive deforestration for the purpose of agricultural field and transmigration area has happened lately in Dharmasraya Regency, West Sumatra. Land use change from forest into dry land farming, mixed trees and oil palm plantation, as well as rubber plantation has caused different level of soil fertility as a consequence of ecology changes of the areas. The objectives of this research were to identify the change of soil organic matter content, plant nutrition level, as well as bulk density of the soils at each land use. This research was conducted in Sungai Rumbai, Dharmasraya Regency in 2007. Soil samples were taken from 5 land use, those were dryland farming, mixed trees, oil palm plantation, rubber plantation, and natural forest. The soil samples, then, were analysed for the soil organic matter content (%), N-, P-, and K-content, as well as bulk density (BV) in soil laboratory, Agricultural Faculty, Andalas University Padang. The result showed that land use change from forest ecosystem into other ecosystems had decreased soil fertility level. This was reflected by the decreasing soil organic matter content, increasing soil bulk density. Nutrient status of the soil also decreased, especially potassium (K) level. Compared to the forest ecosystem, soil organic matter decreased by 13, 26, 33, and 36% respectively for dry land farming, mixed trees and oil palm plantation, as well as rubber plantation. Soil bulk density of the land use which was still close to soil under forest ecosystem (0.83 gcm-3) was found in rubber plantation (1.00 gcm-3), then followed by mixed trees (1.11 gcm-3). Potassium level of the land uses which were close to forest ecosystem (0.44 me/100g) was in rubber plantation (0,33 me/100 g), as well as in oil palm plantation(0,34 me/100 g). Based on the results above, it can be concluded that rubber and oil palm plantation was types of land use having better soil ecology compared to the other land use. Kata Kunci: Degradasi Lahan, Ekosistem Hutan, Penggunaan Lahan

The expansion of rubber (Hevea brasiliensis) plantations has been a critical driver for the rapid transformation of tropical forests, especially in Thailand. Rubber plantation mapping provides basic information for surveying resources, updating forest subplot information, logging, and managing the forest. However, due to the diversity of stand structure, complexity of the forest growth environment, and the similarity of spectral characteristics between rubber trees and natural forests, it is difficult to discriminate rubber plantation from natural forest using only spectral information. This study evaluated the validity of textural features for rubber plantation recognition at different spatial resolutions using GaoFen-1 (GF-1), Sentinel-2, and Landsat 8 optical data. C-band Sentinel-1 10 m imagery was first used to map forests (including both rubber plantations and natural forests) and non-forests, then the pixels identified as forests in the Sentinel-1 imagery were compared with GF-1, Sentinel-2, and Landsat 8 images to separate rubber plantations and natural forest using two different approaches: a method based on spectral information characteristics only and a method combining spectral and textural features. In addition, we extracted textural features of different window sizes (3 × 3 to 31 × 31) and analyzed the influence of window size on the separability of rubber plantations and natural forests. Our major findings include: (1) the suitable texture extraction window sizes of GF-1, Sentinel-2, and Landsat 8 are 31 × 31, 11 × 11 to 15 × 15, and 3 × 3 to 7 × 7, respectively; (2) correlation (COR) is a robust textural feature in remote sensing images with different resolutions; and (3) compared with classification by spectral information only, the producer’s accuracy of rubber plantations based on GF-1, Sentinel-2, and Landsat 8 was improved by 8.04%, 9.44%, and 8.74%, respectively, and the user’s accuracy was increased by 4.63%, 4.54%, and 6.75%, respectively, when the textural features were introduced. These results demonstrate that the method combining textural features has great potential in delineating rubber plantations.

Water stable aggregates and the associated active and recalcitrant carbon in soil under rubber plantation

Impact of Rain Forest Transformation on Roots and Functional Diversity of Root-Associated Fungal Communities

Plant and bird diversity in the Indonesian jungle rubber agroforestry system was compared to that in primary forest and rubber plantations by integrating new and existing data from a lowland rain forest area in Sumatra. Jungle rubber gardens are low-input rubber (Hevea brasiliensis) agroforests that structurally resemble secondary forest and in which wild species are tolerated by the farmer. As primary forests have almost completely disappeared from the lowlands of the Sumatra peneplain, our aim was to assess the contribution of jungle rubber as a land use type to the conservation of plant and bird species, especially those that are associated with the forest interior of primary and old secondary forest. Species-accumulation curves were compiled for terrestrial and epiphytic pteridophytes, trees and birds, and for subsets of ‘forest species’ of terrestrial pteridophytes and birds. Comparing jungle rubber and primary forest, groups differed in relative species richness patterns. Species richness in jungle rubber was slightly higher (terrestrial pteridophytes), similar (birds) or lower (epiphytic pteridophytes, trees, vascular plants as a whole) than in primary forest. For subsets of ‘forest species’ of terrestrial pteridophytes and birds, species richness in jungle rubber was lower than in primary forest. For all groups, species richness in jungle rubber was generally higher than in rubber plantations. Although species conservation in jungle rubber is limited by management practices and by a slash-and-burn cycle for replanting of about 40 years, this forest-like land use does support species diversity in an impoverished landscape increasingly dominated by monoculture plantations.

In Sumatra, Indonesia, the establishment of oil palm and rubber plantations is widespread. However, it occurs at the expense of forest area. Since global demand for palm oil and rubber is increasing, forest conversion is expected to continue. Furthermore, studies have shown that forest destruction and the establishment of agricultural land uses influence the soil–atmosphere exchange of the climate-relevant trace gases carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and nitric oxide (NO). Nevertheless, trace gas measurements from oil palm and rubber plantations are scarce. Additionally, researchers have so far not considered oil palm canopy soils as a possible source or sink of trace gases. The present thesis consists of three studies, which assess the impact of forest conversion into smallholder oil palm and rubber plantations on soil CO2 and CH4 fluxes, as well as on soil N2O and NO fluxes, and which investigate the importance of oil palm canopy soil for N2O and CH4 fluxes. We conducted the studies on highly weathered tropical soils in Jambi Province, Sumatra, Indonesia and selected two soil landscapes which mainly differ in texture (clay and loam Acrisol). To examine the impact of land-use change on soil trace gas fluxes we investigated four different land uses per landscape: lowland forest and jungle rubber (rubber trees interspersed in secondary forest), as reference land uses, as well as smallholder rubber (7–17 years old) and oil palm plantations (9–16 years old), as converted land uses. Each land use was replicated four times in both landscapes.
\n\tThe first study investigated changes in soil CO2 and CH4 fluxes with forest conversion to smallholder oil palm and rubber plantations. We determined soil CO2 and CH4 fluxes monthly from December 2012 to December 2013, using static vented chambers. Our findings show that soil CO2 fluxes in oil palm plantations were reduced and that fluxes from the other three land uses were comparable among each other in both landscapes. We attributed this decrease to strongly decomposed soil organic matter, reduced soil carbon (C) stocks as well as to phosphorus fertilization and liming, which led to a lower C allocation to roots. Due to reduced nitrogen (N) availability in the converted land uses CH4 uptake was lower in oil palm and rubber when compared to the reference land uses in both landscapes. Thus, soil fertility appeared to be an important controller of soil CO2 and CH4 fluxes in this tropical landscape.
\n\tThe second study focused on the impact of forest conversion into smallholder oil palm and rubber plantations on soil N2O and NO fluxes. Additionally, we compared soil N2O fluxes from smallholder oil palm plantations with fluxes from a large-scale oil palm plantation. We determined soil N2O fluxes monthly from December 2012 to December 2013 in the two landscapes and weekly to bi-weekly from July 2014 to July 2015 in the large-scale oil palm plantation, using static vented chambers. Using open dynamic chambers, we measured soil NO fluxes four times in all land uses of both landscapes between March and September 2013. Our results show that land use change did not affect soil N2O and NO fluxes because of low initial N availability in the reference land uses, so that N2O and NO fluxes were also low, and any changes due to conversion might have been too small to identify. However, the large-scale oil palm plantation, although not significantly different, showed, because of their higher fertilizer input, on average 3.5 times higher soil N2O fluxes than the smallholder oil palm plantations.
\n\tThe aim of the third study was to quantify N2O and CH4 fluxes from oil palm canopy soils. We measured soil N2O and CH4 from three different stem heights in eight smallholder oil palm plantations across the two landscapes from February 2013 to May 2014, on a bi-weekly to monthly basis, using in-situ incubation. Oil palm canopy soil emitted N2O and CH4 from all stem heights. However, fluxes were low compared to ground soil fluxes. This was due to a low amount of canopy soil on a hectare basis and due to high nitrate contents, which might have suppressed CH4 production.
\n\tIn the synthesis of this dissertation, data on soil trace gas fluxes were embedded into a broader context to gain information on changes of the net biome exchange (NBE) and on partial N budgets with land-use change. Soil CO2 and CH4 fluxes were combined with an ancillary study on net primary production and harvest as well as with estimations on the contribution of heterotrophic soil respiration to total soil respiration. Soil N2O and NO fluxes were combined with ancillary studies on N inputs and outputs via fertilization, bulk precipitation, leaching and harvest. The results revealed that the NBE of oil palm plantations was higher compared to forest. Nevertheless, implications for climate change are negative since forest conversion itself results in a huge C loss, which cannot be compensated over time by oil palm plantations. The lowest partial N budget was detected in oil palm, indicating that N inputs via precipitation and fertilization were smaller than the huge N loss via harvest. Overall, these results illustrate that land-use change has negative effects on the C and N budgets of tropical ecosystems.

Terrestrial pteridophytes as indicators of a forest-like environment in rubber production systems in the lowlands of Jambi, Sumatra

Changes in soil carbon stocks under plantation systems and natural forests in Northeast India