| dc.description.abstract | Deforestation plays an essential role in land cover changes in tropical area. From 1990 to 2012, Indonesia lost about 20,7 million hectares (Mha) of forest area, and the highest deforestation occurred in Sumatra. One of the areas with extensive forest transformation on Sumatra Island is Jambi Province. Deforestation in Jambi was caused by various driving factors such as forest fire, transmigration project, and land allocation to specific land-use such as plantation and dryland agriculture. This deforestation will impact on the environment in many ways, such as changes in surface energy balance, water surface budget, and carbon cycle.
In some cases, forest transformation in Jambi Province is not through direct conversion to oil palm or rubber plantation. Based on remote sensing data, shrub/bushland and dryland agriculture have become intermediate state of forest loss due to oil palm and rubber expansions. In this study, we try to analyse biogeophysical and biogeochemical processes of forest and its transformation processes into shrub, grass, or dryland agriculture (soybean) using Community Land Model version 5 (CLM5). We also conduct an analysis of coupling strength between the land cover and atmosphere near the surface through the interaction between soil moisture and surface fluxes.
Partition of surface energy balance from forest, shrub, grass, and soybean showed higher utilization of energy for latent heat fluxes. In monthly variation, no considerable fluctuations are found in the partition of surface fluxes in forest, shrub, and grass, while in soybean, the surface fluxes change dramatically. This pattern follows the planting time of soybean. In diurnal variation, the net radiation in soybean slightly lower than other land uses. Forest transformation into shrub, grass, or soybean decreased latent heat fluxes and increased sensible heat fluxes, especially during strong El Nino. Forest, shrub, and grass had more substantial variation in Bowen ratio (β), but soybean conserved fluctuation in Bowen ratio. Soybean had a smaller change in β because it used irrigation system, so the water was not a limitation for evaporation.
Land-use changes alter carbon uptake, although it did not necessarily reduce the Net Primary Production (NPP) and efficiency. Forest transformations into soybean and grass will increase NPP, while its transformation into shrub will decrease NPP. Among all land covers, soybean showed higher carbon use efficiency (CUE) due to the availability of water and soil nutrient supplies. In comparison, the forest had lower CUE due to its high respiration to maintain its biomass. Coupling strength between soil moisture and latent heat fluxes in all land covers was positive, but the R-squared was relatively low. This result indicated that there was another factor impacting surface energy balance partition. | id |
