Abstract:
Environmental degradation in Sri Lanka has accelerated since the 1870s, as commercial agriculture
expanded, driving widespread deforestation that resulted in severe land degradation through
soil erosion and carbon loss. This study evaluates carbon storage and soil erosion across five
land use types in the Belihuloya region: natural forests, forest patches, plantation forests, home
gardens, and tea plantations. InVEST Sediment Delivery Ratio (SDR) and Carbon Storage
models (version 3.12.1) were employed to generate spatially distributed predictions, evaluating
how land-use changes impact ecosystem services. Land Use Land Cover (LULC) classification
identified 16 land cover types, with forests and forest patches achieving the highest mean
carbon storage (129.30 t ha-1), while home gardens and tea plantations showed reduced storage
due to human management practices. Soil erosion modelling revealed a mean annual potential
of 315.81 t ha-1 based on RKLS (R × K × LS) values, though actual Universal Soil Loss Equation
(USLE)-based erosion rates were significantly lower (9.16 t ha-1), exceeding the national
soil erosion tolerance threshold of 5 t ha-1. Avoided erosion and sediment export values further
demonstrated the protective capacity of forested landscapes. Results identified erosion hotspots
concentrated in tea plantations on steep slopes, where cultivation practices and vegetation removal
increase vulnerability. Conversely, forested areas provided superior carbon retention
while maintaining effective erosion control. These findings emphasise the critical need for soil
cover management and conservation strategies to prevent further degradation. This research
demonstrates the effectiveness of GIS-based modelling tools for assessing environmental impacts
of land use change and supports integrating conservation practices, such as agroforestry
and reforestation, into land-management planning.
