The Impact of Forest Use and Reforestation on Soil Hydraulic Conductivity in the Western Ghats of India: Implications for Surface and Sub-Surface Hydrology

background

This article presents research on the surface and sub-surface permeability of degraded and restored forests and their dominant stormflow pathways  in the humid tropics of Uttar Kannada district, Karnataka, India. The authors attempt to determine to what extent field saturated hydraulic conductivity (K*) isaltered due to long-term forest degradation as compared to other studies in the humid tropics. They quantify changes in permeability following forestation of plantations and degraded landscapes and investigate the likely effect of wet-season conditions and the implications this has for predicting hydrologic consequences of forest degradation.

Research Goals & Methods

K* was sampled at 23 sites at four depths (0m, 0.10m, 0.45–0.60m, 1.35–1.50m) under forest, degraded forest, and tree plantations. The sampling strategy was also undertaken across three physiographic blocks (coastal, mid-ghat/midlands and up-ghat) and under three main soil types (black, laterite, and red).

Conclusions & Takeaways

The study showed lowest surface permeability progressively declining with depth in the laterite and red soils associated with the degraded forests, lending support to the notion of a loss of macro-porosity due to multi-decadal disturbance, as reported elsewhere in the humid tropics. Plantations of Acacia auriculiformes on red and laterite soils had a small increase in the surface permeability but the surface K* still remained low. Significantly, forestation with Tectona grandis on black soils had minimal impact on soil permeability. The authors conclude that the intensity of forest use and effects of monoculture plantations on soil ecology (relative to native, mixed forests) is likely to be the critical factor in affecting surface K* over time.