Impacts of disturbance on soil properties in a dry tropical forest in Southern India.

Grazing, fuelwood extraction and burning are common human activities in Indian forests. These activities can represent forest disturbances that drive the degradation of natural deciduous forest cover to scrub forest, with concurrent impacts on soils. The effects of human forest use on ecosystem functions were investigated in Bandipur National Park (BNP) in Peninsular India. This paper reports the impacts on surface soils. Soils were sampled from 200 locations covering four watersheds within the Park. These samples spanned a degradation gradient measured by a field disturbance index (FDI). Soil physical, nutrient and hydraulic properties were measured. Cation exchange capacity (CEC) and saturated hydraulic conductivity (Ks) were analyzed as key response variables describing nutrient availability and infiltration respectively. Effects of cattle and jeep trails on infiltration and bulk density were evaluated by sampling on-and-off trails. Trail density in research watersheds was estimated with satellite imagery. Soil nutrient availability is negatively impacted by disturbance, resulting from negative impacts on soil organic carbon (SOC) and clay content. Available water capacity (AWC) and saturated moisture content (SMC) were significantly higher in protected watersheds, attributed to reduced clay content in degraded watersheds. Off trails, high spatial variability in infiltration overwhelmed any meaningful trends with disturbance. However, infiltration was substantially reduced on trails as a result of significant increase in bulk density. The density of trails was considerably higher in degraded watersheds compared to protected watersheds. These results provide ground-based and remotely sensed evidence that forest disturbance within the Park has negative impacts on soil organic matter, nutrient availability and hydraulic characteristics. These have consequences for related ecological, nutrient cycling and hydrological processes, and the continuation of the services currently enjoyed by local human populations. Copyright  2008 John Wiley & Sons, Ltd.