Predicting soil depth to bedrock in an anthropogenic landscape: a case study of Phewa Watershed in Panchase region of Central-Western Hills, Nepal

The Soil Depth to Bedrock (SDtB) parameter is highly variable over the landscape and is an important input for soil surface modeling including various types of mass movement that most often ignores the variability of soil depth. In landscapes that have been heavily modified by humans, SDtB parameters do not necessarily depend on natural processes, making it difficult to apply physically-based approaches. This study explored the possibility of using topographic attributes to model the SDtB in the complex topography of Phewa watershed in the Panchase region of Nepal. In June 2017, 865 SDtB points were surveyed along the excavated rural roads (approximately 300 km) within the watershed (111 km2). Topographic attributes such as slope, curvatures, altitude and compound terrain index were derived from a Digital Terrain Model along with Land use land cover attributes derived from recent Landsat remote sensing images. Utilizing these attributes as explanatory variables, we implemented simple kriging (SK) and multiple linear regressions (MLR) to predict SDtB for the watershed. The results showed that the MLR predicted SDtB map was statistically significant (R2 = 68%, EC = 0.93) over the SK (R2 = 12%, EC = -0.46). We concluded that the MLR approach in predicting SDtB for the complex geo-morphologic landscape such as the Phewa watershed in the Panchase region of Nepal can effectively be used, helping to inform the evolution of land-use as the region continues to develop.

Links between terrain characteristics and forage patterns of elephants (Loxodonta africana) in northern Botswana

Spatial vegetation utilization of elephants was investigated within mixed woodland savanna along the Chobe River in northern Botswana in the dry season of 1998. Using multiple linear regression, accumulated stem breakage by elephants was predicted by a terrain index, distance to water, stand density, number of trees > 4 m tall, tree height, density of Combretum apiculatum, C. elaeagnoides, C. mossambicense and the density of other (accumulated) tree species. Within mixed woodland at 2–7 km distance from the river fine-grained terrain ruggedness was the most important factor contributing to 55% of observed differences in use by elephants, while distance to water and the density of C. apiculatum contributed an additional 20% and 4%, respectively to the multiple linear regression model. Stem breakage was, on average, almost twice as high in rugged terrain compared with flat terrain at similar distance to water within the same vegetation type. Rugged terrain had 2–3-fold higher proportion of plots with very high Combretum shrub densities. These results suggest that the terrain index may be useful in management, predicting the areas most sensitive to vegetation change in a woodland system with increasing elephant densities.