Forest Soil Along an Elevation Gradient With Varying Forest Types

ABSTRACT This study examined soil properties along an elevational gradient (350–2200 m) in the Central Himalayas to understand how soil properties with increasing elevation are affected by geological factors, forest types, and forest fires. Annual precipitation remains > 1500 mm throughout the elevation transect. Soil samples were collected from seven forest sites dominated by sal ( Shorea robusta ), chir pine ( Pinus roxburghii ), oak ( Quercus ) species, and mixed chir pine‐banj oak ( Q. leucotrichophora ) at three depths (0–10, 10–20, 20–30 cm). Sal occurs in alluvial plains, pine in the Shiwaliks, and oaks in the Lesser Himalaya. The proportion of coarse material was the highest at mid‐elevations, from where the main boundary thrust (MBT) passes through pine‐dominated forests. Chir pine forests at mid‐elevations showed high soil organic carbon content despite frequent surface fires, largely because of slow litter decomposition. Old growth sal forest had higher organic carbon and nitrogen compared to young sal forest, partly because of management practices. The linear relationship between increasing elevation (decreasing temperature) and soil properties, such as soil organic carbon (SOC) and soil coarse material was modified by the mid‐elevation (1750 m) presence of chir pine forest and MBT, where rocks are broken, fissured, and disintegrated. Frequent small and mild surface fires seem to have only a moderate effect on SOC and have led to increased coarse matter by eroding fine particles. Forest management practices and disturbance regimes also impact soil characteristics, as old growth sal forest had higher soil organic matter and nitrogen than the adjacent young sal forest. Located in the Shiwalik, near the main boundary thrust, the chir pine site is prone to erosion. The effect of forest type on soil properties, particularly soil organic carbon and nutrients along the study elevation gradient, was conspicuous as indicated by the comparison between pine, mixed oak‐pine, and oak forests. Thus, the relationship between elevation and soil is considerably modified by forest type and disturbances associated with fire and geological factors.