Organic carbon stock in the forest soils of Himalayas and other areas in India

Abstract The Himalayas, originated from the tectonic collision between India and the Tibetan plates, is a mountain range characterized by varying altitude, slope, aspect as well as the climate of the mountain resulting extensive ecological diversity. The Indian Himalayan region (IHR) covers 16.2% of the Total Geographical area (TGA) of India and spreads across 12 Indian states covering an area of 625,000–750,000 km2. Because of the varied climatic and physiographic features and heterogeneous nature of geological formations, there is a formation of various types of soils supporting variable forest flora and fauna. With the variation in altitude and climate, quite contrasting flora occurs at different altitudes. These lead to the formation of diverse type of forests from the foot hills to middle and upper hills and ultimately to alpine meadows above timber line. This sort of variation in forest type influences the development of different types of soils. In the Himalayas, different soil parameters (organic carbon, total N, fractions of humus carbon) bear significant positive correlation with altitude. However, soil pH and exchangeable bases show negative correlation with altitude. Studies conducted in the lower hills of the Himalayas indicate that teak (Tectona grandis) being a calcicolous plant increases the base saturation and organic matter content of soils over years and might help in developing organic-rich thick epipedon (surface horizon) in soils in near future to qualify many Inceptisols in this area into Mollisols (with organic matter-rich mollic epipedon). The northeastern part of the Himalayas is the convergence of different types of floras, including east Himalayan flora, Paleoarctic flora of the Tibetan highland and wet green flora of southeast Asia and Yunnan resulting tremendous biodiversity. In this region, there is a considerable variation of soil organic carbon (SOC) content in the surface layer. Of the total geographical area of northeastern region (15.61 million ha), variability of organic carbon content reveals that more than 1% SOC occupied by 98.54% area, more than 1.5% SOC by 57.68% area, more than 2.5% SOC by 13.44% area, and more than 3.5% SOC by about 1.0% area. The estimation of biomass carbon pool under T. grandis plantation in Darjeeling and Kurseong Himalayas indicates that aboveground biomass contributed major share (82%) toward the total biomass in comparison to that of the below-ground biomass (root biomass) (18%). The estimated total biomass carbon pool ranges from 57 to 136 tC ha−1, and the average carbon stock up to 90 cm soil depth was 189 tC ha−1. The higher SOC to biomass carbon ratio reflects the influence of altitude and climate especially precipitation toward the increasing SOC. The SOC stock measured up to the depth of 60 cm in upper and middle hill soils of Sikkim, and the Darjeeling Himalayas is more than double in comparison to that of lower hill soils suggesting the increase of SOC content with altitude. The same is true for the soils of temperate forest soils of Ladakh and Kashmir Himalayas. Soil organic carbon stock in Garhwal Himalayas is mostly influenced by its aspects. Northern aspects were reported to have more stable communities along with more fertile soils that eventually sequester more carbon stocks. SOC stocks in moist temperate forests soils in Himachal Pradesh are much higher in comparison to lower hill soils. Besides the soils of the IHR, the brown forest soils (Mollisols) of the Western Ghats and the Satpura range contain higher SOC (3%–4%) and are maintaining the SOC stock of 0.062 Pg mha−1 (per million hectares) (1 Pg, Petagram is 1015 g). Based on the estimation of the SOC stock under IHR and in other areas, it is evident that major part of the Himalayas maintained the minimum threshold value of SOC stock due to the congenial pedo-environment maniatined by the forst vegetations and, therefore, need to be protected. However, there are few areas which require more attention to improve the forest vegetation.