Degradation of oak forests in the Himalaya: impacts on diversity, carbon stock, and regeneration

In the Himalayan region, relentless extraction of forest products has led to modified forest structure, species composition, and productivity of the forests. Degradation is a slow process and becomes evident generally after a long time, when recovery is difficult. The Himalayan Forests are depleting at a very fast rate, 0.36 km 2 year -1 . In the IHF (Indian Himalayan Forest), deforestation is less evident, but human-induced anthropogenic activities like lopping, livestock grazing, and wildfires can lead to the complete disappearance of the tree canopy, and only the stump remains. The oak-dominated forests in the Indian Himalayan region sustained the agro-pastoral communities, and as a result, finding unexploited oak forests is becoming difficult. In the present study, we compared the regeneration, plant diversity, carbon stock, and soil organic carbon (SOC) stock in highly disturbed (HD) forests with less disturbed forests (LD) of three dominant oaks, namely Quercus leucotrichophora, Q. floribunda , and Q. semecarpifolia , between an elevation of 1800 and 2700m. A total of six sites were selected (3 HD and 3LD) for each oak forest site (a Total of 18 sites). Regeneration is a problem in all three oaks in the HD sites, but even the LD sites seem to be at risk. The seedling to sapling conversion percent was less than 30% in all three oak species. Among the oak species the seedling density was highest in Q. floribunda LD site (196-311 indi/ha) and lowest in Q. semecarpifolia HD site (38-34indi/ha). Both Shannon diversity and richness were consistently higher in LD forest sites 1.48 in Q. leucotrichophora forest, 1.10 Q. floribunda forest and 1.05 in Q. semecarpifolia forest than in HD forests. The tree biomass was maximum in Q. floribunda LD site (S6) 849.8(t ha -1 ) and minimum 234.8(t ha -1 ) in Q. leucotrichophora HD (S1) site . The biomass and carbon stock varied significantly across forest (P<0.001) and disturbance level (P<0.001); however, there was no significant variation in the biomass and carbon stock of all three Quercus species. The SOC also varied significantly with soil depths ( p <0.001) and was highest at the top layer (0-10cm) and decreased with the soil depth. The soil organic carbon stock was maximum in Q. leucotrichophora forests, 73.4 t C ha -1 (LD), and minimum in 29.1 t C ha -1 in Q. semecarpifolia HD sites up to 30cm depth. There is an urgent need for the Conservation of the oak of the Himalayan region, along with long-term assessment of the sustainable level of resource utilization from the oak forest by the local communities. Alternate sources of energy and green fodder can be promoted to fulfill the requirements of the dependent communities on these forests.