Forests of Himalaya with particular reference to man and forest interactions in Central Himalaya

Abstract

Migration of the Indian Plate northwards after the isolation from Madagascar about 80 million years ago, its collision with the Asian Plate and consequent under thrusting of the Indian Plate led to the rise of the Himalaya. Owing to its varied topography and climate, Himalaya supports a variety of forests up to the timberline. This forest wealth provides several important ecosystem services. However, in most parts, and particularly below the altitude of 2,200 m. often the forests are degraded and interspersed with deforested open 'blanks' and village settlements. Presently less than 5% of the geographical area of the Central Himalaya has forest with crown densities over 60%. The agroecosystems are centres of massive energy consumption and their viability depends on the supply of energy from the forest. Each kcal of agronomic yield (including milk) requires the expenditure of about 7 kcal from the adjacent forest in terms of fodder, fuel and leaf manure. Even with the massive subsidy from the forests, the agronomic production in Central Himalaya is sufficient for only 50% of the needs of the population. The harvest and forest clearing release 10.2xl0¹² g carbon annually. The net annual release of carbon to the atmosphere from the Central Himalaya amounts to 4.6xl012 g making the forest a source of C0₂ for the atmosphere instead of a sink. Although all types of the Central Himalayan forests have been under severe biotic stress during the last one century, man's onslaught on oak forest ecosystems has been particularly severe. The human interference has caused changes in species composition. The density-diameter distribution curve for all species in the entire region shows an overall convex appearance (largely second derivative negtive). Such a structure reflects predominantly an early successional forest. Pine has been invading the oak forest. Characteristics of pine (high nutrient withdrawal efficiency, high C:N ratio, nutrient immobilization in decomposing litter) enable it to invade and hold the site against future reinvasion of oak. Thus the diverse and multistratal forest is being converted into species-poor and little or unstratified forest. The Central Himalayan catchments are subsurface flow systems and are prone to landslides. The nonforested ted sites produce seasonal overland flow greater than the forested sites and the soil loss is dependent on the volume of overland flow produced! The pine zone suffers from more landslides. Canopy of the multistratal forest (e.g. oak) is more protective to soil against raindrop impact than single layered canopy (e.g. pine).