Himalayan arc and treeline: distribution, climate change responses and ecosystem properties

Abstract

This study adopts a twofold strategy by reviewing literature from scattered Himalayan studies (145 sites) to use meta data (i) to synthesize the ecosystem properties of treeline ecotone, treeline response to climate change and influencing biotic factors, (ii) to analyze patterns of distribution of treeline species and their elevations, and (iii) to test relationship between treeline altitude and longitude and latitude across the 2500 km wide Himalayan Arc. Himalayan treeline is highly heterogeneous with regard to (i) species composition (58 species of 10 genera), and (ii) elevation (1700 m wide range in Treeline Elevation, TLE). Apart from temperature, variation in non-climatic factors, such as livestock grazing, and topography contribute considerably to the wide elevation range in TLE. Rhododendron, Juniperus, Abies, and Betula are common Himalayan treeline genera. Treeline elevation (3200–4900 m) and it increases (i) from NW to SE (18.4 m 1°−1 longitude), (ii) from periphery (from both north and south sides) to central part of the ranges, and (iii) from north to south aspect. A shift in dominance from deciduous Betula utilis (birch) to evergreen rhododendrons is discernible from the NW to SE. Treelines in the Himalayas differ between south and north aspects in species, elevation and anthropogenic activities, such as pastoralism. Response of treeline species to climate change could vary considerably, depending upon whether warmer temperatures of pre-monsoon months are accompanied by increased precipitation of the intensify droughts. Biomass accumulation rate declines rapidly towards treelines, and its role in treeline formation needs detailed investigations. An ecosystem approach is required to improve our understanding and management of Himalayan treeline areas.