91 9 – Structure and Functioning of Timberline Vegetation in the Western Himalaya: A Case Study Structure and Functioning of Timberline Vegetation in the Western Himalaya: A Case Study Ishwari Datt Rai 1* , Rupesh Ranjan Bharti 1 , Bhupendra Singh Adhikari 1 , and Gopal Singh Rawat 1,2 1 Wildlife Institute of India, P.O. Box 18, Chandrabani, Dehradun, Uttarakhand, India 2 International Centre for Integrated Mountain Development, GPO Box 3226, Kathmandu, Nepal * ishwari.rai@gmail.com A n ecological assessment of timberline vegetation was carried out during 2008–2011 at selected locations in the Indian Himalayan states of Uttarakhand and Himachal Pradesh. The objectives were (i) to establish baseline data on the vegetation structure and composition along the timberline ecotone, (ii) to assess the functioning of major communities (net primary productivity, litter decomposition, and nutrient dynamics), and (iii) to study the effects of interannual climatic variation on the phenological responses of the tree species forming the alpine timberline in the study area. Geospatial analysis of the timberline ecotone (3,000– 4,000 masl) showed that fr (Abies spectabilis) occupied the greatest area within the timberline (1,886 km 2 ) followed by oak (Quercus semecarpifolia, 1,142 km 2 ), birch (Betula utilis, 433 km 2 ), and krummholz (412 km 2 ). An area of approximately 81 km 2 had undergone major change during the last three decades, with a proportionally greater change in the last ten years (44 km 2 ) than in the previous decades. Fir forest had increased by 33 km 2 since 1980. The phenological study showed that the broadleaf deciduous species Betula utilis was more sensitive to interannual climatic variation and early snow melt. This Paper discusses the broad fndings of the study, especially the extent and changes in the forests along the timberline ecotone, the pattern of tree species regeneration, the population structure, and phenological responses under different conditions. Keywords: change detection; phenology; remote sensing; timberline; Western Himalaya Introduction The timberline ecotone, marked by the culmination of the forested zone, is the most prominent ecological boundary in the high mountains governed by climatic factors (Holtmeier 2003). The microclimate, topography, altitude, and herbivory play a significant role in determining the structure and function of plant communities along the timberline. In addition, several anthropogenic, topographic, and climatic factors influence the overall physiognomy and