Woody species Structure as Influenced by Biotic Regimes at Timberline Ecotone in the Eastern Himalaya: Implications for Management

Abstract

The timberline ecotones support distinctive vegetation all over the globe but they are under intense biotic pressure in the Himalayan region; inadequate information on such forests makes their management a difficult preposition. This study investigates the Eastern Himalayan timberline, a least studied site, to assess- what is the woody species composition at timberline ecotones? How biotic pressure influence woody species composition in these stands? And how the species structure would be if similar biotic pressure prevails in near future? A total of 5 tree species and 11 shrub species were recorded from three investigated forest stands. Abies densa showed overall dominance at all stands; it formed mono-dominant community at least-disturbed stand, mixed-community at moderately-disturbed stand, and co-dominant community with Sorbus microphylla at highly-disturbed stand. Shrub density, however, was highest at highly-disturbed stand, Berberis being the main species. Abies densa recorded maximum seedling and sapling density at all stands with maximum numbers at moderately-disturbed stand. The DBH-distribution exhibited maximum individuals in <10 cm class at least- and moderatelydisturbed stands, and in 10-20 cm class at highly-disturbed stand showing that young population was significantly affected by the intensity of the disturbance. A comparative analysis of data on tree density, total basal area and regeneration exhibited that our results fall in intermediate to higher side than those reported for other timberline forests. The moderate disturbance seems to improve micro-habitat conditions that support better growing condition at this site. Though the species structure may be same in near future, high disturbance however, may significantly change species composition and structure that could bring some irreversible changes in species distribution. Selective management measures, such as plantation of native species and advancing conservation education along with promoting economic activities such as commencing ecotourism in such areas could help to improve status of degraded forest stands.