Shrestha, K. B. 2013. Treeline and vegetation dynamics in response to environmental changes in Nepal, the central Himalaya. Ph.D. Thesis, Faculty of Science, University of Bergen, Norway. Aims: To describe and evaluate patterns of vegetation response to ongoing environmental changes across climate-limited (alpine treeline ecotone) and humanmodified (temperate Himalayan oak forests) ecosystems in Nepal, central Himalaya. Methods: I used dendroclimatological techniques to examine spatial and temporal changes in tree growth responses (paper I) and recruitment patterns (paper II) to climatic variability across a dry Pinus wallichiana and a mesic Abies spectabilis treeline ecotone. Trees from various ecological elevations (forest line, treeline and krummholz line) were cored, annual growth was measured and site chronology was developed for analysing climate-growth relationships. Transects were laid out between the forest line and tree species line, crossing the treeline. Seedlings, saplings and trees were sampled in each transect for age analysis. Alpha, beta and gamma diversity were studied across a forest border from a forested to open landscape in a subalpine-alpine region (paper III) and an anthropogenic disturbance gradient (paper IV). Vascular plant species richness and environmental variables were recorded in each plot (10 m × 10 m). Alpha diversity was estimated as average species richness per plot. Beta diversity was based on gradient length estimated by Detrended Correspondense Analysis (DCA). Gamma diversity was estimated as total species number present in the landscape. Main results: At the dry locality, tree growth at the forest line responded positively to warm summers and after cold winters: possibly a response to early onset of growing season. At the mesic locality, growth at lower altitudes (forest line) showed signals of drought limitation, whereas at higher altitudes, decreased growth was associated with an early onset of the monsoon. Reduced growth at the treeline was related to the high winter snow fall and delayed onset of growing season. The current treelines in both areas have remained stationary over the decades. Climate and land-use are both important factors for treeline structuring processes. vii List of papers My thesis is based on the following four scientific research papers; hereafter referred to by their roman numerals (Papers I-IV). Papers III & IV are reproduced with the kind permission of Folia Geobotanica and International Journal of Biodiversity Science, Ecosystem Services & Management respectively.
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