Abstract
AbstractCompositional changes in Himalayan vegetation in response to the major drivers of biodiversity loss, climate change and land‐use change, are barely documented. We quantify temporal changes in the alpine vegetation of central Nepal and attribute these changes to temporally varying climatic and land‐use factors. We re‐surveyed the alpine vegetation of two locations within Langtang National Park, central Nepal, after 25 yr using 127 plots of 100 m2. Using ordination, regression, and weighted average regression and calibration techniques, we analyzed the changes in terms of species abundance, frequency, and elevational shift in relation to changing atmospheric temperature, precipitation, and livestock grazing. We found a significant increase in the frequency and relative abundance of the majority of species, which was significantly related to the temporal trends in climatic factors and grazing intensity. Out of 12 species with unimodal responses along the elevation gradient during both surveys, the optima of eight species decreased over the time period. The observed elevations of 62 out of 92 sample plots (hence, species composition) in 2014 were lower than the elevations calibrated from species composition and elevation of 1990, indicating an overall downward shift of species assemblages. However, an upward shift of assemblages was also observed at higher elevations. These results indicate that the observed temporal changes in alpine vegetation, largely contrasting the expected upslope shift of species due to climate warming, are driven most likely by interactions of contemporary climate and land‐use changes, especially reduced grazing. The complex interactions and feedback mechanisms between warmer winters, increased precipitation, reduced grazing pressure, and thereby altered species interactions most likely facilitated the downslope shift of alpine species assemblages. Climatic and land‐use responses of plant species assemblages should therefore be studied focusing on the potential interactions between both the climatic and the land‐use factors because such interactions and feedback mechanisms have potential to mask or modify the expected climatic or land‐use response of biodiversity.
Highlights
Changes in plant species composition due to climate and land-use changes have been documented for several vegetation types throughout the world (Parmesan and Yohe 2003, MEA 2005, Newbold et al 2015)
These results indicate that the observed temporal changes in alpine vegetation, largely contrasting the expected upslope shift of species due to climate warming, are driven most likely by interactions of contemporary climate and land-use changes, especially reduced grazing
Climatic and land-use responses of plant species assemblages should be studied focusing on the potential interactions between both the climatic and the land-use factors because such interactions and feedback mechanisms have potential to mask or modify the expected climatic or land-use response of biodiversity
Summary
Changes in plant species composition due to climate and land-use changes have been documented for several vegetation types throughout the world (Parmesan and Yohe 2003, MEA 2005, Newbold et al 2015). The type, intensity, and frequency of land-use change differ significantly among geographic regions and vegetation types (MEA 2005, Newbold et al 2015), and sensitivity to environmental change varies among species and vegetation types (Parmesan 2006) Because of this variation, the patterns of climate-driven changes revealed at one spatial scale or for one vegetation type may not necessarily reflect those at other scales or for other vegetation types. A paucity of standard vegetation and land-use data from many biodiversity-rich regions, such as the Himalayas, makes the task even more challenging It is worth analyzing the effects of temporally varying climate and land-use regimes on Himalayan plant species assemblages that represent different vegetation types and that are in different geographic locations
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