Understanding the pattern, shifts and environmental impacts of dynamic plant communities in the Himalayan alpine zone (>4100 m.a.s.l.) under climate change

This PhD research aims to advance academic understanding of the ecological systems in the Himalayan Alpine zone (HAZ) with a specific focus on alpine plant community distribution, their ecohydrological impacts, and elevation-driven vegetation shifts under climate change. This study initially concentrated on Khumbu district in northeastern Nepal before expanding to six study regions across the Himalayan mountains. The HAZ was chosen as the research region because unlike areas at lower elevation it has been relatively neglected in ecological studies, despite its hypothesised importance in regulating the downstream water supply for billions of people across the region (Ives and Messerli 1990). The HAZ is also noted as being sensitive and vulnerable to climate change (Golovatch and Martens 2018). Despite its likely importance, its remoteness, high altitude, and lack of scientific attention have hindered comprehensive research efforts. Currently, the limitations of available remote sensing products constrain our understanding of long-term vegetation dynamics, while the lack of in-situ measurements prevents a detailed examination of interactions between alpine plant communities and environmental metrics. These knowledge gaps that centre on the HAZ are prohibiting understanding of the potential environmental implications of future climate shifts, which have been shown in modelling studies and in a few limited remote sensing investigations to lead to a greener mountain system at higher altitude. This PhD uses remotely sensed data from multiple scales, coupled with in-situ measurements and observations in the alpine regions within Khumbu, to create the first land cover map of Sagarmatha National Park at a plant community level. The work then uses a field experiment in the Gokyo valley to understand ecological influences on land surface temperature, simulating the impacts on processes of potential evapotranspiration for different dominant plant species (Rhododendron spp. and Juniperus spp.). Large-scale cloud-based analysis of Landsat series data were then used to identify and track over time the changing upper limits of vegetation across 6 regions (organised longitudinally according to a major climatic gradient from west to east) in the Himalayan mountains. Additionally, field data from community-maintained trail cameras were used to monitor vegetation dynamics at two alpine villages, akin to a simple low-cost PhenoCam but using different spectral principles (Red, Green and Blue bands). The major results of the study were as follows: • A systematic review of alpine and Arctic studies revealed that there are likely to be profound hydrological implications arising from a greening HAZ (published in the journal Ambio). • Dwarf shrubs belonging to the Rhododendron and Juniperus families dominate the ecology of the HAZ above 4100 m.a.s.l (published in the journal Arctic, Antarctic, and Alpine Research). • Altitude and aspect are dominant drivers of vegetation community distribution (published in the journal AAAR). • The presence of plants not surprisingly reduces maximum temperature (with 9.92-30.09 °C difference during the daytime) and increases the minimum temperature under shrub canopy compared to open areas (journal article in second review for Journal of Mountain Science). • Juniperus plants were found to have stronger impacts on temperature than the Rhododendron plants, but the potential evapotranspiration of Rhododendron plants are higher than Juniperus plants (journal article in second review for JMS). • in-situ observations from low-cost trail-cam phenological observations show distinctions between these two plant communities, and Juniperus plants are found to have longer growing seasons at higher altitudes (published in the journal Progress in Physical Geography). • Across the entire Himalayan arc we found consistent upward trends in the location of the vegetation line, with varying rates from 1.42 m/year in Bhutan (the most eastern region) to 6.95 m/year in Manthang (central Himalayas; accepted to the journal Ecography). • Across all regions, greening trends were more prevalent than browning trends, and larger area of greening with higher annual changing rates were particularly shown in central regions (Reckong, Ngari and Manthang; accepted to the journal Ecography). This PhD is interdisciplinary, working between physical geography, remote sensing and social science. The problems that this PhD addresses are a complex combination of the current ecosystem situation, their likely changes under future climate warming, and the recognition that there is lack of long-term in-situ data existing for the Himalayan alpine zone, resulting from the lack of scientific attention and complicated by the remote geographical mountainous location.<p></p>

Author dc:creator

• Ruolin Leng (21058679)

• dynamic plant communities
• Himalayan alpine zone
• climate change

Statement dc:rights

• All rights reserved
• Open Access after 2027-09-16

Identifier

10779/exe.31809937.v1

OAI identifier oai:identifier

oai:figshare.com:article/31809937