Knowing drought response of forest ecosystems in remote mountain regions: A Throughfall-Exclusion Experiment to Simulate Monsoon Failure in the Bhutan Himalayas

Abstract ID: 3.10980 | Accepted as Talk | Talk | TBA | TBA

Georg Gratzer (1)
Wangdi Norbu, Mayer Mathias, Nirola Mani Prasad, Orong Karma, Zangmo Norbu, Schindlbacher Andreas
(1) BOKU University, Peter Jordanstraße 82, 1190 Wien, AT
(2) 2Department of Ecosystem Management, Climate, and Biodiversity, Institute of Forest Ecology, BOKU – University of Natural Resources and Life Sciences, Vienna, Austria, 1090 Wien

Categories: Ecosystems
Keywords: Drought response, monsoon failure, throughfall exclusion, Bhutan Himalyas, Forest

Categories: Ecosystems
Keywords: Drought response, monsoon failure, throughfall exclusion, Bhutan Himalyas, Forest

The Himalayas are located in a region that is part of one of the tipping points of the Earth’s climate system, with the South Asian summer monsoon providing water resources for the livelihoods of over a fifth of the world’s population. Although there is a high degree of uncertainty in future precipitation scenarios, models collectively suggest that climate change could make the Asian summer monsoon increasingly variable in time and space, and that the likelihood of extreme events, such as failure of the summer monsoon and subsequent extreme drought, could increase by the end of the 21st century. Despite the critical role of this climate system, little is known about the consequences of changing precipitation patterns or even monsoon failures. This follows a global knowledge divide with huge inequalities in the scientific studies leading to the development of informed adaptation measures. Studies and experiments are concentrated in rich countries and almost non-existent in poor countries. In this presentation, we discuss the challenges of implementing a throughfall-exclusion (TFE) experiment to simulate monsoon failure in the Bhutan Himalayas, and present results in terms of the response of eastern Himalayan forests to future droughts. We established 30×25 m roofs in two representative forest types of Bhutan, a mixed oak forest at 2650 m asl and a mixed conifer forest at 3250 m asl.. With the experimental setup, we were not able to simulate monsoon failure, most likely due to roof removal in winter and foliar water uptake during vegetation periods. Throughfall exclusion did not cause tree mortality, stem increment only showed reductions in the third year, with Tsuga dumosa being most affected (-60%). Fine root biomass stocks were little affected by TFE. Increased root necromass and faster fine root growth in the lower elevation forest suggest that the oaks increased belowground C allocation. Soil CO2 efflux decreased significantly in both forests during all three TFE years. Aboveground litter input was unaffected by TFE until the second treatment year. Overall, both forest ecosystems appeared highly resistant to the imposed moderate soil drying, with no signs of tree mortality and stable living root biomass stocks.

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