Climate Change-Induced Shift of Tree Growth Sensitivity at a Central Himalayan Treeline Ecotone

Niels Schwab,Ram Chaudhary,Jürgen Böhner,Ryszard Kaczka,Karolina Janecka,Udo Schickhoff,Thomas Scholten

doi:10.3390/f9050267

Niels Schwab, Ram Chaudhary + Show 5 more

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https://doi.org/10.3390/f9050267

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Abstract

Himalayan treelines are exposed to above average climate change impact, resulting in complex tree growth–climate relationships for Himalayan Silver Fir (Abies spectabilis (D. Don) Spach) at central Himalayan treelines. The majority of recent studies detected current tree growth sensitivity to dry conditions during pre-monsoon seasons. The aim of this study was to analyze growth–climate relationships for more than a century for a treeline ecotone in east-central Nepal and to test for Blue Intensity (BI; used as a surrogate of maximum late wood density) as climate proxy. We determined the relationships of Abies spectabilis radial tree growth and BI to climate by correlating both to temperature, precipitation and drought index data. The results showed a significantly unstable dendroclimatic signal over time. Climate warming-induced moisture deficits during pre-monsoon seasons became a major factor limiting radial tree growth during recent decades. Earlier in time, the dendroclimatic signal was weaker, predominantly reflecting a positive relationship of tree growth and summer temperature. Compared to radial tree growth, BI showed a different but strong climate signal. Temporally unstable correlations may be attributed to increasing effects of above-average rates of climate warming. An extended network of Himalayan tree-ring sites is needed to further analyze cause–effect relationships and to solve this attribution problem.

Highlights

Mountains of the world, including the Himalaya, belong to the regions most affected by climate change
Since we found rather weak static tree ring width (TRW)–climate and Blue Intensity (BI)–climate correlations for the entire investigated period (Figure A3), we tested the temporal stability of correlations by applying 31-year moving windows with a one year offset to compare both proxies
Abies spectabilis growth–climate correlations in the Rolwaling valley changed during the 20th century, most likely to be attributed to intensified climate warming during the second half of the

Summary

Introduction

Mountains of the world, including the Himalaya, belong to the regions most affected by climate change. Above-average warming rates trigger multiple vegetation responses such as changes in phenology, productivity, species composition of communities, structure, and elevational ranges of species [4,5,6,7]. In this regard, elevational shifts of alpine treelines and tree growth–climate relationships have received much attention (e.g., [8,9,10,11,12]). More tree-ring based studies on different treeline tree species, tree-ring proxies and various mountain regions are needed to close this knowledge gap

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