Trees record changes of the temperate glaciers on the Tibetan Plateau: Potential and uncertainty.

Abstract The Tibetan Plateau and its surrounding mountains exhibit the largest concentration of glaciers at lower latitudes on earth, providing source water for the large river systems in Asia. However, glacier observations in this region are short and scarce and hence limit a better understanding of glacier behaviors under a warming climate and thereto coupled processes. The purpose of this research is to investigate the potential and the uncertainty for using pioneering trees on glacial deposits/glacier forefields as a proxy record for past glacier fluctuations in the Himalaya-Nyanqentanggula-Hengduan (H2N) area. It was found that Hippophae tibetana spent 4 years to colonize the glacier forefields at Hailuogou glacier and Pinus wallichiana germinated 11 years after glacier retreating at Gangapuna and Raikot glaciers. At deposit sites of glacier avalanche and glacial lake outburst, it took 8 years for Larix griffithii to germinate after the historical events. As shown by bootstrap resampling, the precision of the sampled maximum tree age could reach 2–14 years, which is related to the sample size to ensure the possibility of obtaining the eldest trees. However, if using the traditional sampling method at 100-cm height, errors of tree age estimation may reach up to ±20 years due to uncertainties of pith offset estimation and height-age calibration. If samples are collected with pith from ≤20 cm tree height, an error of <5 years in tree age estimation could be derived. These results suggest that maximum tree ages may be a promising proxy record of glacier fluctuation with decadal precision in the H2N mountain range if the sample-collecting methods are rigidly controlled and the old trees are well replicated. The uncertainties due to the pith offset, tree height age and sample size imply that cautions should be taken when integrating exposure age dating on decadal-multidecadal glacier fluctuations at regional to hemispheric scales. Highlights • Fast (4–11 years) colonization on glacial area by pioneer trees on the Tibetan Plateau • Decadal precision dating on glacier deposits is possible by tree records. • Collecting samples with pith from height ≤20 cm is recommended. • Dating uncertainty due to sample size and sampling methods should be considered. [ABSTRACT FROM AUTHOR]