Abstract
Tree-rings are recorders of environmental signals and are therefore often used to reconstruct past environmental conditions. In this paper, we present four annually resolved, multi-centennial tree-ring isotope series from the southeastern Tibetan plateau. The investigation site, where juniper and spruce trees jointly occur, is one of the highest known tree-stands in the world. Tree ring cellulose oxygen (δ18O) and carbon (δ13C) isotopes were analyzed for a common period of 1685–2007 AD to investigate climate–isotope relationships. Therefore, various climate parameters from a local meteorological station and from the CRU 4.02 dataset were used. Tree-ring δ18O of both species revealed highly significant sensitivities with a high degree of coherence to hydroclimate variables during the growing season. The obtained δ18O–climate relationships can even be retained using a species mean. In contrast, the individual δ13C series indicated a weaker and non-uniform response to the tested variables. Underlying species-specific responses and adaptations to the long-term trend in atmospheric CO2 bias even after a trend correction identified dominant environmental factors triggering the tree-ring δ13C at our site. However, analysis of individual intrinsic water-use efficiency in juniper and spruce trees indicated a species-specific adaptation strategy to climate change.
Highlights
Often-quoted in a broader context as the “Third Pole” [1], an important part of the “Asian WaterTowers” [2], or the “Roof of the World” [3], the Tibetan plateau (TP) exerts a key role for the climatic, hydrological and biological conditions of its highlands, mountain ranges as well as for the adjoiningAsian lowland areas
Besides studies focusing on tree-ring width (TRW), more and more studies display the advantages of using stable isotopes in tree-rings for ecological as well as paleoclimate research on the Tibetan plateau
Since both tree-species are situated within a short elevational range, this is assumed to be caused by slightly different plant-internal fractionations during cellulose synthesis and/or—on a microclimatic scale—a slightly differing moisture availability during the vegetation period
Summary
Often-quoted in a broader context as the “Third Pole” [1], an important part of the “Asian WaterTowers” [2], or the “Roof of the World” [3], the Tibetan plateau (TP) exerts a key role for the climatic, hydrological and biological conditions of its highlands, mountain ranges as well as for the adjoiningAsian lowland areas. Beyond the fact of its substantial role within the global climate system as the key driver of the Asian monsoonal systems [4], the current changes within the regional cryosphere, hydrosphere, biosphere and associated responses of environmental systems on the TP are subjects of intensive research. Geosciences 2019, 9, 151 to the substantial rise in temperature during the recent decades and associated changes of water availability underline the necessity of a precise quantification of these changes [5,6,7,8,9]. Existing datasets, which are mainly available at the earliest since the 1950s, hamper a substantial quantification and classification of the recent climate change within a retrospective context and underline the needs for paleoclimatic datasets [4,10,11,12]. Studies on the δ13 C variations in tree-rings are still underrepresented due to more complex isotope fractionation effects affecting the δ13 C in tree-rings
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