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Long‐term physiological and growth responses of Himalayan fir to environmental change are mediated by mean climate 

作者: Panthi S
刊物名称: Global Change Biology
论文题目英文: Long‐term physiological and growth responses of Himalayan fir to environmental change are mediated by mean climate
年: Nov 2019
卷: online
联系作者: Fan ZX
影响因子: 8.88
Highelevation forests are experiencing high rates of warming, in combination with CO2 rise and (sometimes) drying trends. In these montane systems, the effects of environmental changes on tree growth are also modified by elevation itself, thus complicating our ability to predict effects of future climate change. Treering analysis along an elevation gradient allows quantifying effects of gradual and annual environmental changes. Here we study longterm physiological (ratio of internal to ambient CO2 i.e. Ci/Ca and intrinsic wateruse efficiency, iWUE) and growth responses (treering width) of Himalayan fir (Abies spectabilis) trees in response to warming, drying, and CO2 rise. Our study was conducted along elevational gradients in a dry and a wet region in the central Himalaya. We combined dendrochronology and stable carbon isotopes (δ13C) to quantify longterm trends in Ci/Ca ratio and iWUE (δ13Cderived), growth (mixedeffects models), and evaluate climate sensitivity (correlations). We found that iWUE increased over time at all elevations, with stronger increase in the dry region. Climategrowth relations showed growthlimiting effects of spring moisture (dry region) and summer temperature (wet region), and negative effects of temperature (dry region). We found negative growth trends at lower elevations (dry and wet regions), suggesting that continentalscale warming and regional drying reduced tree growth. This interpretation is supported by δ13Cderived longterm physiological responses, which are consistent with responses to reduced moisture and increased vapour pressure deficit (VPD). At high elevations (wet region), we found positive growth trends, suggesting that warming has favored tree growth in regions where temperature most strongly limits growth. At lower elevations (dry and wet regions), the positive effects of CO2 rise did not mitigate the negative effects of warming and drying on tree growth. Our results raise concerns on the productivity of Himalayan fir forests at low and middle (< 3,300 m) elevations as climate change progresses.
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