气候和地形对青藏高原树线位置的影响

Impacts of climate and topography on the treeline position across the Tibetan Plateau

地形等非温度因子可能对树线位置有显著影响,这在一定程度上解释了为何变暖背景下树线位置的爬升幅度十分有限。为检验这一想法,本文研究了青藏高原阳坡和阴坡的树线位置与气候、地形等非气候因子之间的关系。收集了近10年来青藏高原树线文献中的64个样点及相关环境因子(树线位置、地形等),基于全球气候数据库,利用ArcGIS软件提取了样点气候状况。利用广义线性模型评估了热量因子(生长季温度)和非热量因子(坡向、降水等)对青藏高原树线位置的相对贡献。结果表明:7月最低气温是青藏高原树线位置最显著的预测因子,其可解释方差的40%;而坡向对树线位置的空间分布也有显著影响,其可解释方差的7%。因此,青藏高原树线位置主要受7月最低气温的驱动,且受到坡向的影响。这一结果为理解高山树线位置的驱动因子提供了新认识。

Non-thermal factors,such as terrain,may influence treeline position.Such a fact would explain the uncoupling relationship between recent treeline dynamics and climate warming. Here,we tested this idea by analyzing juniper and spruce-fir alpine treelines across the Tibetan Plateau which were located on sunny and shady slopes,respectively.We tested if slope aspect modulated the relationships between treeline elevation and climate on the Tibetan Plateau.Here- in,treeline variables (elevation,topography)were collected from published investigations per- formed on the Tibetan Plateau to assess the impacts of slope aspect on treeline elevation.Temper- ature conditions at treeline sites were estimated using global climate database.We evaluated the relative contribution of different variables on treeline position including thermal (growing-season air temperatures)and non-thermal (aspect,precipitation)factors.The minimum temperature in July was the most important predictor of Tibetan Plateau treeline elevation,explaining 40%of the variation of treeline elevation,whereas slope aspect accounted for 7%of the variation.We con- cluded that treeline position across the Tibetan Plateau was mainly driven by the minimum temperature in July,whilst slope aspect played a second role.Our results provide insight into the mechanistic explanations for alpine treeline formation.