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作为直立树木分布的高海拔上限和高纬度北界,树线对气候变化具有潜在的敏感性.是全球变化研究的热点内容之一.树线变化不仅包含树线位置(本文中指树线上边界位置)的进退.还涉及到林分结构、空间格局和树木的生长变化等方面.尽管学者们利用不同的假说来解释树线和林线形成机理,但普遍认为温度是影响树线变化的最重要的环境因子.因此,全球变暖背景下,树线位置和种群密度变化趋势的研究备受关注.然而,树线位置的变化对气候变化会有几十年至几百年的的滞后性,在全球变暖的背景下树线位置有可能仅发生微小的变化.相对于树线位置.森林种群密度的变化是更敏感的生态指标.国际上多处树线研究(包括藏东南一带)都揭示了近100~200年来树线过渡带内种群密度的显著增加.但是,国际上已经报道的大多数树线样点不同程度地受到人为活动的干扰,难以区分气候变化和人为干扰对树线波动的影响.值得提出的是.青藏高原具有全球最高海拔的天然树线,且受人类活动干扰少,是研究气候变化对树线动态与格局影响的理想地点之一. “,”As the elevational and northern limit of erect trees and forest, the treeline and timberline are potentially sensitive to climate change, being one of the hotspots in the study of global change. Treeline dynamics not only include changes in upper treeline position but also in stand density, spatial pattern and tree growth. Although several hypotheses were proposed to explain treeline formation, temperature is considered as the most important environmental factor in controlling treeline dynamics. However, treel~ne position may have a lag response to climate change from several decades to centuries. In spite of global warming, treeline position may show a little change. In comparison with the treeline position, forest density may be more sensitive to climate change. Several treeline studies (include the studies on the Tibetan Plateau) reveled significant changes in forest density in the past 100 years. It should be mentioned that many reported treeline sites were disturbed to some degree by human activity. As a result, it will be difficult to separate effects of climate change and disturbances on treeline dynamics. On the Tibetan Plateau, there is the world's highest treeine, being ideal to investigate effects of climate change on treeline dynamics.