云南三江并流地区海拔树线的时空格局、成因及其对气候变化的响应

Altitudinal treeline is one of the most sensitive ecotone to the global warming. The feedback mechanisms of which is a joint frontier between landscape geography and global change studies. Treeline ecotone has a typical hierarchical structure. The spatiotemporal heterogeneity exists in both the climatic dominant of treeline dynamics and its feedback format. The correlated dynamics and underlying mechanisms between the upper and lower altitudinal treelines under the impacts of climate change at regional scale is a project of great theoretical potential. The Three Parallel Rivers Region in Northwestern Yunnan is a hotspot of global biodiversity, where treeline has been uplifted by climate warming. This project aims to study the upper and lower altitudinal treeline of this region at multiple scales. The methods of landscape geography, plant ecology and dendroclimatology would applied to study the radial growth of individuals and population regeneration of treeline species, pattern and dynamics of treeline ecotone, as well as the regional variation of treeline elevational distribution. Based on these, we would explore and compare the contributions of regional climate and landscape factors to the spatial and temporal variation of the altitudinal treelines, and the underlying mechanisms,and test the characteristics and format of growth and regereation of treeline species in responding to climate change. A predictive model will also be established to estimate the distribution changes of upper and lower altitudinal treelines in the studied region, underling the scenarios of climate change.The results of this project is expected to fill the gap in the area of treeline ecology, and provide theoretical advancement regarding the mechanisms of landscape feedback to climate change.

海拔树线是对全球变暖为最敏感的生态过渡带之一，其对气候变化的响应机制是景观地理学和全球变化研究的交叉前沿领域。树线过渡带具有等级结构，树线变化的气候主导因素和响应模式也存在时空异质性。区域尺度海拔上、下树线在气候变化下的关联动态和多尺度因子作用机理是这一领域极具理论意义的课题。滇西北三江并流地区是全球生物多样性热点地区，气候变化已引起高山树线上升。本项目对该区域的海拔上、下树线开展研究，综合运用景观地理、植物生态和树轮气候学方法，从树线树种的个体生长与种群更新、树线景观过渡带的格局动态及树线海拔的区域分布三个层面，探讨和比较区域气候和景观因子对海拔上、下树线格局与动态的影响机理及相对贡献，检验树线种群生长与更新动态响应气候变化的特征与模式，并建立气候变化情景下三江并流地区上、下树线的分布变化预测模型。研究结果将填补树线生态学的研究空白，为气候变化的景观响应机制提供理论进展。

滇西北三江并流地区是全球生物多样性热点之一，以高山峡谷地貌和垂直气候梯度为特色；河谷普遍具有半干旱气候，森林带与高山灌丛草甸、低山干旱灌草丛之间的过渡带显著发育。本项目以该地区高山树线和干旱树线的海拔分布及其环境成因为研究焦点，并扩充到山地植被垂直带谱结构、树线树种种群结构和个体径向生长的海拔格局及其对气候变化的响应、植物多样性海拔格局、整个西南山地干旱河谷的分布范围、气候特征与类型、干旱河谷植被数量分类与梯度分析、植物区系地理、及高山树线以上全国高山带植物区系地理格局。项目调查了西南9大江河干旱河谷1600多个植物群落样方，包含研究区域内7条海拔梯度样带，在重点研究区采集了近1000条树木年轮木芯，结合资料调查收集了全国14座主要高山3647种高山植物的海拔分布数据。主要研究结果包括：1）三江并流地区的高山树线普遍发育在海拔3900-4300m之间，存在自西向东上升的梯度，降水对气温的季节性调节作用是高山树线海拔变化的重要因子；2）该地区干旱树线普遍发育在海拔1000-3000m之间，相对湿度决定了下树线海拔；3）白马雪山东、西坡植物垂直带谱和物种多样性海拔梯度显著不同，主要受西南季风影响下的降水海拔格局差异控制；4）白马雪山森林带上、下树线树种种群结构和树木生长分别受气温和降水调控，当前干旱树线向下延伸的概率比高山树线向上延伸的概率更大；5）中国西南干旱河谷景观面积为40386.7km²，其中干热、干暖、干温、干凉气候类型所占面积比为15.9%、34.4%、29.7%和20%；干旱-极干旱、半干旱、半湿润、湿润气候类型分别占5.9%、33.7%、26.1%和34.2%，故>1/3面积的干旱河谷景观属于森林气候；6）干旱河谷植物区系具有西南–东北向梯度变化，长江水系发育影响了河谷植物区系分异的宏观格局；7）干旱河谷植被主要有稀树草丛-肉质灌丛、落叶小叶灌丛-常绿灌丛-常绿硬叶林、和暖性针叶林-落叶灌丛三大类型；8）干旱河谷植物物种β多样性高，地理隔离效应高于环境异质性的影响，入侵植物物种丰富、分布广泛。