基于3-PG模型的祁连山地区青海云杉树木生长模拟研究

Global climate change influences forest ecosystems dramatically. Forests in arid and semi-arid regions are particularly vulnerable to the current climate change, and are thought to play an important role in determining regional and global climate. Therefore, there is an urgent need to study the response of forests to climate change in the arid and semi-arid area. Model simulation is an important approach that study the forests response to the climate variations. Using process-based forest model in combination with tree-ring data provides a promising way to improve the modeling accuracy, and to understand the process and potential mechanisms of tree-ring records response to climate change. However, few this kind of studies have beed conducted in China until now. In this project, we plan to simulate the response of Picea crassifolia forests to climate change in Qilian Mountains using the 3-PG model. Picea crassifolia is one dominant tree species in Qilian Mountains, located at the arid and semi-arid transitional region in northwestern China. A series of forestry investigating data would be applied to parameterize the 3-PG model, and the dendrochronological measurements will be used for model calibration and verification. We will simulate the trees growth under the past and current climatic conditions, to recovery the process of trees growth and forests development, and to explore the potential mechanisms of climate influences on tree-ring records. Additionally, we will predict the trees growth of Picea crassifolia with future climate change scenarios using the 3-PG model. This research would provide a scientific insight for regional forests protection and management, as well as for future climate change adaptation measures.

全球气候变化正深刻地影响着森林生态系统，干旱半干旱地区森林不仅对气候变化响应敏感，而且对气候有重要反馈作用，研究该区域森林对气候变化响应有重要科学意义。模型模拟方法是开展森林对气候变化响应研究的重要途径之一，而将树轮数据与森林生态过程模型相结合，不仅能提高模型模拟精度，还为理解树轮对气候变化响应过程与机制提供思路，但目前国内该方面研究仍比较薄弱。本项目拟选择我国西北干旱半干旱区的祁连山为研究区，以祁连山主要水源涵养林—青海云杉为研究对象，尝试利用3-PG模型对树木生长及其对气候变化的响应进行模拟研究。基于大量森林调查数据对模型进行参数化，并利用树轮资料对模型进行校准与检验。通过模拟青海云杉树木生长在过去、当前以及未来对气候变化的响应，还原树木生长和林地建立发展过程，揭示树轮记录对气候响应的过程和机制，预估未来青海云杉林的生长变化趋势，为区域森林保护与管理、气候变化应对与适应提供科学依据。

青海云杉是我国西北干旱半干旱区祁连山的主要分布树种和水源涵养林，理解青海云杉树木生长特征及其对气候变化的响应是进行区域未来森林动态评估与生态建设的基础。本研究结合森林样方调查、树木年轮数据、遥感反演资料与森林生态过程模型，利用采自38个森林样点的数据，对祁连山地区的青海云杉树木生长特征与变化、及其对气候变化的响应进行了分析研究。结果显示，祁连山地区青海云杉树木生长特征在空间上表现出明显的差异性，西北部地区树木生长速率较慢、树龄较大，对气候及环境变化响应敏感性更高，而东南部地区树木几何个体更大、生长速率较快。树轮记录显示近60年来青海云杉树木生长呈现出：1961-1980年期间的上升趋势，1980-2001年间显著下降趋势，而2000年以后又开始明显的生长加快。遥感反演数据(NDVI)也显示出同样的区域植被生长变化趋势。树轮-气候响应关系分析表明，大部分地区青海云杉树木生长主要受降水及生长季干旱控制，尤其是受当年生长季5-8月干旱、以及前一年7月至当年6月降水的限制较显著。参数化后的3-PG模型能够模拟38个样点中60.5%的树木径向生长变化达到显著(p<0.05，1957-2016)。借助VS模型对单个样点(P12)树木径向生长的模拟(r=0.67, p<0.01)显示，5-8月份降水对青海云杉径向生长起决定性作用，9月份降水会影响翌年的青海云杉径向生长。祁连山地区近期的暖湿化气候变化趋势是促使青海云杉树木生长加快、植被整体变好的主要原因，同时升温导致的生长季延长对于树木生长应该也有较大的促进作用。本研究结果暗示近期祁连山地区气候比较有利于植被生长和恢复，可适度开展植树造林等生态修复工程建设，但需要综合考虑区域水资源承载力以及未来的气候变化情况。