青藏高原东北部青海云杉生长和更新响应气候变化的机制及模拟研究

Climate change had important and great influences on forest ecosystems. And these influences may continue and strengthen in the possible climate change in the future. Northeastern Tibetan Plateau was proved to be most sensitive to climate change. Forest conditions in this region has changed greatly. Moreover, drought induced growth decrease and mortality was found in forest in this area. Consequently, analysis on growth/recruitment dynamic patterns, exploring growth/recruitment-climate response mechanisms and trying to simulate climate related growth/recruitment dynamics at northeastern Tibetan Plateau has theoretical and practical significance. Qinghai spruce, a dominant tree species in northeastern Tibetan Plateau, was selected as the research object. The objectives are: (1) to analyze the of Qinghai spruce growth/recruitment patterns and age structure with quadrat surveys and dendrocimatic methods; (2) to ascertain whether divergence phenomenon exists in response of Qinghai spruce growth/recruitment to climate changes by investigating the differences in the physiological properties of leaves at various developing stages, the leaves of trees at different ages and the difference of soil characteristics in different environments; (3) to clarify the physic-ecological adaptation mechanism of Qinghai spruce to climate changes from different perspectives; (4) to try to simulate climate related growth/recruitment dynamics with V-S model and DGVMs on the basis of three objectives above. This study is of fundamental importance for the estimation of Qinghai spruce growth/recruitment dynamics on the background of global warming; and it can also provide scientific basis for the protection of forest ecosystem and sustainable utilization of forest resources in the northeastern Tibetan Plateau.

气候变化过程中森林生长和群落结构变化是一个亟待关注的问题，尤其是“干旱导致树木死亡的机理”这一方向被《2015研究前沿》列为“农业、植物学和动物学领域Top10研究前沿”“重点热点前沿”。青藏高原东北部对气候变化敏感性高，且近期观测到有树木生长减缓和死亡率上升现象。因此，分析并尝试模拟青藏高原东北部森林树木生长和更新动态具有重要的理论和现实意义。本项目拟选择青藏高原东北部不同干旱状况下的青海云杉，采用田间试验、野外定点监测，结合生态学和树轮学方法，分析树木生长和群落动态模式，找出其主要限制因子；分析不同林龄、树龄青海云杉生长和更新及其限制因子的时空稳定性，阐明该区青海云杉生长和更新的气候变化响应模式和生理生态机制；在此基础上利用V-S模型和DGVMs模拟该区青海云杉生长和群落结构动态，为气候变化背景下青藏高原东北部青海云杉林发展态势预测提供理论基础，为保护和合理利用森林资源提供科学依据。

青海云杉是青藏高原的主要建群树种之一，具有重要的水源涵养和气候调节作用。然而，气候变暖使青海云杉森林生态系统在结构和功能上显现出一系列负向反馈，其生态保护工作迫在眉睫。为更为科学合理地进行森林管理和保护，本项目以青海云杉为研究对象，利用采自26个野外样方的3486棵树轮样本，以现状分析-未来预测-危机应对为主线，系统揭示了不同温湿梯度下青海云杉生长动态特征及其气候响应的时空差异，主要取得了以下成果：.1. 不同水分梯度下，青海云杉径向生长存在明显差异；20世纪60年代以来，相对湿润区呈现出与升温相反的持续下降趋势，而相对干旱区呈现出与降水类似的“W”形变化；.2. 青海云杉径向生长的差异可能源自于其气候响应随水分条件的变化，干旱区云杉生长对降水的依赖性更高，而湿润区气温抑制作用的影响更突出；.3. 青海云杉针叶元素含量、化学计量特征和稳定同位素比率在不同气候条件、树龄和叶龄之间存在显著差异，说明其生理调控和响应策略存在不同；.4. 20世纪80年代开始，青海云杉普遍出现自然更新过程减弱，而死亡率明显升高的现象；升温引起的干旱及森林虫害加剧对此有重要作用；.5. VS-oscilloscope模型对青海云杉生长变化模拟效果较好，模拟显示，中低升温情景下，青海云杉当前生长持续走低趋势短期内有可能停止，高升温情景下，该趋势可能继续；.6. 青海云杉径向生长的长期走低和异常降低对其死亡率升高有指示意义，结合模拟轮宽特征发现，未来一定时段，部分林区，青海云杉死亡率升高的几率较大；.7. 森林管理措施对环境胁迫加剧引起的青海云杉生长抑制，有明显的缓解作用。这可能源自于森林管理降低了其对升温的敏感性，提高了胁迫后的恢复能力。.本研究多角度、系统性地分析了青藏高原青海云杉的生长现状和未来潜在变化，研究结果弥补了现有青藏高原生态保护策略制定基础资料的不足，为未来气候变化过程中森林危机的有效应对、森林生态功能的科学保护和森林资源的合理利用提供有力的理论支撑和科学依据。