长白山高海拔原始云冷杉林林木异常枯死的成因及机理

Climate-induced global forest decline and die-off have attracted wide attention from researchers, forest managers and the public in the world. Consequently, the research on the mechanism of forest decline and tree mortality has become the current research focus. Presently, original spruce-fir mixed forest growing at high elevation (1400-1800 m asl) on Changbai Mountain Nature Reserve has been declining. Trees’ mortality has been non-normally high, the pests and diseases are very serious, which seriously threatens the survival safety of the spruce-fir forest. However, so far, no research has been carried out on the investigation and formation mechanism of the forest decline. This project draws on the latest research methods and achievements in the world, and uses remote sensing data to identify the status, spatial pattern and historic change of forest decline, and to explore its formation mechanism. Based on samples investigations and dendrochronology methods, deeply understand the effects of climate change on trees growth and the effect differences among species, and reveal the climate driving mechanism of forest decline, pest and disease outbreak and tree mortality. Clarify the differences of the functional traits and physiological features among different health types of trees, and combined with the climate stress control experiment, through the hypothesis verification, revealing the physiological mechanism of climate-induced tree mortality, and further explore the climate threshold for growth decline, occurrence of pests and diseases and mortality of trees; According to the above research, develop a model based on the relationship among climate variables and stand growth, decline and pest occurrence, to scientifically answer the climate-driven mechanism and the physiological mechanism of the spruce-fir mixed forest pest outbreaks and the decline. And then simulate the future trend of the forest under the climate change scenario, and provide the basis for original forest protection, restoration and management.

气候变化造成的全球性的森林衰退和大面积死亡已经引起了世界各国学者的广泛关注，有关森林衰退和死亡机理的研究遂成为热点。目前，长白山自然保护区高海拔(1400-1800m)分布的、东北仅存的原始云冷杉老龄林生长衰退、林木大量枯死、病虫害严重，已经对老龄林的生存造成了严重威胁。然而迄今为止还没有开展相关研究。本项目借鉴最新的研究方法和成果，利用遥感资料，明确森林衰退现状、格局及演变，探明其形成机制；利用地面调查和树木年轮学方法，明晰树木枯死类型的物种和立地差异及其对气候变化的响应，揭示森林衰退、病虫害爆发和死亡的驱动机制；弄清不同健康状况树木的功能性状和生理特征差异，结合控制实验，在验证有关假说的基础上，阐明气候胁迫导致树木死亡的生理学过程，探究森林衰退、病虫害发生和死亡时的气候阈值，揭示其生理学机理；构建林分衰退-气候关系模型，预测未来云冷杉林的变化趋势，为原始林的保护、恢复和管理提供依据。

气候变化背景下森林衰退和大面积树木死亡受到全球学者广泛关注，探究树木死亡机理成为研究热点。目前，长白山自然保护区高海拔（1400 m以上）分布的东北仅存的原始云冷杉老龄林生长衰退、林木大量枯死、病虫害严重，威胁区域生态系统。目前尚无关于长白山云冷杉林死亡机理的相关报道。本研究以长白山云冷杉林为例，通过遥感影像分析、树木年轮分析和控制实验等手段，研究云冷山林群落及主要树种衰退死亡机制，主要结果如下：.1）确定了云冷杉林群落衰退时空格局及群落结构动态：长白山高海拔云冷杉林分布区内3.36%的区域净初级生产力（NPP）显著下降，水分限制及其与立地因子、人为活动间交互作用是长白山自然保护区高海拔（1400 m以上）云冷杉林衰退的重要驱动因子。衰退区域树木死亡严重，树木生长速率降低，群落阔叶树幼树数量增多。.2）明晰了树木响应气候变化的种间差异和时空变化：鱼鳞云杉对气候暖干化响应较长白落叶松敏感，气候暖干化过程中鱼鳞云杉径向生长出现衰退。空间上，不同坡向鱼鳞云杉生长均受春季温度影响，西坡和北坡鱼鳞云杉生长还受春季降水影响。时间上，三个坡向鱼鳞云杉生长与温度的正相关性均随气温升高而持续降低。.3）探明了鱼鳞云杉生长衰退死亡机制：中、低海拔鱼鳞云杉长期生长下降趋势强于高海拔，但高海拔鱼鳞云杉对极端干旱的生态弹性较弱，干旱时死亡风险更高。干旱事件是近年来长白山高海拔树木死亡的重要原因，树木对极端干旱事件的生态弹性与下一次干旱事件发生后树木存活概率显著正相关。.4）阐明了干旱胁迫下幼苗死亡和复水后恢复的生理机理：持续干旱下，碳饥饿是持续干旱下冬季休眠季幼苗死亡的主要原因之一，水力学失败是生长季幼苗死亡的决定因素。复水后，干旱胁迫导致的木质部导管栓塞无法通过在重填（refilling）恢复，可能使得树木恢复力和弹性力较弱，导致单次或重复干旱时树木死亡。.研究结果对于预测未来气候变化背景下长白山自然保护区云冷杉林群落动态、树木生产力变化、以及树木死亡情况具有重要意义。