林草交错区森林死亡后粗木质残体对林木更新的影响机制

Han Mountain is one of the most important forest-steppe ecotone in southern Daxinganling, therefore this area as an ecological barrier is playing a very important role in protecting ecological security of arid- semiarid region and sand fixation of northern China. However, Han Mountain secondary forest has suffered a large area of death and accumulated a large number of coarse woody debris in recent years. The vegetation dynamics marked by forest deaths and recruitment has become a hot topic in plant geography research. This project combines field long-term location observation and model simulation techniques to construct response equations between ecological processes such as forest recruitment and standing trees, fallen trees, and their contribution to nutrients and water holding capacity after decomposing. And investigate the effect of changes in the proportion of standing timber and crown area on the recruitment density and patterns of forests. we will also analysis obstructed effect, intercept effect and overshadow effect from fallen trees. This project summarizes the effects of decomposed fallen wood nutrients and water holding capacity to forest recruitment，and reveals the main driving factors and mechanisms of rapid recruitment in forest-steppe ecotone. The results of this research will contribute to the estimate of pattern, cause of formation and dynamic of forests. According to these results, the methods of regional forest management and protection can be improved. The result will also provide some important suggestions for strengthening management of forest ecosystem.

内蒙古大兴安岭南段“罕山次生林区”是内蒙古东南部半干旱区森林的集中分布区，在维护区域生态安全方面起着非常重要的作用。但是，近些年罕山次生林出现大面积死亡并积累了大量粗木质残体，以森林死亡和更新为标志的植被动态研究成为当前植物地理学研究的热点。本项目采用野外长期定位观测和模型模拟技术，构建森林更新与枯立木、倒木及其分解后对养分和持水力的贡献等生态过程间的响应方程，探讨枯立木比例与冠幅变化对森林更新密度及更新方式的影响，分析倒木对更新的障碍作用、拦截效应和遮阴效应等方面的影响，总结倒木分解后对养分和持水力的贡献对森林更新的影响，揭示林草交错区森林死亡后影响其实现快速更新的主要驱动因子和驱动机制。研究成果对研判林草交错区森林生长格局及动态，制定区域森林经营方案和培育保护措施均具有很强的指导意义。

内蒙古典型的林草交错区大兴安岭南段“罕山次生林区”，是内蒙古东南部半干旱区森林的集中分布区。本研究通过森林大面积非正常死亡后枯立木比例与森林更新的相关性、倒木储量对森林更新数量的影响、木质残体分解对更新数量的影响研究。总体而言，研究区木质残体平均储量为37.32±23.5kg/hm2，分解等级主要以Ⅱ、Ⅲ级为主；木质残体储量在研究区从南到北赛罕乌拉保护区（73.3±18.3kg/hm2）＞罕山保护区（24.9±9.8 kg/hm2）＞青山保护区（13.8±2.3kg/hm2），木质残体的储量分布与森林死亡程度分布一致。森林死亡后具有快速更新的能力，更新方式主要是萌蘖更新，更新数量受木质残体的储量、分解等级及分解释放养分等影响显著，倒木的形成过程造成大量幼苗的压死、砸伤问题比较突出，木质残体分解后养分缓释功能与森林更新的拟合度较高，有机C、N、K、Na和Mg的拟合系数均大于0.8，只有P、Ca和Fe元素的R方值小于0.8，且R方值大小表现为N＞有机C＞Na＞Mg＞K＞P＞Ca＞Fe，N元素对更新苗的数量影响最大。.通过以上具体问题的研究，本项目已发表学术论文12篇，其中：SCI论文 1篇，CSCD论文 6篇，中文核心期刊论文4篇，其他论文1篇；出版专著 1部，毕业博士研究生2名，完全以项目内容培养毕业硕士研究生2名；在本项目的带动作用和基础上，获批省级自然科学基金项目、中央引导地方科技发展资金项目、内蒙古自治区高端外国专家引进项目各1项，参与并主持国家重点研发项目专题1项。研究结果对研究团队的成长，揭示森林大面积死亡后粗木质残体对森林更新和恢复的利弊，制定半干旱区森林资源经营方案和培育保护措施，加强森林生态系统管理均具有很强的指导意义。