东北次生林生态系统林窗更新过程与机制

Forest degradation, one of the seven largest problems in the global environment development of the 21st century, is especially severe in China. Secondary forests, degraded from the original forests after the anthropogenic unreasonable disturbances, have been the major forest resources (i.e., accounting for about 60% of the total natural forests in area) in China. As the critical disturbance factor, canopy gaps play a key role in driving forest regeneration and succession. Furthermore, the impacting processes and mechanisms of canopy gaps on the natural regeneration of dominant tree species are the important basis to realize the restoration and improve the positive succession of the secondary forests. Therefore, the effects of canopy gap characteristics on the regeneration in the typical secondary forest ecosystem of Northeast China are considered as one of the major topics silviculture. The experimental methods applied in this study may include: the definition of canopy gap concept based on ecological principles, the continuous monitoring of gap regeneration, the experiments of gap position effects on the regeneration of dominant tree species, and the gap interpretation of long-time series with high- resolution remote sensing images or aerial photographs. The analysis methods of the isotope and tree-ring analysis will be also used in this study. The specific objectives of this project are as follows: 1) to explore the quantitative standards for upper and lower bounds and the filling standards of the canopy gaps; 2) to explicit the spatio-temporal patterns and driving forces of the secondary forest gaps; 3) to determine the effects of gap position and the gap edge effects on regeneration of the dominant tree species; 4) to reveal the patterns of the carbon accumulation and partitioning for the dominant tree species during the gap regeneration processes; 5) to accurately rebuild the dynamics of canopy gaps in historical periods, and to establish the processes of gap regeneration and succession in the 50 years period; and finally, to find out the measures to promote secondary forest regeneration by artificially controlling the gaps. Besides enriching the field of silviculture, the results obtained in this project certainly will have both important theoretical and practical significances for promoting natural regeneration and realizing the restoration and sustainable management for the secondary forest ecosystems in Northeast China.

森林退化是全球环境发展的七大难题之一；我国森林退化严重，由于人类不合理干扰导致原始林退化形成的次生林已成为我国森林资源主体(占天然林总量60%)。作为驱动森林演替的关键干扰要素——林窗，其对主要树种更新的影响过程与机制则是次生林恢复并实现正向演替的重要基础。本项目以东北典型次生林生态系统为对象，以林窗特征对更新影响为主线，在基于生态学原理对林窗概念完善的基础上，通过连续林窗更新监测、林窗位置效应试验及长时间序列高清影像林窗解译，采用同位素、年轮分析等方法，重点探讨林窗上下限及填充的量化标准；明确次生林林窗时空格局及其驱动力；确定主要树种更新的林窗位置效应；揭示次生林林窗更新过程中主要树种的碳积累与分配机制；精准反演次生林历史时期林窗更新演替动态并寻求通过人为调控林窗促进更新的措施。结果将丰富森林培育学，对指导人工促进次生林天然更新、实现次生林恢复目标具有重要理论与现实意义。

本项目以东北典型次生林生态系统（次生林与落叶松人工林镶嵌分布）为对象，以林窗特征对更新影响为主线，开展了林窗更新过程与机制研究；全部完成了计划内容，对丰富森林培育学、指导次生林恢复，实现正向演替更新等目标具有重要意义。主要结果包括：.1）建立了林窗结构特征量化方法体系：基于树木生长季平均影长与生物学意义，建立了林窗大小上下限标准化方法，解决了林窗大小界限无法确定的难题；另外，结合年轮生长释放与稳定碳同位素技术，建立了精准量化林窗年龄（±2年）方法体系；为次生林恢复提供林窗特征量化指标。.2）明确了林窗特征对主要树种更新的影响机制：落叶松人工林内形成较大林窗，可促进动物传播胡桃楸种子、提高胡桃楸幼苗存活与生长；次生林大林窗中心位置更有利于蒙古栎和色木槭等林窗依赖种早期萌蘖更新；其机理是：林窗大小、位置改变了光环境、土壤C/N/P化学计量比和地表凋落物分解率。.3）揭示了林窗更新过程中主要树种的碳积累与分配机制：林窗位置效应影响萌蘖苗非结构性碳（NSC）积累与分配；林窗边缘木红松针叶、枝条和树干NSC在不同冠层间无明显差异，落叶松冠层上部针片NSC显著高于冠层中部和下部针片；冠层高度对大气4-5 m的CO2δ13C及CO2浓度有显著影响，改变了以往认为仅在1 m高度内有影响的结论。.4）探明了次生林林窗时空分布格局及更新演替动态：通过试验林地1964~2014年高清影像林窗解译（分6期），发现了50年间小林窗数量和面积最大；风雪干扰是林窗形成的主要驱动力，其经营应以促进林窗更新为主，而洪水干扰多形成林间空地，其经营应着重于裸地恢复与森林重建；空间代替时间重建了林窗历史时期更新填充过程，大、中林窗分别在形成30-40年和20-30年后闭合。.5）提出了促进次生林更新对策：通过控制林窗大小及目标树种在林窗中位置，以促进次生林主要树种更新；根据林窗动态过程，适当人工制造大、中林窗以加速次生林生态系统恢复与演替。.成果表达：发表论文17篇，其中SCI 论文15篇（第一标注12篇）；获授权专利3项、中国科学院科技促进发展奖1项；国际会议11人次做学术报告，培养博士、硕士共11人；1份咨询报告被中办采用。基于项目基础研究成果形成的次生林恢复技术方案，在东北东部山区推广应用，相关媒体刊发报道，取得良好生态、社会效益。