人工诱导落叶松人工纯林形成混交林的早期天然更新过程与机制

There have been the problems of mono system structure, lower productivity and discordance between productive and ecological functions for huge amount of pure larch plantations (Larix spp.). Forming mixed conifer-broadleaved forests after artificial induction of pure larch plantation forests is a key approach to improve timber production and coordinate relationships between productive and ecological functions of larch plantations. While promoting the natural regeneration of broadleaved tree species in pure larch plantation forests is the premise of successful induction. Therefore, the effects of stand structure of larch plantation forests on the early natural regeneration process of dominant broadleaved tree species in secondary forests of Northeast China are considered as one of the major topics of silviculture. The experimental methods applied in this study may include: the comparison of stand structure effects on the regeneration of dominant tree species between larch plantations and larch natural forests in Northeast China, and the continuous monitoring of natural regeneration by using isotope labelling and the association between seedling/sapling growth and soil nutrient availability. The specific objectives of this project are as follows: 1) to quantify the distance of seed dispersal for dominant broadleaved tree species in larch plantations with different stand structures; 2) to quantitatively track the seedling establishment of broadleaved trees after seed dispersal and indicate the dependence of seedling establishment on stand structure of larch plantations; and 3) to determine the adaptive mechanisms of broadleaved tree species in larch plantations with different stand structures based on the relationships between seedlings/sapling growth and soil nutrient availability; and finally, to find out the measures to promote regeneration of broadleaved trees by artificially controlling the stand structure of larch plantations. Besides enriching the field of silviculture, the results obtained in this project will have both important theoretical and practical significances for artificially promoting natural regeneration and realizing the multi-objective and sustainable management for the larch plantations in Northeast China.

巨量落叶松人工纯林存在结构单一、生产力低、生产与生态功能不协调等问题。将落叶松人工纯林诱导形成针阔混交林是提高人工林生产力、协调人工林生产功能与生态功能关系的关键途径，而促进阔叶树种在落叶松人工林内的天然更新是成功诱导的前提。本项目以东北落叶松人工林为对象（与落叶松天然林对比），以落叶松人工林林分结构对东北次生林主要阔叶树种早期天然更新过程的影响为主线，通过野外定位试验、同位素标记、地上与地下关联等手段，重点量化阔叶树种在不同结构落叶松人工林内的种子传播/扩散距离；定量追踪种子传播后的幼苗建成对落叶松人工林结构的依赖程度；基于阔叶树种幼苗/幼树生长与土壤养分有效性关系，确定阔叶树种在不同结构落叶松人工林内的适应机制并寻求通过人为调控落叶松人工林结构促进阔叶树种更新的措施。结果将丰富森林培育学，对指导人工促进人工林天然更新、实现落叶松人工林多目标可持续经营具有重要理论与现实意义。

本项目以东北落叶松人工林林分结构对次生林主要阔叶树种早期天然更新过程的影响为主线，开展了树种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、指导人工促进人工林天然更新、实现落叶松人工林多目标可持续经营等目标具有重要意义。主要结果包括：.1）建立了风力传播树种早期天然更新过程的量化方法：基于15N同位素标记法，发现花曲柳种子在落叶松人工林内的传播距离为24 m，与林分结构（林分开阔度/间伐强度）无关，但是一定程度的间伐更有利于形成土壤种子库；6叶期一年生幼苗的δ15N值更适合追踪幼苗来源；为量化种子传播/扩散距离、定量追踪种子传播后的幼苗建成提供新方法。.2）揭示了落叶松人工林结构对动物传播阔叶树种早期天然更新过程的影响机制：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，其机理是：林窗大小改变了林分开阔度和光环境，进而减少了种子被其他动物取食的风险、增加了种子萌发和幼苗更新能力。与上下模式相比，等高线模式样地适宜的地形条件减少了动物在传播种子过程中的能量消耗从而更有利于种子传播。.3）探明了落叶松人工林结构对更新阔叶树种幼苗/幼树生长与环境关系的影响机制：间伐促进了落叶松人工林下阔叶树种的更新并具有时效性，从间伐后短期到长期，更新树种种类逐渐减少、中性耐荫乔木树种占据的优势地位逐渐减弱；更新优势种幼苗/幼树通过增大对基径的碳投入或增加高生长或增大比叶面积或调整叶片生态化学计量特征来适应间伐后不断变化的光照和土壤养分条件。.4）提出了促进人工林下阔叶树种更新对策：通过控制人工林林窗大小、人工林-次生林空间结构、人工林间伐间隔，以促进主要阔叶树种更新、实现人工林可持续发展。.成果表达：发表论文7篇，国家科技进步二等奖1项；国际会议5人次做学术报告，培养博士、硕士共4人。基于项目基础研究成果形成的人工林经营技术方案，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。