基于生态位竞争理论的杉木枯枝叶宿存特性的生态学意义

Chinese fir is one of the most important tree species for timber production in south China. It is characterized that the dead branches and leaves will persist in the canopy for many years during the long-term evolution history, which prolongs the retention time of nutrients and increases the opportunity of nutrients redistribution. However other ecological functions of canopy litter of Chinese fir is unclear besides the nutrient balance regulation function. This project will be based on the principles and methods of canopy ecology, plant physiological ecology and niche competition ecology, following by the main line of exploring the effects of canopy litter on canopy structure, forest light environment and niche competition and species establishment. By simulating different gradients of canopy litter in the monoculture Chinese fir plantation with different planting densities, the spatial and temporal heterogeneity of canopy structure and light environment under different gradients of canopy litter will be carried out. The understory community structure and species niche differentiations under different crown structure caused by canopy litter will be investigated. Meanwhile the species establishment under different canopy litter treatments will be discussed emphatically. Our proposal aims to reveal the ecological adaption significance of long-term occupation of ecology niche of canopy litter of Chinese fir plantations. The proposed study will have important practical significance on canopy ecology theory study, reasonable management and productivity decline alleviating of Chinese fir plantations. This study is expected to become the growing point of new discipline.

杉木是我国人工林面积最大的造林树种，在林业生产中占有重要地位。前期研究发现杉木枝叶枯死后不会马上凋落，而宿存在林冠层多年，增加了养分在树体的再分配机会。但这种宿存特性除了具有重要的养分平衡调节功能，是否还具有其它的生态学适应意义尚不清楚。本项目利用林冠生态学、植物生理生态学、生态位竞争理论和方法，以“林冠枯枝叶宿存→影响林冠结构和光环境→生态位分化及物种建植”为主线，通过在不同栽植密度的杉木人工林设立不同枯枝叶宿存处理的定位观测样地，比较不同枯枝叶宿存条件下引起林冠结构及光环境特征的时空差异，分析不同枯枝叶宿存处理对林下群落结构及物种生态位分化的影响，探讨不同类型杉木枯枝叶宿存对物种生存及建植的影响及作用机制，揭示杉木枯枝叶长期宿存占领林冠生态位的生态学适应意义。本项目对丰富林冠生态学理论、合理经营人工林、缓解杉木人工林连栽生产力下降具有重要现实意义。有望成为新学科生长点。

杉木是我国重要的商品林树种，在进化过程中形成了枯死枝叶长期宿存在树干上的特性，为探讨这种宿存特性的生态学意义，本研究以福建三明莘口教学林场12年生不同栽植密度杉木人工林为研究对象，设置保留（对照）和去除宿存枯枝叶的不同处理，研究了不同密度林分内不同处理对林冠结构、林下光环境、林下植被发育及物种建植的影响，主要结果如下：（1）去除宿存枯枝叶处理降低了各密度杉木林的叶面积指数、增加了冠层开度和叶倾角，增加了林下光合有效辐射、透光率以及红/远红外的光合有效辐射；（2）不同密度杉木林林下植被发育不良，以草本层为主，但去除枯枝叶处理对灌木层多样性的影响更明显；（3）林冠结构与林下光环境及林下物种多样性密切相关，叶面积指数与冠层开度、叶倾角显著负相关，冠层开度与叶倾角显著正相关；光合有效辐射与叶面积指数显著负相关，与冠层开度和叶倾角显著正相关；林下物种多样性指数与叶面积指数显著负相关，与冠层开度显著正相关；（4）去除宿存枯枝叶处理增加了不同树种的种子出芽率、幼苗存活率以及苗高生长，在较大密度林分内（3000～4800株·hm-2）对杉木幼苗生长的促进作用更明显。可见，去除枯枝叶处理林分叶面积指数减小、冠层开度和叶倾角增大，导致林分光强和透光率增加对林下植被发育及幼苗早期生长有利，说明杉木枯死枝叶长期占领林冠生态位对杉木人工林林分环境的改变具有重要的生态学意义。本研究对人工林的合理经营、缓解杉木人工林地力衰退具有重要的理论及实践意义。