中亚热带湿性常绿阔叶次生林自然恢复15年来群落乔木层的动态变化

FIFTEEN-YEAR CHANGES OF TREE LAYER IN SECONDARY CASTANOPSIS-SCHIMA HUMID EVERGREEN BROAD-LEAVED FOREST IN CENTRAL SUBTROPICS OF WESTERN CHINA

在瓦屋山永久性样地上定位研究了中亚热带湿性常绿阔叶林次生群落自然恢复 15年来乔木层的物种组成、结构、组织结构以及材积生产力等的动态变化。结果表明 :在最近 15年的自然恢复中 ,乔木层密度表现为先增大后降低和逐渐增大两种变化特点 ;乔木胸径分布表现为近似正态分布型并随恢复时间的推进而“右移”;乔木层平均胸径和平均高都表现出显著增长变化的特点 ,但在密度小的样地中增长速度快 ,而密度大的样地中增长速度较慢 ;3个样地材积生产力较高 ,均稳步增长 ,但密度最小的样地增长速度最快 ,表明密度可能是决定群落乔木层结构和材积生产力变化的关键。各样地群落乔木层的物种丰富度、物种多样性和均匀度指数较高 ,生态优势度较低 ,但它们随自然恢复的变化及其相互关系在各样地间是有差异的 ,与已有的研究结论有所不同。总体而言自然恢复 15年来乔木层物种丰富度基本保持不变 (11/ 10 ) ,树种多样性得以动态维持和发展。乔木层密度、胸径和树高分布格局的变化和立体空间的分化 ,推动了群落由单层向多层次立体结构发展 ,使群落更复杂化。结果也表明 ,自然恢复的常绿阔叶林不仅有较高的树种多样性 ,也具有较高的材积生产力 ,似乎暗示在森林重建过程中 。

Fifteen year changes in tree layer of secondary Castanopsis Schima forest, a typical humid subtropical evergreen broad leaved forest, were studied. Three permanent 0.04 hm 2 plots were inventoried four times each (April 1982, December 1983, July 1989, July 1997) on Mt. Wawushan, Sichuan, China. During the natural recovery process community level tree density displayed two separate patterns of change in the three plots, firstly increasing followed by a reduction in two plots, and a gradual increase in the other plot. Despite these different patterns all three plots appeared to be tending towards a similar tree density. The average DBH, height, and volume productivity all increased distinctly in all three plots, but much faster in the low density plots. These patterns indicate that tree density is key in determining changes of tree structure. Changes of tree density, DBH, and height distribution during the recovery also suggest that these secondary forests were developing from an initial, single tree layer to two or multiple levels in vertical structure, indicating that the community becomes more complicated and more stable. Changes in richness, species diversity, evenness and ecological dominance showed different features in each of the three plots, not all supporting the conclusion that with larger richness, species diversity, and evenness, ecological dominance in a community is reduced. Furthermore we observed that 11 tree species disappeared over time and another 10 species entered into the tree layer in the stand, keeping tree layer dynamic equilibrium and development of tree diversity. The results of natural recovery during the recent 15 years also indicated no contradiction between tree species diversity conservation and high volume productivity in forest restoration process.