西南岩溶地区天然次生林群落不同层次的构建机制

Construction Mechanism of Natural Secondary Forest Communities at Different Forest Strata in a Karst Area of Southwest China

关键词:  岩溶地区  天然次生林  群落构建机制  林冠层  林下层

Key words:  Karst area  natural secondary forest  construction mechanism of community  canopy  understory

摘要:

以西南岩溶地区天然次生幼龄林、中龄林和近熟林为研究对象，采取以空间代替时间的群落生态学方法，研究不同林分结构特征的变化规律和森林群落不同层次的构建机制。结果表明：岩溶地区天然次生林恢复过程中，林分的结构特征发生了显著变化。由幼龄林、中龄林到近熟林，林冠层(林木胸径DBH>5 cm、树高H>5 m)的个体密度、胸高断面积和地上生物量显著增加，而林下层(DBH<5 cm、H<5 m)的各项指标均显著减少。岩溶地区天然次生林群落不同层次具有不同的构建机制。在幼龄林中，林冠层和林下层物种组成很相似，这与幼龄林中极高的个体密度、尚无明显分化、较高的岩石裸露率和过低的土壤容重阻碍了植物的定居和生长有关，主要表现为生境过滤驱动机制。在中龄林中，土壤性质和林分结构进一步改善，可为植物提供更多样的生境，此时，林冠层植物具有气候主导的生态位，而林下层植物则具有土壤和微生境主导的生态位，导致林冠层和林下层植物组成的差异。在近熟林中，生境过滤作用减弱，生物因子作用增强，树木地上生物量和冠层盖度成为林冠层和林下层植物组成分异的主要驱动因素。

Abstract:

Taking natural secondary young-aged, middle-age and near-mature forests in a Karst area of southwest China as the research object, the community ecology method with space instead of time was adopted to study the change rule of different stand structure characteristics and the construction mechanism of forest community at different forest strata.The results showed that the structural characteristics of forest had changed significantly during restoration process of natural secondary forests in karst areas.The individual density, basal area and aboveground biomass in the young-aged, middle-age and near-mature forest had increased significantly in the canopy layer[i.e.DBH (diameter at breast height) >5 cm and tree height >5 m], while those indexes in the understory layer had decreased significantly (i.e.DBH <5 cm and tree height <5 m).Different strata of natural secondary forest communities in Karst areas had different construction mechanisms.In the young-aged forest, the species composition was very similar in the canopy and understory communities.This was related to the extreme high individual density, no obvious differentiation, high rock exposure rate and low soil bulk density, which stunted the settlement and growth of plants.The main performance was the driving mechanism of habitat filtering.In the middle-age forest, the soil properties and stand structure were improved, which could provide more diverse habitats for plants.At this time, the canopy plants had a climate-dominated niche, while the understory plants had a soil-microhabitat dominated niche, leading to the difference in plant composition between canopy and understory layer.In the near-mature forest, the effect of habitat filtering was weakened, and the effect of biological factors was enhanced.The aboveground biomass and canopy coverage had become the main driving factors for the differentiation of plant composition in canopy and understory.