湖南省阳明山山顶苔藓矮林优势种空间分布格局

山顶苔藓矮林是亚热带山地常绿阔叶林区在极端气候与环境条件下发育的一种群落变型,通过研究优势植物的分布格局与规模,可以有效地指导植被保护与管理活动。在湖南阳明山国家级自然保护区的山顶苔藓矮林区设置3个样地,应用相邻格子法对优势种云锦杜鹃(Rhododendron fortunei)进行每木调查,在不同取样尺度(面积)上采用方差/均值比率法(v/m)、负二项参数(k)、丛生指数(I)、平均拥挤度(m~*)、聚块性指数(m~*/m)、聚集指数(C_a)和格林指数(GI)等聚集强度指数对云锦杜鹃种群分布格局进行分析。结果表明:阳明山山顶苔藓矮林优势种云锦杜鹃种群在北、南、东三个方位上的空间分布格局总体上为聚集分布,随着取样尺度的增大,聚集格局强度和规模依次减弱;而山顶苔藓矮林优势种群不同年龄阶段的空间分布特征为随着种群年龄的增大,其空间分布格局呈聚集强向聚集弱、以至于向随机分布发展;阳明山山顶苔藓矮林优势种群及其分布格局形成的主要原因是云锦杜鹃种群本身的种子繁殖及传播方式和类营养繁殖等生物学特性及方位、坡向等环境因子影响所致。

Distribution patterns of dominant populations in a mountaintop mossy dwarf forest in the Yangming Mountains in Hunan Province, China

The mountaintop mossy dwarf forest is a community of evergreen broad-leaved forests in subtropical mountains facing extreme climatic and environmental conditions. Understanding the distribution pattern and scale of the dominant tree species in this forest can provide insights for effective management measures and an understanding of the mechanisms of community assembly in subtropical forests. In this study, we established 3 plots to explore the distribution patterns of dominant species in a mountaintop mossy dwarf forest in three directions in the Yangming Mountains in Hunan Province, China. An adjacent lattice method was used to survey dominant species (i.e., Rhododendron fortunei). At seven spatial scales, aggregation intensity indexes such as variance/mean ratio (v/m), negative binomial parameter (k), clumping index (I), mean crowding index (m^*), patchiness index (m^*/m), aggregation index (C_a), and Green index (GI) were used to analyze distribution patterns of populations. The results showed that the dominant species in the northern, southern, and eastern plots presented a clumped distribution. However, with increasing surveying scales, the distribution patterns changed from clustered to uniform, and the intensity and size of the aggregation pattern decreased. The spatial distribution characteristics at different developmental stages showed that population aggregation intensities developed from strong via weak to random. Population dominance and resultant distribution patterns were mainly caused by biological characteristics such as seed propagation and vegetative reproduction, and the influence of environmental factors, such as plot orientation and slope direction.