弄岗北热带喀斯特季节性雨林群丛数量 分类及与环境的关系

以弄岗15 ha北热带喀斯特季节性雨林监测样地各样方的相对海拔、坡度、坡向、凹凸度和物种重要值数据为变量, 采用多元回归树方法将喀斯特季节性雨林森林群落分为8个群丛。同时, 按乔木层、亚乔木层优势种为主, 灌木层指示种为辅的方法分别把8类群丛命名为: (A)南方紫金牛(Ardisia thyrsiflora)–苹婆(Sterculia monosperma)–中国无忧花(Saraca dives)群丛, 该群丛类型主要分布于土壤和空气的湿度都较大的谷底边缘; (B)对叶榕(Ficus hispida)–苹婆–董棕(Caryota obtusa)群丛, 该群丛类型主要分布于伴有季节性水淹、土壤和空气湿度都很大的谷底; (C)山石榴(Catunaregam spinosa)–广西牡荆–蚬木(Excentrodendron tonkinense)群丛, 该群丛类型主要分布于受太阳直射时间较长、水分条件中等偏旱的中下坡阳坡地带; (D)垂茉莉(Clerodendrum wallichii)–苹婆–广西棋子豆(Cychidendron guangxiensis)群丛, 该群丛类型主要分布于受太阳直射时间稍短、水分条件适中的中下坡阴坡地带; (E)米仔兰(Aglaia odorata)–闭花木(Cleistanthus sumatranus)–蚬木群丛, 该群丛类型主要分布于土壤湿度中等偏旱的中上坡半阴坡地带; (F)割舌树(Walsura robusta)–闭花木–蚬木群丛, 该群丛类型主要分布于土壤湿度中等偏旱、比较陡峭的半阳坡地带; (G)枝花流苏树(Chionanthus ramiflorus)–广西牡荆–蚬木群丛, 该群丛类型主要分布于坡度缓和、太阳直射的时间较短、水分条件适中的垭口部位; (H)齿叶黄皮(Clausena dunniana)–黄梨木(Boniodendron minius)–蚬木群丛, 该群丛类型主要分布于受到太阳直射时间最长、岩石裸露度最大、气温干燥、土壤水分严重不足的山顶及其周围。群丛划分说明该区域植被差异主要源于相对海拔和坡向变化, 各群丛物种组成并不存在明显界限, 而是随环境梯度逐渐变化, 反映了植被分布具有连续性, 间断只是相对的。

Numerical classification of associations in a northern tropical karst seasonal rain forest and the relationships of these associations with environmental factors

The associations in a northern tropical karst seasonal rainforest plot in Nonggang National Nature Reserve were classified using the multivariate regression tree method in conjunction with the relative elevation, slope, aspect, convexity, and the importance value of species. The results showed that the relative elevation and aspect were critical for the spatial distribution of species. The forest community of the Nonggang plot was divided into eight associations. They were as follows: (A) Ardisia thyrsiflora–Sterculia monosperma–Saraca dives association, distributed primarily at the edge of valley bottoms with high humidity and soil moisture; (B) Ficus hispida–Sterculia monosperma–Caryota obtusa association, distributed primarily at the valley bottom where seasonal flooding occurs and the soil moisture and humidity are high; (C) Catunaregam spinosa–Vitex kwangsiensis–Excentrodendron tonkinense association, distributed primarily on south-facing slopes at lower elevations with slight drought and greater sunlight; (D) Clerodendrum wallichii–Sterculia monosperma–Cychidendron guangxiensis association, distributed primarily on shaded slopes at lower elevations with moderate soil moisture and less sunlight; (E) Aglaia odorata–Cleistanthus sumatranus–Excentrodendron tonkinense association, distributed primarily on upper and middle half-shaded slopes with slight drought; (F) Walsura robusta–Cleistanthus sumatranus–Excentrodendron tonkinense association, distributed primarily on steep half-sunny slopes with slight drought; (G) Chionanthus ramiflorus–Vitex kwangsiensis–Excentrodendron tonkinense association, distributed mainly on passes with a gentle slope, moderate soil moisture, and less sunlight; (H) Clausena dunniana–Boniodendron minius–Excentrodendron tonkinense association, distributed mainly at the top of the mountain and in the surrounding areas, where the longest sunlight periods and the greatest extent of bare rock are accompanied by dry air and a substantial shortage of soil water. According to an analysis of the species components, the changes in species composition were associated with different topographical environmental factors. The spatial distribution of the vegetation was continuous, and there were no obvious boundaries between different associations. These results highlighted the importance of environmental factors as determinants of the distribution of species and the composition of associations in the north tropical karst seasonal rainforest.