海南岛霸王岭热带低地雨林植被恢复动态

热带次生林具有重要的物种保育和固碳功能, 然而高强度的干扰会导致次生林早期出现类似季雨林的阶段, 因而群落恢复速度和方向是当前热带生态学研究中最为关注的议题之一。该文以海南岛在刀耕火种弃耕地形成的不同演替阶段的次生林为研究对象, 比较森林不同恢复时间(12年、25年、55年)群落中的不同年龄(幼树、小树、成年树)个体与低地雨林老龄林的物种组成、多样性和群落结构差异, 探讨刀耕火种弃耕地恢复过程中的群落组配过程。首先, 在海南岛霸王岭林区内建立7个1 hm²(100 m × 100 m)的样地, 并调查样地内所有胸径≥ 1 cm的木本植物个体(不包括木质藤本)的种类、胸径大小和树高。无度量多维标定法(NMS)排序结果表明, 刀耕火种弃耕地恢复群落与老龄林的物种组成存在明显差异, 并且其物种组成差异随着径级增加而逐渐减小。刀耕火种弃耕地群落物种累积速度缓慢, 25年和55年恢复群落的种面积、种个体和种多度曲线无差异, 存在一个明显的停滞阶段。与物种组成相比, 群落结构恢复相对较迅速, 但仍没有形成老龄林阶段中的复杂结构。萌生个体在早期恢复群落中占有较高比例, 其个体密度和胸高断面积分别占总数的39.9%和55.9%, 但在恢复中后期迅速降低。刀耕火种弃耕地恢复群落中以先锋种和非先锋喜光种为主。虽然耐阴种随演替而逐渐增加, 但恢复中后期群落中的耐阴种重要值仅为老龄林的27.7%。这些结果表明, 虽然刀耕火种弃耕地恢复群落缓慢地逐渐接近最终恢复目标, 但仍然存在 很大的不确定性。刀耕火种弃耕地恢复过程中的异速恢复和停滞阶段需要纳入今后群落演替模型构建和森林固碳效益核甘共苦算中。

Vegetation recovery dynamics of tropical lowland rain forest in Bawangling of Hainan Island,South China

Aims Our objective was to elucidate the trajectory and pattern of tree succession on lands abandoned after multiple cycles of shifting cultivation in comparison to old-growth communities.
Methods We established seven 100 m × 100 m plots in lowland sites. There were two old-growth forest plots, one 12-year-old fallow plot, two 25-year-old fallow plots, and two 55-year-old fallow plots. We recorded species, diameter at breast height (DBH), and height of all woody stems (excluding lianas) ≥1 cm DBH in 100 subplots (10 m × 10 m) in each plot. Analysis methods included non-metric multidimensional scaling (NMS).
Important findings NMS showed large differences in community composition between fallow and old-growth forest, even after 55 years of natural recovery. Saplings (DBH < 5 cm) showed more convergence with old-growth forest composition than did adult trees (DBH ≥10 cm). Species accumulation rates for all three ages of fallow plots were slower than for old-growth forests. The recovery of community structure was relatively faster, especially for tree height, but structural complexity did not reach that of old-growth forests. Sprouting stems accounted for 39.9% of density and 55.9% of basal area in the 12-year-old fallow plot, but less in older plots. The proportion of three functional groups (pioneer, non-pioneer light-demanding and shade-tolerant species) showed directional patterns of change during succession, indicating that pattern of recovery was determined by life-history traits. However, cessation of recovery during mid succession indicated that return to pre-disturbance species composition may take centuries or never occur. This should be considered when structuring successional models and predicting carbon accumulation in tropical forest.