中文摘要：

落叶是树木适应环境变化的一种方式,水分梯度往往是导致热带森林落叶物种比例产生差异的最主要原因。为研究落叶树种在森林次生演替过程中的变化规律,我们在海南岛霸王岭林区内调查了4个林龄阶段（5年、12年、25年和55年）的刀耕火种弃耕地自然恢复群落样地。在5.25hm2的全部样地内共记录到高H〉0.1m的落叶木本植物24种,隶属于15科21属。其中紫葳科、大戟科、含羞草科是含落叶树种最多的3个科,黄牛木（Cratoxylum cochinchinens）、猪肚木（Canthium horridum）、山柑算盘子（Glochidion fagifolium）是多度最高的3个落叶树种,枫香树（Liquidambar formosana）、黄牛木、山柑算盘子是胸高截面积最大的3个落叶树种。在次生演替过程中,落叶物种比例以5年恢复群落中最高,而后随群落演替进程下降;不同径级大小个体的落叶物种比例也表现出相同的变化趋势,且较大径级个体（DBH≥5cm）比例高于小径级个体（DBH〈5cm）。落叶物种个体密度比例和胸高截面积比例呈现单峰曲线变化：在恢复12年的群落中达到最大,而后随群落演替进程下降。除幼树（H〉1.5m,DBH〈5cm）外,其他各径级个体中的落叶物种密度和胸高截面积比例也表现出相同的变化趋势。我们的研究表明,在海南岛热带低地雨林刀耕火种后的次生演替和自然恢复过程中,落叶物种比例及其密度随恢复过程而发生相应的变化,在一定的恢复时期内呈现一定的季雨林群落特征。

英文摘要：

Defoliation is an adaptation to environmental changes for some trees, and deciduous trees play important roles in ecosystem functional sustainability and community regeneration. Their proportion in tropical forests commonly changes along water gradients. To better understand the dynamics of deciduous trees during secondary succession, we conducted field investigations along a chronosequence of four recovery stages （stages Ⅰ, Ⅱ, Ⅲ, and Ⅳ representing 5, 12, 25, and 55-year-old stands respectively） on abandoned shifting cultivation lands in Bawangling, Hainan Island. Twenty-four deciduous species with stems ≥0.1 m height were recorded from 5.25 hm^2 stands （four recovery stages combined）, which belong to 21 genera and 15 families. Bignoniaceae, Euphorbiaceae, and Mimosaceae contained the most deciduous species. Cratoxylure cochinchinens, Canthium horridum, and Glochidion fagifolium were the most abundant species, while Liquidambar formosana, C. cochinchinens, and G fagifolium had the highest basal area. Contrary to the change in total species richness （evergreen and deciduous combined）, deciduous species richness gradually decreased during secondary succession. Patterns of deciduous species richness change were similar across size classes. The deciduous species richness was higher for stems 〉5 cm DBH （diameter at breast height） than for stems 〈5 cm DBH. During secondary succession, the proportional changes of deciduous trees stem density and basal area showed unimodal patterns with peaks occurring in recovery stage Ⅱ, and were similar for different-sized stems, with the except of saplings （height〉1.5 m and DBH〈5 cm）. The secondary tropical lowland rain forests we studied share some characteristics with tropical monsoon forests during the same period of recovery on abandoned agricultural lands on Hainan Island.