Abstract:

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. Cratoxylum 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.

Key words: lowland tropical forest, proportion of deciduous species, secondary forest, shifting cultivation, tropical monsoon forest, vegetation recovery