Recovery of tropical moist deciduous dipterocarp forest in Southern Vietnam

Abstract

Characterising the successional stages of secondary forests recovery is key to understanding and aiding forest landscape restoration. To determine the successional stages - and recovery pathways - for mixed dipterocarp forest in Dong Nai Biosphere Reserve (DNBR), Southern Vietnam, we used a dataset of 61 pairs of 1000 m2 plots, representing a range of recovery times (21–38 years), disturbances, and soil types with five categories: (1) Agent Orange affected + Logging (AO + Logging), (2) Logging, (3) Logging + Inundated, (4) Assisted Natural Regeneration + Logging (ANR + Logging) and (5) Protection. We first grouped recovered forest stands based on structure, composition, and dominant species. Each group was then identified by the dominant species types (bamboo, deciduous or evergreen) and indicator species. The forest stand characteristics, including species composition, basal area, tree size distribution, and species biodiversity were assessed for correlation with three site factors: soil type, disturbance type, and recovery time. Our results show that after 27 years recovery, logged mixed dipterocarp forest in DNBR can recover back to evergreen mixed dipterocarp forest, or change to bamboo or deciduous forests. The change in forest community depended on soil characteristics, especially soil water conditions, which are strongly correlated with topography. In addition, the recovered forest structures varied according to disturbance type and recovery time. By determining recovery stage, and the major drivers of the recovery process, site-specific ecological restoration techniques for seasonal tropical forest management can be suggested. Most recovered forest in DNBR is in a late or intermediate stage of vegetation development. However, retrogression and recovery deceleration were associated with invaders, such as grasses, climbers and bamboos, suggesting that their control is necessary in order to accelerate the natural development of native vegetation.