Water-use characteristics of Syzygium antisepticum and Adinandra integerrima in a secondary tropical forestin Khao Yai National Park for environmental management

Abstract

Forests in Southeast Asia have been disrupted by widespread deforestation and land use change. Most countries in this region attempt to return the forested areas through reforestation. However, planting trees efficiently is difficult because changing environmental conditions and tree size could affect the water consumption of different tree-species under climate change. Hence, the information regarding water use characteristics of different tree-species in different tree size classes is important to the selection of tree species for reforestation. Nonetheless, available information on species-specific water-use characteristics is less investigated, especially in secondary tropical forests. To gain the information on species-specific water-use characteristics in secondary forests, we estimated tree water use (T) of dominant tree species including Syzygium antisepticum and Adinandra integerrima, hereafter Sa and Ai, respectively, in a secondary tropical forest at Khao Yai National Park Thailand using sap flow data from custom-made thermal dissipation probes and compare T of both species in different tree size classes. Specifically, we evaluated the responses of T of both species in large and small sizes to environmental factors including soil moisture and vapor pressure deficit (VPD) which represent soil and atmospheric humidity, respectively. Results of different soil moisture conditions in both sizes showed consistently higher T in Sa compared to Ai at across VPD ranges. Our results imply that Ai may be suitable for reforestation in the area where droughts frequently occur in the downstream ecosystem through its conservative water-use behavior and may benefit downstream ecosystems with increasing runoff from the forest during drought. Moreover, Ai has conservative water-use behavior regardless of tree size. Thus, Ai would still provide these benefits to ecosystems when they grow larger in the future. In contrast, Sa seems suitable for reforestation in the area with frequent floods because it has high water consumption during high water availability which may slow down runoff from forest into downstream ecosystems when storms come. However, mixed planting species seem to be suitable for reforestation in the area that extreme events do not frequently occur because both species can maintain their water use at moderate soil moisture regardless of tree size which prevent the depletion of soil water availability. This study highlights that the response of T depends on species and tree size. Such information would benefit the selection of tree species for reforestation that could adapt well to certain environments and support policy design on the management of tropical forests and natural resources. Depending on reforestation purpose, Sa and Ai may provide either benefits or negative effects to the ecosystems.