Responses of Dipterocarp Seedlings to Drought Stress

Abstract

Tropical rainforests are among the wettest terrestrial habitats on the surface of the Earth (Walter 1971). However, even in these wet environments, dry periods of brief duration commonly occur on a diurnal, seasonal and annual basis. Especially in East Kalimantan, prolonged droughts linked with strong El-Niño southern oscillation events occurred in 1982–83 and 1997–98 for the last two decades (see Chapter 2, this volume). Aside from these severe droughts, during the 1990s there were two short drought periods in 1991 and 1994 (see Chapter 2, this volume). Thus, frequent drought events occurred even in the rainforest region in East Kalimantan. As a consequence, plants growing in these habitats may have been often exposed to moderate drought stress. When there was no precipitation for one to two months from January 1998, reduced stomatal conductance and net photosynthetic rate were found in the top canopy leaves of pioneer Macaranga and climax dipterocarp trees in East Kalimantan (see Chapter 12, this volume). Further, during the course of practical forest management, reforested young stands planted after logging may suffer tissue water-deficit because of rapid evaporation from the soil surface and the undeveloped juvenile root system. Thus, it is important to investigate the drought tolerance of tropical rainforest trees for successful reforestation.