Abstract
Despite a high annual rainfall in the rainforest region, unusually prolonged and severe droughts occurred in eastern Borneo from June 1982 to May 1983 (Goldammer and Seibert 1990) and from June 1997 to April 1998 (Toma et al., Chapter 2, this volume). The prolonged droughts were linked to particularly strong El Niño-Southern Oscillation (ENSO) events. In the 1997-98 ENSO, there was no precipitation period from January 2 to April 15 (for 104 days), 1998 Figure 12.1. Although soil water potential was 0–45 kPa at a soil depth of 10 to 60 cm from May 1989 to April 1990 (normally wet years), it was 60–66 kPa from January to February 1998. When the soil water potential decreased (within 2 months of a period of no precipitation), both net photosynthetic rate (Pn)and water vapor stomatal conductance(g,)decreased in the uppermost canopy leaves of a climax tree,Dipterocarpus cornutusDyer Figure 12.1. Similar data were also found in the top canopy leaves of pioneer tree species,Macaranga conifera(Zoll.) Muell. Arg. andMacaranga gigantea(Reichb. f. & Zoll.) Muell. Arg.
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