PARENT SESSION
Oral Session #17: Plant Ecology: Water Relations.
Presiding: W. Pockman
Monday, August 5. 1:00 PM to 3:45 PM. Coconino Meeting Room, TCC.
Drought resistance of seedlings of co-occuring tropical woody plants.
Engelbrecht, Bettina*,1, Kursar, Thomas1,2, Tyree, Melvin3, 1 engelbrb@bci.si.edu, Salt Lake City2 Smithsonian Tropical Research Institute, Panama3 USDA Forest Service, Burlington
ABSTRACT- Annual rainfall and dry season length are the main climatic gradients influencing structure and diversity of tropical lowland forests, and rainfall and/or soil water availability have been shown to influence species distribution, abundance and habitat association. Knowledge of species drought resistance in their habitat is crucial for understanding the observed patterns. It also forms one of the bases for evaluating consequences of global climate change for tropical forest diversity. We conducted a field experiment examining the effects of dry season drought on survival and growth of first-year seedlings of 28 woody plant species, co-occurring in the moist tropical forest on Barro Colorado Island, Panama. Species were from 21 plant families, and differed in their phenological, morphological and physiological characteristics, in their habitat associations and their distribution patterns along the strong rainfall gradient across the isthmus of Panama. We found large differences among species in their response to drought, compared to irrigated controls. The differential survival and the differential growth both ranged continuously from 80 % to no difference at all. However, the effect of drought on the survival and the growth of species were not correlated. In 11 of the species the effect of drought on seedling survival was not significant even after 22 weeks, suggesting that seedlings of many common species in this forest are well adapted to seasonal drought. The observed effects of drought on seedling survival were highly significantly correlated with the strength of the species' habitat associations to wet slopes in the 50 ha forest dynamics plot on BCI. However, they did not correlate with species' abundance along a large-scale rainfall gradient. The quantitative assessment of drought effects on seedling growth and survival in the field forms the basis for an evaluation of the relative importance of different physiological and morphological mechanisms of plant drought resistance.
KEY WORDS: water relations, distribution, functional ecology, mortality