Document: STE-3-35-32

Do lianas mask the effects of treefall gaps in a tropical forest: An experimental test.

SCHNITZER, S.A.* and W.P.CARSON

University of Pittsburgh, Pittsburgh, Pennsylvania, U.S.A. ¹

Abstract:
Treefall gaps have been the central paradigm to explain the maintenance of diversity in forests for over two decades. The gap hypothesis suggests that the high light environment in gaps fosters increased germination, establishment, and growth for the seedlings of many plant species. The gap hypothesis, however, has had limited empirical support, and some recent studies have even suggested that gaps play a "neutral" role in the maintenance of diversity in tropical forests. Most gap studies have ignored the influence of lianas (woody vines), an important group of plants that can be very abundant in gaps. We hypothesize that lianas reduce tree regeneration and diversity in tropical treefall gaps, and specifically, that tree seedling abundance and diversity will depend upon the abundance of lianas. Further, the role of gaps in the maintenance of tree species diversity may be forest dependent, with gaps playing less of a role in liana-rich forests. We tested this hypothesis in 18 relatively young gaps (1 -2 years old) of 3 different sizes in a moderately liana-rich tropical forest in central Panama. We removed all of the lianas in 9 of these 18 gaps and monitored tree seedling (< 50 cm in height) recruitment, growth, and mortality for 1 year following the liana removal. We found that tree seedling recruitment was more than 5-times higher in gaps without lianas compared with control gaps, and that this difference was independent of gap size. Seedling growth rates, however, were not significantly different in the liana-free and control gaps. There was also no significant difference in seedling mortality between the liana-free and control gaps. These data show that lianas reduce tree seedling establishment in gaps, but have no discernable difference in seedling growth or mortality. We argue that, in liana-rich forests, gaps will probably play much less of a role in the maintenance of tree species diversity than in forests with a lower abundance of lianas.

Keywords: species diversity, gaps, forest ecology

This abstract is being presented at: 11:00 AM in session:
Oral Session #42: Disturbance Ecology: Effects of Storms.