Survival by Sprouting Following Fire in Tropical Forests of the Eastern Amazon

Abstract

Current anthropogenic activities in Amazonia are resulting in the widespread occurrence of fire; an ecosystem that is believed to have evolved in a fire-free environment. Even in areas away from intensified human land use, warmer and drier climatic conditions could increase the probability of fire in tropical forests. In this study the capacity of tree species to sprout following fire in disturbed moist tropical evergreen forests was quantified. Additionally, mortality and the modes of survival of standing forest trees at four sites were measured. Crown mortality ranged from 64-97 percent. Eight months after fire, 36-69 percent of all trees present on the sites at the time of burning were dead (i.e., no sprouting occurred). Out of 124 species measured (500 total individuals), 46 percent had the capacity to sprout from subterranean tissues and 27 percent sprouted from epicormic tissues. Forty-one percent of the sampled species were found to lack any capacity to sprout vegetatively. The percentage of individuals that survived by sprouting varied among tree species. Survival of the 14 most common species encountered ranged from 15-83 percent. Survival also varied among sites and this was primarily attributed to differences in fire severity. Fire severity and plant mortality were greatest in selectively logged forests that were intentionally burned for pasture conversion (> 65% mortality). One ecological advantage of sprouting over establishment from seeds is rapid regrowth and a greater capacity for exploitation of limited resources in tropical forests. Mean sprout height was 0.8-1.6 m for 8-month old sprouts and 4.2 m for 20-month old sprouts. IT IS WIDELY ACCEPTED that in undisturbed, closed canopy evergreen tropical forests, fire is an extremely rare, if not an impossible event under current climatic conditions (Mueller-Dombois 1981, Uhl et al. 1988b, Uhl & Kauffman 1990). However, with changes in land use, fire is becoming a widespread disturbance factor in Amazonia. Mosaics of logged forests, cattle pastures, settlements, and farm plots represent a new landscape in which fire is a very common phenomenon. Even in undisturbed rain forest, minor shifts towards warmer and drier conditions would greatly increase the probability of fire. Such shifts are likely if current technological, economic, and demographic trends continue (Salati 1987, Schneider 1989). As a result of an almost complete absence of naturally occurring fires (fire-return intervals of 600 or more years [Sanford et al. 19851), Amazonian moist and rain forest species are believed to have evolved with very few adaptations related specifically to postfire survival (Kauffman & Uhl, in press). Regardless of evolutionary derivation, all plants possess characteristics that may greatly influence their calacity to survive fire or some other disturbance. The capacity to sprout from epicormic tissues (i.e., dormant meristematic tissues beneath bark on trunks and branches) or from subterranean tissues following fire or other disturbance is a very widespread and probably an ancestral trait among many woody dicots (Wells 1969). Sprouting from subterranean tissues, coppicing, and epicormic sprouting has been reported to be a common means of regeneration among tropical forest species following disturbance (Knight 1975, Uhl et al. 1981, Putz & Brokaw