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Arrival and Survival in Tropical Treefall Gaps
Author(s) -
Schupp Eugene W.,
Howe Henry F.,
Augspurger Carol K.,
Levey Douglas J.
Publication year - 1989
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1940206
Subject(s) - citation , library science , computer science , history
Most tropical tree species require light from a treefall gap at some time during their lives to reach maturity. Responses to light conditions have been dichotomized as shade-intolerant pioneers or shade-tolerant climax species (e.g., Whitmore 1975, 1982, 1989). The former typically have small, widely dispersed seeds from which juveniles establish only in gaps, while the latter typically have larger seeds that can germinate beneath the forest canopy and can persist as suppressed juveniles or grow slowly until a gap forms. According to this framework, a new gap promotes shade-intolerant regeneration through germination and shade-tolerant regeneration through release of suppressed juveniles. Truly shade-tolerant species can grow to maturity beneath the forest canopy, but even these are likely to benefit from any increases in light levels beneath the canopy (Uhl et al. 1988, Canham 1989, Lieberman et al. 1989b, Martinez-Ramos et al. 1989). Although useful, we believe this dichotomy limits views of gap dynamics by implying that each species is constrained to a specific pathway to the forest canopy. In reality, all species recruit to differing degrees from dispersal into new gaps and from release of dormant seed or juvenile banks beneath the canopy (see Martinez-Ramos et al. 1989). The probability that a tree of a given species will enter the forest canopy is a function of the joint probabilities of arriving and surviving in particular habitats. We emphasize three issues that, for any species, define probable regeneration at a given site: (1) pattern of seed arrival in gaps and beneath the canopy, (2) proportion of forest area in gap vs. closed canopy, and (3) survival to reproductive maturity of seeds landing in gaps and beneath the canopy. This view enables recruitment of tropical trees to be interpreted from the perspective of relative advantages of given characteristics within the context of those environments in which individuals with those characteristics are located.