Gap-Phase Regeneration of Three Pioneer Tree Species in a Tropical Forest

Abstract

(1) The gap-phase regeneration behaviour of three pioneer tree species in a Panamanian forest is described. For each species recruitment, mortality and height growth of saplings were recorded during the first 8-9 years of regrowth in thirty natural treefall gaps. The gaps were 20-705 m2 in area. (2) Trema micrantha individuals that survived until years 8-9 were recruited (reached 1 m tall) only in the first year after gap formation. This species grows very fast (up to 7 m year-1). After 8-9 years it occurred in only the largest gaps (> 376 m2). (3) Cecropia insignis survivors were recruited mostly in the first year after gap formation, but some survived from years 2 and 3. This species did not grow as fast (up to 4.9 m year-1) as Trema micrantha. It occurred in the larger gaps (> 215 m2). (4) Miconia argentea survivors were recruited mostly in years 2 and 3, but some survivors were recruited as late as 7 years after gap formation. This species had the slowest growth of the three species studied (up to 2.5 m year-1) and colonized gaps from the largest to one of only 102 m2. (5) The gap-phase regeneration behaviour of these species forms a gradient in terms of recruitment, growth, and gap-size requirement. Such dissimilarity could maintain some diversity of gap colonizers, but apparent overlap in regeneration behaviour among these and other pioneer species suggests that chance also promotes their coexistence. Correlates of pioneer species abundance are discussed.