THE CANOPY GAP REGIME IN A SECONDARY NEOTROPICAL FOREST IN PANAMA

We mapped the occurrence of canopy gaps periodically between 1978 and 1990 in a 1.5 ha study plot within a 70-year-old (in 1978) Neotropical forest on Barro Colorado Island (BCI), Republic of Panama. The total area of the forest under canopy gaps in the plot averaged 4.3% (3.1% t o 5.7%, 95% CI). There was high year-to-year variability in the rate o f new gap formation. On the basis of repeated observations for four ye arly intervals, the annual rate of new gap formation ranged from 0.45% y(-1) to 6.5% y(-1) Most gaps were small. The mean size of individual gaps originally was 79 m(2) (range: 8-604 m(2)). However, large gaps (greater than or equal to 150 m(2)) occurred more frequently than expe cted for a secondary forest on BCI. Gaps closed rapidly the first year after formation but the rate of closure slowed thereafter. Despite th e absence of any obvious environmental gradients, gaps were spatially clustered. Even in this relatively small plot, there seemed to be dist inct gap-prone and gap-free areas.