Background/Question/Methods   Succession theory suggests that a forest community will reach a dynamic equilibrium at maturity.  Mature forests would be expected to maintain stable size class distributions, stem density, basal area, a balance between recruitment and mortality, and a tree community without pioneers except in canopy gaps.  Long term (≥15 y) assessment of tropical forest dynamics in permanent plots has largely confirmed the predictions of succession theory.  Most long-term studies have taken place in moist-to-rain forest. Dry forests may approach dynamic equilibrium at a different rate than wetter forests due to a longer dormant season, higher variability in extreme events, lower annual tree growth rates, and lower biomass. In 1981, a permanent 1.44-ha research site was established in Guánica Forest, Puerto Rico. Since 1981, the forest has been impacted by a minor hurricane, a major hurricane, and a pest outbreak that is lethal to columnar cacti. The diameter, height, and species were recorded for all stems ≥ 5.0 cm diameter at breast height (dbh) in fifteen plots, and for stems ≥ 2.5 cm dbh in subplots.  These plots were remeasured in the same manner in 1999 and 2009 and the fate of individual trees was determined based on precise locations recorded in 1981.
Results/Conclusions    In-growth and basal area increased during the first sampling period but were returned to near-1981 levels by Hurricane Georges.  Community composition changed little overall, but some declines were noted in putative pioneer species and cacti.  Despite relatively constant overall structure, there has been >25% stem turnover since 1981.  Guánica Forest exhibits similar characteristics to other mature tropical forests (dry or wet), including:  1) annual mortality ranging from 1-2%, 2) in-growth equaling mortality, 3) slowly increasing basal area, and 4) low species turnover.  Long-term monitoring, as opposed to chronosequence methods, has enabled us to better understand the effects of infrequent disturbances and disease.