El bosque estatal del nuevo milenio antes y después del huracán Georges
We studied changes that occurred between 1997 and 2005 on a secondary wet subtropical urban forest in the University of Puerto Rico’s Botanical Garden (Bosque Estatal del Nuevo Milenio). Hurricane Georges passed south of the forest on November 21, 1998 with 127 km/h winds. The study consisted of identifying species in 40 plots of 254 m2 each, measuring the diameter at breast height (dbh) and height of the trees and estimating the structural indexes (basal area and tree density, species Importance Value [IV], growth and death rates of trees, and recruitment to the > 4cm dbh class). The analysis included the topographic position of the plot (draw, ridge, slope, and river valley) and the position of the canopy relative to the sun (dominant, co-dominant, intermediate, and suppressed). The forest had between 53 (2005) and 56 (1997) species per ha and the species with the highest IV in the forest, and in almost all the topographic positions, was Spathodea campanulata, an introduced species. This species recruited successfully after the hurricane, which suggests that the recurrence of disturbances will maintain this species in the forest. The rate of recruitment for young trees was similar to mortality in almost all of the topographic positions, suggesting that at 68 years, the forest is balanced with respect to its structural indices. In spite of little floristic variation with the topography, the species and tree density, hurricane effects, and growth rate exhibited significant change (p < .05) in different topographic positions. Stands in divergent topographic positions and slopes experienced greater mortality and more snapped trees than those in convergent positions and river valley. The largest trees and the most developed structure were observed in convergent positions and river valleys. Hurricane winds affected the larger trees with dominant and co-dominant canopies more in spite of the fact that mortality for suppressed trees was greater. However, this mortality occurred after the hurricane. The hurricane’s main structural effect was reduction in the height of trees. Trees of every height class, with the exception of classes between 4 to 8m, were of less height in 2005 than in 1997. The mortality rate was significantly higher in the divergent topographic position where it exceeded the rate of recruitment. The rates of diameter, basal area, and height growth were low, negative, or zero for most of the trees and topographic positions. However, a significant proportion of the trees grew at rates comparable with the higher rates observed in native forests and plantations in Puerto Rico.