A 12-YEAR COMPARISON OF STAND CHANGES IN A MAHOGANY PLANTATION AND A PAIRED NATURAL FOREST OF SIMILAR AGE

We compared forest structure over a 12 yr period (1982-1994) that incl uded measurements before and after a severe hurricane in two forests: a 64 yr old Swietenia macrophylla tree plantation and a paired natural forest of similar age in a subtropical wet Forest life zone at 200 m elevation in Puerto Rico. We measured trees greater than or equal to 4 cm diameter at breast height in a 40 X 50 m plot at each forest type. The natural forest had lower total tree height (8.8 vs. 10.2 m in 198 4), and greater basal area (35.7 vs. 28.5 m(2)/ha in 1989) and tree de nsity (1525 vs. 969 trees/ha in 1989) than the plantation. Rates of tr ee mortality and ingrowth to the greater than or equal to 4 cm diamete r class were higher in the plantation than in the natural forest. Both forest types exhibited the same rare of change in these structural pa rameters before and after Hurricane Hugo. However, Hurricane Hugo caus ed a greater reduction in the rate of change of tree density and basal area of the plantation than it did in the natural forest. After the h urricane, the plantation experienced a greater fluctuation in tree spe cies composition and tree species abundance than did the natural fores t. Tree ingrowth was lower than tree mortality in both stands. By 1994 , all measured rates of change were at pre-hurricane levels. The speci es composition and structural changes required to make the plantation more productive in terms of stemwood biomass appear to make the planta tion more vulnerable to hurricane wind effects and this in turn causes greater rates of change in species composition, tree mortality, and t ree ingrowth during the initial phase following the disturbance.