A twelve-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 included 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 1984), and greater basal area (35.7 vs. 28.5 m(2)/ha in 1989) and tree density (1525 vs. 969 trees/ha in 1989) than the plantation. Rates of tree mortality and ingrowth to the greater than or equal to 4 cm diameter class were higher in the plantation than in the natural forest. Both forest types exhibited the same rare of change in these structural parameters before and after Hurricane Hugo. However, Hurricane Hugo caused 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 hurricane, the plantation experienced a greater fluctuation in tree species composition and tree species abundance than did the natural forest. Tree ingrowth was lower than tree mortality in both stands. By 1994, all measured rates of change were at pre-hurricane levels. The species composition and structural changes required to make the plantation more productive in terms of stemwood biomass appear to make the plantation more vulnerable to hurricane wind effects and this in turn causes greater rates of change in species composition, tree mortality, and tree ingrowth during the initial phase following the disturbance.