An altitudinal comparison of growth and species composition in hurricane-damaged forests in Puerto Rico
| Authors: | L.R. Walker, J.K. Zimmerman, D.J. Lodge, S. Guzmán-Grajales |
| Year: | 1996 |
| Type: | Scientific Journal |
| Station: | International Institute of Tropical Forestry |
| Source: | Journal of Ecology |
Abstract
1 The controls over above-ground primary productivity following hurricane damage were investigated in a lowland subtropical wet forest (350–500 m altitude) and a lower montane elfin forest (1050 m) in Puerto Rico. Responses of understorey and canopy vegetation to addition of a complete nutrient fertilizer (both altitudes) or hurricane debris removal (lowland only) were monitored for 47–50 months. Treatments were initiated 1–6 months after Hurricane Hugo severely damaged both forests (18 September 1989).
2 Fertilization stimulated leaf litter production in both forests, but the recovery to prehurricane levels occurred earlier in the lowland forest (20 months after initiation of treatment) than in the elfin forest (38 months). Debris removal also increased leaf litter production in the lowland forest.
3 Tree diameter growth was 10-fold greater at low than at high altitude but the only treatment effect was a time by treatment interaction in the lowland forest, indicating that diameters of trees in the debris removal treatment did not increase as rapidly as in the control or fertilizer treatments.
4 Fertilization altered understorey biomass in the elfin forest (graminoids increased 10-fold, bryophytes decreased three-fold) but not in the lowland forest. Debris removal had no effect on understorey biomass in the lowland forest although woody seedling densities were highest in the debris removal plots. In control plots, understorey biomass was 12-fold greater at high than at low altitude. Saplings of a pioneer tree, Cecropia schreberiana were three- to five-fold denser in fertilized plots than in control or debris removal plots in the lowland forest.
5 The study showed that establishment of woody species by seeds was more important to posthurricane regeneration in the lowland than in the elfin forest and that the recovery of forest productivity was less responsive to increased nutrient availability in the elfin forest. Opportunistic, rapid responses to nutrient addition by Cecropia (low altitude) or graminoids (both high and low altitude) contrasted with the relatively slow responses of mature forest trees. These results suggest that factors regulating primary productivity following disturbance are influenced not only by the physical characteristics of the site but also by the range of potential species-specific responses represented in the flora.