Changes in light availability following Hurricane Hugo in a subtropical montane forest in Puerto Rico

TitleChanges in light availability following Hurricane Hugo in a subtropical montane forest in Puerto Rico
Publication TypeJournal Article
Year of Publication1991
AuthorsFernandez, E, Fetcher, N
Accession NumberLUQ.155

The changes in light availability in the understory of a subtropical wet forest (Luquillo Experimental Forest, Puerto Rico) were monitored after the passage of Hurricane Hugo on 18 September 1989 Gallium arsenide phosphide sensors were placed 1 m apart along a 32 m transect. Data were collected for periods of 7-10 d in October and December 1989, and in March, July, and November 1990. Daily histograms were generated for observations of photosynthetic photon flux density (PPFD) taken every two seconds. Mean total daily PPFD was calculated for each sensor in each data set. During the 14 mo after the passage of the hurricane, the PPFD showed a highly skewed distribution with most values <200 $\mu$ mol m$^{-2}$ s$^{-1}$ The maximum spatial heterogeneity was observed in July 1990 because of the shading of some sensors by the growing pioneer vegetation. Median values of total daily PPFD for ten months after the hurricane ranged from 7.7 to 10.8 mol m$^{-2}$ d$^{-1}$, which is similar to values previously observed for large (>400 m$^2$) treefall gaps. Median total daily PPFD fell to 0.8 mol m$^{-2}$ d$^{-1}$ in November 1990 because of almost complete coverage of the transect by a canopy of Cecropia schreberiana Miq. ex. C. peltata. An analysis of semivariance was used to discern patterns of autocorrelation in total daily PPFD along the transect. Through March 1990 patches of high and low light separated by distances of 10-12 m were detected. By July 1990 the patchiness was replaced by a pattern that showed no autocorrelation at distances of 1 m or greater.