Puerto Rico (PR) represents an archipelago in the Caribbean exposed to natural hazards and potential impacts of climate change, including a higher frequency of extreme meteorological events such as hurricanes. Forests cover approximately 55 percent of PR’s land area and are mostly composed by secondary stands of young structure, with combinations of native and introduced tree species representing natural regeneration after the abandonment of agricultural land. After a phase of forest cover steadiness since 2004, forest inventory and monitoring data were showing a trend of increase in the total net volume and total aboveground biomass of trees, suggesting a tendency towards more mature stages of development within the secondary forests. However, hurricanes Irma and María made landfall in PR during September 6 and September 20, 2017 respectively causing overall defoliation and substantial loss of branches and apical dominance. By making use of data from the USDA Forest Service, Forest Inventory and Analysis program, we analyze the effects of hurricanes Irma and María on the forests of PR, emphasizing on ecosystem resilience.
Results/Conclusions
Preliminary data collected after the hurricanes shows that while 7.7 percent of seedling/saplings (diameter at breast height (d.b.h.) 2.5 cm - 12.4 cm) showed a broken top, 33 percent of trees (d.b.h. ≥ 12.5 cm) showed a broken top. A mean of 42 percent of the total length of trees was loss due to such an abnormal termination, with 60.3 percent of individuals showing some structural sign of wind effect, including > 20 % of broken branches and loss of foliage. Consequently, canopy cover was extensively reduced, but new foliage was observed two weeks after hurricane María in most individuals, suggesting that rain events following such event may have help reduce physiological stress due to the widespread loss of tree crowns and high temperatures. One to three months after the hurricanes, forested plots display a range of 10 to 95 percent live canopy cover, and initial data suggests diverse ecosystem resilience according to pre-hurricane stand structure and forest type. The hurricanes resulted in around 8.4 percent mortality, with 7 percent directly related to wind and rainfall effects (e.g. uprooting) and 1.4 percent indirectly related due to land-clearing activities after the storms. The transition to a forest mature stage is likely to change in particular forest stands according to the severity of storm effects regarding mortality, loss of tree crowns, and consequent colonization of new ingrowth.