University of Puerto Rico, Rio Piedras, Puerto Rico, United States
Background/Question/Methods
Mangrove forests have unique ecosystem functions and services, yet the coast mangroves in tropics are often disturbed by the tropical cyclones. Hurricane Maria swiped Puerto Rico and nearby Caribbean islands in September 2017 and caused tremendous damages to the coastal mangrove systems. Understanding the vulnerability and resistance of mangrove forests to disturbances is pivotal for future restoration and conservation. In this study, we used LiDAR point clouds to derive the canopy height of five major mangrove forests in the coast of Puerto Rico before and after the hurricanes, which allowed us to detect the spatial variations of canopy height reduction. We then spatially regressed the pre-hurricane canopy height and the canopy height reduction on biophysical factors such as the elevation, the distance to rivers/canals within and nearby, the distance to coast, tree density, and canopy unevenness.
Results/Conclusions
We found that: (1) The pre-hurricane canopy height increased with elevation when elevation is low and moderate, but decreased with elevation when elevation is high. (2) The canopy height reduction increased quadratically with the pre-hurricane canopy height. (3) The canopy height reduction of four sites with true mangroves decreased with elevation. However, the site of Palma del Mar experiencing the strongest wind, is dominated by Pterocarpus, a mangrove associate growing at higher elevation, and the canopy height reduction increased with elevation. (4) The canopy height reduction decreased with the distance to rivers/canals only for sites with low to moderate mean elevation of 0.36-0.39m. (5) In addition to the hurricane winds, the rainfall during the hurricanes is an important factor to cause canopy damage by inundating the aerial roots. In summary, the pre-hurricane canopy structures, physical environment, and external forces brought by the hurricanes interplayed to affect the vulnerability of coastal mangroves to major hurricanes.
