Interactions of storm, drought, and sea-level rise on coastal forest: A case study

Sea-level rise, changing intensities of tropical storms, and changing rainfall patterns are all components of global change that are predicted to affect coastal systems. These factors may interact in shaping coastal ecosystems. The occurrence of a violent storm and a historic drought during an 8-year study of sea-level rise effects on coastal forest in west central Florida presented an opportunity to study these interactions. The system studied was a marshy coastline, on a tectonically stable, karstic limestone platform, where coastal hydric hammock (a wetland hardwood forest) abutted salt marsh. Both the storm and the drought that occurred during the study were associated with pulses of tree mortality that selectively removed Juniperus virginiana var. silicicola (southern red cedar) from stands. Stable isotope data suggested that these trees used less fresh ground water and more sea water as these stands declined in the face of rising sea level. Drought-associated tree death only occurred in a stand in very late stages of sea-level-induced decline, where ground water became hypersaline during the drought. A storm that occurred in 1993 also selectively removed Juniperus from stands, damaging stands primarily in areas where tree reproduction had already ceased or declined due to sea-level rise. Thus, although these episodic events (drought and storm) caused notable tree death, the projected inability of forest stands to recover from these events was due to prior effects of sea-level rise.