Master of Science (MS)
Oceanography and Coastal Sciences
The impact (i.e., defoliation and mortality) associated with large-scale natural disturbance events is capable of significantly altering ecosystem structure (e.g., biomass) and function (e.g., productivity) in mangrove wetlands. These pulsing events provide an opportunity to assess ecosystem resilience (i.e., recovery to pre-disturbance conditions) by evaluating the immediate and long-term ecosystem response trajectory (i.e., disturbance magnitude, recovery time). I hypothesized that 1) there are specific properties of disturbance that can be characterized and fit to a general forest disturbance model, and that 2) a mangrove forest recovery trajectory (i.e. recovery duration and rate) is dependent on the disturbance magnitude and initial forest structure, such that species with optimal ecophysiological traits (i.e., resprouting capacity, shade tolerance) will recover at a faster rate. I used long-term (15 year) data sets obtained from three mangrove sites (SRS-4, SRS-5, SRS-6) along the Shark River estuary, southwestern Florida Everglades, USA. The disturbance events I evaluated included three hurricanes (category range: 1-Cat.4) that preceded two major events: Hurricane Wilma (category 3) in 2005 and a cold snap in 2010. Hurricane Wilma caused >90% defoliation and 6-15% tree mortality and the resulting disturbance magnitude was a decrease in annual Litterfall Net Primary Productivity (NPPL) by at least 65% in SRS-5 (5.53 Mg C ha-1 yr-1) and SRS-6 (7.84 Mg C ha-1 yr-1), yet, NPPL recovered within 4-5 years. Similarly, the SRS-6 had the greatest reduction from pre- (2001-2004) to post-Wilma (2009-2015) periods for the stem Net Primary Productivity (NPPS; 20%), basal area (28%), and stem density (40%) variables. The cold snap also caused significant defoliation (3-fold increase in NPPL), but productivity recovered within one month. Impact from the hurricanes preceding Wilma showed that lower intensity storms were also capable of significantly impacting NPPL via defoliation (up to 2-fold increase). My results showed that disturbance impact and magnitude are directly coupled and resulted in different response trajectories among the sites and forest properties. The findings and discussion of the mechanisms influencing response trajectory included in this thesis will help to further advance the development of such models and provide comparative information to advance our understanding of disturbance theory.
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Danielson, Tess Marie, "Everglades Mangrove Forest Response to Large-Scale Disturbance: Long-Term Assessment of Structural and Functional Properties" (2016). LSU Master's Theses. 4387.