Linking vegetation dynamics to hydrologic changes in the southern Everglades marl prairies

Background/Question/Methods:

Hydrology is an important driver of vegetation dynamics in wetlands. As such, the severe anthropogenic modifications of hydrologic regime in wetland systems around the globe have resulted in deterioration of wildlife habitat. One example from the Florida Everglades is the seasonally-flooded marl prairie landscape inhabited by the Cape Sable seaside sparrow, a federally listed endangered species that has gone through management-induced hydrologic changes. With a goal of understanding the response of landscape-level ecological processes to hydrologic changes, we characterized marl prairie vegetation assemblages in relation to existing hydrologic regime during a three year period (2003-2005), and subsequently assessed vegetation change by re-sampling the sites during the next four years. We developed a weighted-averaging partial least square regression model using vegetation and hydroperiod data from 293 sites along six transects of 2.5-11 km, and applied the model to species abundance data collected repetitively at 613 sites distributed throughout the Everglades marl prairies. We reasoned that a significant change in vegetation-inferred hydroperiod over time would support the hypothesis that vegetation at the sampled sites changed in response to hydrologic conditions.

Results/Conclusions:

Our results revealed that vegetation change patterns in the marl prairie landscape, especially west of the Shark River Slough, were spatially differentiated, primarily responding to varying hydrologic regimes. The vegetation in the north-eastern part of the sparrow habitat showed a drying trend, while vegetation in the extreme west became more hydrophytic in the late 2000s than earlier in the decade. This spatial pattern in vegetation change was consistent with a change in the hydrologic regime estimated from Everglades Depth Estimation Network (EDEN) water depth data, suggesting that vegetation-inferred hydroperiod can be used to track flooding-induced changes in seasonally inundated wetlands. Moreover, since the wetting trend in the western portion of the area reflected deteriorated sparrow habitat, formulation of a strategy that achieves desirable sparrow habitat conditions while satisfying the broader ecosystem restoration goals of the Comprehensive Everglades Restoration Plan is needed.