Assessments of the influence of flooding and sea level upon wetland bird and plant distributions in Georgia, USA

Abstract

Organisms that inhabit wetlands experience inundation both as a stress and disturbance, and as beneficial resource subsidy, mode of habitat connectivity, or protection from predation or competition. Birds and plants in floodplains and coastal marshes in Georgia, USA experience some common kinds of risks and benefits by residing in habitats subject to inundation. With this work, I examine some of the primary effects of fluctuating water level on avian and plant communities in these wetlands. Drawing upon surveys of birds in coastal wetlands, I first assess the ability of a commonly used sea level rise (SLR) landscape change model (LCM) to predict current bird distributions. The predictive ability of models built from the SLR LCM habitat classifications performed well for some species, and poorly for others. I discuss the implications of this discrepancy for making reasonable predictions of species-level SLR, and identify general habitat niche types apparent in our set of species.

In Chapters 3 and 4 I combine results of surveys of bird and plant communities along six Georgia river floodplains, with flooding models based upon a type of radar satellite imagery (Synthetic Aperture Radar, SAR). I derive flood metrics expressing several components of the flood regime at a given site, on both a yearly basis and in the growing or breeding season: total time flooded, variability in time flooded, duration of flood events, and flood return interval. In Chapter 3 I use these metrics to build models of occurrence probability for both Prothonotary Warbler (Protonotaria citrea) and Swainson's Warbler (Limnothlypis swainsonii), and find that the two species occupy fairly distinct regions of a multivariate hydrologic gradient. In Chapter 4, I choose among the metrics to find the one that is best able to discriminate plant assemblages at survey sites. I find that duration of flood events is apparently the most important factor in structuring these communities, and discuss the implications for the applicability of the Flood Pulse Concept in southeastern rivers.