Mechanisms of Coastal Species Migration in Response to Climate Change
Mechanisms by which coastal species migrate in response to changing sea levels and disturbances are poorly understood. We initiated a study in 2004 to investigate effects of global climate change and natural disturbance on estuarine-upland transitions along the northern Gulf of Mexico. The main hypothesis is that tropical storms catalyze landward migration of species that are increasingly exposed to sea level rise. Transects that parallel the coastal transitions have been established at Jean Lafitte National Historical Park and Preserve (LA), Grand Bay National Estuarine Research Reserve (MS), Weeks Bay NERR (AL), and Apalachicola NERR (FL). Data analyses indicate similar patterns of vegetation and topographic profiles across the region. Three of the four sites have been struck by hurricanes since the transects were established, and post-hurricane community trajectories are being tracked. My students and I have established several field experiments in which we are manipulating propagules and wrack material that is typically deposited during storm surge events. The most exciting result of this work to date is that forests are retreating as a result of salinity pulses from hurricane-induced storm surge, and marsh species are establishing further inland. This network of sites should prove beneficial now and into the future for studying climate change impacts at the sea-land interface.
Assisted Migration as a Management Tool in Coastal Ecosystems Threatened by Climate Change
We initiated this study to investigate effects of global climate change and hurricane disturbance on estuarine-upland transitions along the northern Gulf of Mexico. Specifically, we are using storm surge and sediment experiments to examine the effects of intensified hurricane activity on coastal communities that span an estuarine gradient from brackish marsh to upland pine savannas on Eglin Air Force Base in northwestern Florida. This five year project is funded by the Department of Defense (SERDP) and began in April 2009. In one set of plots, recovery and natural regeneration are being tracked in response to the surge treatments; the second set of plots receive the storm surge treatments, as well as propagule additions of species spanning the gradient. These experiments test the vulnerability of different communities, as well as the ecological feasibility of assisted migration.
Effects of Shrub Encroachment on Flotant Marsh Communities in the Mississippi Deltaic Plain
Wax myrtle (Morella cerifera), a native actinorhizal shrub species, and the exotic Chinese tallow tree (Triadica sebifera) are invading floating freshwater marsh communities (called flotant in southern Louisiana). We are examining effects of shrub encroachment and reestablishment of fire regimes on community dynamics and ecosystem stability of the flotant.
Coastal Forests and Climate Change
This is a collaborative project with Dr. Julie Denslow. We initiated this study to investigate effects of relative sea level rise on coastal forest dynamics in the Mississippi River Deltaic Plain. In 1998, we established a 5 hectare plot spanning the natural levee to the backswamp of Bayou des Familles, a former distributary of the Mississippi River. The plot is located in the Barataria Preserve Unit of Jean Lafitte National Historical Park and Preserve. All trees > 2.5 cm DBH were tagged, identified, and measured. These trees and recruits were surveyed in 2000, 2002, and again in 2006 and 2008 following Hurricanes Katrina and Rita. Prior to the hurricanes, we found high mortality and low regeneration of dominant canopy species. The hurricanes have dramatically opened up the canopy, which may promote regeneration of shade-intolerant species in particular. Alternatively, we may find that the storms are contributing to a speedier demise for some species. This ongoing, long-term study of forest dynamics in one of the most rapidly changing areas in the world can be used as a model system to study ecological response to rapid environmental change.
Restoration of Coastal Communities
There is great uncertainty as to what the compositional targets for restoration of coastal communities that are already experiencing the effects of climate should be. We are using recently abandoned FEMA sites that abut the Grand Bay NERR to test the efficacy of reference vs. alternative restoration targets. We established replicated donor propagule banks that span the coastal transition of communities at GBNERR, and we are tracking establishment and survival of the different communities in the degraded FEMA sites. These sites were historically pine savannas, but preliminary data indicate that species from most points along the coastal gradient are capable of establishing here. These results suggest that building in ecological resilience to buffer against effects of future climate change may be possible. However, strong propagule pressure from invasive species in this highly disturbed landscape could undermine restoration of native vegetation. Thus, restoration success is likely to require intervention.
Non-native Species Invasions
Our lab also conducts inventory and research studies of non-native invasive plants on the Gulf Coast and in the Shawnee National Forest here in southern Illinois. One product of these efforts is a database maintained here at SIUC that contains over 11,000 occurrence records for such species in southern Illinois. These records were assembled from herbaria and reports of several agencies and organizations, as well as our own inventory efforts. Many of those involved are partners in the River to River Cooperative Weed Management Area, as is our lab. The overall aim of this work is to improve our understanding of the role invasive species play in the dynamics of native communities.
Other Ongoing Projects
a) responses of floating aquatic macrophyte communities to acute and chronic saltwater intrusion; b) ecology and consequences of laurel wilt disease in coastal bay forests; c) using molecular ecology techniques to guide restoration of salt marsh communities; and d) resilience of pristine and restored coastal wiregrass communities to hurricane disturbance