Louisiana State University
Department of Biological Sciences
107 Life Sciences Building
Baton Rouge, LA 70803
My research objective is to explore mechanisms that result in the persistence of populations of woody reseeders and resprouters in coastal habitats where interacting disturbances such as fire and sea level rise are important. I am focusing on the habitat associations and populations of three conspecifics that are locally abundant in the same coastal habitats of the Florida panhandle. Hypericum chapmanii is an obligate reseeder, H. microsepalum is an obligate resprouter, and H. brachyphyllum is a facultative reseeder/resprouter. I hypothesize that: (1) the current distributions of Hypericum species are driven by a gradient in fire intensity, which is influenced by tidal flooding, canopy cover, and fuel loads, and (2) the current distributions of Hypericum reseeders and resprouters, which are found at different positions along a shoreline elevation gradient, result from differences in flood tolerance.
Effects of multiple disturbances on congeneric reseeders and resprouters ( Hypericum spp.) along Gulf coast ecoclines
Raelene Crandall, Louisiana State University,
GCA Progress Report
During 2005 field season (late summer and fall), I established 300 1m x 1m plots along transitions from upland dry habitats to wet depressions (called ecoclines ). The picture below shows one series of continuous plots with an upland habitat in the foreground transitioning into a wetland depression in the background. I sampled each of the plots for elevation, canopy cover, soil moisture, salinity, and fire spread. I am now in the process of measuring Hypericum stem density, diameter/height distribution, and life stage. Furthermore, I am collecting soil samples that will be analyzed for texture, nitrogen, phosphorous, and other soil mineral characteristics.
I will use these data to model the probability of occurrence of each species with gradient position, fire spread, and environmental variables. Hypericum habitat associations will be tested using Chi-square, permutation tests, and torus-translation. Furthermore, I will use these data in demographic models to predict responses of woody reseeders and resprouters to multiple disturbances. By altering parameters in these models I will be able to predict how populations with different life histories will respond to changing disturbance frequency and intensity. Once developed, area land managers will be able to use these models to conserve ecoclinal specialists in habitats where fire is likely to interact with the effects global climate change, such as sea level rise and more frequent and intense hurricanes. The models will also facilitate wetland conservation and enable land managers to plan for global climate change along Gulf of Mexico ecoclines.
Hypericum chapmanii is an obligate reseeder. Fires kill established individuals, so the species maintains its place by reproducing by seeds after every fire. This species requires long fire-free intervals to reach reproductive maturity and begin producing seeds. The picture to the left shows an H. chapmanii flower.
The picture to the right shows a mature individual. After many years with no fires, this reseeder develops a tree-like form with one main stem. It can grow to 4 m.
Hypericum chapmanii is also an obligate wetland species. It is usually found in low lying areas where water stands throughout much of the year. Because its wet habitat does not promote homogeneous fires, this Hypericum species is unlikely to burn as often as those in upland dry areas.
Full Proposal: Effects of multiple disturbances on congeneric reseeders and resprouters
(Hypericum spp.) along Gulf coast ecoclines