Plant Structure and Function
Plants can survive fire by avoiding top-kill, and thick bark increases the probability of survival. I am interested in the effects of fire frequency and intensity on inter- and intra-specific variation in relative bark thickness and stem survival.
The ability to resprout from belowground organs allows plants to persist when fire consumes aboveground biomass. Plants that resprout after fire undergo a decrease in stem height and leaf area. Because the root system is often relatively undamaged by fire, this decrease in stem size results in a decrease in the ratio of leaf area to root area. I am interested in the effects of this change in structure on plant water relations and photosynthesis.
The ability to resprout from belowground organs allows plants to persist when fire consumes aboveground biomass. Plants that resprout after fire undergo a decrease in stem height and leaf area. Because the root system is often relatively undamaged by fire, this decrease in stem size results in a decrease in the ratio of leaf area to root area. I am interested in the effects of this change in structure on plant water relations and photosynthesis.
Plant Population Dynamics
Both natural and anthropogenic disturbances can affect plant population dynamics. I have studied the demography of both sub-species of Paronychia chartacea (Caryophyllaceae), which are threatened and endemic to Florida. The short-lived perennial P. chartacea ssp. chartacea occurs in Florida rosemary scrub and along roadsides created as fire breaks. Managing Florida rosemary scrub with prescribed fire should maintain P. chartacea ssp. chartacea populations, but roadsides may not be a viable long-term habitat. The annual P. chartacea ssp. minima occurs along the edges of karst ponds in the Florida panhandle. P. chartacea ssp. minima has higher occurrence in infrequently flooded areas, which suggests that this sub-species may have a low tolerance for disturbance.
Community Composition
In desert scrub ecosystems, shrubs (e.g., Larrea tridentata) create patches of high nutrient availability, i.e., fertility islands, which support high densities of annual plants. In both the Mojave and Sonoran Deserts, native annuals reach higher densities under shrubs, whereas non-native annuals reach high densities in the open areas among shrubs. Thus, non-native annuals create connectivity among shrubs and can facilitate the spread of fire, which has become an important disturbance in deserts invaded by non-native annuals. Fertility islands may break down when fire becomes more frequent, which could affect the community of native annuals.
Ecosystem Processes
Differences in the biogeochemistry of nitrogen (N) and phosphorus (P) – N volatilizes at lower temperatures than P and can accumulate via N-fixation – suggest that fire should have differential effects on the availability of these nutrients. I am interested in the short- and long-term effects of fire on soil nutrient availability and plant nutrient status. I conducted a nutrient addition experiment in Florida scrubby flatwoods to test the hypothesis that fire causes shifts in N versus P limitation of primary productivity. I found that productivity in scrubby flatwoods was co-limited by N and P at all times after fire. At the species level, however, the dominant shrub species, Quercus inopina and Serenoa repens, increased growth with P and N addition, respectively, possibly due to differences in mycorrhizal associations.