Florida scrub contains a large diversity of endemic plant species. Many of these endemics occur mostly in gaps within a matrix of shrubs. Fire plays a critical role in reducing competition and altering the demography of these species. We formulated a model consisting of a system of periodic difference equations to evaluate the effect of different fire frequencies and relative spatial arrangements on population persistence of scrub plants. We simulated the interactions among three dominant shrub species (two kinds of resprouters: oaks, Quercus spp., and palmettos, Sabal etonia and Serenoa repens, and one seeder: Florida rosemary, Ceratiola ericoides), and between these shrubs and four subdominant herbaceous species (one biennial, two short-lived perennial herbs that do not resprout, and one long-lived resprouting perennial herb). Modeled species differ in several critical vital rates including life span, intrinsic growth rate, ratio of root/shoot biomass, importance of seed bank, seed dispersal and survival post-fire. We evaluated different scenarios of fire frequency combined with dispersal capabilities and plant spatial arrangements. We used bifurcation diagrams to divide parameter space (including fire frequency, seed investment, seed germination and dispersal, and shoot/root allocation) into regions with different outcomes (e.g., species persistence and relative dominance).

Results/Conclusions

Our results indicate that the seeder consistently dominates with longer fire returns and a smaller seed investment. When competing with the palmetto, the seeder can only dominate when the resprouter has extreme root-to-shoot allocation tradeoff.  When competing with the oak, the root-to-shoot allocation tradeoff has minimal effect on the seeder. The seeder also dominates with a higher germination rate. The oak dominates with short fire returns and benefits from a higher root-to-shoot allocation tradeoff.  The palmetto dominates with short fire returns as well.  Our simulations are consistent with changes of shrub relative dominance in Florida scrub with different time-since-fire. We are expanding these simulations to include the subdominant herbs and different spatial arrangements.