Short-term demographic effects of fire on two endemic plant species of the longleaf pine ecosystem

Background/Question/Methods

Because of its substantial effects on demographic vital rates, fire has been used successfully to manage for fire-dependent plant species in a number of ecosystems. However, not all plant species respond positively to fire, even in fire-dependent ecosystems, making it particularly important to study the effects of fire on rare and threatened species. Astragalus michauxii and Pyxidanthera brevifolia are two rare plant species endemic to the fire-dependent longleaf pine-wiregrass ecosystem of the southeastern USA; currently, both species are vulnerable to extirpation. We constructed transition matrices and projected population growth using multi-year data collected on the demographic vital rates of these species at different times since fire.

Results/Conclusions

In contrast to many species in this ecosystem, both species had short-term vital rates that were negatively affected by fire; fire increased mortality of small individuals and reduced flowering and fruit production. Stochastic population growth rates of both species were reduced under annual burning. Although the current longleaf pine-wiregrass ecosystem is fire-dependent and has experienced frequent fire for at least several thousand years, we propose that the two endemic species may be “holdovers” from a past vegetation community that experienced less frequent fire. Despite the short-term negative effects of fire on the vital rates of these species, longer-term benefits such as reduction of woody encroachment and litter removal may be important for their ultimate success.