Hypericum edisonianum (Edison's St. John's Wort) is a state threatened shrub endemic to a five-county area in Central Florida. With its native range being lost to urban development and agriculture, it is important to study the persistence of populations within low intensity agricultural lands, such as cattle ranches. H. edisonianum relies heavily on rhizomal propagation to maintain existing stands, displaying only rare, episodic recruitment from seed. In Florida cattle ranches, management has shifted the season of fire from the early wet/transition season (summer) to the dry season (winter). Hence, the aim of this study was to examine the response of H. edisonianum stands to seasonality and frequency of fire. We measured the density (stems/m²) and size of patches in areas last burned at different times within the last decade. To measure the effects of season of fire on clonal re-sprouting, we performed controlled, experimental burns in the dry season (February 2015) and early wet season (June 2015). We measured stem density before the fire and counted new stems 3 months after. Additionally, we measured the soil moisture for the areas burned during wet season to test the hypothesis that soil moisture would affect clonal recovery.
Results/Conclusions
We found that stand size and density of H. edisonianum were significantly greater in areas burned recently (23±12 stems/m² for 2014 fires) and decreased significantly with time since fire (8±7 stems/m² for 2005 fires). Regeneration from rhizomes was high for dry-season burns (average of 38 stems/m²) when compared to new stems in unburned areas (average of 27 stems/m²). Conversely, burning in the early-wet-season seemed to inhibit regeneration (average of 12 stems/m²). For this last group, clonal recovery showed an inverse relation with soil moisture, with less re-sprouting in areas of higher water content. Over all, these results suggest that 1) prescribed fire is required to maintain populations, 2) relatively frequent (3-6 years) winter burns are needed to maintain Hypericum edisonianum stands, and 3) wet season prescribed fires should be used with caution, as flooding following fire can inhibit clonal recovery. Future studies concerning the impact of altered fire regimens on genetic diversity could help assess the value of cattle ranches for the persistence of the species.