Weekley, Carl W. , Menges, E.S. .
Postfire population dynamics of Polygala lewtonii, an endangered herb endemic to central Florida sandhills.
Fire drives the population dynamics of many plant species adapted to pyrogenic ecosystems. Polygala lewtonii, a short-lived herb endemic to fire-maintained Florida sandhills, is killed by fire but recruits postfire from a persistent seedbank. To investigate the effects of fire on the population dynamics of P. lewtonii, we established 220 0.25-m radius circular quadrats in a sandhill site prior to an August 2001 prescribed burn. Preburn, half of the paired quadrats were occupied by P. lewtonii and half were unoccupied. We recorded survival and seedling recruitment in quarterly censuses from December 2001 through September 2007; in annual censuses, we also recorded morphometric and fecundity data. Fire effects were most pronounced in the first two postburn quarterly censuses. For this period, burned quadrats outpaced unburned quadrats in seedling recruitment by 10 to 1. There was a 6% loss of quadrat occupancy in unburned quadrats but a 10% gain in burned quadrats. Burning increased plant density fivefold compared to unburned quadrats. For the first two postburn cohorts, seedling survival was significantly greater (3-4 fold greater median survival time) in burned than in unburned quadrats. Relative growth rates of these cohorts did not differ significantly with burning. However, in burned quadrats, plants flowered earlier and recruits survived to reproduce >2 times more often than in unburned quadrats. The combined effects of higher seedling recruitment, earlier flowering, and higher survival to reproduction suggests that P. lewtonii plants recruiting into burned sites make a greater contribution to the seedbank, and thus to the long-term viability of the population, than do plants recruiting into unburned sites. This study supports other studies showing frequent burning benefits the sandhill ecosystem.
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Archbold Biological Station web site
1 - Archbold Biological Station, Plant Ecology Lab, P.O. Box 2057, Lake Placid, Florida, 33862, USA
Lake Wales Ridge.
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Alpine B/Snowbird Center
Date: Tuesday, July 28th, 2009
Time: 10:15 AM