PARENT SESSION
Oral Session #27: Fire Ecology.
Presiding: C. Allen
Tuesday, August 6. 8:00 AM to 11:30 AM. Graham Meeting Room, TCC.

Fire effects on scrub buckwheat individuals, seedling recruitment, and population viability.

MENGES, ERIC^*,1, SATTERTHWAITE, WILLIAM², MCCONNELL, KELLY³, QUINTANA-ASCENCIO, PEDRO¹, ¹ Archbold Biological Station, Lake Placid, FL² University of California Santa Cruz, Santa Cruz, CA³ NatureServe, Arlington, VA

ABSTRACT- Scrub buckwheat (Eriogonum longifolium Nutt. var. gnaphalifolium Gangog.), is a threatened perennial herbaceous plant found in xeric uplands in Florida. Fire stimulates flowering and subsequent seedling recruitment, yet scrub buckwheat is found under a range of fire regimes. Experiments mimicking fire showed that only top removal produced high flowering and that only litter removal promoted seedling recruitment. Ash additions and shrub canopy removal had no significant effects. We used a variety of modeling approaches on ten years of data (including five fires) to assess the effects of fire on the population viability of scrub buckwheat. Under unburned conditions, matrix modeling predicted relatively stable populations in unburned habitats under optimistic fertility scenarios (= 1.002, 95% confidence interval 0.975-1.033), but almost certain decline given pessimistic fertility estimates (= 0.981, 0.962-1.003). Under both scenarios, burned populations are predicted to increase (95% confidence intervals on always above 1.08). The s calculated for periodically burned populations had 95% confidence intervals entirely above one for fire return intervals shorter than 20 years (optimistic) or 5 years (pessimistic). Stochastic simulations yielded highly uncertain estimates of the probability of quasiextinction over 250 years, with only fire return intervals shorter than 20 years (optimistic) or 5 years (pessimistic) yielding quasiextinction confidence intervals entirely below one. Population growth rates in partially burned areas increased linearly with the proportion burned. Fire management at 5-20 year intervals (shorter for partial burns) is important to encouraging viable populations. These fire return intervals are consistent with those often used in scrub buckwheat habitats. No single substitute for prescribed burning is likely to provide the same benefits to scrub buckwheat populations.

KEY WORDS: population viability analysis, fire effects on plants, Florida scrub and sandhill, matrix modeling techniques