PARENT SESSION
Poster Session #41: Plant Demography.
Thursday, August 9, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Evaluating population viability with fire in Eryngium cuneifolium: deciphering a decade of demographic data.

Menges, Eric¹, Quintana-Ascencio, Pedro¹, ¹

ABSTRACT- We model the demography of Eryngium cuneifolium, a Florida scrub endemic, based on 10 annual censuses (1990-1999) of 11 populations at Archbold Biological Station. We built 54 stage-based matrices representing different times-since-fire, and evaluated twelve fecundity and seed bank scenarios. We also evaluated the effects of prior stage with current stage on population dynamics. The stochastic simulation program DISTPROJ was used to obtain estimates of extinction probability under different regular fire intervals. The scenario with high seed bank survival (0.5) and low germination rates (0-0.4) was the best predictor of observed maximum population size (year 8) and aboveground disappearance (years 30-34). Demographic rates were influenced by stage, age, and prior stage, but time-since fire had the greatest effects on demography. For example, survival of seedling cohorts recruiting shortly after fire was greater than for later cohorts. Finite rates of increase were > 1 only during the first decade postfire, and decreased with time-since-fire. Elasticities for survival increased with time-since-fire, while other elasticities decreased. Our results indicated that frequent fires with return intervals of 15 years or less are necessary for E. cuneifolium persistence. Since rosemary scrub may burn less often, local extinctions and metapopulation dynamics may be the norm for this species. Other rosemary scrub specialists (e.g. Hypericum cumulicola) thrive with less frequent fires. Therefore, we suggest that variation in fire regimes will allow co-existence and hedge against local extinctions.

KEY WORDS: population viability, fire effects on demography, extinction risk, Florida rosemary scrub