Population persistence in Florida torreya: Comparing modeled projections of a declining coniferous tree

The Florida torreya (Torreya taxifolia) is a coniferous tree endemic to a 3 5-km stretch of bluffs and ravines along the east side of the Apalachicola River in northern Florida and southern Georgia. This formerly locally abund ant tree has declined as a result of disease during the 1950s and is on the U.S. endangered species list. With no seed production in the wild, this sp ecies is headed toward extinction. We conducted a survey on roughly 200 tre es from 1988 to 1996 and used these data to estimate the likelihood of popu lation persistence during the next several decades. We compared a stage-cla ss transition matrix model (RAMAS) and an individual-based stochastic model (TORSIM) of growth and mortality to project future populations. Given the current lack of seed production in the wild, all models predict extinction. The question of concern is the imminence of this predicted extinction. Dif fering predicted times to extinction would suggest different immediate mana gement recommendations. Both models predicted an over 90% likelihood of per sistence during the next 50 years. Predictions differed in that the transit ion matrix model was less optimistic than the individual-based model regard ing persistence. Model sensitivity analysis showed that the results were ro bust to significant decreases in growth and sprouting probabilities. Submod els identified different persistence likelihoods in different populations. Nonetheless, unless management of the population can facilitate maturation and seed production, extinction of this species in the wild is inevitable.