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Land managers seeking to reestablish historical fire regimes need guidance on how to apply prescribed fire to promote the population persistence of endangered species. We explored extinction risks of Hypericum cumulicola, a fire‐dependent plant endemic to the Lake Wales Ridge, Florida ( U.S.A ). Stochastic and deterministic matrix population models based on six censuses ( 1994–1999 ) and data from several germination and seedling survival experiments were used to compare H. cumulicola demography and extinction probabilities under different fire regimes. Environmental variation associated with site, year, and winter precipitation was included in these models. We estimated time to extinction of unburned populations of different sizes and the probabilities of extinction under no fire, different regular fire‐return intervals, and alternating short and long fire‐return intervals. Following an initial fire, even relatively large populations of thousands of individuals may become locally extinct within 300–400 years without additional fires. Extinction probability declined as intervals between fires decreased. Fire intervals openface>50 years resulted in an appreciable extinction probability after 200 years. Cycles of highly staggered short and long fire‐return intervals caused slightly higher chances of extinction than regular fire‐return intervals. The simulations were sensitive to estimates of survival in the seed bank. Active management will be required to restore favorable fire regimes in areas where fire has been suppressed. To maintain biodiversity, managers should consider variable fire regimes to match the requirements of a variety of species with different life histories.

Questions: Studies of gap effects have been conducted mainly in forests. We studied gap ecology in a pyrogenic Ceratiola ericoides (Florida rosemary) dominated shrubland and asked: How do gap size and the frequency of large gaps change across the fire chronosequence? Do larger gaps differ from smaller gaps in vegetation structure or species diversity? Are effects of gaps independent of, or dependent upon, time‐since‐fire? Are larger gaps refugia for herbs and subshrubs? Location: Archbold Biological Station, Lake Wales Ridge, south‐central Florida, USA. Methods: We investigated plant species occurrence and diversity in 805 gaps (areas free of shrubs taller than 50 cm) in 28 fire‐dependent Florida rosemary scrub sites. We collected quantitative cover data in a subset of seven sites. Results: Gap area distribution was lognormal. The largest gaps occurred throughout all but the longest time‐since‐fire intervals. Gaps were smallest in the longest unburned site but otherwise did not show strong patterns across the fire chronosequence. Species diversity measures increased with increasing gap area, with herbaceous diversity increasing with both gap area and bare sand. Herb diversity (H') decreased with time‐since‐fire. Larger gaps are refugia for some species. Of 14 species occurring in 25–75% of gaps, 13 had increased occupancy with increasing gap area, and gap area was the strongest predictor of occupancy for seven species of herbs and shrubs. Time‐since‐fire was the strongest predictor of occupancy for five species, including four ground lichens that increased with time‐since‐fire. Conclusions: Community structure within Florida scrub gaps is influenced by gap size, which in turn is affected by fire, the dominant ecological disturbance. We present a conceptual model that considers both gap size and time‐since‐fire as drivers of community structure and herbaceous plant diversity in Florida scrub. Because gap properties (independently of fire) have strong influences on species assemblages in Florida rosemary scrub gaps, fire management should consider the number and size of gaps across the landscape.

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