Fire Ecology and Management of Florida Scrub

Florida scrub is a xeromorphic shrubland found on xeric, low-nutrient sands, dominated by oaks, palmettos, and ericads. Pine canopies vary from complete to absent. Herbaceous plants are secondary but are prominent in gaps among shrubs. Species composition varies among different ridges in Florida and between Florida and neighboring states. Florida scrub is notably high in endemic plants, herptiles, and invertebrates, many of which are specialists for postfire environments and gaps.

Most dominants of Florida scrub respond to fire with resprouting; notable examples include oaks and palms. Two species of pine can resist and survive fire and one species retains an aerial seed bank in serotinous cones. Florida rosemary and many herbaceous plants form persistent seed banks that promote population pulses after fire. Combinations of these life history strategies have been documented. Postfire recovery strategies affect the trajectories of vegetation in different fire regimes.

Although no direct, long-term fire history data exists for Florida scrub, many inferences of its fire regime can be made from weather patterns, species’ life histories, and observations of fire behavior. Lightning during the late spring and summer months is the major ignition source, and fires burn the largest areas near the end of the dry season in May when lightning becomes common. Native Americans may have burned during the winter and there is a culture of winter burning for agriculture and forestry. Various types of Florida scrub probably burn at intervals ranging from 5 years up to many decades. However, endemic plants and the Florida scrub jay generally benefit from fires recurring every 5-20 years. Very frequent or infrequent fires can potentially convert certain types of Florida scrub to other vegetation types. Fires can be complete or quite patchy, creating a complex mosaic of burned and unburned habitats.

Although fire intensity is variable, most scrub fires are very intense. Generally, the shrub canopy carries the fire and is completely consumed. When shrubs become overgrown and form a tall subcanopy or canopy, they are less likely to be top killed by fire and the burn becomes ineffective at restoring open conditions. Fire intensity also affects pine survival.

Much research has been conducted on the short- and long-term effects of fire in Florida scrub. Fire top-kills shrubs and thus opens up the landscape. Gaps become larger and support thriving populations of gap specialist plants and animals. After fire, the recovery of diversity and cover occurs within 1-5 years. Height growth continues for longer periods for many species. In most scrub stands, herbaceous plant diversity and densities are highest in the years immediately following fire. However, fire suppression can eliminate seed banks and blunt this effect. Generally, changes in species composition are slow due to the long life span of the dominant shrubs. Florida scrub can act as a fire barrier in the larger landscape, because it is often juxtaposed with plant communities that tend to burn more frequently (e.g., sandhill, flatwoods).

Habitat fragmentation has reduced fire frequency and extent, and prescribed fires have often been outside the lightning season and of lower fire intensity. Relative to times before European settlement, prescribed fires today are probably smaller in area, shorter in duration, and occur during a smaller proportion of the day than lightning-ignited fires.

Currently, fire suppression is a widespread and serious condition in Florida scrub. Fire suppressed areas lack open gaps, and local extinctions of gap-specialist organisms may occur. Litter and ground lichens increase, and larger shrubs suppress herbaceous plants and eventually their seed banks. Fire suppression results in detrimental changes in the habitat of the Florida scrub-jay, eventually causing abandonment of territories. Growth of tall shrubs may separate ground layer fires from the shrub canopy and make restoration fires difficult.

Additional research is needed on ecosystem ecology of Florida scrub, fire behavior models, fire return intervals, and mechanical surrogates and pretreatments for fire. Mechanical treatments are becoming widely used although there is little research to show that they produce the same beneficial effects as fire on Florida scrub.

Prescribed fires have been used on Florida scrub for decades, although most knowledge resides in the experience of individual burners rather than in literature accessible to others. Restoration burns typically occur during winter months, but ecological maintenance burns are conducted mainly in the spring and summer months. The range of fire intensity and patchiness that is used appears to vary by burner and agency, although this has not been well documented. The effectiveness of prescribed burning on particular sites is usually not studied. Impediments to current and future burning include urbanization and smoke management concerns.