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.

Florida Scrub Description and Extent

Florida scrub is shrub-dominated vegetation growing on xeric sands in Florida and neighboring states (U.S. Fish and Wildlife Service 1999). Many of these areas are relict beach ridges and bars (Stout and Marion 1993), with scrub vegetation having variable but continuous presence for at least 50,000 years (Watts and Hansen 1994). Major areas of Florida scrub occur in north-central Florida on the Ocala National Forest, in south-central Florida on the Lake Wales Ridge, along the Atlantic Coastal Ridge, on the Brooksville Ridge in west central Florida, and near the Gulf of Mexico in the Florida Panhandle. Florida scrub is known for its high level of endemism, with the major hotspot on the Lake Wales Ridge. The Lake Wales Ridge is one of the longest (160 km) and certainly the oldest (several million years) ridge in Florida (Watts and Hansen 1994). However, some plants and insects are endemic to other ridges. To the north and west, Florida scrub grades into shrub-dominated communities in coastal Georgia and Alabama.

About 80-90% of Florida scrub has been converted to agricultural and urban uses, and this loss has been especially acute near the Orlando and Tampa areas. The main threats to Florida scrub include habitat loss, habitat fragmentation, fire suppression, and trampling of lichens and soil crusts (Menges 1999). Road building and other soil disturbances encourage invasion of exotic species (Greenberg et al. 1997).

Climate and Soils

The climate of Florida is humid and largely subtropical, with many hot summer days and very rare freezing weather. Rainfall exceeds 120 cm, with most falling as convectional or tropical storms in the summer (from June through September). Although precipitation exceeds potential evapotranspiration (Fernald and Purdum 1992), dry periods during winter and spring can stress plants (Menges and Gallo 1991). Winter fogs are important in providing water to plants (Menges 1994). The warm dry month of May is particularly conducive to wildfires.

Florida scrub is found on distinct sandy soils. Most scrub soils are Entisols derived from quartz (Kalisz and Stone 1984, Schmalzer et al. 1999). These soils are very low in nutrients and are excessively well drained. Although the soil surface is not always far from the water table by non-Florida standards, they are elevated relative to soils of neighboring plant communities such as flatwoods and hammocks. The level of the surficial water table drops during the winter but can come within a meter of the surface of some scrubby flatwoods soils during wet summers. The xeric, nutrient-poor nature of the soil is reflected in the xeromorphic adaptations of scrub organisms, despite annual rainfall of ca. 50 inches.

Scrub soils are acid and infertile (Kalisz and Stone 1984), although the younger coastal soils have higher pH and soil nutrient levels (Schmalzer and Hinkle 1996, Schmalzer et al. 1999). Various types of coastal scrub vary in soil characteristics (Schmalzer et al. 2001) but this type of information is lacking for interior scrub sites. Tissue nutrient concentrations vary little with time-since-fire. Scrub soils include those with yellow (reddish) or white layers just beneath the surface. Sandhill vegetation occurs on yellow/red soils as well, and one study found few differences in soil properties between sandhill and scrub on yellow sands (Kalisz and Stone 1984). Florida scrub soils are much poorer than soils supporting California chaparral (Carrington and Keeley 1999). Florida scrub plants can extend roots well beyond their aboveground spread (Hunter and Menges 2002) and are capable of acquiring nutrients at these greater distances (Hawkes and Casper 2002). Cryptobiotic soil crusts fix nitrogen, which can be passed to vascular plants (Hawkes 2003).

Major Species and Compositional Variation

Florida scrub is often a shrubland, although some areas are dominated by sand pine in the tree layer. Oaks are the major species, especially Q. myrtifolia, Q. inopina, Q. chapmanii, and Q. geminata. Florida rosemary (Ceratiola ericoides) dominates some areas and may be mixed with oaks. Dwarf palmettos (Serenoa repens, Sabal etonia) are a consistent element. Other common shrub genera (at least in some areas) include Lyonia, Vaccinium, Befaria, Osmanthus, Palafoxia, Sideroxylon, Ilex, and Persea. These shrubs vary widely in form and life history. The families Fagaceae and Ericaceae are dominant.

Above the shrubs can be a canopy of pines (Pinus clausa, P. elliottii var. densa, P. palustris). However, Florida scrub can have a scant or absent canopy of pines. Because pines are quite characteristic of other ecosystems that abut Florida scrub (notably sandhill and flatwoods) and because pine distribution changes temporally (especially compared to most of the shrub species), characterizations of Florida scrub as a forest or savanna are somewhat misleading. For this reason, I recommend avoiding the term “sand pine scrub” as a general term for Florida scrub as this is only one variant, although it does occupy a considerable area.

In some areas, a subcanopy of hardwoods 3-10 meters tall can form above a shrub layer. This may reflect fire suppression or a history of low intensity or winter fires. The evergreen oaks mentioned earlier can attain the subcanopy (especially Q. myrtifolia and Q. geminata). On yellow sands, the deciduous trees Q. laevis, Q. incana, and Carya floridana can be prominent (the first two species are more characteristic of sandhill vegetation, however).

Herbaceous plants are secondary in most types of scrub, although some occur in gaps of various types of scrub. Gaps are most prevalent in rosemary scrub and gap specialists are prominent in rosemary scrub (e.g., Polygonella basiramia; Hawkes and Menges 1995, Eryngium cuneifolium, Menges and Kimmich 1996). Joining the herbs are some gap-specialist subshrubs, e.g., Dicerandra christmanii and D. frutescens on yellow sands (Menges et al. 1999). In one type of oak-dominated scrub (scrubby flatwoods), gaps are more ephemeral (Young and Menges 1999) but still important to many species. The interaction of fire and gaps explains much variation in Florida scrub vegetation (Menges and Hawkes 1998, Quintana-Ascencio and Menges 2000). Gaps are obvious aboveground, but belowground gaps are smaller from those aboveground. The dominant shrubs that form the matrix in Florida scrub have massive rhizome and root systems that store carbon from many years of photosynthesis (Langley et al. 2002). Belowground gaps among these shrubs are smaller than aboveground gaps, e.g. Ceratiola ericoides (Florida rosemary) (Hunter and Menges 2002). Even herbaceous plants are able to take up nutrients at distances much greater than their aboveground extent (Hawkes and Casper 2002). The extent to which gaps are openings aboveground vs. belowground may also affect species composition (Petru and Menges 2003).

Florida scrub is characterized by vegetation with xeromorphic attributes including deep roots, small evergreen leaves often with thick waxy cuticles, hairs, or inrolled shapes (to conserve water, presumably), and high allocation to belowground structures (Johnson et al. 1986, Langley et al. 2002). Uptake of water and nutrients in scrub oaks occurs from deep soil horizons (Johnson et al. 2003). Many animals avoid desication through behavior, including burrowing in the loose sand.

Florida scrub has moderate variation in species composition depending on soil type and geographic position. It also varies along an elevation gradient from xeric to less xeric based on distance to the water table (Abrahamson et al. 1984, Schmalzer and Hinkle 1992a). Although many classifications of Florida scrub exist (e.g. Abrahamson et al. 1984, Schmalzer et al. 1999), I will describe variants from Menges (1999). These range from relatively open stands dominated by Florida rosemary (rosemary scrub), various sorts of dense oak-dominated scrub (with sand pines: sand pine scrub; with mainly oaks: scrubby flatwoods; with substantial palmetto in coastal areas: oak-palmetto scrub (Schmalzer and Hinkle 1992a,b, Schmalzer 2003)); on yellow sand with scrub hickory (Carya floridana) (oak-hickory scrub or southern ridge sandhill; hickory phase of Abrahamson et al. 1984), and scrub overgrown into a forest (xeric hammock; Myers and White 1987). Also sharing xeric soils is sandhill vegetation, dominated by pines, grasses and herbs but with few shrubs. All these types of vegetation grade into one another, although regions of relatively rapid vegetation change (ecotones) can be delimited (Boughton et al in preparation).

Vegetation composition among different ridges in Florida can be inferred by comparisons of published studies (e.g. Laessle 1958, Myers 1985, Schmalzer and Hinkle 1992a, Menges et al. 1993, Greenberg 2003) but there has been little integration of these datasets. Across Florida scrub sites, some species nearly always occur (e.g., Quercus geminata, Serenoa repens), but some species that are common in some areas are much sparser or absent in others (e.g., Quercus inopina, Osmanthus megacarpa). Scrub-like communities in Alabama and Georgia have some species in common with typical Florida scrub, but often in unusual combinations (Menges 1999).

See: Endemism in Florida Scrub.

Florida scrub is a hotspot for endemism (e.g., Dobson et al. 1997, Estill and Cruzan 2001). Many plant species endemic to Florida scrub are found largely on the Lake Wales Ridge (Christman and Judd 1990). In recently burned areas, there are greater numbers of species that are endemic, herbaceous, and specialists for gaps (Johnson and Abrahamson 1990, Menges and Kohfeldt 1995, Menges and Hawkes 1998). Many plant species are very abundant shortly after fire. These include endemics such as Dicerandra species (Menges et al. 1999), Eryngium cuneifolium (Menges and Quintana-Ascencio 2004), Hypericum cumulicola (Quintana-Ascencio et al. 2003), Bonamia grandiflora (Hartnett and Richardson 1989), and Warea carteri (Menges and Gordon 1996). In contrast, most species that are more abundant with fire suppression are common and woody (Menges and Kohfeldt 1995).

Endemic animals also are found in Florida scrub, and many of these are specialists for fire-maintained scrub and open microsites. These include the Florida scrub jay (Woolfenden and Fitzpatrick 1996, various herptiles (Greenberg et al. 1994, McCoy and Mushinsky 1992, Hokit et al. 1999) and a myriad of insects and spiders (Deyrup 1990, Deyrup and Eisner 1996, Marshall et al. 2000, Carrel 2003). Invertebrate groups such as flightless grasshoppers are endemic to some scrub ridges that have few or no endemic plants (Deyrup and Franz 1994).

Historic Fire Regime

Florida scrub has occupied xeric ridges for at least 50,000 years, during which time the extent of xeric elements has fluctuated considerably (Watts and Hansen 1994). Presumably, the frequency of fire has varied as well, especially in response to species that might increase the amount of fine fuels such as pines and grasses. Without a studied direct record of past fires in fire scars, peat, or pollen, our understanding of the historic fire regime is based on current fire behavior, recent fire history, and inferences from the life history of Florida scrub organisms.

Most pre-European-settlement fires were likely caused by lightning. Lightning is very frequent in central Florida (Fernald and Purdum 1992) and even today, initiates many fires in Florida. Lightning occurs primarily in summer, and the intersection of the end of the dry season with the beginning of the lightning season creates the peak fire season in May.

Native Americans likely also played a role in recent centuries, particularly in initiating fires outside the primary lightning season. Robbins and Myers (1992) compiled literature from various places in North America and inferred that the original Native Americans deliberately used fire for a number of purposes, and that their use could have increased fire frequencies outside the lightning season. By the 1700s, Seminole Indians had moved into Florida and did use fire extensively. However, Native American populations have never been great in interior Florida and their impact was probably never primary. Early European settlers burned primarily to improve forage for cattle and did so during the winter dry season (Robbins and Myers 1992). Currently, accidental, prescribed, and lightning fires are all important in Florida and in Florida scrub (but see: Human Alterations of Fire Regimes in Florida Scrub).

Fire season reflects ignition sources, with a presettlement regime dominated by lightning fires having a peak in May and a trough in mid-winter, and regimes featuring Native Americans or European settlers including a wide variety of ignition times (Robbins and Myers 1992). Summer (June-September) lightning ignitions are common, but these storms occur during the rainy season and less area is burned than in fires ignited during drier times.

Fire Return Intervals

No direct fire history studies can pinpoint fire return intervals for Florida scrub. Fire frequencies are inferred by reference to the life history of component species, fire movement patterns through areas with different vegetation structure, and vegetation regrowth between fires. Fire return intervals listed in Menges (1999) range from 5-20 years for oak dominated scrub types to 15-100 years for rosemary scrub. Similar intervals are listed by other authors (e.g., Myers 1985). Fires in Florida scrub tend to be less frequent than in adjoining vegetation (e.g. pine flatwoods) that have more fine fuels (Breininger et al. 2002).

Explicit population viability analyses of population growth and extinction of scrub endemics in relation to fire return intervals can be used as a guideline. Optimal fire return intervals range from < 5 to 20 years for Eriogonum longifolium var. gnaphalifolium (Satterthwaite et al. 2002), < 50 for Hypericum cumulicola (Quintana-Ascencio et al. 2003); < 15 years for Eryngium cuneifolium (Menges and Quintana-Ascencio 2004), and 6-10 years for Dicerandra frutescens (Menges et al. in preparation). Florida scrub-jays are thought to require fire return intervals of about 8-15 years on the Lake Wales Ridge (Woolfenden and Fitzpatrick 1996). Breininger and Carter (2002) suggest that Florida scrub-jays could survive well in a landscape burned every 20 years, if it was burned by extensive fires that would affect fire-resistant vegetation patches.

Other disturbances besides fire may be important in coastal scrubs on or near barrier islands. Wind and storm disturbances may affect vegetation dynamics (Johnson 1997) and the demography of individual species (Gibson and Menges 1994). Nevertheless, even barrier islands may experience frequent fires (Huffman et al. 2004).

Fires more frequent than every 10 years have the potential to divert scrub toward sandhill communities on yellow sands (Myers 1985) and can eliminate Florida rosemary from xeric scrub on white sand (Menges, personal observation). Very infrequent fire can potentially convert scrub to hammocks (forests), especially in northern Florida or where seed sources of mesic oaks are nearby (Myers and White 1987). In south-central Florida, fire suppression in scrub leads to slow structural development toward xeric hammock on yellow sands but with little species compositional turnover (Givens et al. 1984, Menges et al. 1993).

Fire Intensity and Consumption

Florida scrub can be classified as a high intensity fire system. Like other well-studied shrublands (e.g., California chaparral, bushlands in Australia), fires move through the shrub canopy. Green leaves on palmettos, oaks, and other shrubs are usually consumed or at least scorched. Ground vegetation and litter (and sometimes duff) tend to be consumed as well. Pine trees often torch but crown density is too low to support active crown fires, although passive crown fires can occur during spring droughts on hot days with high winds and low humidity (Hough 1973).

Nonetheless, there is great variation in fire intensity in Florida scrub at both large and small scales (Outcalt and Greenberg 1998, Wally et al. submitted). Unburned patches of varying size are typical of Florida scrub burns. Lightly burned patches with only the litter and lower branches burned are also common. In areas where scrub oaks and other shrubs have grown tall, or where there is a subcanopy of turkey oak or scrub hickory, those taller trees may be consumed incompletely. Moreover, fire intensity is usually greater in the interior than on the edge of burn units (Outcalt and Greenberg 1998).

Effects of varying fire intensities on vegetation and wildlife responses are not well studied, but can be important in predicting fire effects (see Fire Effects in Florida Scrub). For example, higher char height is associated with bark beetle damage and subsequent mortality of south Florida slash pine (Menges and Deyrup 2001). Patterns of consumption can also affect life history responses to fire.

There have been some attempts to measure and manipulate fire intensity during prescribed burns. Measurements of fire intensity have been made using thermocouples, pyrometers, and calorimeters (Wally et al. submitted). Pyrometers may be the most practical means of estimating relative fire intensity in planned fires and are correlated with temperatures obtained by thermocouples. Post-hoc, fire intensities can be gauged by char height, residual twig diameter, and other means. Mechanical pretreatments have treatment-specific effects, with fire intensity depending in part on the lag between the pretreatment and fire (Wally et al. submitted).

Organic soil in many Florida ecosystems can burn, especially during droughts and with artificial drainage. This can create horrendous smoke management problems. Since Florida scrub does not usually have organic soils, this is generally not an issue. However, duff buildup in long unburned areas can create flammable top layers to soils. This duff layer can be exposed by initial restoration fires and is thereafter very vulnerable to ignition when dried and exposed to sparks from nearby fires (Menges, personal observation).

Habitat fragmentation and active fire suppression have worked together to reduce the frequency of fire in Florida scrub and across the Florida landscape. Lightning ignited fires probably burned over large areas before roads and developments were built. These features, even covering as little as 10% of the landscape, cause a 50% reduction in fire extent (Duncan and Schmalzer 2004).

Even in areas managed actively by prescribed fire, human practices have altered the fire regime. Most prescribed fires in Florida have had agriculture or forestry goals and have been done during the winter months. Only small areas of Florida scrub would likely have burned from lightning ignitions during winter months. Prescribed fires probably have reduced mean fire intensity and would have less variation in fire intensity than uncontrolled fires. Wildfires are likely to burn more land during windy, droughty conditions, whereas prescribed fires tend to be lit during times when control is easier. Prescribed burns are also likely to change the patchiness of burned vs. unburned areas. More uniform burning conditions could translate to less patchiness, or more benign conditions could translate to larger unburned patches. Aerial ignitions, which are becoming more common, could also leave more unburned areas. Prescribed burning is conducted entirely during daylight hours with fires being extinguished before nightfall due to smoke management considerations. Presettlement fires likely burned both day and night, and for longer durations than prescribed fires. Due to lack of monitoring of areas actually burned, we cannot thoroughly evaluate the characteristics of the current fire regime.

Fire Suppression Effects

With fire suppression, several changes occur. Gaps in the vegetation, crucial to many herbaceous plants and some animals (Hawkes and Menges, 1996, Hokit et al. 1999, Greenberg et al. 1994, 1995), begin to close (Hawkes and Menges 1996). The matrix vegetation also becomes taller and thicker (Abrahamson 1984 a, b, Schmalzer 2003). Surface litter builds up (Schmalzer and Hinkle 1996) because litterfall rates exceed litter turnover rates (Lugo and Zucca 1983). The continued growth of tall shrubs tends to suppress herbaceous plants and smaller shrubs (Givens et al. 1984). However, this process is slow and not particularly directional (Menges et al. 1993). As light levels drop, sand pine mortality begins to occur and is not balanced by recruitment (Conway et al. 1997, Parker et al. 1997). Ground lichens also spread, and this suppresses seedling recruitment (Hawkes and Menges 2003).

One effect of continued fire suppression is that potential postfire colonists can be locally eliminated, so that the postfire recovery lacks some species characteristic of recently burned patches in recurrently burned areas (Abrahamson and Abrahamson 1996). This is likely due, in part, to depletion of soil seed banks of obligate seeders (Menges et al. in preparation). In some cases, local extinctions have been documented (e.g., Menges and Quintana-Ascencio 2004). Fire suppression also eliminates gaps that may have to be created by a combination of mechanical treatments and fire (Schmalzer and Boyle 1998).

Fire suppression has particularly devastating effects on Florida scrub jays, causing reduced fitness and, ultimately, territory abandonment (Breininger et al. 1995). Population viability is reduced in low quality, fire-suppressed landscapes (Root 1996, Breininger et al. 1999). Scrub jay abandonment depends on the rate of shrub height growth (and other factors) and occurs more rapidly in coastal than interior scrub (Breininger and Schmalzer 1990, Fitzpatrick et al. 1991). Scrub jay abandonment is probably not due to reductions in acorn supply in fire-suppressed stands, as acorn supply remains relatively constant (Abrahamson and Layne 2002b). Across the landscape, both short-height, recently burned scrub and tall, unburned scrub act as population sinks, receiving excess birds produced in optimal scrub habitat (Breininger and Carter 2002).

Fire suppression also alters subsequent fire behavior. As oaks and other shrubs become small trees, they are both unlikely to carry fires off the ground and unlikely to be killed by fires. These fire resistant clumps of oaks are termed “oak domes” if they occur as patches within a more open matrix (Guerin 1993). Fire suppressed areas become more resistant to restoration using subsequent fires (Duncan et al. 1999).

Most Florida scrub plants are top-killed by fire but use resprouting (often with clonal growth) to recover (Schmalzer and Hinkle 1992b, Menges and Kohfeldt 1995). Woody plants are usually strong resprouters, but so are dwarf palm species (Abrahamson 1999). Even tiny palm plants can resprout (Abrahamson 1995); they are essentially forming a seedling bank although the factors causing their “release” are not well known. Some herbs are very strong resprouters (McConnell and Menges 2002) but others are weak resprouters (Weekley and Menges 2003). Resprouting is probably affected by fire intensity, but little research has been conducted in this area.

While resprouters dominate most types of Florida scrub, other mechanisms also are important. Resistance to fire is an uncommon adaptation, but does occur in longleaf and south Florida slash pine. The thick bark of pine and grass stage of these pines helps them survive fire. Mortality in fires increases with fire intensity and time-since-fire and also varies seasonally (Menges and Deyrup 2001). When scrub oaks get to be tree-sized, they may also resist fire, making the use of fire to top kill shrubs in long-unburned areas difficult.

Florida rosemary (Ceratiola ericoides) and many herbaceous plants are killed by fire but recover from seeds in soil seed banks (Johnson 1982, Carrington 1996, Quintana-Ascencio et al. 2003). This creates a characteristic increase in herbaceous plant diversity and density in recently burned Florida scrub (Hawkes and Menges 1996, Carrington 1999) but this pulse of seedlings is lower than in similar situations in California chaparral (Carrington and Keeley 1999). Sand pine (Pinus clausa) stores seeds in an aerial seed bank. A few species have no adaptation to fire per se, but are able to disperse from unburned patches back into burned areas. Fire patchiness must affect their distribution, although this has not been well studied.

Combinations of postfire recovery strategies occur in many species (Menges and Kohfeldt 1995). For example, large postfire increases in the density of scrub morning glory are due to both resprouting and germination from a persistent seed bank (Hartnett and Richardson 1989). This combination is also found in Lechea species (Maliakal Witt et al. in preparation). The herbaceous goldenrod Solidago odora var. chapmanii recovers from fire via resprouts, clonal shoots, and seedling recruitment (Menges and Root 2004).

Variation in postfire recovery strategy affects vegetation structure in Florida scrub. Areas dominated by Florida rosemary, which recovers via a soil seed bank, remain relatively open and afford opportunities for herbaceous species including many scrub endemic plants (Menges and Hawkes 1998). Aggressive clonal growth by blueberries postfire (Menges and Kohfeldt 1995) is probably the cause of their peak in cover within a few years of fire (Abrahamson 1984b). Postfire flowering by resprouting plants (Ostertag and Menges 1994) can lead to delayed pulses in seedling recruitment, as in scrub buckwheat (McConnell and Menges 2002). Obligate seeders with delayed reproductive maturation (e.g. Florida rosemary) may be eliminated by frequent fires, while resprouters are vulnerable to high fire intensities that can kill root systems, although this occurs rarely.

See also: Fire Effects in Florida Scrub.

In Florida scrub, most areas affected by fire are burned with an intense fire that moves through the shrub canopy, not merely along the ground. The shrubs are top-killed, although most readily resprout. As a result, the most obvious effect of fire is reducing shrub heights (Schmalzer 2003). This reduction in shrub height is considered key for habitat of the Florida scrub jay (Woolfenden and Fitzpatrick 1996, Breininger et al. 1995). Low intensity patches may fail to kill small shrubs, creating spatial heterogeneity that may be key to some species that lack seed banks and are killed by fire. Patches of tall oaks are also potential nest sites for the Florida scrub jay (Woolfenden and Fitzpatrick 1996).

Fires increase the size of gaps as shrub canopies are temporarily reduced (Schmalzer 2003). Intense patches may also completely kill small areas of oaks and palmettos, creating new gaps (Menges, personal observation). Individual species have a range of life history strategies with respect to fire (e.g. Menges and Kohfeldt 1995, Menges and Hawkes 1998, Ostertag and Menges 1994, Weekley and Menges 2003), and these are part of the effects of fire. For example, fires kill Florida rosemary so that rosemary-dominated areas may be very open for years postfire. The spatial and age structure of rosemary stands reflects its disturbance history (Gibson and Menges 1994).

Fire may kill some animals, although most are able to flee or take cover. Gopher tortoise holes are thought to provide temporary shelter for many species. Fire behavior and lighting patterns probably affect animal survival, with unburned patches promoting survival and ring fires causing higher mortality. As with plants, various animal species are benefited by the postfire environment to various degrees. Gopher tortoises benefit postfire from the increased herbaceous growth. Florida scrub jays recolonize large burned areas once acorns are produced (about 1-4 years; Abrahamson and Layne 2002a) and continue to utilize patchily burned areas immediately after fire. Effects of Florida scrub fires on soil and water have not been studied. Fire destroys the alga-dominated biological soil crust, but its recovery is fairly rapid (Hawkes 2004).

Short- and Long-term Post-fire Recovery Patterns

Florida scrub recovers from fire within a few years, depending on what feature of recovery is considered. Shrub regrowth is rapid; as palmettos increase leaf production rates and actually carry more leaves in recently burned stands than in long-unburned stands (Abrahamson 1995). Cover, diversity, and general species composition return to preburn levels within 1-5 years (Abrahamson 1984a, Abrahamson and Abrahamson 1996, Greenberg 2003, Schmalzer 2003) but height increases are gradual and may take many years (Schmalzer 2003, Greenberg 2003) However, long-unburned scrub that is finally burned may not show the characteristic increase in herbs (e.g., Weekley and Menges 2003) that are seen in periodically burned stands (Abrahamson and Abrahamson 1996). Soil crusts recover various functions in months or a few years (Hawkes 2004). Florida scrub jays return to burned scrub once acorns are produced on oaks, varying from 1-4 years depending on the oak species (Abrahamson and Layne 2002a). Ground lichen recovery is slower. These organisms are not visible for about 4 years or so, and continue to increase their cover with time-since-fire (Johnson and Abrahamson 1990, Menges and Kohfeldt 1995, Yahr 2000).

Longer–term changes in vegetation structure and composition are slow and variable in direction in space and time (Givens et al. 1984, Menges et al. 1993). This is probably due to the high survival and competitive ability of the clonal shrubs that dominate long-unburned scrub. For example, palmettos have high survival even in droughts (Abrahamson and Abrahamson 2002). Oak genets probably have extremely high survival. However, ramet turnover varies among oak species. Those with more rapid ramet turnover (e.g., Q. inopina; Johnson and Abrahamson 2002) are likely to decline in long-unburned scrub as taller oaks overtop them (Menges et al. 1993).

Florida scrub influences the fire dynamics of associated ecosystems by acting as a fire barrier during the first decade or so postfire, when flatwoods, sandhills, and seasonal marshes that have more continuous fuels are likely to burn. Conversely, seasonal marshes and other grassy areas (e.g., cutthroat dominated areas; Yahr et al. 2000) probably increase the fire frequencies of associated scrub patches. Scrub patches isolated by permanent water are likely to have had a lower fire return interval than those embedded in flammable vegetation.

Ecosystem Maintenance and Restoration

In areas that have received fire, continued prescribed burning is used to maintain key attributes of vegetation structure (e.g. low vegetation height, low pine tree density, patches of bare ground). Many of these key attributes are important to the Florida scrub jay and to endemic plants, especially gap specialists. Fires also reduce fuels and that, together with a more convenient structure, helps reduce the intensity and size of subsequent wildfires, a major issue in Florida. Maintenance fires are usually conducted in the spring and summer. Most fire managers tolerate patchiness in these fires. In fact, there is a tendency to be satisfied with lighting the perimeter of burn units and inadequate monitoring of the percent of area burned. Obviously, a burn unit with only 10% of the area actually burned will not be a biologically effective fire, nor will it reduce fuel loads significantly. However, high-intensity crown fires have been prescribed and successfully implemented (e.g., Custer and Thorsen 1993, Outcalt and Greenberg 1998, Main and Menges 1997).

Although prescribed burning has been used aggressively by many land management agencies for decades, large areas of Florida (especially in private hands and near urban areas) continue to be fire suppressed. The dense vegetation can be a fire hazard and does not support the biodiversity of periodically burned areas. As these areas come into ownership by public or private agencies that are able to use fire management, a difficult restoration phase begins. Areas that are extremely overgrown are likely to be particularly difficult to restore using fire (Duncan et al. 1999).

Initial fires in overgrown areas are often conducted during winter months to take advantage of lower humidity and consistent winds that can carry fire through dense vegetation. Most areas are switched to spring and summer maintenance burns after an initial winter burn.

Mechanical pretreatments (or even surrogates) are increasingly used in the restoration phase. These include roller chopping, mowing (with a range of machines), logging, and chain sawing. The goals vary with the type of vegetation and include removing or reducing tree canopies, reducing shrub heights, producing a more uniform fuel bed, and creating a more homogenous fire. These treatments may be designed to reduce fire intensities or, conversely, allow fire-resistant areas to burn. Although many mechanical treatments are being used in scrub and other ecosystems statewide, most are being applied with little monitoring. There are a few ongoing studies on the effects of these treatments on wildlife, vegetation, and rare species showing varying results (Schmalzer and Boyle 1998, Roberts and Cox 1999, Menges et al. 2001, Berish et al. 2002, Schmalzer et al. 2003).

Implementation

Fires are conducted in all seasons in Florida, with a tradition of winter (December-February) burns for restoration and for agriculture and forestry, and spring and early summer (March-July) burns for ecological goals. Few burns are conducted in late summer due to high humidity and rainfall, and fall burns are avoided because they tend to be associated with high pine mortality (Menges and Deyrup 2001).

Fire return intervals (FRI) are often fixed by fire management plans. FRIs for scrub ecosystems are usually designed to match historic ranges (5-20 years), although there is some variation. Some agencies burn on fixed schedules, while some allow more variation in FRI. Fuel reduction concerns have lead some agencies to burn scrub on shorter FRI (5-10 years) although fire suppression in recently acquired lands is still the norm. Lightning ignited fires, accidental fires, and escapes can burn more areas and alter plans for future burning. Likewise, weather and other logistical constraints (including problems obtaining authorizations for various reasons) leave planned burns undone.

Fires are carried out by teams ranging in size from 3-20, by individual agencies or multi-agency task forces, usually with little or no monitoring or associated research. Crews generally depend on vehicles on the ground and hand lighting in Florida scrub. Aerial ignitions, used extensively in Florida in wetland and flatwoods areas, are used in Florida scrub by some agencies. Aerial ignitions often result in a very patchy, low intensity burn. Florida agencies are relatively sophisticated with respect to training, although certainly continued improvement is needed.

Lighting patterns for on-the-ground ignitions usually include backing fires, flanking fires from the edges, and a final head fire (Main and Menges 1997, Outcalt and Greenberg 1998). Many lighters make forays into the burn unit to light spot fires or strip head fires (e.g., Custer and Thorsen 1996). Because Florida scrub is very dense, mown lines are often used within the unit to provide access and to help fires get rolling. Mown lines are often used around the unit to reduce heat on firelines and to facilitate backing fires, which often do not burn well in Florida scrub.

Smoke management is an increasingly important issue in urbanizing Florida. Smoke management planning is now required to obtain burn authorizations from the Florida Division of Forestry. Some tracts of Florida scrub and other vegetation essentially cannot be burned because they are surrounded by roads and other development and there is no place to put the smoke. However, because Florida has a tradition of prescribed fire in agriculture, forestry, and natural lands management, many (most?) Floridians outside of major metropolitan areas tolerate some level of smoke and understand that prescribed burning has benefits despite this inconvenience.

The effectiveness of prescribed burning is not usually measured. Fire coverage, fire intensities, and responses of key species would be useful variables in post-burn monitoring. Most burns are not monitored at all beyond indicating what burn units were lit. Mapping of patchiness of burns using aerial images and GPS might be an eye-opener to land managers. Patchy burns may not provide the same beneficial effects for species that depend on fire (e.g., Satterthwaite et al. 2002).

Additional research on fire behavior, appropriate fuel models for Florida scrub, and the appropriateness of mechanical surrogates and pretreatments for fire would all benefit prescribed fire in Florida scrub (see: Research Gaps).

Little is known about the ecosystem ecology of Florida scrub. With respect to fire, research gaps include the effect of fire on nutrient cycling, the potential effects of frequent fires on nutrient stores, the effects of fire on soil water dynamics, and atmospheric-vegetation interactions during fire.

Fire behavior in Florida scrub is extreme, but little documented. Fuel models for scrub systems are in development, but not tested for Florida scrub. Most land managers have used fuel model 4, which was developed for California chaparral (e.g., Custer and Thorson 1996). This fuel model can underestimate fire behavior in Florida scrub (Menges, personal observation). Fire managers feel that there is sometimes a narrow ledge between being unable to get fire to carry and conditions that are dangerous to burn. However, this judgment is based on intuition and experience. The role of live fuels in carrying fire and their variation over seasons and with weather conditions is not well known and could help predict fire behavior. Although something is known of fire intensity variation (Wally et al. submitted), there needs to be more work on fire intensity effects on vegetation and rare species recovery. Smoke management is another applied issue that would benefit from research into predictive models.

Fire recovery strategies are known for many plant and animal species although some species still need direct studies. Fire return intervals are only guessed at for many types of scrub, and there is a tendency of land managers to use narrow ranges. We need to understand the full range of fire return intervals that provide variation and support biodiversity in Florida scrub. Some information is known on effects of fire season (e.g. Robbins and Myers, 1992) but more information is needed.

Because of the difficulty of applying and controlling fire, and smoke management issues, many land managers are using mechanical treatments such as roller chopping, mowing, logging, and chain-sawing as surrogates or pretreatments for fire. Ongoing studies on the effects of these treatments on wildlife, vegetation, and rare species show varying results (Schmalzer and Boyle 1998, Roberts and Cox 1999, Menges et al. 2001, Berish et al. 2002, Schmalzer et al. 2003). One study in the Ocala National Forest found that wildfire followed by salvage logging had similar effects to clearcutting, but this study was hampered by the lack of an unsalvaged burn treatment (Greenberg et al. 1994, 1995). The widespread use of mechanical surrogates and pretreatments for fire needs to be looked at more critically. The standards for evaluating the use of mechanical treatments should go beyond their effects on a single species (usually the Florida scrub jay) to multi-species responses and include effects on soil properties and invasive species. The standard to which mechanical treatments should be compared is periodic fire.