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KUCHLER TYPE FIRE ECOLOGY AND MANAGEMENT

KUCHLER TYPE: Cypress savanna
FUELS, FLAMMABILITY, AND FIRE OCCURRENCE : Fuels: On the driest sites, rapid decomposition and occasional flooding prevent organic matter accumulation [17]. Most of Big Cypress Swamp, however, is covered with sufficient fuel to carry fire. Occasional freezes may influence fuel characteristics by killing back the cold-sensitive vegetation and increasing litter [39]. Mean standing stock of litter in a dwarf cypress savanna was 344 (+/- 94) grams per square meter [3]. In years of average precipitation, fires may burn in grasslands and dwarf cypress savanna, but will not burn very far into the middle of cypress domes or strands. Conversely, in a drought year fire may be more severe in the centers of domes and strands than on the edges. When peat is dry enough to burn, the larger amount of litter and organic material in the center will support a more severe fire than on the edges. Fires that consume peat may kill trees due to root damage and loss of structural support. Fires are rarely severe enough to kill trees in dwarf cypress savanna because of sparse organic matter [3,6]. Flammability: In cypress swamps, ericaceous evergreen shrubs are particularly flammable community members [17]. Cypress domes and strands and hardwood swamps probably constituted natural barriers to the spread of wildfire in presettlement times; fire burning in grasslands and savannas around cypress domes would burn into the dome only as far as soil and vegetation moisture levels would permit. Drainage of these wetlands has increased the flammability of cypress domes [42]. Fire During Presettlement Human Occupation: Human occupation occurred within a few hundred years of vegetation establishment in southern Florida [39,24]. Most cypress swamps in southern Florida contain evidence of past fires [42]. It is generally assumed that lightning fires have always been an important factor in southern Florida fire regimes. Prior to European settlement, human-caused fire may have substantially increased fire frequency over the background frequency of lightning fires [14,38,39]. It is likely that most Native American-caused fires were set in the dry season, as soon as fuels could carry fire [39]. Fire in the Postsettlement Period: The frequency of fires increased with European settlement of southern Florida. Fires were set for numerous reasons and many fires were started through carelessness or accident. Drainage of swamps increased the frequency and intensity of fires, with concomitant severe damage to peat exposed by drainage [41]. Fire Frequency: The Everglades and Big Cypress National Preserve are the most fire-prone ecosystems in the National Park Service system. Southern Florida experiences 70 to 90 thunderstorm days per year, the highest number of any area in the United States. The mean annual number of ground strikes is from 4 to 12 per square kilometer. Most of the cloud-to-ground strikes occur during the wet season and 87 to 93 percent of lightning fires occur from May to August; lightning fires have been recorded in all months except January and February. Fewer strikes but more lightning fires occur in the Everglades than in Big Cypress Swamp [39,41]. Taylor [41] estimated that the interval between extreme fire years (years in which a very large number of fires or large number of acres burned) in the Everglades is 5.8 to 7.5 years, and that there is a moderate fire season every 3.2 years. In southern Florida, widespread and severe fires occurred in more than one-third of the years between 1900 and 1952. In very dry years, organic soil fires occasionally burned from one dry season to the next, through the normally wet summer months. Between 1948 and 1979, there were 682 fire reports and 451,082 burned acres in the Everglades. For the first 21 months of fire records for Big Cypress (starting in 1979), there were 131 reported fires, which burned 40,370 acres (16,716 ha). Many fires in Big Cypress burn out before discovery. Both Parks have been disturbed by drainage, logging, farming, off-road vehicle use, and invasion by exotic species, all of which affect fire frequency to some extent. Other changes in fire intensity, frequency, and type have come from fire suppression, prescribed fire programs, and incendiary fire. Wildfires and incendiary fires are extinguished [41]. Wet-season prescribed fires have replaced dry season lightning fires in many grasslands. Drainage has decreased hydroperiods and increased flammability of peat [5,41]. In Big Cypress Swamp, lightning-caused fire is minor relative to human-caused wildfire and prescribed fire. Human-caused wildfires occur in the dry season, and are strongly correlated with moisture conditions [39]. Of the 1,068 fires recorded in Big Cypress Swamp from 1979 to 1988, about four-fifths were incendiary or accidental [39]. The number of fires is positively correlated with peak backcountry use during wild turkey season in March and concides with dry conditions. "Sunday is a particularly popular day for starting fires" [39]. The average fire return interval for all community types in Big Cypress is approximately 12 years [39]. Cypress in dwarf cypress savanna show fire scars and may reveal fire frequency in the dwarf cypress type; however, the slow growth of the trees makes interpretation of rings difficult [41]. Snyder [39] estimated the fire return interval for dwarf cypress savanna as 24 years. Wade and others [42] reported an estimate of seven to nine fires per century in dwarf cypress savanna. Cypress-mixed hardwood strands and cypress domes have a fire return interval of 110 years according to Snyder [39], but Ewel [17] stated that they experience three to five fires per century. Strands appear to have longer fire rotations than domes or dwarf cypress savanna [42]. FIRE EFFECTS ON SITE : Peat based habitats such as cypress domes and strands can support both ground and surface fires. Fire may remove aboveground vegetation only or may also consume peat. FIRE EFFECTS ON VEGETATION : The effects of fire on southern Florida ecosystems are compounded by changing hydrologic relationships. Presettlement fires had different effects than current fires due to human-caused changes in drainage patterns, fire frequency, and the introduction of exotic species [42]. Cypresses survive surface fires better than competing hardwoods [20]. Low-severity surface fires therefore tend to maintain monospecific cypress stands by suppressing hardwood regeneration and killing young hardwoods [9,17]. For example, in Okefenokee Swamp, woody species invade peat islands between fires but most are killed by fire [12]. Young cypress trees (less than 200 years old) may sprout after fire if damage to roots is slight. Sprout production and viability decline with tree age [5]. The characteristic rounded shape of cypress domes and strands appears to be related to peat depth, fire frequency, and site conditions. In Corkscrew Swamp, trees are generally larger and older on sites with deep peat. The deeper peat is in contact with water for longer periods and dries out more slowly. Fires are therefore more frequent and more severe on the edges of domes and strands than in the center where peat is deepest. The less frequent the fire on a microsite, the more likely cypresses will survive to larger size. Outside the strand, hydrologic conditions favor fire that is frequent enough to kill young cypress trees before they can grow large enough to survive low-severity fire; the community is therefore maintained as grassland. In Gordon Swamp, a small cypress strand on the edge of Corkscrew Swamp Sanctuary, a different pattern was recorded. Peat depth increased towards the center of the strand, but tree size was uniform (rather than increasing in the center) and trees were younger in the center of the strand. This situation was probably caused when fire killed trees in the center but not the edges. Following fire, newly established cypresses grew faster than the trees on the edges of the strand. Better site conditions in the center may have contributed to faster tree growth; relative sizes of trees may be partly due to the poor condition of fire-damaged trees on the strand edge. Strands and domes probably expand and contract in response to fire occurrence and hydrologic conditions. During extreme drought, even large strands and domes may experience stand-replacing fire [12]. In a north-central Florida cypress dome, a wildfire killed most shrubs, hardwoods and pines, but killed less than 50 percent of the dominant cypress trees. By 3 years after the fire, the study site flora was composed almost completely of cypress, but the site was being colonized by hardwoods and shrubs [20]. Gunderson [25] proposed a conceptual succession model for southern Florida swamps that shows the effects of logging and fire on cypress and mixed hardwood swamps. After logging, mixed hardwoods and remnant cypress are maintained in the absence of fire. With a severe fire, willow (mostly Coastal Plain willow) colonizes open areas. Willows are maintained by repeated fire, but in the absence of fire succeed to mixed hardwoods. After logging, stands of mixed hardwoods and remnant cypress may experience low-severity fires, which favor cypress over hardwoods, and could return the stand to conditions approximating the prelogging conditions. In the absence of fire, cypress regeneration returns the stand to a mixed swamp (cypress and hardwoods, but with continued lack of fire succession to mixed hardwoods occurs). Cypress and mixed hardwood stands may be converted to monospecific cypress forests by surface fires; in the absence of fire, monospecific cypress stands are invaded by hardwoods. With severe fire, monospecific cypress stands and cypress and mixed hardwood stands are converted to willow and remnant cypress stands. Willow-remnant cypress stands may develop to monospecific cypress stands with occasional surface fires, if cypress regeneration occurs. More frequent or more severe fire that eliminates cypress regeneration will maintain a willow-remnant cypress stand [25]. Since cypress seed dispersal in limited, recovery from severe fires that consume peat may be very slow, particularly where water flow is slow to negligible. In areas where severe fires have burned old-growth cypress stands, there is little sign that communities are recovering to prefire conditions [5]. FIRE EFFECTS ON RESOURCE MANAGEMENT : Prescribed fire in and near cypress swamps is used mainly to enhance wildlife habitat, particularly for endangered species [39]. FIRE USE CONSIDERATIONS : Dye [13] reported on firing techniques in the Everglades and Big Cypress Swamp. In the past, prescribed fire in Big Cypress was usually conducted in the cooler months: November to April [39]. The current trend is to conduct prescribed fire in May and June during the "natural" lightning fire season, which fulfills the goal of approximating original conditions. Most fires are set as headfires; burn plots are small (600-1,000 ac [243-405 ha]); blacklines are wide; and multiple firing patterns are employed. Dye [13] recommended staggered headfires after the establishment of backing and single flankfires within zone perimeters. Plowing lines and the use of firing patterns leading to development of broad coalescing fire fronts are not recommended. FIRE MANAGEMENT CONSIDERATIONS : Low-severity fires do no apparent damage to dwarf cypress savannas and prevent invasion by hardwood species. Fuel build-up could result in crown scorch and cypress mortality. It is unlikely that wet season lightning fires ever occurred with any regularity in presettlement times; fuels were either inundated or too sparse to carry fire. Lightning fires were probably common whenever the water table dropped. Low-intensity, prescribed headfires are recommended for this type at approximately 10-year intervals [42]. Fire management in cypress domes and strands will be an incidental effect of prescribed fire in dwarf cypress savanna. Some domes will be moist enough to prevent fire spread, while others (in the same year) will carry fire. Prescribed fire in dwarf cypress savanna will, therefore, create a patchwork of fire that burns into domes to some extent. Because of reduced hydroperiods, however, some prescribed fires may burn severely in cypress domes. Fire management in cypress swamps must be "fine-tuned". Fire cannot be excluded, but cypress is vulnerable to severe fire [42]. In northern Florida, periodic fire in seasonally dry cypress domes will perpetuate cypress at the expense of pine [20]. An intense fire every 2 or 3 decades kills most pine and hardwoods, but leaves cypress. The removal of a thin layer of organic soil appears to be tolerated by cypresses and other species. It is possible that more frequent, low-intensity fires (every 2-3 years) could be used to achieve the same goal, although this has not been demonstrated [42]. The nature of fires in both northern and southern Florida has changed [17]. Drainage of southern Florida has resulted in soils that are dry early in spring which contributes to wildfires that are more destructive than fires that occurred before widescale drainage. Under current conditions, fires consume large amounts of organic soil and kill the roots of most fire-adapted plant species (as well as fire sensitive species) [42]. Fire in logged cypress swamps is more severe than in unlogged swamps due to remaining slash and the presence of dense regrowth. Fires burn hotter, destroy cypress seeds and roots in the soil, and eliminate cypress sprouts. This situation favors the replacement of cypresses by willows which are followed by mixed hardwoods [25]. The detrimental effects of severe fires in cypress swamps include smoke production (hazardous to health), loss of organic soils, loss of vegetation, damage to wildlife habitat, loss of esthetic value, and scars and damage caused by suppression efforts [42]. Melaleuca invasion occurs on sites that have been drained and severely burned. The flammability of melaleuca increases the probability of crown fires in cypress stands, particularly where melaleuca has invaded the ecotone between cypress stands and pine flatwoods [39,41]. Fire management programs in southern Florida will probably be designed to bring about desired effects rather than recreate a specific fire regime. Prescribed fire use is limited by public tolerance; visible smoke is produced, and high intensity fires are feared [39]. REHABILITATION OF SITES FOLLOWING WILDFIRE : NO-ENTRY

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Information Courtesy: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Fire Effects Information System

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