Fire weather and fuels: Lightning ignitions are common throughout sweetbay's range, and fires are common during the dry season. Dryness of surrounding upland vegetation and, more importantly, substrate dryness in sweetbay habitats determine fire likelihood, fire severity, and postfire regeneration.
Southern Florida has one of the highest frequencies of lightning strikes in the United States. However, in 14 years at the Archbold Biological Station in Highlands County, just 30 strikes out of an estimated 2,100 to 2,600 strikes started fires . From 1970 to 1990 in the Kisatchie National Forest of Louisiana, 94% of lightning fires occurred between April and September (Martin, unpublished data, cited in ). Thunderstorms were more frequent in July and August than in May and June, but rain-free periods lasted about 12 days in mid-June and 5 to 6 days in July and August . On the southeastern Coastal Plain, winter and spring fires are most common .
Drought conditions are typically necessary for fires to burn in moist to wet sweetbay habitats. Often fires originate in adjacent upland habitats and, when peat soils are dry, spread into lowland sweetbay habitats. The slash pine-hardwood forest cover type burns only after prolonged drought . In the 1,359,000-acre (550,000 ha) pine barrens of New Jersey, burned area increased with an increased number of dry months between January and September. Based on regional fire data from 1906 to 1977, no less than 3 consecutive dry months (Palmer Drought Index level <0) occurred in any year when large areas were burned. In years with 5 or more dry months, average burned area was large and increased with increasing drought duration. Drying of the usually saturated peat soils in Atlantic white-cedar and hardwood swamps likely increased their flammability and area burned . In bay or pocosin vegetation on the southeastern Coastal Plain, accumulations of peat raise the surface elevation many feet above neighboring lowland swamps. During the wet season the water table is at or near the soil surface, and during the dry season the surface peat layer may dry and burn . In the Okefenokee Swamp of Georgia and Florida, droughts and accompanying fires occurred in 1844, 1860, 1910, 1932, 1954, and 1955. In 1954, annual precipitation at the Swamp was 30 inches (760 mm) below average. Effects of fire on vegetation are discussed in General postfire regeneration .
On the southern Coastal Plain from Maryland to southeastern Texas, fires in the sweetbay-swamp tupelo-redbay forest cover type often originate in surrounding uplands . In eastern North Carolina's Holly Shelter Refuge area, fires starting in highly combustible savannas with pineland threeawn (Aristida stricta) may move to into bay vegetation. Pineland threeawn can burn within a few hours of receiving rain. Bay vegetation types dominated by sweetpepperbush (Clethra spp.), sweetbay, loblolly-bay, and large gallberry may burn if surface water is lost during infrequent water-logged periods. Fire is more likely in low bay communities dominated by shrubby forms than in high bay vegetation dominated by tall vegetation with high humidity. In high bays, "ordinary ground fire with little wind will go out" . In the Big Thicket area of Texas, fires in mesic lowland and floodplain forests spread from upland longleaf pine forests during times of extreme drought. The researcher noted that "very rarely does fire devastate an entire area, but instead it creates a mosaic pattern which is always changing with wind and weather" .
Depth of burn and fire severity typically increase with decreasing moisture in sweetbay habitats. When organic peaty soils from shrub and tree pocosins in North Carolina were burned in the laboratory, maximum temperatures in the burning zone reached up to 1,160 Â°F (625 Â°C) . In low and high pocosins in North Carolina, severe fires are associated with droughts . In south Florida, "wet-season fires" on bayhead islands "prune back the woody plants but otherwise do little damage", whereas "drought-season fires" may consume the organic soil layer to the water table. Depressions left in the soil typically fill with water and support only aquatic species . Bayhead vegetation in southern Florida may burn "intensely" when temperatures and winds are high and fuels are dry. During very dry conditions, fires may smolder indefinitely in the "muck" and organic soil. Without moisture to extinguish smoldering, sweetbay and other hardwood roots may be killed, eliminating sprouting potential .
Fire behavior: Severe fires and extreme fire behavior are possible in sweetbay habitats. Extreme fire behavior, including sudden increases in fire intensity and spread rates, often with "violent combustion", is common in pocosin vegetation in North Carolina. Control efforts during extreme fire behavior may be impossible [129,138]. The likelihood of extreme fire behavior ranges from moderate to high in several pocosin fuel types where sweetbay occurs. In dense, low pocosin vegetation with closely spaced brush clumps that average 4 feet (1 m) tall and have about 8 years of accumulated litter, there is moderate potential for extreme fire behavior. Extreme fire behavior potential is moderate to high when pocosins are dominated by high switch cane (Arundinaria gigantea subsp. tecta) vegetation with an open, loose litter layer 3 to 6 inches (8-20 cm) deep. The potential for extreme fire behavior is high when pocosin brush heights average 8 feet (2 m) tall, the organic layer is 10 to 12 inches (25-30 cm) deep, and litter thickness averages 2 inches (5 cm) . A review reports that fires in Coastal Plain pocosins are often "intense" due to the continuous shrub layer. Fires may burn to the water table or to mineral soil .
Fire frequency: Sweetbay is possible in a variety of vegetation types that experience widely different fire frequencies. Fires are frequent in pocosins. Fire-return intervals are variable in bay vegetation types and may range from 26 to 300 years [40,41].
Pocosins and some bay vegetation types on the southeastern Coastal Plain burn often. Soils collected from southeastern pocosins typically have "large amounts" of charcoal from periodic fire . Wells  reported that southeastern Coastal Plain pocosins may burn every 5 years. Peat profile samples taken from North Carolina's Jerome bog, which supports Carolina bay vegetation, contained charcoal fragments in all layers. The researcher concluded that the bog was never "completely free from fire" . In Florida, bay vegetation does not likely support fire spread "except during severe summer droughts" which occur about once every 15 years . In bay swamps of Georgia where peat soils are rarely flooded but constantly wet, fire-return intervals are estimated at 50 to 150 years . In a comprehensive fire study of the southeastern United States, the presettlement fire-return interval estimates for bay forests ranged from 26 to 300 years. The study combined the use of landscape environmental factors, historical evidence, and remnant fire-indicator species to estimate fire frequencies. The presettlement period (time before first European contact) ended around 1565 in eastern Florida and about 1800 in southern Appalachia. On Savanna River sites in South Carolina, the swamp bay (Persea palustris)-sweetbay-loblolly-bay type often occurred between frequently burned upland vegetation and water or nonflammable vegetation [40,41].
See the Fire Regime Table and references therein for additional information on FIRE REGIMES in sweetbay habitats.
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