Plant response to fire
Sprouting from root crowns, roots [111,137], and/or underground lignotubers  is typical following top-kill of sweetbay by fire. Postfire seed dispersal and seedling establishment on burned sites is likely, but timing and environmental factors best suited to successful dispersal and postfire germination are unclear. Kologiski  reported that sweetbay invades pine savannas soon after fire.
Postfire sprouting: Exposure of sweetbay roots, although not commonly described in the literature, may limit postfire sprouting potential on some sites. In the Okefenokee swamp it was reported that a "large percentage" of sweetbay trees were killed in a 1932 fire that burned during "very dry" conditions. The fire burned east until winds changed direction and then burned west. Sites not burned in the first pass burned in the second pass, and some sites may have burned twice; whether or not this affected sweetbay mortality is unknown. However, the researcher noted that sweetbay was killed because of vulnerable aboveground roots (Hopkins 1947, as cited in ). While aboveground root growth has not been directly reported elsewhere, Wharton  described something similar in bay swamps of Georgia. The surface of bay swamps were described as irregular and often higher than adjacent areas, and Wharton suggested that "roots may be exposed and highly convoluted".
Sweetbay sprouted 1 to 2 years after fire in the Okefenokee Swamp that consumed 1 to 2 feet (0.3-0.6 m) of peat in areas with peat 2 to 8 feet deep (0.6-2 m) . In seepage savannas on Louisiana's Kisatchie National Forest, sweetbay produced more first-year postfire sprouts after a June fire than after an August fire, although average maximum fire temperatures were not significantly different (P>0.05) .
General postfire regeneration: Small-diameter sweetbay trees are most vulnerable to fire kill; however, fire effects are often variable. On Florida's Gulf Islands National Seashore, sweetbay trees between 0.4 and 4 inches (1-10 cm) DBH were absent after prescribed fires in sand pine (Pinus clausa), longleaf pine, and ecotone stands. Sweetbay trees of this size were present on all stand types that were unburned for 50 years or more. Sites were evaluated 8 months after early-spring prescribed fires. The fire in sand pine scrub was stand-replacing and "destroyed" a large amount of aboveground vegetation. Descriptions of fires in other stands were not provided . In loblolly pine-shortleaf pine-mixed hardwood stands in Mission Tejas State Park in eastern Texas, sweetbay was absent from unburned stands but had a density of 49 stems/ha on 4-month-old burns. Stands were burned in an early March prescribed fire . Three sweetbay trees that averaged 2.2-inch (5.6 cm) DBH were dead by the 2nd year after a summer fire in a longleaf pine stand in southwestern Alabama. The flank fire burned on 23 July and was described as "intense". At the time of the fire, air temperatures reached 99 Â°F (37 Â°C), and relative humidity was as low as 34% .
Typically the density of sweetbay trees was similar on burned and unburned pond cypress (Taxodium ascendens)-dominated sites 14 to 15 years after fires in the Okefenokee Swamp. Fires burned during an extreme drought and consumed up to 2 feet (0.6 m) of the deep peat layers. Sweetbay density on burned swamp tupelo-bay swamps was much greater than that on burned or unburned pond cypress sites, probably due to greater prefire density and habitat preference. Peat consumption was greatest on the pond cypress stand with the shallowest peat layer, but the researcher noted that tree roots typically extended into the sandy soil layer below the peat. A summary of the study findings is presented below [25,26]:
|Density (trees/acre) of sweetbay trees 1 to 4 inches in DBH on various unburned and 14- to 15-year-old burned sites within the Okefenokee Swamp [25,26]|
|Site characteristics|| |
Tree size (DBH in inches)
|Unburned pond cypress; no peat consumption||4||10||6||3|
|Burned pond cypress; nearly all of the <2-foot peat layer consumed||3||9||1||0|
|Burned pond cypress; about 1 foot of an 8-foot peat layer consumed||17||4||0||0|
|Burned swamp tupelo-bay swamp; 1 foot of a 6-foot peat layer consumed||76||66||20||6|
Following multiple disturbances in wetland longleaf pine-loblolly pine forests in the Big Thicket National Preserve of southeastern Texas, sweetbay trees were present in all size classes ranging from seedlings to trees with over 2-inch (5 cm) DBH. These forests were first damaged by a 1983 tornado, then burned in a winter prescribed fire in 1986, and burned again in a 1991 spring prescribed fire. The spring fire was "cool and patchy", did not produce temperatures over 487 Â°F (253 Â°C), and burned only 12 of 20 plots. Sweetbay seedlings and small saplings were reduced but not eliminated by fire, and seedlings may have established as early as the first postfire growing season. Study findings are summarized below :
|Density (stems/ha) of sweetbay seedlings, saplings, and trees after a tornado and prescribed fires |
|Size class|| |
Time since disturbance and disturbance type
|Predisturbance||2 years after tornado||4 years after 1st prescribed fire||1st growing season after 2nd prescribed fire|
(<50 cm tall)
|Small saplings |
(51 cm-1.3 m tall)
|Large saplings |
(1.4-2 m tall)
|Small trees |
(2-5 cm DBH)
|Large trees |
(>5 cm DBH)
|Basal area |
(mÂ²/ha) of large trees
There was substantial sweetbay mortality in the sapling and understory layer after prescribed fires in 32-year-old longleaf pine-turkey oak (Quercus laevis) stands in southeastern Virginia's Zuni Pine Barrens. Area 1 was burned twice: once in February 1986 and again in July 1987. Area 2 burned once in February 1988. Fires occurred when conditions were warm and dry. Fires were described as "hot" and produced flame heights that often reached 20 feet (6 m). February fires were especially severe due to heavy fuel accumulations. The July fire occurred at night when temperatures were lower and relative humidity higher. In swamp areas, ground fires consumed up to 20 inches (60 cm) of the organic soil. Sweetbay density was significantly reduced (P<0.05) from prefire levels on both burned areas. Sweetbay was eliminated from the understory layer within 1 year of the second fire in area 1. Reductions in sweetbay's density and frequency in the sapling layer are provided for mesic and swamp sites of area 1 :
|Density, frequency, and mortality of sweetbay in the sapling layer before and after fires in area 1 |
|Attribute measured||Mesic site||Swamp site|
(1 year after 1st fire)
(1 year after 2nd fire)
(1 year after 1st fire)
(1 year after 2nd fire)
|Density (individuals/100 mÂ²)||4||0.83||0.67||3.5||0.67||0.33|
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