© 2002 Gary J. Kling
Sweetbay is recognized as a dominant or important species in the following habitat types and plant communities:
Eastern United States:
© 2006 Steven J. Baskauf
GENERAL BOTANICAL CHARACTERISTICS:
This description provides characteristics that may be relevant to fire ecology and is not meant for identification. Keys for identification are available (e.g., [38,42,104,112]).
Aboveground description: Sweetbay normally grows as a multistemmed shrub or slender tree in the Northeast and as a single-trunked tree in the Southeast . In its more northern distribution, sweetbay may be only 33 to 66 feet (10-20 m) tall, and in its southern distribution, sweetbay may grow to 98 feet (30 m) tall and 3.9 feet (1.2 m) DBH [33,38,43,99]. In the northernmost sweetbay population of Massachusetts, clumps averaged 12 feet (3.6 m) tall . An exceptionally large tree in Mississippi was 83 feet (25 m) tall and had a 31-inch (79 cm) diameter and a 98-inch (249 cm) circumference . Sweetbay crown spread is typically 10 to 20 feet (3-6 m) . Although Alden  reports that sweetbay grows slowly, Phillips  suggests that sweetbay may reach "full size" in less than 30 years. In the Big Thicket National Preserve of Texas, radial growth of sweetbay trees with a DBH exceeding 1.8 inches (4.5 cm) averaged 0.24 cm/year in a little bluestem (Schizachyrium scoparium) meadow and 0.26 cm/year in a closed-canopy mixed pine-oak (Pinus-Quercus spp.) forest . Little  estimated that sweetbay lives approximately 130 years.
Systematists describe sweetbay as "tardily deciduous" to evergreen . Distribution and climate determine leaf deciduousness which ranges from evergreen in the Southeast to deciduous in the Northeast. Sweetbay leaves are glossy above, silky white or gray below, and have a leather-like texture. Leaves measure 3.2 to 5.9 inches (8-15 cm) long with widths about half that [33,34,42,44,110,141].
|© 2002 (flower) 2006 (fruit) Steven J. Baskauf|
Sweetbay flowers occur singly at branch ends [102,110]. Flowers have 6 to 12 petals and 2 to 3 sepals that detach soon after flowers open [44,104]. Once open, flowers measure 1.5 to 2.8 inches (4-7 cm) across . Sweetbay produces an aggregate of follicles that turn bright red in the fall . Fruiting cones measure 0.8 to 2 inches (2-5 cm) long and nearly as wide. Seeds are generally 6 to 9 mm long [44,104] and drop soon after maturation . Seeds may fall individually or as a cone .
Belowground description: While direct observations and/or excavation studies of sweetbay rooting depth and root spread were lacking, some fire effects studies partially describe belowground structures. Sprouting after top-kill has been reported from root crowns, roots [111,137], and/or underground lignotubers . In some cases, sweetbay roots may grow partially above ground. In bay swamps of Georgia, surfaces are irregular and "roots may be exposed and highly convoluted" . In the Okefenokee swamp, high sweetbay mortality after fire was partially attributed to the death of aboveground roots (Hopkins 1947, as cited in ).RAUNKIAER  LIFE FORM:
Pollination and breeding system: Sweetbay produces perfect flowers . No additional information on pollination or breeding system was available in the literature (2008).
Seed production: General statements on sweetbay seed production vary, and specific numbers were rarely reported. A review reported that sweetbay produced "good seed crops practically every year under normal conditions" and seed occurred on trees as young as 10 years old . Halls  reported that sweetbay produces seed annually but yields may be small. Little  also reported that sweetbay produces seed annually but "in what would seem to be abundant amounts". Sweetbay stems of sprout origin produced "appreciable amounts of seed when stems were only 1 inch in diameter".
Seed production may be affected by associated vegetation, shading, disturbance history, and/or population distribution; however, there are too few sweetbay seed production studies to determine which factors affect production most. Sweetbay seedlings planted in a thinned shortleaf pine (Pinus echinata)-loblolly pine stand in eastern Texas produced fruit at 6 years old in open sites but failed to produce fruit by 9 years old when beneath trees. Fruit yields were "never very large"; a maximum of 20 g of fruit was produced/plant . In the northernmost sweetbay population in Massachusetts, only 33% of the population produced fruits . Sweetbay failed to produce fruit in 3-year-old and recently burned slash pine plantations in southeastern Georgia. Burned plantations were 16 to 30 years old and visited 2 years after fire. Fire severity was not described. Researchers suggested that harvesting, fire, or shading in older stands may have affected fruit production .
Seed dispersal: Sweetbay seeds are likely dispersed by mammals, birds, heavy rains, and/or gusty winds [72,75,115].
Seed banking: Information on sweetbay's seed bank persistence and importance is lacking. In the few available seed bank studies, sweetbay was not dominant and did not emerge from soil samples. Although present in highly disturbed and undisturbed longleaf pine (P. palustris) stands on poorly drained soils in the Croatan National Forest, sweetbay seedlings did not emerge from any soil samples . In the Welaka Research and Education Center in north-central Florida, sweetbay made up 0.8% of the relative tree density, 0.4% of the relative basal area, and 0.04% of the relative seedling density but did not emerge from substrate samples collected in February and August from a variety of microsites .
Germination: Different findings were reported from the few studies of sweetbay seed germination. For sweetbay seeds collected on 13 October from Glouster, Massachusetts, time required to germinate decreased and germination percentages increased as exposure time to cold temperatures increased :
|Germination time and percentages with increasing duration of cold exposure for sweetbay seeds |
|Days of cold stratification||Days to germinate||Percent germination|
Sweetbay seeds collected in the fall from southern New Jersey pine barrens germinated slowly and with low percentages. Seeds exposed to cold germinated at a lower percentage than those without cold exposure. Germination was 3% after 169 to 440 days with cold exposure and 15% after 78 to 420 days without cold exposure . Information from literature reviews, observations, and studies by Little  suggest that germination of sweetbay seed is often slow. When 100 sweetbay seeds collected in New Jersey were cut open, about 90% had embryos, but germination in the greenhouse was less than 18% .
Seedling establishment/growth: Sweetbay seedlings tolerate shading and typically develop in the understory of hardwood or conifer stands. Continued flooding and extended dry periods are not tolerated. A review reports that partial shading of first-year seedlings may increase sweetbay establishment but that regeneration is often best in natural openings or clearcuts. Generally, seedlings survive if there is not an "extended period" of inundation. Height growth of 12 to 24 inches (30-60 cm) is possible in the first year . In the northernmost sweetbay populations, seedlings were absent, even though about 33% of the population produced fruits .
Shading: Sweetbay seedlings often establish in the shade of pine and hardwood forests. In a greenhouse study, sweetbay seedlings in medium and heavy shade produced heights and taproot lengths similar to those of seedlings grown in light shade. Above- and belowground biomass and total root length were, however, negatively affected by shading. In heavy shade, total root length and root weight were 27% and 21%, respectively, those of seedlings grown in light shade :
|Sweetbay seedling growth as a proportion (%) of seedlings grown in light shade (30-45% full sun) |
|Attribute measured||Medium shade
(12-25% full sun)
(6-16% full sun)
|Oven-dry weight of aboveground portion||49||45|
|Total root length||51||27|
|Oven-dry root weight||33||21|
Sweetbay seedlings may occur in open, regenerating, and mature forest stands. On Bradwell Bay, Florida, sweetbay seedlings occurred on every transect sampled in an open, old-growth slash pine stand. Slash pine trees over 98 feet (30 m) tall dominated the canopy, and swamp tupelo and sweetbay saplings up to 39 feet (12 m) dominated the midstory . Abundant sweetbay seedlings (1,600-3,600 stems/acre) were produced in lowland forests of New Jersey receiving 1.3% to 17.7% of full sunlight. Seedling density was much lower (400 stems/acre) in an abandoned cranberry bog where light levels were 38.3%. Light intensities were measured at the seedling layer (about 4 inches (9 cm) above the soil surface). Studies showed that sweetbay saplings were also shade tolerant .
Moisture: Too much or too little water can reduce sweetbay seedling establishment. In bottomland hardwood forests on the floodplain of South Carolina's Upper Three Runs Creek, there were 0.32 sweetbay seedlings/m² on unflooded sites but none on flooded sites. Flood events (overland water for 1-6 days) occurred 41 times at flooded sites and did not occur at unflooded sites. Mature sweetbay trees were also lacking in flooded areas . On an experimental tree island in Palm Beach County, Florida, 6-month-old sweetbay seedling transplants suffered high mortality during dry conditions. The island was above water for 2 months after planting, and researchers suggested that the low water table was the reason for sweetbay seedling survivorship of 3% or less .
Aboveground sweetbay seedling growth was relatively unaffected by water levels up to 6 inches (15 cm) below the soil surface in a greenhouse study. However, roots were heavier and larger where the top water level was lower .
Vegetative regeneration: Sweetbay sprouting after top-kill has been described as vigorous , and sprouts may originate from roots, root crowns [111,137], and/or lignotubers . While sprouting after stem damage is the most common type of vegetative regeneration by sweetbay, regeneration in the northernmost Massachusetts population occurred through the rooting of stems bent to the ground. New sweetbay clumps were found at 10-foot (3 m) distances from parent clumps. The largest sweetbay tree in the area produced 104 stems .
Sweetbay was described as "a particularly strong sprouter, producing large and vigorous sprouts on almost every stump" after cutting in a swamp tupelo-dominated floodplain in Alabama's Escambia River basin. Sweetbay stumps ranged from 3 to 50 inches (7.6-127 cm) in diameter, and larger stumps produced more sprouts (P=0.024). Two years after cutting, sweetbay averaged 11.5 sprouts/stump, and 8 years after cutting, sweetbay averaged 11 sprouts/stump. Eight years after cutting, the tallest sweetbay sprout measured 20 feet (6 m) .SITE CHARACTERISTICS:
A review reports that sweetbay habitats are generally restricted to depressions or floodplains where saturated conditions are common and flooding occurs but is not persistent. Soils are usually organic, acidic, and low in nutrients . In north-central Florida, sweetbay was more common in bayheads than in mixed hardwood swamps. Bayheads were more acidic, had less nutrients, and were not flooded as deeply as swamps. Calcium and magnesium levels were several orders of magnitude greater in swamps than bayheads, and the pH averaged 3.9 in bayheads and 5.4 in swamps. Maximum flooding depth in bayheads was 6 inches (15 cm) and in swamps was 19 inches (48 cm) . Soils and flooding in sweetbay habitats are discussed in further detail below.
Climate: Sweetbay's limited distribution implies narrow climatic tolerances. A review reports that sweetbay occurs in humid to moist climates. Minimum temperatures average -10 °F (-23°C) in Massachusetts and 40 °F (4.4 °C) in Florida. The growing season lasts about 180 days in the northern part of sweetbay's range and about 340 days in its southern range. Annual precipitation averages 48 inches (1,220 mm) on the northern Atlantic Coast and 64 inches (1,630 mm) on the Gulf Coast of Florida . The climate is oceanic near Maryland's Pocomoke Swamp where sweetbay is common in the understory. July and February temperatures average about 77.8 °F (25.4 °C) and 36.6 °F (2.6 °C), respectively. Rainfall averages 39 inches (990 mm)/year and is well distributed throughout the year. Snowfall averages 11 inches (28 cm)/year . On the Gulf Coast Plain, temperature extremes are rare. Winters are short and mild, and temperatures average 50 °F (10 °C). Summers are long and humid, and temperatures average 85 °F (29 °C). Evenly distributed rainfall averages 50 inches (1,270 mm)/year .
More extreme weather events are reported from the fringes of sweetbay's distribution. In Massachusetts, severe frosts can kill sweetbay stems, although survival through sprouting is common . In areas exposed to high winds in Virginia Beach, Virginia, sweetbay was sensitive to salt spray . In southern Florida, sweetbay typically produces flowers in the spring or summer (see Seasonal Development), but after defoliation caused by Hurricane Donna in 1960, sweetbay trees developed some fruit in the fall and winter .
Elevation: Sweetbay in the southeast is most common at elevations less than 660 feet (200 m) , but throughout its range may occupy sites between 0 and 1,800 feet (540 m) .
Soils: Organic, acidic, moist to wet soils are most common in sweetbay habitats. A review reports that sweetbay growth is best on moist, well-drained sites near streams or swamps . The sweetbay-swamp tupelo-redbay forest type on the Coastal Plain from Maryland to southeastern Texas occurs on sandy, often acidic, moist to saturated soils . The slash pine-hardwood forest type on the Coastal Plain occurs on moist to wet, nutrient poor, highly acidic (pH 3.4), peaty soils . Bayhead vegetation in Highlands County, Florida, occurs on "strongly acid muck soils" subject to periodic flooding . In northern Florida, stunted hardwood forests dominated by swamp tupelo and sweetbay occur on soils with a severe phosphorus deficiency . In eastern Texas, sweetbay is common in "wet sour habitats" including neutral to alkaline "seepy slopes" and sandy swamps . In North Carolina, sweetbay occurs in rare wetland forests and woodlands on mineral soils . For more information on these rare types, see Successional Status.
Flooding: Fluctuating water tables are common in sweetbay habitats. In bay or pocosin vegetation on the southeastern Coastal Plain, peat accumulations make these types many feet higher than 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 out. Tolerance of fluctuating water and soil oxygen levels is necessary in these environments . Conner  reports that "extended periods of flooding" may kill sweetbay trees. Based on data from 216 sites in 44 Southeast counties, Peet and Allard (1993, cited in ) found that the frequency of sweetbay was 8.9% in xeric and subxeric sites, 9.5% in mesic sites, and 27.5% in hydric sites. In central Florida's hardwood-dominated Flatford Swamp, sweetbay population size and basal area were typically greater at infrequently flooded than frequently flooded sites . In southern mixed hardwood forests of north-central Florida, sweetbay was absent from dry or dry-mesic stands but frequency was 4% in mesic, 20% in wet-mesic, and 9% in wet stands . Adjacent to Florida's Escambia River, sweetbay occurred on sites flooded less than 5 months a year but not on those flooded 9 to 12 months of the year .
Through controlled studies, researchers have investigated some causes and mechanisms of sweetbay's flooding tolerance and susceptibility. Mortality of sweetbay seedlings collected from Shark Slough in Everglades National Park was 38% after 25 weeks of high-flood treatments. All seedlings survived 25 weeks of no-flood and low-flood treatments. In the high-flood treatment, water was at the soil surface by week 10. In the low-flood treatment, water exceeded the bottom of the pots at week 10, but pots were not inundated by the end of experiment . Average sweetbay growth (differences between measurements taken at the beginning and at the end of the experiment) was 13% in mesic, 22% in half saturated, and 2% in fully saturated conditions. Observations made on flooded plants showed that they produced shoot lenticels to increase oxygen transport to the roots and produced large-diameter roots with more air spaces .SUCCESSIONAL STATUS:
In many areas, sweetbay is considered a late-seral or climax species. In eastern Texas, sweetbay was noted in a "mesophytic climax forest type" . Bayhead communities dominated by loblolly-bay, sweetbay, and redbay in north-central Florida were considered the climax type on seasonally flooded, peaty areas . On the southeastern Coastal Plain, sweetbay was reported as a likely climax species on sites not wet enough to support swamp forests  and occurred in the slash pine-hardwood forest type considered part of the "climax acid swamp complex" . On Maryland's eastern shore, loblolly pine dominates early succession and sweetbay is likely in the climax stage . In a review of evergreen bay forests, McKevlin  noted that since successional change is affected by fire frequency, fire severity, climate, hydrology, and site fertility a "myriad" of successional types is possible, but also noted that mature evergreen bay forests are "indeed both climax and ancient relative to surrounding cover types".
Often the lack of fire in pine forests and flatwoods, cypress swamps, and Atlantic white-cedar stands leads to the development of bay forests or mixed hardwood swamps where sweetbay is common [13,89,108,130,133]. On Bradwell Bay, in Florida's Apalachicola National Forest, the understory of an open, old-growth slash pine stand of trees over 100 feet (30 m) tall was dominated by swamp tupelo and sweetbay. Sweetbay seedlings occurred on every transect, and researchers presumed that the slash pine forest would become a bay forest in the absence of fire . In Alabama's Flomaton Natural Area, sweetbay made up less than 0.1% of the tree layer basal area, but contributed more to the sapling and seedling layers in longleaf pine stands unburned for 45 years or more. Researchers suggested that sweetbay importance increased in the absence of fire . Sweetbay seedling and sprout clump densities increased with fire exclusion in 38-year-old shortleaf pine stands in southern New Jersey .
The rate and path of secondary succession in potential sweetbay habitats is dependent on the predisturbance environment, the severity and/or frequency of the disturbance, as well as the postdisturbance environment. After studying succession in north-central Florida, Monk  indicated that "soil fertility seems more important in the direction of succession to different portions of the climax communities than as a limiting factor maintaining communities in a successional stage". In North Carolina, fire and hydroperiod were important in pocosin and bay forest development and maintenance. Mature vegetation developed rapidly on dry sites and more slowly on the wettest sites. The relationship among potential vegetation types, with hydrology and fire frequency in North Carolina's Green Swamp are illustrated in Figure 1 below :
Figure 1. Potential vegetation types of North Carolina's Green Swamp depending on fire frequency and hydroperiod .
Postfire community composition is determined by depth of burning and postfire water levels. If fires burn deeply in evergreen bay forests and postfire water levels are low, a deciduous bay forest is typical after fire. If water levels are high after a shallow burn, pocosin vegetation or Atlantic white-cedar forests are common. If water levels are high after a deeply penetrating fire, sedge bogs will likely dominate . Fire frequency is also important in determining the vegetation composition in bay swamps, pocosins, and savannas of the Southeast. Without fire, swamp forests may develop; on sites where fires occur about every 10 years, pocosins are likely; and on annually burned sites, grass-sedge savannas are most common  (Wells and Whitford, as cited in ). This topic is also discussed in Fire frequency.
Sweetbay typically sprouts and is present soon after top-killing disturbances
when it was present in the predisturbance community. In the available literature
(2008), the dispersal and establishment of sweetbay on new sites received little
attention. In the Croatan National Forest, sweetbay occurred in longleaf pine
stands that were logged, planted to loblolly pine plantations, and burned at 5-
to 10-year intervals . Sweetbay averaged 11.5 sprouts/stump 2 years after
clearcutting in a forest dominated by sweetbay and swamp tupelo in Escambia
River Drainage basin in southwestern Alabama. Eight years after logging, the
density of sweetbay sprouts was greater on helicopter-logged than on conventional
skidder-logged sites . In bottomland hardwood forests in southeastern Virginia
or northeastern North Carolina, sweetbay was present 2 to 15 years after clearcutting .
In 8-year-old loblolly pine plantations in the South, sweetbay occurred in
plantations where herbaceous vegetation was controlled for 4 years but did
not occur in plantations without control .
Sweetbay flowering may occur from March to July throughout its range. Sweetbay flowers likely appear earlier in the Southeast than in the Northeast [33,34,42,110,112]. In the Carolinas, sweetbay typically produces fruits from July to October .
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 °F (625 °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.
Immediate fire effect on plant:
Sweetbay is often top-killed by fire, but survival of large diameter stems in low-severity fires is possible.
|In an experiment conducted in the late summer and early fall, sweetbay trees with 0.2-inch thick bark reached a lethal cambium temperature of 140 °F (60 °C) in 30.8 seconds when a standard heat source was applied to the bark. Trees with 0.3-inch thick bark took an average of 67 seconds, and those with 0.4-inch thick bark took 152 seconds to reach the lethal temperature. Time to reach lethal cambium temperature also increased with increasing diameter at breast height. Trees with a DBH of 9.1 to 11.0 inches (23-28 cm) took just under 100 seconds, and those with a DBH of 15.1 to 17 inches (38-43 cm) took a little over 300 seconds . Bark thickness of mature sweetbay trees is generally 0.5 to 0.75 inches (1.3-1.9 cm) . In southern pine stands, sweetbay bark thickness ranged from 0.1 to 0.3 inch (2.5-7 mm) for trees with 3.9-5.5-inch (10-14 cm) DBH .|
© 2002 Steven J. Baskauf
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 °F (37 °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]|
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 °F (253 °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 |
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)
(51 cm-1.3 m tall)
(1.4-2 m tall)
(2-5 cm DBH)
(>5 cm DBH)
(m²/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 m²)||4||0.83||0.67||3.5||0.67||0.33|
Effects of repeated fire: While the above studies suggest sweetbay tolerates multiple disturbances, some suggest that sweetbay may be eliminated by repeated burning. A review rated magnolia species as "sensitive" to "long-term" repeated fire . Long-term repeated fire was not directly defined. Conner  reported that sweetbay is resistant to fire but may be killed by repeated burning. However, Wells and Shunk  found shoots produced from persistent stumps that were 30 to 60 years old in a annually burned grass-sedge bog on the southeastern Coastal Plain. Sweetbay also occurred in the understory of annually burned longleaf pine forests on Louisiana's Fort Polk Military Reservation, though stem density was much lower on repeatedly burned sites than on a site not burned for 20 years. Sweetbay densities were 2.5 stems/ha on annually burned sites and sites burned on a 2- to 3-year cycle. On the unburned site, sweetbay density was 147.5 stems/ha . In an old-growth longleaf pine stand in Alabama's Flomaton Natural Area, sweetbay was present before and after 3 prescribed fires in 3 years. Abundance was not reported, and the stand had not burned for 45 years or more before the first prescribed fire .
FIRE MANAGEMENT CONSIDERATIONS:
Fire management information specific to the management of sweetbay was lacking; however, more generic information on the use of fire in some potential sweetbay habitats was available. Prescribed fire use to re-create or mimic past fire regimes and to maintain species and community diversity may be difficult in some eastern ecosystems. Severe fire behavior during extremely dry conditions, while important to the establishment and maintenance of some species, is difficult or impossible to control in many vegetation types. In the Big Thicket Region of Texas, Watson  suggests that prescribed fires should mimic natural patterns. Points of ignition should be placed in upland habitats and "allowed to progress and stop where (they) will". This would be possible only if human-valued properties were not in the fire path, which is not likely in most habitats.
In pocosin vegetation on the Atlantic Coastal Plain, prescribed fires are rarely similar to wildfires. Prescribed fires are set when control is easy. Prescribed fires rarely burn deep into peat layers and may not be useful in the facilitation of seed regeneration of some species and/or the maintenance of high diversity . Extreme fire behavior is common in pocosin vegetation and often alters or restricts control efforts, which can be difficult regardless of fire conditions. Dense tangled understory vegetation makes foot travel slow, and a high water table can make areas inaccessible to heavy equipment [129,138]. The potential for extreme fire behavior in sweetbay communities is discussed in Fire behavior.
FIRE REGIME TABLE:
|Fire regime information on vegetation communities in which sweetbay may occur. For each community, fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Models , which were developed by local experts using available literature, local data, and/or expert opinion. This table summarizes fire regime characteristics for each plant community listed. The PDF file linked from each plant community name describes the model and synthesizes the knowledge available on vegetation composition, structure, and dynamics in that community. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Eastern woodland mosaic||Replacement||2%||200||100||300|
|Surface or low||89%||4||1||7|
|Surface or low||65%||12|
|Northern hardwoods (Northeast)||Replacement||39%||>1,000|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|South-central US Grassland|
|South-central US Woodland|
|Surface or low||96%||4|
|South-central US Forested|
|Gulf Coastal Plain pine flatwoods||Replacement||2%||190|
|Surface or low||95%||5|
|West Gulf Coastal plain pine (uplands and flatwoods)||Replacement||4%||100||50||200|
|Surface or low||93%||4||4||10|
|West Gulf Coastal Plain pine-hardwood woodland or forest upland||Replacement||3%||100||20||200|
|Surface or low||94%||3||3||5|
|Surface or low||58%||100|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Southern Appalachians Grassland|
|Eastern prairie-woodland mosaic||Replacement||50%||10|
|Surface or low||50%||10|
|Southern Appalachians Woodland|
|Appalachian shortleaf pine||Replacement||4%||125|
|Surface or low||92%||6|
|Southern Appalachians Forested|
|Bottomland hardwood forest||Replacement||25%||435||200||>1,000|
|Surface or low||51%||210||50||250|
|Mixed mesophytic hardwood||Replacement||11%||665|
|Surface or low||79%||90|
|Appalachian oak forest (dry-mesic)||Replacement||6%||220|
|Surface or low||79%||17|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Southeast Gulf Coastal Plain Blackland prairie and woodland||Replacement||22%||7|
|Everglades (marl prairie)||Replacement||45%||16||10||20|
|Pond cypress savanna||Replacement||17%||120|
|Surface or low||57%||35|
|Gulf Coast wet pine savanna||Replacement||2%||165||10||500|
|Surface or low||98%||3||1||10|
|Surface or low||97%||4||1||5|
|Surface or low||10%||43||2||50|
|South Florida slash pine flatwoods||Replacement||6%||50||50||90|
|Surface or low||94%||3||1||6|
|Atlantic wet pine savanna||Replacement||4%||100|
|Surface or low||94%||4|
|Atlantic white-cedar forest||Replacement||34%||200||25||350|
|Surface or low||59%||115||10||500|
|Surface or low||80%||9||3||50|
|Surface or low||97%||2||1||8|
|Surface or low||93%||63|
Replacement: Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed: Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects.
Surface or low: Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area [49,64].
American black bears: In the Southeast, American black bears feed on sweetbay and utilize sweetbay habitats. In coastal Virginia and North Carolina, pocosins provide important refuge for American black bears . In the Great Dismal Swamp, new sweetbay leaves and stems had a frequency of 43% in the spring diets of American black bears. Scat analyses indicated that use of sweet bay was much lower in other seasons . On Florida's Eglin Air Force Base, riparian habitats made up just 5% of the available area but were the habitats used most frequently by American black bears. Sweetbay was a primary species in riparian habitats that were utilized by bears year round .
White-tailed deer, cattle: Sweetbay is likely browsed by deer throughout its range. In New Jersey's Lebanon State Forest, white-tailed deer browse new sweetbay sprouts, particularly in the first growing season. White-tailed deer may clip stems to 1 to 2 feet (0.3-0.6 m) tall . The degree of white-tailed deer browsing on sweetbay in longleaf pine communities in National Forests of Alabama, Mississippi, and Louisiana led researchers to classify sweetbay as an intermediate browse choice . In longleaf pine-slash pine stands in southeastern Mississippi, sweetbay made up a high of 8.3% of the total diet composition in March. Cattle diets contained much less sweetbay, and March diets were only 0.16% sweetbay .
Other mammals: Beavers fed extensively on sweetbay in the St Tammany Parish of southeastern Louisiana. Although sweetbay made up just 2.2% of the available woody plants, it was utilized at 79.3%. Bark removal was much more common than felling and/or girdling, and tree mortality was rare . In southern Mississippi, cotton mice were captured most often from bayhead vegetation, suggesting this habitat is important .
Birds: Eastern kingbirds, mockingbirds, robins, wood thrushes, and red-eyed vireos feed on sweet bay seeds and often use sweetbay leaves as nest material . Swainson's warblers also use sweetbay leaves in nest construction .
Palatability/nutritional value: Several references report the palatability and/or nutritional content of sweetbay. For information from wetlands of the New Jersey pine barrens, see ; from pine forests of the Siecke State Forest in Texas, see ; and from longleaf pine-slash pine stands in southeastern Mississippi, see .VALUE FOR REHABILITATION OF DISTURBED SITES:
Wood: Sweetbay wood is used for a variety of products including furniture and interior finishing work . For additional information on sweetbay wood properties and potential uses, see the following references: [2,75,123].
OTHER MANAGEMENT CONSIDERATIONS:
Climate change: In one study, researchers predicted that a doubling of CO2 levels would increase the amount of suitable sweetbay habitat ; however, an expansion of sweetbay's range would depend on successful dispersal and establishment in these areas. McKenney and others  described sweetbay distributions with predicted changes in climate and CO2 both if sweetbay dispersed successfully into newly suited habitats and if it did not.
Threatened ecosystem: Several sweetbay habitats and their associated ecosystem processes are threatened by anthropogenic land use and resource extraction. In Louisiana, the live oak-pine-magnolia ecosystem has declined by 70% to 84% . Pocosins are also threatened by mining, logging, agricultural operations and/or land development [106,111]. These operations may affect rare and threatened species as well as ecosystem processes including changes in carbon flux, hydrology, and dissolved nutrient availability and transport . Slow water movement through dense organic peats in pocosins function to remove nutrients, acidify water, and maintain proper salinity, nutrient, and acidity levels in associated wetland systems .
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