Throughout its range, sweetbay is most common in wet woods, swamps, swamp margins, savannas, hammocks, bogs, and floodplains [38,42,43,44,141]. Sweetbay is common and often reaches its greatest abundance in areas generically and locally referred to as bay forests, Carolina bays, bayheads, baygalls, evergreen shrub bogs, or pocosins [82,88,134].
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 Â°F (-23Â°C) in Massachusetts and 40 Â°F (4.4 Â°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 Â°F (25.4 Â°C) and 36.6 Â°F (2.6 Â°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 Â°F (10 Â°C). Summers are long and humid, and temperatures average 85 Â°F (29 Â°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 .
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 .
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