Chamaecyparis thyoides (Atlantic white cedar, Atlantic white cypress, southern white cedar, whitecedar, or false-cypress), a species of Cupressaceae, is native to the Atlantic coast of North America and is found from southern Maine to Georgia and along the Gulf of Mexico coast from Florida to Mississippi. It is one of two species of Chamaecyparis found in North America. C. thyoides resides on the East Coast and C. lawsoniana can be found on the West Coast. There are two geographically isolated subspecies, treated by some botanists as distinct species, by others at just varietal rank: Chamaecyparis thyoides thyoides and Chamaecyparis thyoides henryae (H.L.Li) E.Murray (syn. Chamaecyparis thyoides subsp. henryae (H.L.Li) Little; Chamaecyparis henryae H.L.Li) The species grows in forested wetlands where they tend to dominate the canopy. The trees are associated with a wide variety of other wetland species because of their wide north-south range. The remaining populations are now found mostly in remote locations that would be difficult to harvest, so its popularity as a source of lumber has decreased.

Distribution and habitat

Chamaecyparis thyoides grows within 100 miles of the coastline and less than 50 m above sea level Rare populations grow in the foothills of the Appalachian Mountains, where the tree may be found up to 460 m above sea level. Nationally, Atlantic white cedar is protected in the Great Dismal Swamp National Wildlife Refuge, Alligator River National Wildlife Refuge, Pinelands National Reserve, Cape Cod National Seashore, Croatan National Forest, Francis Marion National Forest, Ocala National Forest, and Apalachicola National Forest. Altered fire regimes, logging, and draining of wetlands outside of the few protected areas have all contributed to the general decrease in the size and occurrences of Atlantic white cedar stands. The tree is listed as Rare in Georgia and New York, of Special Concern in Maine, and Extirpated in Pennsylvania. In Mississippi, the species is at risk of extirpation as a consequence of overexploitation, changes in land use, and extreme weather events.

Chamaecyparis thyoides lives almost exclusively in freshwater wetlands and is considered an obligate wetland species. It prefers habitats where the soil is saturated with water at least during the majority of the growing season. The soils in these regions have a thick organic layer, often classified as a histic surface horizon, with sandy material at greater depths and poor drainage. Atlantic white cedar wetlands are acidic and there is little oxygen stored in the soil because water has displaced the air. Plants that live in these environments must be specially adapted to such conditions.

Ecology

Red maple and black gum trees are often found in the canopy along with Atlantic white cedar throughout its range. Sphagnum mosses also often grow in these wetlands.

The trees themselves grow on hummocks, small mounds, with water pooling in the depressions surrounding them. This keeps the tree from being underwater year-round and helps to protect from floods. The tree benefits from periodic low-intensity fires which expose seedlings to sunlight and limit competition with other canopy flora, particularly red maple. Too frequent or intense fires or flooding can damage seedlings stored in the top layer of soil and full-grown trees. Height and diameter of the tree increase steadily until the tree is 50 years old, at which point height growth slows. Both height and diameter no longer increase once the tree is 100 years old. Stands are generally all younger than 200 years, though some trees as old as 1000 years have been reported. Because they have relatively shallow roots, C. thyoides are vulnerable to being blown over by wind.

Subspecies variation

  • Chamaecyparis thyoides thyoides: Leaves and immature cones usually glaucous blue-green; cones mature to dark brown-black; facial leaves flat, not ridged, but with visible glands.
  • Chamaecyparis thyoides henryae: Leaves and immature cones green, not glaucous; cones mature to light brown; facial leaves with a longitudinal ridge with glands less obvious or absent. 'Andelyensis' (dwarf, dense foliage), 'Ericoides' (juvenile foliage), and 'Glauca' (strongly glaucous foliage).

Conservation

Prior to European colonization of the Americas, there were an estimated of swamps and bogs dominated by stands of Atlantic white cedars. At present, less than still remain. Though the tree is not listed as threatened, Atlantic white cedar wetlands are considered a globally threatened ecosystem, and often serve as carbon sinks because of their peat-building abilities.