Thuja occidentalis

White Cedar

White Cedar, BWCAW
Photo © by Earl J.S. Rook

Flora, fauna, earth, and sky...
The natural history of the northwoods

Name:

• Thuja, from Theophrastus' name for a resinous, fragrant-wooded tree. Perhaps the most important and influential botanist of Antiquity, Theophrastus (371-286 BCE) was a pupil of Aristotle and author of De historia plantarum (A History of Plants) and De causis plantarum (About the Reasons of Vegetable Growth).
• occidentalis, from the Latin "of the West"
• Common Name, from the light color of the wood
• Other common names include Northern White Cedar, Eastern White Cedar, Arborvitae, Eastern Arborvitae, Swamp Cedar, Cèdre blanc, Thuya du Canada (Qué), Tuja (Swe), Amerikanischer Lebensbaum (Ger)

Taxonomy:

• Kingdom Plantae, the Plants
  • Division Coniferophyta, the Conifers
    • Class Pinopsida
      • Order Pinales
        • Family Cupressaceae, the Cypress, Cedars, and Junipers
          • Genus Thuja, the North American Cedars
• Taxonomic Serial Number: 505490

Description:

• Leaves evergreen, scale-like, on main shoots, ¼" long with long points. Lateral shoots are flattened, 1/8 inch long with short points. Leaves - opposite; scale-like, closely overlapping, successive pairs at right angles; upper and lower leaves flat, with a protruding resin gland, lateral leaves folded, clasping the flat leaves.
• Stem
  • Twig: New growth is green and scale-like, turning brown, occurring in very flattened foliar sprays.
  • Bark: Fibrous, red-brown to gray where weathered. Diamond-shaped patterns are usually apparent.
• Flowers Monoecious; solitary, females green with 4 to 6 scales; males are green tipped with brown and globose.Flowers - monoecious, the male and female flowers of eastern white-cedar are usually borne on separate twigs or branchlets; they are tiny, terminal, cone-like bodies. Male flowers are yellowish and arise from branchlets near the base of the shoot; female flowers are pinkish and appear at the tips of short terminal branchlets.
• Fruit A cone
• A monoecious conifer with a narrow, almost columnar crown.
• Branches on open-grown trees extend to the ground.
• Trunk often divided into two or more secondary trunks of equal size.
• Foliage scalelike
• Bark fibrous,sometimes shredding
• Height at maturity 40'-50' with diameter of 12"-24", infrequently to 70'-80' with diameters of 48"-60". Extremely slow growing; to 40' after 50 years on good sites; perhaps only 15' or less on poor sites.
• Age can exceed 800 years, making it the oldest tree in the North Woods, with the possible exception of some Aspen clones.
• Roots: Seedlings develop deep roots in well-drained soil and shallow roots in saturated soil. With age develops a widespreading root system well adapted to obtain water and nutrients from cracks in rocks.

Identification:

Distribution:

• Manitoba to the Gaspé, south to Minnesota, Wisconsin, Michigan, upstate New York, and northern New England. Isolated populations farther to the south, especially in the Appalachians.

Habitat:

• Both uplands and lowlands. Uplands primarily seepage areas, limestone cliffs, boulder fields; lowlands swamps, streambanks, and lakeshores.
• Prefers lowland sites with strong flow of moderately mineral-rich soil water of near neutral pH and where the organic peat is moderately to well decomposed, usually 1'-6' thick and containing rotten wood.
• Prefers upland sites in calcareous soils, including calcareous clays and shallow loam overlying broken limestone. Grows best where soils are neutral to moderately alkaline.
• Although shade tolerant, it is not as tolerant as Balsam Fir (Abies balsamea) or Sugar Maple (Acer saccharum). Seedlings may only be intermediate in shade tolerance; they can survive severe shade for several years, but if not released, they die. Vegetative shoots are more tolerant than seedlings. Although sometimes considered a climax species because of its longevity and shade tolerance, it cannot reproduce by seed under dense shade to any degree.
• Will invade and form even-aged stands in openings created by windfall or cutting and recently burned swamps. Replaces Speckled Alder (Alnus incana) thickets that form in swamps after fire or after changes in water levels. A pioneer on limestone cliffs and talus slopes where the roots grow in small pockets of organic material between rocks. Succeeds less tolerant, shorter lived species such as Balsam Poplar (Populus balsamifera), Tamarack (Larix laricina), and Black Spruce (Picea mariana).
• Uneven-aged stands form on poor lowland sites where vegetative reproduction is the primary mode of reproduction.
• Often succeeded by more shade-tolerant species, usually tree by tree, but major disturbance (excluding fire) can accelerate succession by releasing shade-tolerant species like Balsam Fir, Sugar Maple, and Black Ash (Fraxinus nigra) growing in the understory.
• An important species in the wet-mesic coniferous forests of the northern lowlands. It is often present in the transition between sphagnum bog and upland hardwood communities. It may dominate rich swamp forests, poor swamp forests, and the cedar string bog and fen complex.
• A slow-growing species, seedlings are frequently damaged by heavy browsing. Many former cedar stands are now dominated by Balsam Fir (Abies balsamea), spruce (Picea spp.), aspen (Populus spp.), or Speckled Alder (Alnus incana).
• Relatively free of serious insect injury. The principal pests are Arborvitae Leafminer (Argyresthia thuiella) and black and red Carpenter Ants (Camponotus pennsylvanicus and C. ferrugineus). Affected by few serious diseases.
• Higher than normal water levels will reduce growth and eventually kill trees. Beaver damming and road construction are often responsible for impeded drainage. the eastern white cedar is most often associated with cool, moist, nutrient-rich sites, particularly on organic soils near streams or other drainage-ways, or on calcareous mineral soils.

Fire:

• Highly susceptible to fire because of thin bark, shallow roots, and high oil content; usually killed by surface fire. Large trees may survive if ground cover is sparse. In the understory of a pine, aspen, or birch (Betula spp.) forest, acts as a fuel ladder, carrying fire into the overstory.
• Risk of fire on most White Cedar sites is low, but fires occasionally originate on drier sites and spread into cedar stands. Given sufficient winds, White Cedar stands can carry a crown fire.
• Fires are infrequent and usually severe. The longest lived specimens occur in locations where fire is infrequent or nonexistent because of rocky substrate, sparse ground cover, or low stand density.
• Reproduces well on moist organic soils exposed by fire if a seed source is nearby. Many White Cedar forests originated after fire. However, if the peat burns and the humus is destroyed, cedar may not become established for some time. Recurring fire may be responsible for the exclusion of White Cedar from some sites.
• Fire serves to remove competition and also removes the moss layer that dries out in the summer and results in seedling mortality.
• White Cedar slash is a fire hazard for 20-30 years because of its resistance to decay.

Associates:

• Trees: White Spruce (Picea glauca), Balsam Poplar (Populus balsamifera), Bigtooth Aspen (Populus grandidentata), Quaking Aspen (Populus tremuloides)
• Shrubs: Moose Maple (Acer spicatum), Speckled Alder (Alnus incana), Bunchberry (Cornus canadensis), Red Osier Dogwood (Cornus sericea), Creeping Snowberry (Gaultheria hispidula), Wintergreen (Gaultheria procumbens) Labrador Tea (Ledum groenlandicum), American Fly Honeysuckle (Lonicera canadensis), Blueberries (Vaccinium angustifolium, Vaccinium myrtilloides)
• Herbs: Woodferns (Dryopteris spp.), Canada Mayflower (Maianthemum canadense), Dwarf Red Blackberry (Rubus pubescens), Pitcherplant (Sarracenia purpurea), False Solomons Seal (Smilacina spp.)
• Ground Covers: Sphagnum Moss (Sphagnum spp.), Liverworts
• Mammals: White-tailed deer, snowshoe hares, and porcupines heavily browse the foliage. One of the best winter browse species for deer, it is often overbrowsed. Overbrowsing can retard growth and even kill a tree if it is less than 7' tall. A high browse line is frequently evident on larger trees. Moose browse only when other food is scarce. Stands provide thermal cover for white-tailed deer, moose, and black bear.
• Birds: Pileated woodpeckers feed on carpenter ants that, in turn, nest in and feed on the heartwood. Other birds abundant in White Cedar forests include White Throat Sparrow, Golden Crown Kinglet, Yellow Belly Flycatcher, Ovenbird, Northern Parula, Winter Wren, Swainson's Thrush, Blackburnian Warbler, Cape May Warbler, and numerous other warblers.

History:

• Foliage is rich in vitamin C; Native Americans and early European explorers used it to treat scurvy, hence the name Arborvitae, "Tree of Life". The name arborvitae or "tree of life" dates from the 16th century when the French explorer Jacques Cartier learned from the Indians how to use the tree's foliage to treat scurvy.
• Once native to Europe, it was doomed to extinction by its inability to escape the advancing ice sheets of the Ice Age.

Uses:

• Wood resistant to decay. Used for products that come in contact with water and soil, such as fence posts, shingles, paneling, and boats. Popular for log cabins because of good insulating qualities. Also used for kraft pulp and particle board.
• Widely planted as an ornamental with a large number of varieties.
• Leaf oil is distilled from boughs and used for perfume and medicines.
• Because of its long life span, a valuable species for dendroclimatic research.

Reproduction:

• Reproduces by seed and vegetatively by layering.
• Seed production: begins producing cones as young as 6 years of age and large quantities by age 30. Best production occurs after age 75. Good crops occur at 2-5 year intervals with intervening years having fair to medium crops. Seeds have lateral wings and are disseminated by wind, dispersed to 150'-200 feet' from the source tree.
• Germination occurs when daytime temperatures reach about 84 degrees F, on a variety of substrates including both mineral and organic soils, but seedling establishment is limited to sites with a constant moisture supply.
• Seedling growth is slow, averaging 3" in the first few years. Partial light is needed for continued seedling growth. Drought is a major cause of mortality. Those that germinate on old stumps are likely to die when the stumps dry out in late summer, and seedlings that germinate in fast-growing sphagnum moss (Sphagnum spp.) may be smothered. Seedlings prosper on recently burned sites.
• Vegetative reproduction: under favorable moisture conditions, reproduces by layering. Seedlings may reproduce by layering at age 5 or earlier. Layering accounts for a considerable amount of reproduction. It is common in swamp forests where trees often fall or tip slowly. Trees established on logs and stumps may fall as their weight increases and the substrate rots.
• Branches on a fallen tree with functional roots may begin growing vertically. Eventually, with the increased weight of new growth, the stem will contact the soil and put out adventitious roots.
• Phenology: Flower buds form in autumn and expand the following spring. Pollen is dispersed from late April to June. Cones are full grown by mid-August, ripen in August and September, and open 7-10 days after ripening. Seeds germinate the following spring or early summer when temperatures warm sufficiently.

Propagation:

• By seed, following cold stratification.
• By layering.

Cultivation:

• Hardy to USDA Zone 3 (average minimum annual temperature -40ºF)

Links:

• Fire Effects Information System (FEIS)

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