White cedar

Appearance

''T. occidentalis'' has fan-like branches and scaly leaves. Unlike the closely related species ''Thuja plicata'', it is only a small tree, growing to a height of 10–20 metres tall with a 0.4 metres trunk diameter, exceptionally to 30 metres tall and 1.6 metres diameter.

The tree is often stunted or prostrate. The bark is red-brown, furrowed and peels in narrow, longitudinal strips. The foliage forms in flat sprays with scale-like leaves 3–5 millimetres long. The cones are slender, yellow-green ripening brown, 10–15 millimetres long and 4–5 millimetres broad, with 6-8 overlapping scales. The branches may take root if the tree falls.

Naming

The name arborvitae is particularly used in the horticultural trade in the United States. It is Latin for "tree of life" - due to the supposed medicinal properties of the sap, bark and twigs. Despite its common names, it does not belong to the cedar genus, nor is it related to the Australian white cedar, ''Melia azedarach''.

Distribution

''Thuja occidentalis'' is native to Manitoba east throughout the Great Lakes region and into Ontario, Québec, Vermont, New Hampshire, Maine, Prince Edward Island, New Brunswick, and Nova Scotia. Isolated populations exist to the south in Massachusetts, Connecticut, Ohio, Kentucky, Tennessee, North Carolina, Pennsylvania, Maryland, Virginia, and West Virginia.

Habitat

''Thuja occidentalis'' grows naturally in wet forests, being particularly abundant in coniferous swamps where other larger and faster-growing trees cannot compete successfully. It also occurs on other sites with reduced tree competition, such as cliffs. Although not currently listed as endangered, wild ''Thuja occidentalis'' populations are threatened in many areas by high deer numbers; deer find the soft evergreen foliage a very attractive winter food, and strip it rapidly.

The largest known specimen is 34 m tall and 175 cm diameter, on South Manitou Island within Leelanau County, Michigan.

This can be a very long-lived tree in certain conditions, with notably old specimens growing on cliffs where they are inaccessible to deer and wildfire; the oldest known living specimen is just over 1,100 years old, but a dead specimen with over 1,650 growth rings has been found. Despite their age, these very old trees are small and stunted due to the difficult growing conditions. The Witch Tree, a ''T. occidentalis'' growing out of a cliff face on Lake Superior in Minnesota, was described by the French explorer Sieur de la Verendrye as being a mature tree in 1731; it is still alive today.

''T. occidentalis'' specimens found growing on cliff faces in southern Ontario are the oldest trees in Eastern North America and all of Canada, growing to ages in excess of 1,653 years.