Thuja  (Thuja sutchuenensis)

Classified as Critically Endangered (CR) on the IUCN Red List (1).

Thuja sutchuenensis shot to fame in 1999, when it was rediscovered not far from the locality in central China where the only known specimens were collected a century before. Formerly classified as Extinct in the Wild, it was the only conifer in the world believed to have disappeared from nature in historic times (1) (2) (3). T. sutchuenensis is a lustrous green, evergreen tree with moderately long spreading branches that form a conical or pyramidal crown. The bark is fibrous and fissured, and exfoliates in thin, curling flakes, varying in colour from cinnamon-red to grey-brown (2). It is quite easily distinguished from other species of Thuja by its tiny leaves and cones (3). A monoecious species, the pollen cones are yellowish green, maturing brown, while the seed cones are green, becoming a lustrous yellowish-brown or orange-brown at maturity (2).

T. sutchuenensis is only known from the southern slopes of the Dabashan Mountains in Chengkou county, central China (1) (2) (3).

Grows on steep slopes and ridges at altitudes of 800 to 2,100 metres above sea level. The soil is generally shallow and some specimens will even grow in rock crevices devoid of soil. The surrounding vegetation is largely deciduous, broad-leaved temperate forest (1) (2).

Thuja sutchuenensis is monoecious (2), meaning that the male and female reproductive structures are borne on the same plant. Unfortunately, owing to the recent nature of its rediscovery, virtually nothing else is reported on the biology of this species.

The wood of T. sutchuenensis is soft, light, and easily worked, as well as being fragrant and rot-resistant, and therefore is often used by local people in construction and craftwork. Consequently, many of the most accessible trees have already been cut down, leaving only the smaller shrub-like trees growing in remote locations at higher altitudes (1) (2). With its small population size, estimated at just 200 trees (4), it is probable that the species has gone through a genetic bottleneck, and thus inbreeding amongst the remaining individuals may be a serious problem. In addition, seedlings are scarce, and plant diseases caused by micro-organisms have been observed, but the extent of their impact is not yet known (1) (2).

As the only member of its genus distributed in central China, T. sutchuenensis is of great scientific value in studies of the origin and evolution of the flora of central China (2). The conservation of this rare tree is thus considered a high priority. The Global Trees Campaign is working with two Chinese institutions to ensure the long-term conservation of T. sutchuenensis. The aims of the project are to conduct further surveys of potential habitat; to study the remaining population to identify the causes of the species’ poor regeneration; and the ex-situ propagation of seedlings in nurseries, which will provide plants for potential re-planting in the wild (4).

To find out more about the Global Trees Campaign, visit:

• The Global Trees Campaign:
  http://www.globaltrees.org/chinese_conifers.htm