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Scientific name: Thuja koraiensis T. Nakai 1919
Synonyms: -
Common names: Korean arborvitae, Chaoxian Yabai (Chinese), Nioi-Nezuko (Japanese), Nun-chuk-paek (Korean)
Tree to 10(-20) m tall or spreading shrub to 2 m at high elevations, often persistently shrubby in cultivation, with trunk to 0.3(-0.8) m in diameter. Bark scaly, reddish brown. Crown conical to dome-shaped dense or more open with slender, widely spreading horizontal to upwardly angled branches bearing ball-like chumps of foliage. Scale leaves 1-3 mm long, dark green above, concave beneath and with very prominent white stomatal zones. Facial leaves with an obscure to prominent resin gland on the midline near the base. Leaves of main branchlets to 15 mm long, with short spreading tips. Pollen cones 1-3 mm long, with three to five pairs of pollen scales, reddish purple. Seed cones (6-)8-10 mm long, with four to six pairs of scales, of which the middle two (or three) are fertile, each scale with a triangular point just below the tip. Seeds (one or) two per scale, 4-6 mm long, including the slightly longer wings, each wing slightly narrower than the body.
Northern and central Korea and adjacent China (Jilin province). Scattered in mixed forests of valleys and moist mountain slopes; 700-2,000 m.
Red List Category & Criteria: Vulnerable
Although there is little or no information about the conservation status of Thuja koraiensis in North Korea, there is sufficient documentation concerning the critical state of the forests to assume that the species is under threat. Most of the loss of forests in North Korea’s is related to the policy of increasing arable land in mountainous areas (UNEP 2003, Hayes 2009). The level of deforestation is suspected to have caused a loss in the area of occupancy (AOO) and had a negative impact on the extent and/or quality of any existing habitats and caused severe fragmentation. In South Korea the species is more secure but the underlying problem here and throughout the global population is the lack of recruitment due to the paucity of mature individuals. Even in the Changbaishan reserve where there is an estimated 2,500 individual plants, only 15 individuals are sexually mature. Some locations, for example, Mt. Taebaek (M.Gardner pers. obs. 2010) have no mature individuals. The total number of mature reproducing individuals is uncertain but is estimated to be between 250 and 1,000. The AOO is estimated to be between 500 and 2,000 km2 with subpopulations severely fragmented. A recent survey could not locate plants on Mt. Hwaak due to disturbance from military buildings, indicating a decline in the number of locations and probably mature individuals (H. Lee pers. comm. 2011). As a result Thuja koraiensis is assessed as Vulnerable.
The subpopulation in Changbaishan straddles the border between China and North Korea, this and the seven other North Korean locations have a fragmented distribution and typically are restricted to upper slopes of mountains. In South Korea there is less fragmentation with most locations clustered along the Taebaek Mountains. It is notable that locations throughout the global population have few or no sexually mature individuals, for example, even the relatively large subpopulation in the Chinese sector of the Changbaishan is estimated to have only 15 mature individuals.
It mostly forms dense low thickets to 60 cm tall but in some locations it will form a tree to 10 m tall (Fu and Jin 1992). Typically it occurs on middle and upper mountain slopes at altitudes between 700-2,000 m. At the higher elevations it forms low dense thickets on exposed rocky boulder screes, but in more sheltered habitats, such as forests, it can form a small upright tree. It can be associated with a range of other conifer and broad-leaved species. For example, in the Changbaishan, which straddles the boarder between China and North Korea, it is associated with Abies nephrolepis, Betula ermanii, Taxus cuspidata, Acer ukurunduense and Sorbus pohuashanensis. In South Korea it can be associated with Abies nephrolepis, Sorbus commixta, Prunus padus, Betula ermanii, Quercus mongolica and Acer tschonoskii var. rubripes and with Rhododendron schlippenbachii and Rhododendron yedoensis (M. Gardner pers. obs.). Other conifer associates include Pinus pumila, Picea koraiensis, Picea jezoensis, Pinus koraiensis and Pinus sibirica. It appears to avoid rocks of volcanic origin and grows most abundantly on exposed, granitic slopes and crags with acidic skeletal soil.
The forests where the subpopulation in Changbaishan (China) and the Baekdu-san (North Korea) occur regularly suffer from wind-blow and of particular note is the damage caused in 1987 (Tang 2010). Although logging is strictly prohibited in the Chinese sector of this Biosphere, there has been a 50% loss of primary forest and 75% loss of the primary forest landscape in the core area up to 2007 in the North Korean sector (Tang 2010). Such a loss is suspected to have had a detrimental effect on the Thuja although there is no documented evidence for this. There is no specific information about the state of the Thuja habitats in six other locations in North Korea but we have assumed that as a result of a 30.9% loss of forest cover within the last two decades (UNEP 2003, Hayes 2009), at least some of these are likely to have been affected. In South Korea some important habitats are in protected areas, but most locations are very small and with few or no mature individuals. A recent survey of these locations failed to observe any sort of regeneration and could not locate plants on Mt. Hwaak due to disturbance from military buildings (H. Lee pers. comm. 2011).
Due to its small stature the species it is not utilised widely for its wood although it is sometimes used for construction and for making furniture. It is not listed in the Chinese Pharmacopoeia (2010) or earlier editions (C. Leon pers. comm. 2011) but may have local medicinal uses. It is occasionally used as an ornamental shrub in China and Korea. It was first introduced to the UK in 1917 by E.H.Wilson, but today it is only represented in specialist conifer collections where some specimens are notable for growing much taller (up to ca 15 m) in cultivation than in the wild. Recent collections were made in 2010 by RBG Edinburgh from Mt. Hambaek and Mt.Taebaek
The subpopulation in Changbaishan (China) and the Baekdu-san (North Korea) is protected within a Biosphere Reserve which is contiguous across the country’s border. The former was established in 1979 and the latter in 1989. However, over 50% of this area has deteriorated due to seed harvesting of pines, and systematic logging (Tang 2010). While much of the logging in the Changbaishan reserve occurred before it became a protected area, however, there is a continuing deterioration in the Baekdu-san reserve (North Korea). Furthermore, there are huge pressures from tourism in both reserves, which has dramatically increased since the early 1980s; the Changbaishan reserve receives almost 1 million visitors per annum and the Baekdu-san reserve has 200,000 visitors. In South Korea, the largest location of Thuja koraiensis is protected in Soeraksan (Mt. Sorak) National Park.
Copyright © Aljos Farjon, James E. Eckenwalder, IUCN, Conifers Garden. All rights reserved.
