Distribution

Recorded from Japan: S Honshu, Kyushu, Shikoku, Yakushima; and South Korea: Ullung-Do [Dagelet Island]. The Korean population is genetically very distinct (Havill et al. 2008) and may represent a distinct taxon. Yakushima and Tageshima Islands represent its southern limit.

In Japan, Yakushima has a large and continuous population, but elsewhere in Shikoku, Kyushu and Honshu at lower altitudes the forests have been mostly logged (since 140 years ago, and there was also increased logging just after World War 2) so the remaining populations there are now very sparse and scattered.

Habitat and Ecology

Tsuga sieboldii (a large tree to 25 m) grows in hills and mountains at altitudes between (100?-) 400 m and 1,500 m a.s.l. (from 500 m to 950 m on Shikoku). It grows on various soils derived from
granitic or volcanic rock. The climate is moist temperate, with annual precipitation between 1,000 mm and 2,000 mm, the winters are relatively mild. Tsuga sieboldii is usually associated with conifers such as Abies firma, Pseudotsuga japonica, Chamaecyparis obtusa, Cryptomeria japonica, Pinus densiflora, P. parviflora, and Sciadopitys verticillata, and with broad-leaved trees, e.g. Stewartia monadelpha, Distylium racemosum and Trochodendron aralioides. It rarely grows in pure stands

Tsuga sieboldii, along with Picea torano (K.Koch) Koehne is one of the natural hosts of the Hemlock woolly adelgid (Adelges tsugae Annand) that is decimating Tsuga forests in eastern North America. In Japan this adelgid can occasionally reach high densities on individual trees, but it is very rare that it causes damage. This is probably due to a combination of host resistance, host tolerance, and a diverse complex of arthropod predators that seems to regulate HWA populations (Havill 2014)

Conservation Status

This species has been exploited in the past 100 years, but the population reduction is not likely to exceed 30% over three generations (100 years), it is more likely to be in the range of 20-29%, hence this species is listed as Near Threatened. The reduction is based on direct exploitation, and there is a growing impact from browsing by deer in central Japan as many seedlings are eaten (i.e. it almost qualifies as Vulnerable under criterion A2de).

Conservation Actions

This species is present in a number of protected areas. The subpopulation on Ulung Island shows significant genetic differentiation from those on the mainland and may represent a new taxon that requires additional protective measures (Havil et al. 2008).