Scientific name: Tsuga sieboldii Carrière 1855

Synonyms: Abies araragi Siebold, Abies hanburyana Gordon, Abies tsuga Siebold & Zucc., Micropeuce sieboldii Gordon, Pinus araragi Endl., Pinus araragi Siebold, Pinus sieboldii (Carrière) W.R.McNab, Pinus tsuga (Siebold & Zucc.) Antoine, Tsuga araragi (Endl.) Koehne, Tsuga tsuja A.Murray bis

Common names: Southern Japanese hemlock, Japanese hemlock, Siebold hemlock (English), Tsuga (Japanese)

Description

Tree to 25(-30) m tall, with straight or curved trunk to 1(-2.5) m in diameter. Bark furrowed, scaly, gray-brown. Crown sparser than in Tsuga diversifolia, broadly conical in youth, broadening and becoming flat-topped with age. Twigs hairless. Winter buds pointed, 2-2.5 mm long. Needles variable in length, 0.7-1.2(-2) cm long, widening gradually toward the notched tip, with smooth edges, the white stomatal bands beneath each with 8-10 lines of stomates. Pollen cones 4-5 mm long, reddish brown maturing yellow. Seed cones green before maturity, ripening light brown, (1.5-)2-2.5(-3) cm long on stalks 2-4 mm long, opening to (1.2-)1.5-2(-2.5) cm wide, the seed scales 8-11 mm long. Seed body 4-5 mm long, the wing 5-6 mm longer.

Southern Japanese hemlock is the species that gave its name to the genus. Philipp Franz von Siebold (1796-1866), coauthor of the second botanical flora of Japan, used the Japanese common name, Tsuga, when naming it Abies Tsuga. When Carrière gave the hemlocks their own genus, he used this species name as the generic name. He then had to find a new name for the species, because botanical nomenclature, unlike zoological nomenclature, does not allow tautonyms, species names that repeat the generic name. Carrière followed a common botanical precedent in coining a replacement name of honoring the author of the name that was being replaced, in this case, von Siebold.

Southern Japan, from southern Honshu to Yakushima, and on Ullung Island (Korea). Wet mountain slopes and ridges in mixed forest; (100-)400-1,500 m.

Conservation Status

Red List Category & Criteria: Near Threatened

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).

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.

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, Pinus parviflora, and Sciadopitys verticillata, and with broad-leaved trees, e.g. Stewartia monadelpha, Distylium racemosum and Trochodendron aralioides. It rarely grows in pure stands.

The species has been heavily logged in the past, especially in the northern lower altitude parts of its range. In central Japan, the deer numbers are increasing and they browse the seedlings and also cause damage to mature trees.

The uses of the wood of Southern Japanese Hemlock are mainly construction, carpentry and furniture making. It grows less abundantly than Northern Japanese Hemlock and was therefore not used on such a large scale as a source for paper pulpwood. As an ornamental tree it is grown in Japanese gardens and parks, temple grounds and also in large pots. This species was introduced to Europe (the Netherlands) in 1850 by Von Siebold and is still in cultivation on both sides of the North Atlantic, but uncommon. It is slow growing and often makes a shrubby, spreading tree with a dense crown.

This species is present in a number of protected areas. The subpopulation on Ullung 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).

References

Farjon, A. (2010). A Handbook of the World's Conifers. Koninklijke Brill, Leiden.
Eckenwalder, J.E. (2009) Conifers of the World: The Complete Reference. Timber Press, Portland.
IUCN Red List of Threatened Species, International Union for Conservation of Nature and Natural Resources. Cambridge, UK /Gland, Switzerland