Tsuga heterophylla

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Western hemlock

Least Concern  (IUCN 3.1)[1]
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Gymnospermae
Division: Pinophyta
Class: Pinopsida
Order: Pinales
Family: Pinaceae
Genus: Tsuga
Species:
T. heterophylla
Binomial name
Tsuga heterophylla
(
Raf.) Sarg.
Natural range

Tsuga heterophylla, the western hemlock[2] or western hemlock-spruce,[3] is a species of hemlock native to the west coast of North America, with its northwestern limit on the Kenai Peninsula, Alaska, and its southeastern limit in northern Sonoma County, California.[4][5] The Latin species name means 'variable leaves'.[6]

Description

Western hemlock is a large

mountain hemlock) reaching a maximum height of 59 m (194 ft). The bark is brown, thin, and furrowed (outwardly appearing similar to that of Douglas-fir).[6]
The crown is a very neat broad conic shape in young trees with a strongly drooping lead shoot, becoming cylindrical in older trees, which may have no branches in the lowest 30–40 m (100–130 ft). At all ages, it is readily distinguished by the pendulous branchlet tips. The shoots are very pale buff-brown, almost white, with pale pubescence about 1 millimetre (1⁄32 in) long.

The leaves are needle-like, 5–23 mm (3⁄16–29⁄32 in) long and 1.5–2 mm (1⁄16–3⁄32 in) broad, strongly flattened in cross-section, with a finely

serrated margin and a bluntly acute apex. They are mid to dark green above; the underside has two distinctive white bands of stomata with only a narrow green midrib between the bands. They are arranged spirally on the shoots but are twisted at the base to lie in two ranks on either side of the shoot. The cones appear on trees over about 25 years old;[6] they are small, pendulous, slenderly cylindrical, 14–30 mm (9⁄16–1+3⁄16 in) long and 7–8 mm (9⁄32–5⁄16 in) broad when closed, opening to 18–25 mm (23⁄32–31⁄32 in) broad. They have 15–25 thin, flexible scales 7–13 mm (9⁄32–1⁄2 in) long. The immature cones are green, maturing gray-brown 5–7 months after pollination. They are usually plentiful enough to cover the ground beneath the tree.[6] The abundant seeds are brown, 2–3 mm (3⁄32–1⁄8 in) long, with a slender, pale-brown wing measuring 7–9 mm (9⁄32–11⁄32 in) long.[4][5][6]

Initial growth is slow; one-year-old seedlings are commonly only 3–5 centimetres (1+1⁄8–2 in) tall, and two-year-old seedlings 10–20 cm (4–8 in) tall. Once established, saplings in full light may have an average growth rate of 50–120 cm (20–47 in) (rarely 140 cm, 55 in) annually until they are 20–30 m (65–100 ft) tall, and in good conditions still 30–40 cm (12–16 in) annually when 40–50 m (130–165 ft) tall. The tallest specimen, 82.83 m (271 ft 9 in) tall, is in Prairie Creek Redwoods State Park, California (United States). The species is long-lived, especially at higher elevations,[6] with trees over 1,200 years old known.[5]

  • Young specimen
    Young specimen
  • Bark
    Bark
  • Branch with mature seed cones that have released their seeds
    Branch with mature seed cones that have released their seeds
  • Western Hemlock Blue Sky
    Western Hemlock Blue Sky

Distribution and habitat

The species often grows on coarse woody debris such as nurse logs and cut stumps.

T. heterophylla is an integral component of

timber tree throughout the region, along with many of its large coniferous associates.[8]
The species is closely associated with
northern Idaho, it grows up to 1,500 m (4,900 ft), particularly on north-facing slopes.[6] In the interior part of its range in Idaho, it can be found up to 1,800 m (5,900 ft).[4][5]

Ecology

Western hemlock is a very

Douglas-fir, where they can persist for decades waiting to exploit a gap in the canopy. They eventually replace these conifers, which are relatively shade-intolerant, in climax forest. However, storms and wildfires will create larger openings in the forest where these other species can then regenerate. Its thin bark and shallow roots makes it susceptible to fire.[6] At higher elevations, the species can be found mingling with T. mertensiana (mountain hemlock), seeming to take on some of its characteristics although there is no hard evidence of hybridization.[6]

Western hemlock forms

dwarf mistletoe, and leaf-consuming insects such as Acleris gloverana and Lambdina fiscellaria.[6]

Uses

The bark has long served as a source of tannin for tanning leather.[6]

Cultivation

Western hemlock is cultivated as an

temperate regions worldwide. It has gained the Royal Horticultural Society's Award of Garden Merit.[12][13]

It can also be found in large gardens in northwest Europe and southern New Zealand.

Forestry

When planted on the banks of a river, western hemlock can help reduce erosion. Outside of its natural range, the tree is of importance in forestry.

Until the early 1920s, the tree was largely ignored for use as lumber due to its presumed similarity to the poor-quality

eastern hemlock.[6] Since then, it has been greatly utilized for timber (as a softwood) and paper production;[6] it is used for making doors, joinery, and furniture.[14] Its fiber is used to make rayon and various plastics.[6]

It has naturalised in some parts of Great Britain and New Zealand—not so extensively as to be considered an invasive species, but as an introduced one.

Food and medicine

The edible

hemorrhage.[6] The bark could also be boiled to make dark red dyes to make fishing nets and lines less visible to fish.[6]

Western hemlocks have been submerged to collect

Tlingit people.[citation needed
]

Tender new-growth needles can be chewed directly or made into a bitter tea, rich in vitamin C (similar to some other hemlock and pine species).[citation needed]

Culture

Western hemlock is the

state tree of Washington.[16]

References

  1. doi:10.2305/IUCN.UK.2013-1.RLTS.T42435A2980087.en
    . Retrieved 19 November 2021.
  2. ^ USDA, NRCS (n.d.). "Tsuga heterophylla". The PLANTS Database (plants.usda.gov). Greensboro, North Carolina: National Plant Data Team. Retrieved 12 December 2015.
  3. ^ BSBI List 2007 (xls). Botanical Society of Britain and Ireland. Archived from the original (xls) on 26 June 2015. Retrieved 17 October 2014.
  4. ^
    ISBN 3-87429-298-3
    .
  5. ^ a b c d Gymnosperm Database: Tsuga heterophylla Archived 2005-09-24 at the Wayback Machine
  6. ^
    OCLC 1141235469
    .
  7. ^ Tallest Hemlock, M. D. Vaden, Arborist: Tallest known Hemlock, Tsuga heterophylla
  8. ^ a b Packee, E.C. (1990). "Tsuga heterophylla". In Burns, Russell M.; Honkala, Barbara H. (eds.). Conifers. Silvics of North America. Vol. 1. Washington, D.C.: United States Forest Service (USFS), United States Department of Agriculture (USDA) – via Southern Research Station.
  9. PMID 17123812. Archived from the original
    (PDF) on 14 August 2011.
  10. PMID 21148873
    .
  11. ^ "Fungi from decayed wood as ectomycorrhizal symbionts of western hemlock". Archived from the original on 13 March 2018.
  12. ^ "RHS Plant Selector – Tsuga heterophylla". RHS. Retrieved 5 March 2021.
  13. ^ "AGM Plants - Ornamental" (PDF). Royal Horticultural Society. July 2017. p. 103. Retrieved 27 December 2018.
  14. ^ Buckley, Michael (2005). "A basic guide to softwoods and hardwoods" (PDF). worldhardwoods.com. Retrieved 1 October 2017.
  15. ISBN 0-394-73127-1
    .
  16. ^ "State Symbols". Washington State Government. Archived from the original on 15 November 2007. Retrieved 20 February 2022.
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