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Tsuga mertensiana - mountain hemlock


Mountain hemlock is a tree of the upper slopes of the mountains of western North America, its range extending from Alaska to California. It grows in moist soils in forests, thin-peated spruce mires and rocky areas, favouring cool, moist, northern slopes. It is often considered the beauty of the genus. Unlike the other species, mountain hemlock’s concave needles are the same colour on both surfaces and spread in all directions. This gives the tree an attractive, fluffy, cedar-like appearance. The needles are wax-covered and the tree generally bluish in colour, with some provenances a strong blue-grey. The cones, looking rather like spruce cones, are larger than those of the other hemlocks.

In A. F. Tigerstedt’s tests the mountain hemlock proved slow-growing and demanding regarding siting, growing best on the protected moist northern slopes. There is still a small stand of these original test trees, from seed of Alaskan provenance planted in 1909, the tallest specimens currently about 10 metres high. When young, mountain hemlock is susceptible to frost, especially when combined with wind in spring, so it needs the shade and protection of a canopy layer, but hardiness improves with maturity. The severe winters of the 1980s caused some damage and a few of the worst-hit trees had to be removed.

Near these old plantings there are newer trials established in 2005 with seedlings whose provenance is Hanna Ridge in the upper reaches of the River Nass, behind the Coast Mountain Range in the north of British Columbia. This provenance has so far proved excellent at Mustila. The trials also include two truly continental provenances from isolated stands in the Rocky Mountains. In the case of mountain hemlock, the effect of provenance on success is decisive, so planting seedlings of unknown provenance is very much a gamble. Read more »

Tsuga heterophylla - western hemlock


Western hemlock, native to the western parts of North America, is the largest of the hemlocks. Capable of standing deep shade, it grows in mixed forest on mountain slopes and forms dense stands. The crown is narrowly conical and the branches almost horizontal, though the leader and tips of the branches droop in typical hemlock fashion. The needles vary in length, growing outwards and upwards from the branches, covering them so that with age they appear from a distance to be covered in mossy layers.

In Europe, western hemlock is considered a tender maritime species, which is true if seed provenances from the Pacific coast are used. The first plantings of the species at Mustila were destroyed by the record frosts of the winter 1939-1940, when a young plantation of Alaskan provenance froze down to the snow level. However, a plantation of trees from seed of inland British Columbian provenance dating from the 1930s survived, and has now achieved logging dimensions – the tallest trees exceed 25 metres and they continue to grow robustly. Beneath and around the trees there are lots of naturally generated seedlings, which indicate that the provenance has adapted well to the site. There is a remarkable, impressive atmosphere in this wood, with faint light filtering through the thick layers of needles to the forest floor.

Based on experience at Mustila, western hemlock is the hardiest of the genus when seed of suitable provenance is used. The species is fairly undemanding regarding soil, but when young requires an upper canopy to protect it from the combined drying effects of spring sunshine and wind.


Tsuga diversifolia - northern Japanese hemlock


The hemlock (Tsuga) genus gets its scientific name from the Japanese word tsuga. The northern Japanese hemlock is one of the two hemlock species native to Japan, and its natural habitat is the mountains of Honshu Island between 900-2200 metres, approaching the tree line. On the best sites it reaches heights of 25 metres but higher up the slopes remains a low shrub. Compared with other hemlocks the crown is exceptionally dense and broad, reminiscent of broadleaf trees. On their undersides the needles are strongly silver-white, of varying length, broad and notched at the tip. In good seed years the branches are covered in slim fingertip-sized cones.

Groups of handsome old northern Japanese hemlock are found in scenically important places in the Mustila landscape. The first specimens were obtained by A. F. Tigerstedt from St. Petersburg in 1906 as 6-year-old seedlings. The latest plantings are plants grown from seed received from Japan in 1991, which were collected in the Kiso Valley in Nagano prefecture. Despite having developed into handsome trees at Mustila, these natives of a maritime climate aren’t completely winter-hardy. In exceptionally cold winters they suffer needle damage, and some large trees have even died, most recently during the hard winters of the 1980s.


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