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Plantwise Technical Factsheet

Siberian larch (Larix sibirica)

Description
General

Larches are deciduous conifers, shedding their needles in winter. Their soft, fine needles, grouped in fascicles on short shoots, distinguish them from other boreal conifers. All larch species have similar morphological features, especially for their vegetative traits. The surest way to recognise the different larches is by comparing the morphological features of the female cones and to some extent, by examining the bark colour of young branchlets (Ostenfeld and Larsen, 1930; Lepage and Basinger, 1991; Vidakovic, 1991).

L. sibirica is an elegant tree with a remarkably narrow crown. The straight stem sometimes shows some tendency toward basal sweep. Branches are irregularly-arranged, slender, and close to horizontal (Alberta, 1999), with somewhat drooping branchlets. The bark is typically scaly, resembling that of a spruce tree, but its inner bark is a vivid reddish purple (Alberta, 1999). Of the other species of larch, L. sibirica most resembles L. decidua (Ostenfeld and Larsen, 1930; Horsman, 1988). In the absence of flowers or cones, they are difficult to distinguish; their leaves are similar, although those of L. sibirica are somewhat longer than those of L. decidua.

In the north of Russia and in Siberia, the West-Siberian larch is, as a rule, only a small tree, but along rivers, where it is protected, and where the soil is fresher, it may develop better. In the extreme north, where it occurs on the forest-line, only stunted individuals are found. Under the most favourable circumstances, it may attain a height of over 40 m with a diameter of about 1.5 m (Ostenfeld and Larsen, 1930; Abaimov et al., 1998; Earle, 1999). The crown can reach a width of 7.5 m. The tree has a life span of about 2 centuries.

Foliage

The needles of L. sibirica, grouped in fascicles of 10 to 50, measure 5 to 60 mm long and 0.5 mm wide, are keeled, and have several rows of stomata (Abaimov et al., 1998). The young shoots are usually straw-yellow or whitish-grey, hairless. The buds of the short shoots are very dark, and surrounded by a dense ring of hairs (Earle, 1999). The young tree is perhaps most easily recognised by the sweet, pleasant scent which becomes apparent under dry conditions, and is not found in the L. decidua (which it resembles most) (Ostenfeld and Larsen, 1930). Before being shed in the fall, the needles take on a spectacular golden yellow colour.

Inflorescences, flowers and fruits

The mature female cones of L. sibirica are borne on the dwarf twigs. They stand erect on short stalks and open when mature to release the winged seeds (Alberta, 1999). They are light brown, 24 - 45 mm long and 20 - 30 mm wide, with 22 to 40 scales (Lepage and Basinger, 1991). Their shape is usually wide-ovoid, but shows many variations, including globe-shaped, globe-egg-shaped, wide-egg-shaped, oval, rounded, and oblong (Yurasov and Lobanov, 1998). During the flowering season, the cone bracts are most often different shades of red, very seldom green (Abaimov et al., 1998), and much longer than the cone scales (Ostenfeld and Larsen, 1930). On mature cones, however, the bracts are hidden by the cone scales, which are spoon-shaped, with a rounded, entire upper edge (Ostenfeld and Larsen, 1930; Abaimov et al., 1998). The seeds measure 4 to 5 mm long by 3 to 4 mm wide, with a wing 4 to 6 mm long by 3 mm wide (Lepage and Basinger, 1991). Mean weight of 1000 seeds in L. sibirica varies with site class, between 8.3 and 9.2 g. The percentage of filled seeds varies in populations from 17 to 80% (Kuzmina, 1998).

Phenology

Flowering of L. sibirica begins at a temperature sum of 18-20°C (April or May, depending on climatic conditions), and needle bursting, at 50-60°C (Kruklis and Milyutin, 1977; cited in Abaimov et al., 1998). Within a given tree, pollen is usually shed from the male cones one or two days before the female flowers become receptive. Leaves appear during or just after flowering, and usually drop in early fall. Seeds are mature in October or November. Cones open in fall and seeds are dispersed throughout the winter and following spring. The empty cones usually persist on the tree for 2 to 3 years.
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