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Biomes and Regions of Northern Eurasia

Mixed and Deciduous Forests

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Deciduous Forests of Transcaucasia

Subtropical forests occur in the Colchis (Kolkhida) and Talysh (Lenkoran) lowlands and on the surrounding slopes. Both lowlands were densely forested in the past. However, the development of agriculture has led to extensive deforestation, especially on the Talysh lowland, where almost all natural forests have been destroyed.

The climate of the Colchis lowland is mild and humid. On the lowland, the mean temperature of August (the warmest month) is about 23-24°C; mean monthly temperatures in winter are seldom below 4°C. Annual rainfall averages 1500 mm and exceeds 2200 mm in the foothills with a maximum between September and November. Abundant heat and moisture supplies support lush vegetation. Productivity of these forests is very high and exceeds productivity of the deciduous forests of Central Russia by a factor of two. The phytomass reserves exceed 400 t ha-1 and the share of wood is 80 per cent (Bazilevich, 1993). The accumulation of litter reaches 8-10 t ha-1 and of dead phytomass 60 t ha-1 (Bazilevich, 1993).

Deciduous species dominate forested areas on the lowland and only in the mountains do coniferous stands occur locally (Dolukhanov, 1980). The Colchis lowland is swampy and floodplains are frequently inundated. Woodlands are composed mainly by Alnus barbata and forests developing in stream valleys are represented by Pterocarya, Acer lactum, and Albizia julibrissin. Forests composed of deciduous species (Ouercus hartwissiana, Q, imeretina, Q. iberica, Carpinus caucasica, Castanea saliva, and locally, Vagus orientalis) occur in drier habitats, mainly in the foothills and on the lower slopes. The admixture in such forests consists of Fraxinus excelsior, Tilia platy-phyllos, Ulmus spp., and in some places Zelkova carpini-folia. On the middle slopes, between 1000 m and 1500 m, Fagus forests are totally predominant, while at higher altitudes (up to 1800 m) Fagus is supplemented by Abies nordmanniana and Picea orientalis.

The forests of the Colchis lowland have specific undergrowth, composed predominantly by evergreen broad-leaved shrubs (Rhododendron ponticum, R. smirnowii, R. luteum, Laurus officinalis, and Ruscus). In favourable microclimatic conditions, these shrubs develop an appearance of low, erect trees or form dense thickets, reaching 3-4 m in height (Dolukhanov, 1980). These shrubs frequently invade deforested slopes and, being resistant to low temperatures and deep snow cover, occur at altitudes of up to 2000 m. Tree felling, natural hazards (avalanches, mudflows, windfalls) favour the widespread development of these shrubs. The undergrowth of the Colchis forests includes also other evergreen plants: Buxus colchica, Ruscus spp., Arbutus andrachne, and Hypericum x inodorum. Leaf-falling shrubs like Crataegus spp., Corylus spp., and Vaccinium arctostaphylos are also common as well as woody wines (Hedera colchica, H. helix, Dioscorea caucasica). The herbaceous cover contains many heat-loving relics which migrated to the Caucasus from Europe during the Pleistocene glaciations and spread over the Colchis lowland.

The coastal lowland and slopes of the Talysh mountains are distinguished by a warmer and drier climate than that of the Colchis lowland although annual precipitation is still high (on Talysh lowland, it averages 1200 mm with the maximum in autumn). In the past, the region was much more densely forested. Now, natural forests occur mainly in the Talysh mountains. Subtropical forests containing numerous relics and endemics (Ouercus castaneifolia, Parrotia persica, Alnus subcordata, Acer velutinum, A. insigne, Albizia julibrissin, Gleditschia caspica, Pyrus spp.) dominate the lower slopes, up to 500-600 m, where yellow earths occur. Persian iron wood (Parrotia persica), which is a representative of the Hyrkanian flora of Tertiary age, forms numerous small-size stands. The evergreen undergrowth is poorer in comparison with that of the Colchis forests. Hedera pastuchowii is very common among woody vines and Danae racemosa is most widespread among shrubs. At higher altitudes (up to 1700-1800 m) on mountain brown earths, forests, typical of the Caucasus in general, occur. These are dominated by Ouercus imeretina, Carpinus caucasica, and Fagus orientalis.

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