The northern coast of the Okhotsk sea lies within the discontinuous permafrost zone. The terrestial vegetation of the Shelikhov bay coastal region is characterized by different types of tundra with moss, dwarf shrubs and sedge communities and lowland and montane larch forest. To the south of Shelikhov bay in the Tauyskaya Guba region lowland tundra landscapes alternate with small forested patches. According to Puzachenko's climatological classification of typical northern landscapes, this region corresponds to the forest-tundra tree-line zone: the sum of mean daily temperatures above 10C is 700-800 C,the growing season is 105-110 days, total ammount of rainfall is 250-300 mm and minimum humidity is 75%.
It was previously considered that winter wind was the limiting factor of plant growth in this region. Snow deflation leads to frost desiccation and physical injury of trees. Results of microclimatological research in the Tauyskaya Guba region in 1994-95 allow us to reassess the role of winter wind.
The sums of positive temperatures (SDD) obtained for tundra and forest areas for 20cm soil depth are similar (400-500 C), suggesting that summer microclimate does not have a strong influence on the landscape mosaic. In contrast, minimum soil temperatures at 20 cm depth differ significantly: -6 to -8 C at the forested sites and -13 to -14C at the tundra ones. Maximum snow cover thickness in the forested sites is 1.5 m, whereas the tundra sites are almost bare of snow. As a result, the mean annual soil temperature (MAST) calculated for the tundra sites is -3.0 to -3.5 C and for the forested ones is 0.5 to 0.7 C; mean annual air temperature (MAAT) is -4 to -5 C in both forest and tundra. Such a climatological regime leads to the formation permafrost soils under the tundra sites and seasonaly frozen soils under the forest.
Thus, strong wind in the Okhotsk sea coastal regions does not only have potential to injure the exposed parts of the vegetation, but it causes snow deflation. This constant deflation of the snow cover leads to hard freezing of the soil and, as a result, permafrost develops on the open treeless terrain. In contrast,in the forest thick snow cover protects the soil from freezing and leads to the formation of seasonally frozen soils. The possible consequences of these differences that may contribute to the maintainance of the forest-tundra mosaic are as follows.
Marina Y. Prokopets P.O.Box 750595 Fairbanks, AK 99775-0595. E-mail: ftmyp@aurora.alaska.edu A.V. Alfimov Institute of biological problems of the North laboratory of biocenology K.Marx street, 24 IBPN, 685000, RUSSIA PHONE: (413 22)25801 FAX:(413 00)20166 E-MAIL: IBPN@IBPN.MAGADAN.SU