To the north there comes sooner or later a limit beyond which the cold and winds make further tree growth impossible. Here we come to a tundra region, where the place of trees is taken by low-growing shrubs, with small leaves and other adaptations to ensure against excessive loss of water. It is, as it were, the reappearance of the Mediterranean type, but here the cause is, not the absence of water, but the fact that the cold makes it impossible for the roots to absorb it. A condition of physiological drought results, and only plants well adapted to prevent undue loss of water can resist such conditions of life.
A somewhat similar type of vegetation occurs over vast areas in the more northern parts of Europe, forming the moors and heaths of much of Scotland, of parts of England and Ireland, of parts of Germany, and so on. Here the presence of peat produces conditions very unfavourable to plant life, except to certain shrubby plants such as heather and other plants of the heather family, juniper, bog myrtle, and so on, and some grasses and sedges, etc., all of which have special adaptations to life in a peaty soil. Over the large areas, therefore, covered by these heaths, trees are absent, or few, and this stunted shrubby vegetation takes their place.
Large areas of natural grassland, except for the tracts of pasture land already described in the mountain regions, are infrequent in Europe. They occur in Southern Russia and in the Hungarian plain, and form part of that great series of steppes and plains which stretches into Asia, and passes into a region of deserts.
The conditions favourable to the growth of grass here, instead of trees, seem to be purely climatic. Very important is the prevalence of strong cold winds during winter, which is a period of drought. The scanty rains come in early summer, which suits grasses admirably, while the total precipitation is too slight for trees. The summers are hot, and the rains cease early and give place to a period of drought, very injurious to trees, while it injures the grasses little, owing to the fact that they have had time to make their growth.
The abundant natural growth of grass makes these steppe regions well suited to the pastoral industries, which tend, as civilisation progresses, to give place to agriculture.