The above classifications have reference chiefly to great geographical floras or societies. But there are societies within societies. There are small societies coming within the experience of every person who has ever seen plants growing in natural conditions. There are roadside, fence-row, lawn, thicket, pasture, dune, woods, cliff, barn-yard societies. Every different place has its characteristic vegetation. Note the smaller societies in Figs. [8] and [9]. In the former is a water-lily society and a cat-tail society. In the latter there are grass and bush and woods societies.
Fig. 8.—A Wet-region Society.
Some Details of Plant Societies.—Societies may be composed of scattered and intermingled plants, or of dense clumps or groups of plants. Dense clumps or groups are usually made up of one kind of plant, and they are then called colonies. Colonies of most plants are transient: after a short time other plants gain a foothold amongst them, and an intermingled society is the outcome. Marked exceptions to this are grass colonies and forest colonies, in which one kind of plant may hold its own for years and centuries.
Fig. 9.—A Mid-region Society.
In a large newly cleared area, plants usually first establish themselves in dense colonies. Note the great patches of nettles, jewel-weeds, smart-weeds, clot-burs, fire-weeds in recently cleared but neglected swales, also the fire-weeds in recently burned areas, the rank weeds in the neglected garden, and the ragweeds and May-weeds along the recently worked highway. The competition amongst themselves and with their neighbours finally breaks up the colonies, and a mixed and intermingled flora is generally the result.
In many parts of the world the general tendency of neglected areas is to run into forest. All plants rush for the cleared area. Here and there bushes gain a foothold. Young trees come up; in time these shade the bushes and gain the mastery. Sometimes the area grows to poplars or birches, and people wonder why the original forest trees do not return; but these forest trees may be growing unobserved here and there in the tangle, and in the slow processes of time the poplars perish—for they are short-lived—and the original forest may be replaced. Whether one kind of forest or another returns will depend partly on the kinds that are most seedful in that vicinity and which, therefore, have sown themselves most profusely. Much depends, also, on the kind of undergrowth that first springs up, for some young trees can endure more or less shade than others.
Fig. 10.—Overgrowth and Undergrowth in Three Series,—trees, bushes, grass.