XLIII. THE SWALE "Bubble, bubble, flows the stream, Giving up their pungent smells. -Maurice Thompson. Waste land is land we have not learned how to use. Much of it is too dry, and lacking water-the prime requisite for plant growth-it produces little, even of wild crops. Much of it is too wet and, therefore, unsuited to our agricultural methods, though nature produces on it her most abundant crops. Much of it is too rocky, and unsuited to the use of our implements of tillage. Deserts and rocks and swamps overspread vast areas of the earth's surface. But miniature waste places of like character appear in sandridge and stony slope and swale on many an inland farm. Let us study the swale a bit-that most interesting and most productive of waste areas. We will find it among the tilled fields, where their gentle slopes run together, forming a depression that is poorly drained. We will find it overspreading the level surface of some miniature valley between upland hills, or by the stream-side or at the head of a bay or pond. In such places the crops that we know how to raise on farms will not thrive. There is too much water. The soil is soft under foot. Though black with humus, and enriched with the washings from surrounding slopes, it is sour, and unavailable to our field crops. It has its own crops, and they are never-failing. Always it is a flowery meadow, densely crowded with plants of many kinds in interesting association. It is a place of rushes and sedges, rather than of grasses. It is a place of abundant flowers the whole season through, from the cowslips and cresses of spring to the asters and gentians of autumn. It is a place where crawfish sink their wells, unmolested by the plow, piling little circular mounds of excavated earth about the entrance; a place where rabbits hide, and where song-birds build their nests; a place where the meadow mice and shrews spread a network of runways over the ground: in short, a place where rich soil and abundant light and moisture support a dense population, among which the struggle for existence is keen. If a fence-row extend down from the field into the swale, let us follow that, and see how the wild plants change with increasing soil moisture. The grasses of the fence-row begin to be crowded out by sedges as the water-level comes nearer the surface of the soil. Dry-ground asters and goldenrods and lobelias disappear, and wet ground species of the same groups appear instead. Bracken fern is replaced by marshfern and sensitive fern; hazel by willow. Under foot, the soil is growing softer, blacker and more spongy. If the swale has been cleared of woody plants, still alders and willows are prone to linger about the wetter places, and black-berried elder, osier-dogwood and meadowsweet about the edges. Cat-tails and bulrushes (fig. 16, p. 36) will fringe any open wet spot, and tussock-sedges and clumps of juncus will rise on mounds of gathered humus, like stumbling-blocks before our feet, where diffused springs abound. No two swales are alike in the character of their plant population. But all agree in their meadowlike appearance, in being made up of patches of rather uniform character, where uniform conditions prevail, and in having each of these areas dominated by one or two species of plants, with a number of lesser plants as "fillers" in its midst, and a greater variety of miscellaneous plants growing about its edges. The dominant plants that cover considerable areas of the swale, almost to the exclusion of other plants are mainly grass-like plants, capable of close growth above ground and nearly complete occupation of the soil. They are such marsh grasses as the panicularias (from which marsh hay is made) and reed, on wetter soil; such bulrushes as Scirpus fluviatilis; such other plants, as cat-tails and burreeds (fig. 16); and, over smaller areas, sweet flag (Acorus calamus) and blue flag (Iris versicolor). Where these grow most compactly, there are a few lesser plants intermixed, filling the niches, reaching into light above and spreading roots in the superficial layers of the soil. FIG. 125. A heavy clus(Panicularia laxa) after ter of manna-grass Britton and Brown. With permanent conditions, the mixture of plants will remain much the same year after year. They are nearly all perennials, holding their place by continuous occupancy of it. Each is striving to extend its domain, but there is little opportunity. In the permanent association of certain species together there are some fine mutual adjustments. The taller broad-leaved perennials, like swamp-milkweed and joe-pye-weed and boneset, root rather deeply, and stand stiffly erect. The top layers of the soil are left by them to such lesser things as marsh skullcap, bedstraws, and tear-thumbs, whose straggling sprays reach out and find the light. The annual herbs of the swale are few; they are such as jewel-weed and Spanish needles, that depend for their opportunity FIG. 126. Flower and fruit of the jewel to find a place on some disturbance of existing conditions. A muskrat or a mole upheaves a mound of earth, and the seeds of these annual weeds, falling into this unoccupied soil, flourish there for a season ere the rootstocks of more permanent perennials again invade it. The annuals of the swale are quick-growing things, that depend for their success in the world upon their ability to shift from place to place, to find new openings, and to get in and mature a crop of seeds before the perennials crowd them out again. There are many beautiful and interesting flowers in the swale: yellow flowers, such as Saint John's wort, buttercups, goldenrods and loosestrife; blue flowers, such as monkeyflowers, lobelias and gentians; white flowers, such as meadowrue, turtleheads, avens and cresses; pink flowers, such as cockle-mint, willow-herb, fleabane and marshmallows; red swamp-lilies and flaming scarlet cardinal-flowers; and others in great variety and in continual succession. Forms like those that grow on shoals (mentioned on page 35) will appear if there be permanent open water. Indeed, a careful study of even a small swale might discover the presence of a hundred or more plant species. Ten or a dozen of these are likely to be found to comprise the greater bulk of the plant population. The dominant species are mainly those having comparatively simple and inconspicuous flowers, whose pollen is distributed by winds. The dominant species extend their domain chiefly by strong vegetative offshoots, occupy the soil with strong roots, and never let go. Study 43. Observations on the Plant Life of a Swale Some small open area of wet ground, well grown up in wild meadow, undrained, and not pastured, should be selected for this study. An outline map should be provided, unless the form be simple. Digging tools will be needed, and also facilities for washing roots. The program of work may consist of: 1. A general survey of the swale as to: I. (a) The mixing of dry-ground and wet-ground forms at its margin. (b) The areas into which it is naturally marked out by the uniformity of the plant growth covering them ("plant associations”). (c) The relation between topography, soils and water and these plant associations. 2. An examination of the plants in several associations as to the relations they bear to one another both above and below ground. Some should be cut so that the leafage may be viewed from the side as well as from above; and some should be dug up, so that the depth and distribution of the roots may be noted. The record of this study may consist of: I. A map of the swale, with topographic features and the principal plant associations (including bordering shrubbery) marked out upon it. Explanations to the map should name at least the dominant species present in each association. 2. Diagrams, illustrating vertical sections of the swale herbage, showing the relations of the principal components of several associations, both above and below ground. These should show how the branches of each species are placed to reach the light, and how the roots are distributed in the soil. [NOTE: The above program is laid out in the belief that the study of the swale will be most instructive if we seek to learn how the various members of nature's dense wet-ground population get on together; but if an acquaintance with the entire plant population be desired, the record may take the form of an annotated and illustrated list of species.] |