THE OWNER BUILT HOME & HOMESTEAD
(Page 2 of 13)
September/October 1972
By Ken Kern
Plant ecologists present the clearest perception of optimum plant development in the presentation of the Climax Growth concept. We are told that there is a subtle response between plants and changes in the environment. Individual plants become more abundant or less abundant in a community, depending upon soil and climate factors. One species is gradually replaced by another higher and more adapted variety, until finally vegetation attains the climax form characteristic of the soil and climate. This is a good explanation of why a climax sod crop is the only important soil builder of any consequence. When a native sod us plowed and put into rowcrop production, a climax has been destroyed but the soil remains productive for many years. When this happens in a humid forest situation the soil becomes unproductive after a few short years, of cultivation; the wider spacing of trees offers little root development and soil-aggregation buildup.
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A sod growth, however, reaches climax as more and more topsoil is formed and accumulated. Each succession contributes to the next higher plant development. An example of California rangeland climax is illustrated below.
Climax succession is also apparent when overgrazed or cultivated land is abandoned and sod crops allowed to return: first, annual weeds (crab grass, pigweed, Russian thistle) appear; then so-called poverty grasses (wire grass, broom sedge) replace the native weeds; as the organic content of the soil increases, poverty grasses get so thick they cannot withstand their own competition. Thus, short-lived perennials like bunch grass appear and progress, finally, to semi-climax and climax grasses native to the region.
The importance that weeds play in this succession cannot be overstated. Weeds condition the soil; their vigorous root system opens up the soil, fiberizes it, and enlarges the feeding zone for the benefit of succeeding plants. Grass will return and thrive in a pasture situation only when weeds have first prepared the way; grass has the power to disperse the weeds once the environmental conditions are right.
The director of the Rocky Mountain Forest and Range Experiment Station, Dr. David Costello, studied the value of weeds on the western range. He found that weeds, surprisingly, made up the greater portion of cattle diet. Furthermore, perennial weeds and shrubs were found to have a higher crude protein content than native grasses. From Dr. Costello's research we deduce that low-protein grass pastures would best be grazed in summer when food values are highest. Superior pasture—containing abundant weeds and shrubs—should be grazed in late summer, fall and winter when the food value of grass is low. The nutrient value of standing grass herbage drops during fall and winter, because at that time nutrients drain back into the root zone, whereas the food value of browse plants remains high.
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