Page:Popular Science Monthly Volume 80.djvu/227

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THE GREAT AMERICAN DESERT

be reduced two inches or more, but seldom are the plants uprooted. It is to the rhizome habit of propagation that Redfieldia owes its success in thus so completely capturing the blow-out. The later invaders are also provided with this device, which certainly is the key to the whole situation.

After Redfieldia has once taken charge of the habitat other species soon begin to wander over the rim of the blow-out and to invade the area occupied by the first blow-out pioneer. Among the first of these early invaders we must number the spiny blow-out grass (Muhlenlergia pungens), sand grass (Calamovilfa longifolia), and the hair-like eragrostis (EragrosUs trichodes). From the appearance of these grasses the decline of the blow-out is rather rapid. As these various species wander up the steep sides, and the force of the wind striking upon the upper slopes is reduced and the sand held from blowing, other species wander in from the bunch-grass association. If these new plants are properly provided with a rhizome device like that of their predecessors they soon begin to weave themselves into the now conspicuous blow-out association. The plants that most commonly gain entrance soon after the grasses have become well established are prairie pink (Lygodesmia juncea), small-flowered psoralea (Psoralea micrantha), long-leaved milk vetch (Phaca longifolia), and the hairy golden aster (Chrysopsis villosa). Indeed, some of these species may get a start in the declining blow-out almost as soon as Redfieldia.

In this manner the effect of blow-out conditions are finally so far removed that the bunch-grasses enter and take possession of the area so well prepared by the pioneers in the succession. It is almost pathetic to find that Redfieldia, the first plant to appear in the blow-out

PSM V80 D227 Square meter quadrat showing conspicuous vegetation growth.png

Fig. 10. A Square Meter Quadrat in the Blow-out shown in Fig. 9. The bunch grass is now conspicuous with a few tufts of Redfieldia at the right.