105 



STABILIZATION OF THE BLOWOUTS AND THEIR 

 REVERSION TO BUNCH-GRASS 



Stabilization of the blowouts may take place in any or all of the 

 four parts. Usually it begins on the windward slope and takes place 

 last on the deposits. The windward slope is already occupied by 

 bunch-grasses, although at a considerable distance apart. When the 

 movement of sand ceases, other species invade the area at once and 

 appear in large numbers between the bunches. Aristida tuberculosa 

 and other members of the blowsand association are prominent but 

 do not become dominant. Following them come Oenothera rhombi- 

 petala and Lespedeza capitata, making a thick weedy growth, and 

 later various species of bunch-grass. 



In the basin and on the lee slope stabilization begins with the 

 extraordinaiy development of the blowsand association. It is fol- 

 lowed immediatel}' by large bunches of Sporobolus cryptandrus and 

 by a rank growth of Oenothera rhoinbipetala and Lespedeza capitata 

 (PI. XI, Pig. 2). Sporobulus cryptandrus sometimes lives in actively 

 blowing sand, but only in small depressed bunches (Hart and Glea- 

 son, igoy: pi. XVIII, fig. 2). In partly stabilized blowouts it forms 

 dense bunches one to two feet (3-6 dm.) wide and 1-1.5 ft. (3-5 dm.) 

 high, surmounted by culms two or three feet (6-9 dm.) tall. Be- 

 neath the shelter of these three plants a number of interstitial 

 species colonize, many of which are not common in the blowsand 

 association. Some of these are Hedeonia hispida, Polygonum temie, 

 Scutellaria parvula, Silene antirrhina, and Festuca octoflora. This 

 weedy growth lasts a comparatively short time. One blowout was 

 observed where only about half as many plants of Lespedeza were 

 growing as had grown the previous year, as shown by the dead 

 stems. Since stabilization usually begins near the bottom of the 

 bloA\outs, some may be found in which Lespedeza and Oenothera- 

 have already left the deepest part and occupy a ring around the sides. 

 This also shows that the bunch-g'rasses which follow are not plants 

 which slide in from the sides, as was intimated in an earlier paper 

 (Hart and Gleason i^oy: 169). In this tangle the bunch-grasses 

 gradually appear (PI. X, Fig. 2), and by their growth restrict the 

 interstitials, as was explained in connection with the bunch-grass 

 association. Mats of Antennaria, Cladonia, and moss also appear 

 very early. The perennials follow the bunch-grasses. The order of 

 their apj^earance is not definite, but depends upon the composition of 

 the neighboring bunch-grass association. Stabilization of the basin 

 and windward slopes may take place at the same time, or there may be 



