THE GREAT AMERICAN DESERT 



215 



A continuous association composed of hunch-grasses is the typical 

 vegetation of the whole Sand Hill region. This covers the hills and 

 ridges over thousands of square miles, being absent only from the 

 " blow-outs " and the moister valleys. Once established in the sandy 

 soil the bunch-grasses cope very successfully with the fury of the wind 

 and the shifting sand. However, if fire or over-grazing seriously 

 reduces the bunches in size and vitality, subsequent winds may uproot 

 and carry them away. But on the whole the bunch-grasses are very 

 effective sand binders, and it would be a great calamity indeed if they 



Fig. 2. A frequent Sight : Over-geazixg often Results in Bare Hills 



AND Blowing Sand. 



were to be removed and nothing substituted. It is due to them more 

 than to any other single type of plants that the vegetation of the hills 

 is enabled to persist. Within the shelter of the bunch-grass association 

 scores of valuable species thrive that in its absence would never have 

 found access to the region. 



The bunch-grass par excellence is the little blue stem {Andropogon 

 scoparkis), but associated with it are others, such as sand grass 

 {Calamovilfa longifolia), and needle grass (Stipa comata). Andro- 

 pogon scoparius is the dominant species throvighout the region, the other 

 species being present only occasionally. It is the little blue stem that 

 gives the first greenish hue to the sand hill landscape in the spring, and 

 it is the same species that clothes the hills with the rich reddish-purple 

 in the autumn and through the winter. Hall's blue stem (Andropogon 

 hallii), common on the upper slopes of the hills and the tops of ridges, 

 is usually of secondary importance. Its few tall whitish or bluish stems 



