GRAZING TYPES. 281 



sandhill areas occur in Nebraska, Kansas, and Colorado, though they are 

 scattered throughout the grassland cUmax from North Dakota to Texas and 

 New Mexico. Such areas differ from dunes chiefly in extent and complexity, 

 and in the fact that they are no longer connected with an active shore-line 

 from which the sand is derived. They are essentially stable dunes with blow- 

 outs as characteristic features, and for the most part they exhibit subcHmax 

 communities. The succession in sandhills and dunes is practically identical 

 for the same cUmax, but differs greatly between climaxes, especially in the 

 later stages. The largest and most important sandhill region is that of cen- 

 tral Nebraska, which covers an area of about 20,000 square miles. It has 

 received much study during the past 30 years, and the ecological results have 

 been summarized by Pool (1914) in a monograph on their vegetation. The 

 typical conmiunity of the sandhills is the bunch-grass subcUmax, consisting 

 of Andropogon hallii and A. scopariiis. The blow-sand condition, typical of 

 blowouts especially, is indicated by Redfieldia, Psoralea, and Petalostemon, 

 which have little or no grazing value. More stable conditions are denoted by 

 Muhlenbergia and Calamovilfa, and these are correlated with increasing graz- 

 ing value. The next stage is that of the Andropogon subclimax, which pos- 

 sesses a much higher value. By the entrance of Stipa and Koeleria, the bunch- 

 grass subchmax passes into the true prairie, while in the western portion the 

 invasion of Bouteloua and Bulbilis indicates the appearance of the short-grass 

 climax, or of mixed prairie when Stipa and Agropyrum occur also. The hydro- 

 sere is a regular feature of the innumerable wet valleys and of the extensive 

 lake region. The first community to indicate grazing is composed of rushes 

 and sedges, and this changes slowly into the typical meadow associes of 

 Agropyrum, Andropogon, Elymus, Panicum, and Spartina, which is essentially 

 an extra-regional portion of the subclimax prairie. The grazing value of 

 such a group of dominants is obvious, but in practice such meadows are used 

 for hay, since the hills furnish ample summer grazing (plate 67). 



Like the sandhills, bad lands are found throughout the West. Massive 

 bad-land complexes are most typical of the States which touch the Black 

 Hills, but they are frequent also in practically all those along the Rocky 

 Mountain axis, while outlying areas of much interest are found in Texas, 

 Oregon, and California. The actual communities of the sere likewise differ 

 with the climax. The two most important seres are the xerosere of the 

 Tertiary bad lands in the Great Plains region of the grassland climax, and the 

 halosere of the Great Basin sagebrush climax. The former possesses a num- 

 ber of herbaceous stages which have an increasing value for sheep-grazing as 

 they become denser, but grazing proper is indicated only when Agropyrum 

 becomes abundant. Bouteloua and sometimes Bulbilis also enter somewhat 

 later to form mixed prairie, and the latter then becomes definitely constituted 

 by the appearance of Stipa. The lower valleys are often controlled for a time 

 by sagebrush, but this ultimately yields to the grasses. The juxtaposition of 

 weed, grass, and sagebrush types indicates the value of bad land areas for 

 mixed grazing, and suggests the importance of hastening the course of suc- 

 cession in them. The bad lands of the sagebrush climax are characterized in 

 the intial stages by colonies of halophytic annuals, which have some grazing 

 value where they make a definite cover. The first stage of much importance 

 is formed by the low perennial species of Atriplex, such as A. nuUaUii, A. 



