ECOLOGY. 405 



the climatic control. In consequence, particular attention is being 

 paid to the physical factors and to competition in the respective eco- 

 tones. Instrument and phytometer stations have been established in 

 the chaparral at Colorado City, the mixed prairie at Colorado Springs, 

 and in the pine forest on the Platte-Arkansas Divide. These have been 

 equipped with instruments for measuring humidity, air and soil tem- 

 peratures, wind, light, water-content, and evaporation, while batteries 

 of sunflower phytometers are employed to determine differences in 

 transpiration and growth. Changes in each communit}^ have been 

 followed by means of permanent quadrats, while experimental quadrats 

 are used to show the process of ecesis in detail. 



Changes in Vegetation, by F. E. Clements and E. S. Clements. 



Further progress has been made in tracing the profound effect of 

 grazing on grassland and scrub and in reconstructing the grass com- 

 munities as they existed a century ago. In doing this considerable 

 evidence has been obtained of secular changes in grassland and scrub 

 since the Pleistocene, and these furnish many suggestions as to the 

 nature and extent of grassland during Tertiary times. 



While the almost complete destruction of the bunch-grass prairie of 

 the Pacific Coast has been caused by overgrazmg, aided by fire, the 

 final effect has differed in the two regions. In Oregon, Idaho, and 

 Utah, the sagebrush has entered as the grass has disappeared, while in 

 California the native perennial grasses have been replaced by exotic 

 annual ones. This difference is due partly to fire as factor, but chiefly 

 to the abundance of ruderal invaders available in California. This is 

 shown by the fact that Bro7nus is now spreading rapidly through Utah 

 and Idaho in consequence of the practice of burning the sagebrush to 

 increase the spring forage. Stipa comata has been recognized as an 

 important dominant, while Andropogon saccharoides forms a charac- 

 teristic consociation on the driest hills in southern California. In the 

 north, Stipa occideninlis seems to have been a dominant, often asso- 

 ciated with S. comata, while in the south S. coronata is still dominant 

 in considerable areas toward the desert edge, though it usually occurs 

 sparsely in chaparral. Stipa speciosa is likewise controlling in sandy 

 areas of Antelope Valley, and was doubtless once characteristic of such 

 soils over a much wider area. 



The mixed prairie is second only to the bunch-grass association in 

 the degree to which it has been changed by overgrazing. The effect 

 has been very different, however, because of the presence of the short- 

 grasses. These have taken possession as the tall-grasses w^ere de- 

 stroyed, and have given character to the so-called short-grass pkins. 

 These were so striking in appearance and extent as to make it inevitable 

 that they should be regarded as a distinct formation. However, a 

 comparative study of the two soon revealed the close relationship 



