84 CARNEGIE INSTITUTION OF AVASHINGTON. 



A Successional Study of the Transitions between Climaxes, by F. E. Clements. 



The use of developmental methods in the analysis of the cUmax 

 formations of western North America has been continued during 

 the summer of 1915. For a number of reasons, especial attention has 

 been given to the transition zones between climaxes, particularly 

 grassland and scrub, which cover the largest areas and show the great- 

 est complexity. It has been found possible to standardize the results 

 of such study for purposes of comparison by dealing directly and chiefly 

 with the dominants and subdominants, i. e., consociations and societies, 

 of the contiguous cUmaxes. The first transition studied was that from 

 the subchmax and climax prairies of eastern Nebraska and South 

 Dakota to the short-grass plains of western Nebraska and eastern 

 Wyoming. The alternation of dominants was first traced through 

 northern Nebraska and parts of South Dakota to the plains, and then 

 eastward through the sandhills of eastern Nebraska to the prairies 

 again. The second region traversed was from northeastern Kansas to 

 western Oklahoma, southward through the Panhandle of Texas to the 

 Pecos River, and northward through eastern New Mexico to the Great 

 Plains. The change from the Bouteloua-Bulbilis grassland to the 

 Prosopis-Aristida savannah was first traced southward through Texas, 

 and then checked in the reverse direction through New Mexico. A 

 similar study was made of the transition between the desert scrub of the 

 Southwest and the sagebrush formation of the Great Basin. This was 

 first traversed from south to north from southeastern California to 

 Nevada and Utah, then southward through eastern Utah and north- 

 ward tlirough western Colorado. Consequently, the successional rela- 

 tions of the climax dominants were noted scores of times, within as well 

 as between successive chmaxes. This not only afforded a constantly 

 recurring check on the developmental historj^ and the regional limits 

 of the different climaxes, but also furnished decisive evidence of 

 their climatic relations, especially with reference to the effect of future 

 cycles. In this connection, much attention was paid to the competition 

 responses in the ecotone between two or more dominants, and sugges- 

 tive results were obtained in the attempt to use these responses as an 

 index of present as well as of future chmatic tendencies. Finally, an 

 endeavor was made to test more rigorously the assumption that the 

 habitat, like the formation, has a developmental history which ends 

 in a permanent or mature condition determined by the climate. 



The Vegetation of a Desert Mountain Range as Conditioned by Climatic Factors, 



by Forrest Shreve. 



The work on the vegetation and physical factors of the Santa Cata- 

 Una Mountains, which has been in progress for five years (see previous 

 annual reports), has been elaborated up to the close of 1914 and pub- 

 lished. The principal aim of this work has been to correlate the cli- 



