34 CONCEPT AND HISTORY. 



Basing studies. Initial studies of grassland were made in Nebraska from 

 1893 to 1898. These included a journey along the Missouri and Niobrara 

 Rivers during the summer of 1893, one to the plains and foothills in 1897, and 

 to the Black Hills in 1898. The first ecological expedition to Colorado was 

 made in 1896, at which time a provisional outline of the plant communities 

 was drawn up. Beginning with 1899, all the summers were devoted to inves- 

 tigations in Colorado until 1913, with the exception of that of 1911, which was 

 spent abroad. During the spring and fall from 1899 to 1907, studies in prairies 

 and woodland in eastern Nebraska were carried on with the aid of advanced 

 classes. The six summers from 1913 to 1918, inclusive, have been devoted to 

 vegetation studies throughout the West, with especial emphasis upon succes- 

 sion, indicator plants, and climatic cycles. From 1912 to 1917, the work of the 

 Botanical Survey of Minnesota was directed along similar lines. 



The use of quadrats was begun in 1897 and the instrumental analysis of 

 habitats in 1898. The principles of succession were formulated into a working 

 system for the field in 1898 (Clements, 1904: 5), while studies of the echard 

 and chresard were first made in 1900. The fundamental importance of the 

 distinction between climax and serai communities was recognized in 1913, 

 and the significance of climatic cycles in 1914. The two most recent advances 

 which extend the use of indicators are the organization of the field of paleo- 

 ecology in connection with the study of Badlands in 1915-16 and the formu- 

 lation in 1916 of the concept of the biome as the basic biotic unit. 



Shantz (1906) began the ecological study of Colorado vegetation in 1903 on 

 the basis of instrumental, quadrat, and successional methods. This led to 

 the direct study of indicator plants on the Great Plains (1911) and in the 

 Great Basin (1914). Out of this grew the extensive series of water require- 

 ment studies, as well as of transpiration, made by Briggs and Shantz between 

 1912 and 1916. During the same period much attention was paid to western 

 vegetation, and this was crystallized in the list of indicator types for land- 

 classification (Shantz and Aldous, 1917) and a map of the climax communities 

 of the United States (Zon and Shantz, 1919). The text accompanying the 

 map contains much information relating to the indicator value of the different 

 vegetation types. 



