ECOLOGY. 



Clements, F. E., Tucson, Arizona. Associate in Ecology. (For previous 

 reports see Year Books Nos. 16-21.) 



The experimental work of the summer has again been carried on, largely at 

 the Alpine Laboratory, from June 1 to October 1, and further investigations 

 of the volume and composition of soil-air have been made during the autumn 

 and winter. The studies at Tucson have been continued at both the Desert 

 Laboratory and the Santa Rita Range Reserve, the chief attention being paid 

 to the water cycle, the quadrat method, and the climatic control of growth and 

 regeneration in grassland. Experimental and statistical studies of the 

 Madiese and Haplopappus have been prosecuted at the University of Cali- 

 fornia, together with an ecological inquiry into the development and modifi- 

 cation of laticiferous tissues. The two major transects for experimental 

 evolution, the Sierran and the Petran, have been extended and the transplant 

 areas and gardens considerably augmented. Root studies have been further 

 developed at the University of Nebraska, as well as studies in root behavior 

 under irrigation at Greeley, Colorado. The field stations from eastern 

 Nebraska through Kansas into Colorado have been kept up, and a special 

 series of installations have been made in order to determine the transpiration of 

 different types of vegetation and its possible relation to rainfall. 



In addition to numerous short trips throughout southern Arizona during 

 the winter, which were devoted primarily to the origin and development of the 

 desert-plains grassland, a large portion of the West was again covered by 

 motor. The first journey traversed the Colorado and Mohave Deserts in 

 early spring, and several days were devoted to making a complete circuit of 

 Death Valley, the major objectives being the reconstruction of the original 

 grasslands of these deserts and the climatic significance of the bad lands and 

 their sediments. During the spring and early summer frequent trips were made 

 along the coast and the mountain ranges of southern and central California, 

 followed by an expedition through the redwood belt and the Coastal forest of 

 northern California, Oregon, and Washington. At Mount Rainier especial 

 attention was given to the alpine vegetation, to snow parks near timber-line, 

 and to natural parks in the three forest climaxes. A careful scrutiny was made 

 of the ecotones between the Coastal forest, sagebrush savannah. Transition 

 forest, and bunch-grass association on the journey through eastern Washington 

 and Oregon, Idaho, Utah, and Wyoming. The origin and relationships of the 

 three eastern grassland associations, mixed, true, and subclimax prairie, were 

 further studied from eastern Colorado through Nebraska to eastern Kansas. 

 Finally, the contact between grassland and forest or scrub was again traced 

 from Kansas through Oklahoma to the coastal prairie of Texas and thence 

 westward through New Mexico and Arizona to Tucson. 



Factor stations, with the full equipment of physical instruments and often 

 with phytometers as well, have been maintained at the Alpine Laboratory, at 

 Greeley, on the Santa Rita Range Reserve near Tucson, and through the 

 series of grassland stations. At the first, these have been employed in the 

 further analysis of phytometers as habitat measures, while in the last a single 

 battery was utilized successively at the three stations in the endeavor to 

 compensate in some measure for differences in altitude and the corresponding 

 lag in the season. 



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