• Seed produced 



Treatment : 1974 : 1975 ; 1976" 



Range : N : X ± se^ : Range : N : X ± se^ : Range 



Open pollination 26 1,222+199* 11-3,000 16 1,845±345* 10-4,000 42 1,575±322* 0->5 000 



Intrapopulation 25 115+40 0-1,000 26 11±5 0-100 41 77±21 0-500 

 Interpojiulation 



°— I _ 25 78±24 0-300 14 16±7 ■ 0-94 39 31±10 0-250 



Interpopulation 



6 62±14 0-300 14 14±7 0-100 40 24±9 0-300 



Control 26 3:'±12 0-300 10 10±3 0-30 42 12±5 



0-200 



Taxa involved in hybridization experiments include A. arbuscula, A. bigelovii, A. aana, ssp. visoidula, 

 A. nova, A. pygmaea, A. tridentata ssp. tridentata, A. t. ssp. vaseyana, A. t. ssp. wyomingensis, and 

 A. trzpartita_s sp. tripartita. 



^The * in the X (mean) ± se (standard error of the mean) column indicates a significant difference in the 

 open pollination treatment from all other treatments. None of the other treatments were significantly 

 different, according to the multiple range test (p<.05). 



ssp. tripartita^ and A. cana ssp. viscidula; A. tridentata ssp. tridentata with A. tri- 

 partita ssp. tripartita and A. tridentata ssp. wyomingensis. Beetle (1960) reported 

 finding intermediates between the following: A. tridentata ssp. tridentata with A. tri- 

 dentata ssp. vaseyana, and cana ssp. cana with A. nova. 



Ward (1953) examined two mixed populations of A. tridentata and A. cana. In one 

 population the A. tridentata was diploid and the A. cana was tetraploid. In the other 

 population, A. tridentata was tetraploid while the A. cana was diploid. The putative 

 hybrids from both populations were tetraploid and blended in with the tetraploid parent. 



Because of its plasticity and the apparent ease with which it hybridizes, there 

 are great opportunities for developing improved forms of big sagebrush for different 

 purposes. Controlling the hybridization, however, may prove very difficult. 



Distribution and habitat . --Big sagebrush is the most widespread and common shrub 

 of western North America. It is especially common in the Great Basin. This species 

 covers approximately 58,655,000 hectares (226,374 square miles) in the 11 western States 

 (Beetle 1960). It grows in a variety of soils on arid plains, valleys, and foothills 

 to mountain slopes from 500 to 3,400 meters (1,600 to 11,200 feet) and is frequently 

 associated with such shrubs as shadscale saltbush, rubber rabbitbrush, low rabbitbrush, 

 fourwing saltbush, spiny hopsage {Grayia spinosa) , spiny horsebrush {Tetradymia spina sa) , 

 winterfat, and broom snakeweed. 



Although it is tolerant of quite alkaline as well as quite acid soils, its optimum 

 growth is in deep, fertile, alluvial loams (Sampson and Jesperson 1963). 



Although big sagebrush has spread with settlement of the West (Cottam 1961; Chris- 

 tensen and Johnson 1964; Hull and Hull 1974), nevertheless, it was clearly an important 

 and widespread plant before this settlement. As early as the Pleistocene Epoch, sage- 

 brush was already an important part of the Intermountain Flora. Eight to ten thousand 

 years ago, sagebrush dominated large tracts of land in areas where it is still found 

 (Tidwell and others 1972; Van Devender 1977). Vale (1975), quoting from early pioneer 

 and explorer diaries, has shown it was a common western plant prior to 1850. 



Big sagebrush and its section Tridentatae relatives (table 1) are subject to insect 

 and microbial pests and benefactors--most notably, the sagebrush defoliator moth {Aroga 

 websteri) . Wide ranging and periodic outbreaks of this insect have caused extensive 

 sagebrush mortality over much of the range of A. tridentata and its relatives (Henry 

 1961; Hall 1965; and personal observations of the authors). Flowever, exce]it on some 



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