of plant species to these factors in the initiation and length of 

 dormancy is hereditarily controlled. Prior to dormancy or full 

 rest formation in fall or early winter, an unusual cold wave can 

 result in freezing injury to native as well as exotic plants. In 

 late winter after dormancy has ended, an unusual warm spell 

 that stimulates growth activity, followed with a return to winter 

 cold, can result in freezing injury. Leaf and shoot kill of 

 evergreen plants during winter and spring is usually expressed 

 later during the summer as the foliage turns brown (for exam- 

 ple, Felt 1943). The other type of winter injury, desiccation, is 

 thought to result from lethal dehydration resuhing from contin- 

 ued transpiration with lack of sufficient water absorption from 

 the root system (Kramer 1969). With the absence of snow 

 cover, th^ soil and root systems may freeze; or with severe 

 cold, lower stems may freeze, preventing replacement of tran- 

 spirational water loss in upper plant parts (Olberg 1955; Sakai 

 1970). Rapid temperature fluctuations, drying winds, and bright 

 sunny winter or early spring days are believed to be related to 

 this type of winter injury (White and Weiser 1964; Watanabe 

 1969). 



METHODS 



Extensive kill of sagebrush was called to our attention by 

 Walt Mueggler and Ed Schlatterer of the USDA Forest Service, 

 and G. A. Schumaker, USDA Science and Education Adminis- 

 tration, Boise, Idaho. They observed areas of recently killed 

 plants in central and southern Idaho during summer 1977. We 

 visited these areas and others in Utah during September 1977 in 

 an attempt to determine the cause. The extensive nature and 

 pattern of damage, not only to sagebrush but also to other 

 shrub species, implicated winter injury as the probable cause. 

 In view of the extraordinarily low precipitation during winter 

 1976-77 throughout most of the West, it seemed worthwhile to 

 determine the extent of winter injury to sagebrush and other 

 shrub species throughout the West. To accomplish this, it 

 seemed expedient to make a survey of land management units 

 of the Forest Service, Bureau of Land Management, and State 

 Divisions of Wildlife Resources. Because our primary interest 

 was big sagebrush (Artemisia tridentata), we limited the survey 

 to the general distributional Limits of this species (Little 1976), 

 excluding Washington, Arizona, New Mexico, and southern 

 California (fig. 1). Information requested included (1) shrub 

 species affected, (2) location, (3) elevation, (4) intensity of in- 

 jury, and (5) symptoms observed. 



Figure 1.— Distribution of Artemisia triden- 

 tata in the western United States. Dotted line 

 encircles the general limits of t! te winter injury 



survey. 



2 



