Winter Injury of Sagebrush and 

 Other Wildland Shrubs in the 

 Western United States 



David L. Nelson and 

 Charles F. Tiernan 



INTRODUCTION 



Wildland shrubs are increasingly important on western 

 rangelands (McKeU and others 1972; McKeU 1975a, 1975b; 

 McArthur and others 1974) in the restoration of disturbed areas 

 (McArthur and others 1974; Monsen 1975) and for use on big- 

 game ranges (Plummer and others 1%8). Sagebrush, Artemisia 

 spp., alone occurs on more than one-third of the 820 million 

 acres (332 million ha) of western shrublands (Beetle 1960; 

 Plummer 1974). Its importance stems, if not from its ubiquity, 

 from its aggressiveness and tremendous diversity and adaptabil- 

 ity (Beetle 1960; McArthur and Plummer 1978). 



Weather extremes are a recognized important environmental 

 element in the survival and natural selection of plants. The low 

 precipitation period during the winter of 1976-77 may have 

 been an example of such an extreme. Precipitation during this 

 period was near the lowest in recorded history over most of the 

 West. Following that winter, extensive areas of sagebrush kill 

 were observed in Idaho, Nevada, Utah, western Wyoming, and 

 western Colorado. Severe damage to other shrub species was 

 also observed. Winter injury appeared to be the primary cause. 

 Some plant species appear to have been killed or damaged by 

 drought alone. 



The objective of this paper is to briefly review winter injury 

 of plants and shrubs in particular, document the observed 

 winter injury of 1976-77, and correlate the occurrence with 

 weather records. 



REVIEW 



Winter injury of conifers, hardwood trees, and ornamental 

 shrubs is well documented (for example, Hubert 1918; Hilbom 

 1937; Nash 1943; Hunter-Blair 1946; Spaulding 1946; Wiscon- 

 sin Department of Agriculture 1948; Curry and Church 1952; 

 Duffield 1956; Daubenmire 1957; Day and Peace 1946; Powell 

 1972). However, reference to winter injury of endemic wildland 

 shrubs is relatively rare. Cottam (1937) reported extensive 

 damage to Covillea tridentata (Larrea divaricata Cav. , creosote 

 bush), Strombocarpa ordata (Prosopis pubescens Benth., mes- 

 quite), and Prosopis glandulosa (Prosopis juliflora [SW.] DC) 

 following a cold period in southwestern Utah. In this instance 

 the damage was probably caused by freezing of plant tissue, 

 and m.ost of the plants apparently recovered (Frosberg 1938). 

 Frost injury of bitterbrush (Purshia tridentata) occurred over a 

 large area of eastern California when several unusually cold, 

 below freezing days followed an unusual warm spell in early 



April that stimulated bud growth (Smith and others 1%5). Ex- 

 posed bitterbrush foliage was damaged in northern Utah ap- 

 parently from extreme temperatures of -35°F (-37°C) and 

 -37°F (-38°C) in early December and January following 

 relatively warm periods (Jensen and Umess 1979). Fourwing 

 saltbush (Atriplex canescens) received winter injury in two off- 

 site performance plantings in central Utah (Van Epps 1975). 

 The injury in this case was attributed primarily to unusually 

 low temperatures; hardiness varied with the point of origin of 

 the 20 accessions. Schumaker and others (1979) and Hanson 

 and others (1982) reported the loss of Artemisia tridentata ssp. 

 vaseyana (mountain big sagebrush) in an area of southwestern 

 Idaho that occurred during winter 1976-77. Areas of most in- 

 tense kill were those normally covered by 3.3 ft (1 m) or more 

 of snow. They hypothesized that sagebrush plants remained ac- 

 tive during most of the winter and became desiccated due to 

 lack of normal soil moisture. A 50 percent loss of shrub cover 

 and increase in grass and forbs followed the sagebrush kill. 

 Buckbrush (Ceanothus sp.) (Stickney 1%5) and manzanita 

 {Arctostaphylos spp.) commonly incur winter injury throughout 

 the West during winters of incomplete snow cover. Perhaps due 

 to the commonness of this injury and usual recovery little at- 

 tention is given. Tarry and Shaw (1966) associated Armillaria 

 mellea, a root pathogen, with a dieback disease of Ceanothus 

 spp. following winter injury in the Pacific Northwest. 



Winter injury has a rather broad meaning, and the mech- 

 anism is not completely understood (Slatyer 1976). Plants pre- 

 sumably suffer winter injury by freezing due to a lack of suffi- 

 cient innate cold hardiness or absence of winter dormancy in 

 cold-hardy plants, and due to winter drought or desiccation 

 (Michael 1%3, 1%7; TranquilUni 1964; Kramer 1%9; Mazur 

 1%9; Sakai 1970; Alden and Hermann 1971). Winter injury to 

 nortindigenous or exotic plants adapted to warmer regions can 

 usually be attributed to direct freezing. Plants in their native 

 habitat or exotics may suffer damage from absence of winter 

 dormancy or from desiccation, and the critical periods are 

 usually in early and late winter (Day and Peace 1946; Peace 

 1%2; Parker 1%3). 



Dormancy is an adaptive phenomenon in plants that enables 

 them to resist and survive moisture and temperature extremes 

 of the external environment where they are indigenous. Exter- 

 nal environmental factors that initiate dormancy by influencing 

 growth are usually a combination of temperature, moisture, 

 nutrition, light quality, photoperiod, and temperature during 

 light and dark periods (Vegis 1964). The characteristic response 



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