Phenology of the Aerial Portions of Shadscale and Winterfat in Curlew Valley, Utah

Abstract

Highlight: Phenological development of aboveground portions of shadscale and winterfat was observed for 7 years in Curlew Valley, Utah, and graphically related to patterns of precipitation and temperature. The considerable variation in year-to-year phenology should be noted by those taking data in other basic and applied studies. Preset dates for livestock management actions that ignore yearly phenological differences could result, in some years, in the plants being used during phenological states that are susceptible to damage by browsing. Seed set cannot be counted on every year, complicating one of the assumptions of rest-rotation grazing. Explanations of various rangeland plant phenomena often require an understanding of the phenological course of development of the organisms under study. For example, transpiration rates of desert plants are only partially explained by soil moisture depletion. Loss of ephemeral leaves sharply cuts transpiration losses by cold-winter desert shrubs during summer drought (Moore et al. 1972). Productivities are often inferred from what are thought to be peak standing crops (Holmgren and Brewster 1972). However, if the periods of growth were better defined, one could more accurately gauge when peak standing crop occurs. Nutritive values also vary with phenological stages. Sampling of materials on a preset date for several years may result in collection of materials in radically different phenological stages. Management plans are dependent on plant development. Desert ranges are best suited for livestock utilization during the dormant periods. Although desert plants commonly provide more palatable and nutritious forage during their periods of growth, the plants can withstand much less grazing pressure and have high mortality rates if grazed at that time (Cook 1971). If phenological patterns and their likely variations due to climatic differences were more completely known, we could better adjust livestock use to avoid excessive damage by grazing. Although some data are available on the phenology of the aboveground growth of cold winter desert and semidesert species, particularly sagebrushes, (Morton and Hull 1975) only Authors are professor and former Rockefeller Foundation graduate fellow, respectively,

Ecotypic Variation in Selected Fourwing Saltbush Populations in Western Texas

“…Wats.] (West and Gasto 1978). Each plant was given a numerical rating corresponding to its growth stage.…”

Plant Phenology and Water Relations in a Saline Pan-Dune Mosaic in the Western Mojave Desert

“…Our studies broadly parallel earlier research on the ecophysiology of saltbush scrub communities carried out at Curlew Valley, Utah, in the early 1970s as part of the Desert Biome program of the National Science Foundation. These included measurements of seasonal patterns of net assimilation, water relations and phenology of Atriplex confertifolia and Krascheninnikovia lanata (Moore et al 1972;Fernandez and Caldwell 1975;Caldwell et al 1977;West and Gasto 1978;Holthausen and Caldwell 1980;Caldwell 1985). These studies clearly established the adaptive significance of C 4 metabolism in Atriplex species in allowing these shrubs to maintain a high level of water use efficiency and maintain active growth into early summer well past the time when most C 3 shrubs have become dormant.…”

“…and saltbush (Atriplex spp.) scrub are widespread across the Great Basin in areas of endorheic drainage associated with dry playa lakes and topographic sinks (Billings 1949;West 1983;Caldwell 1985). Extensive studies of these plant communities in these cold desert ecosystems have been carried out in northern Utah, with a focus on plant growth dynamics and ecophysiology (Caldwell 1985;Smith and Nowak 1990).…”

Reference Unit-Based Estimates of Winterfat Browse Weights

“…This was done so as to minimize the possibility that there was any growth of plants during the intervening period. y=u+bx All field sampling was done during the month of August 1982, after all aboveground growth for the season had occurred and the majority of the ephemeral leaves had been lost (West and Gasto 1978). There is thus little possibility of growth having occurred within the sampling period.…”

“…Bjerregaard et al (1984) give details of the soils here. Details of the climate of this study area can be found in Caldwell et al (1977) and West and Gasto (1978). The mean annual temperature is 7.1°C; yet during summer months, average daily temperatures are high (up to 32°C).…”