Velvet Mesquite Seedling Development in Three Southwestern Soils

Abstract

Knowledge of the effects of saturated soils and flooding on Wyoming big sagebrush (Artemisia tridentata wyomingensis), green rabbitbrush (Chrysothamnus viscidiflorus), and black greasewood (Sarcobatus vermiculatus) can enhance our understanding of their distribution. The responses of these 3 species to elevated water tables were studied on 4 contours bordering an expanding lake in southeast Oregon during the 1983 and 1984 growing seasons. When plants were initially selected for study, contours were 0, 10, 20, and 40 cm above the lake surface. Continued expansion of the lake flooded the lower contours and elevated the water tables under the upper contours. Wyoming big sagebrush rapidly succumbed to surface flooding and elevated water tables within 10 cm of the surface. Green rabbitbrush behaved similarly, but responses lagged about 1 week behind sagebrush. Black greasewood tolerated surface flooding for 40 days before effects were apparent. Water tables within 25 to 30 cm of the surface had no effect on greasewood. Given adequate topography and water supplies, water spreading techniques could be used to control Wyoming big sagebrush and green rabbitbrush. Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis Beetle and Young) and black greasewood (Sarcobatus vermiculatus (Hook.) Torr.) are dominant or codomninant shrubs on large expanses of western rangelands (Tisdale and Hironaka 1981, Franklin and Dyrness 1973, Romo 1985). Green rabbitbrush (Chrysothamnus viscidiflorus (Hook.) Nutt.), typically a minor shrub component in climax communities, may also dominate areas where fire, overgrazing, or other disturbances have reduced the competitive ability of the accompanying vegetation (Young and Evans 1974). These 3 species, either singularly or collectively, shape the character and competitively control large areas within the Great Basin. Due to the importance of these shrubs in the region, land manAuthor is range scientist, United States Department of Agriculture-Agricultural Research Service, Eastern Oregon Agricultural Research Center, Squaw Butte Station, Burns, Oregon 97720. This article is Technical Paper No. 7592. Oregon Agricultural Experiment Station. Manuscript accepted 21 October 1985. agers must consider the biotic and abiotic factors affecting their establishment, health, or distribution. Water relations play a particularly prominent role in influencing the distribution of plants in this arid region, and abundances of water are typically not a concern. Several workers have noted, however, that excessive soil moisture is detrimental to big sagebrush (Artemisia tridentata) (U.S. Dept. Agr., Forest Serv. 1937, Branson 1956, Vallentine 1971) and speculated that anaerobic conditions in some soils prevent successful colonization of big sagebrush (Fosberg and Hironaka 1964). Lunt et al. (1973) found root growth of big sagebrush hindered by oxygen concentrations of 5% or less and observed low rates of recovery of big sagebrush after weakened plants were returned to ambient oxygen concentrations. These same workers speculated big sagebrush was excluded from fine textured and poorly drained soils by its high oxygen requirements. Greasewood has been classified as a phreatophyte (Robinson 1958), and Romo (1985) found water tables ranging from 3.5 to 15 m below greasewood dominated communities in Oregon. No information was found, however, regarding tolerances of greasewood or green rabbitbrush to saturated soils or low oxygen concentrations in the rooting zone. Given this lack of information, the objective of this study was to evaluate the relative tolerances of Wyoming big sagebrush, greasewood, and green rabbitbrush to elevated water tables and surface flooding. Study Area and Methods Studies were conducted on 6 locations bordering Malheur Lake in Harney County, Oregon. Elevations were approximately 1,245 meters. Harney Basin is internally drained and annually receives between 20 and 30 cm of precipitation. The historic meander of Malheur Lake encompasses approximately 25,000 ha; however, above-normal precipitation between 1978 and 1984 expanded the lake to 68,000 ha, inundating large areas of shrub-steppe vegetation in the process. Three study sites, approximately 2 km apart, were evaluated during the 1983 growing season. Rapid expansion of the lake in 1984 blocked access to the original study areas and 3 334 JOURNAL OF RANGE MANAGEMENT 39(4), July 1986 This content downloaded from 40.77.167.124 on Mon, 17 Jul 2017 15:35:13 UTC All use subject to http://about.jstor.org/terms