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Characterizing circadian activity patterns is one of the essential steps to understanding how a species interacts with its environment. This study documented activity patterns of pygmy rabbits (Brachylagus idahoensis) in free-ranging populations at 5 sites in Nevada and California. Infrared-triggered camera systems were placed within areas occupied by populations of pygmy rabbits and operated for 1 year. The number of photographs obtained per hour was used as an index of aboveground activity. Activity was analyzed for diel and seasonal patterns as well as for differences among populations. All populations showed a bimodal diel activity pattern with most activity occurring at dawn and at dusk during all seasons....
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Predawn plant water potential (Ψw) is used to estimate soil moisture available to plants because plants are expected to equilibrate with the root-zone Ψw. Although this equilibrium assumption provides the basis for interpreting many physiological and ecological parameters, much work suggests predawn plant Ψw is often more negative than root-zone soil Ψw. For many halophytes even when soils are well-watered and night-time shoot and root water loss eliminated, predawn disequilibrium (PDD) between leaf and soil Ψw can exceed 0.5 MPa. A model halophyte, Sarcobatus vermiculatus, was used to test the predictions that low predawn solute potential (Ψs) in the leaf apoplast is a major mechanism driving PDD and that...
Widespread degradation of the sagebrush ecosystem in the western United States, including the invasion of cheatgrass, has prompted resource managers to consider a variety of approaches to restore and conserve habitats for sagebrush-associated species. One such approach involves the use of greater sage-grouse, a species of prominent conservation interest, as an umbrella species. This shortcut approach assumes that managing habitats to conserve sage-grouse will simultaneously benefit other species of conservation concern. The efficacy of using sage-grouse as an umbrella species for conservation management, however, has not been fully evaluated. We tested that concept by comparing: (1) commonality in land-cover associations,...
The ability to exploit short-duration nutrient pulses may be an important factor in the competitive balance of plants and in shaping plant community structure. We investigated the growth responses and biomass production of six Great Basin plant species growing in monocultures in the field following a single pulse of nitrogen applied in early, mid, or late spring. As a control, we applied the same total quantity of N that was in each of the individual pulses as a continuous series of applications at twice-weekly intervals over 10 wk in the spring. Surprisingly, most of the species grown under the control, continuous N supply had lower growth rates, fewer tillers, and less biomass production than plants receiving...
Despite fire cycles of increasing severity and frequency in the arid western U.S., very little empirical analysis has examined the success of plant seeding on arid rangeland following fire. This manuscript uses a unique dataset to assess causal factors underlying the measured densities, several years after fires, of: (1) unwanted invasive grasses, (2) seeded grasses, and (3) sagebrush, on rangeland in a western U.S. state. To accommodate various characteristics of the data, we employ trivariate tobit maximum likelihood estimation. Results indicate that the success of reseeding efforts is sensitive to the timing of and techniques used in reseeding, as well as whether grazing is allowed on the land. Our findings have...
We show how land use and potential climate changes occurring in sagebrush communities in the Great Basin of North America are affecting the pygmy rabbit, a sagebrush obligate species. We revisited 105 sites where pygmy rabbits were collected before 1950 and determined the current presence of the species using infrared-triggered camera surveys. Pygmy rabbits were present at 36% of the sites. Fourteen percent of the sites showed signs of pinyon?juniper woodland encroachment, with only one of these sites still harboring pygmy rabbits. Sites also showed current evidence of fires (16%), urbanization (13%), and agricultural conversion (6%). At a local scale, fire frequency reduction due to livestock grazing and fire suppression...
Plants of four Great Basin grass species were grown from seed in two greenhouses at low (340 ? l l-1) and high (680 ? l l-1) CO2 concentration. In all four species, high CO2 promoted mean increases in the number of basal stems, leaf area, specific leaf weight and above-ground dry weight. High CO2 resulted in an increase in CO2 assimilation in two C3 grasses but not in a C4 grass, while all three species showed decreases in stomatal conductance. Mean increases of 60% in aboveground dry weight and 80% in water-use-efficiency are consistent with previously reported high CO2 effects on grasses. No consistent differential effects of high CO2 were observed when comparing annual vs perennial species. Global CO2 enrichment...
Although dew is an unimportant source of moisture in humid areas, plants and arthropods living in some arid regions depend on it for survival. Further, this moisture is occasionally available during the dry summer months when plants are experiencing the greatest stress. To assess dew contribution to the annual water balances in semi-arid desert valleys, we conducted two experiments; one in a heterogeneous semi-arid desert valley in north-eastern Nevada, U.S.A. (Site A), and the other one in an irrigated homogeneous alfalfa (Medicago sativa L.) field of a semi-arid desert valley in central Utah, U.S.A. (Site B). Both sites are located in the Great Basin, Western U.S.A. Site A is considered a closed desert valley...
Variable densities of an invasive species may represent variation in invasion resistance, due to variation in resource availability. This study determined whether low- and high-density cheatgrass (Bromus tectorum L.) patches within a shadscale-bunchgrass community of western Utah, USA, can be explained by variation in resource availability. It also explored the possible role of seed limitation and enemy pressure on invasion patterns. Two parallel field experiments were conducted:(1) increasing resources within low-density cheatgrass patches and, conversely (2) reducing resources within high-density cheatgrass patches. Treatments were applied at three life stages separately and across all stages. In low-density cheatgrass...
Understanding the terrestrial carbon budget, in particular the strength of the terrestrial carbon sink, is important in the context of global climate change. Considerable attention has been given to woody encroachment in the western US and the role it might play as a carbon sink; however, in many parts of the western US the reverse process is also occurring. The conversion of woody shrublands to annual grasslands involves the invasion of non-native cheatgrass (Bromus tectorum) which in turn leads to increased frequency and extent of fires. We compared carbon storage in adjacent plots of invasive grassland and native shrubland. We scaled-up the impact of this ecosystem shift using regional maps of the current invasion...
Limited information exists of the differences in soil physical and hydrologic properties in invasive Bromus tectorum L. (BT) (cheatgrass) habitats versus native Artemisia tridentata Nutt. (AT) (big sagebrush) habitats. Our objective was to assess differences in soil physical and hydrological properties by comparing measures of soil particle size; aggregate stability; hydrophobicity; bulk density; penetration resistance; surface roughness; and infiltration (double-ring and mini-disk tension infiltrometer) between habitats. BT sites were sampled following AT stand replacing fires that resulted in near continuous BT establishment. Sites characterized by AT, and not burned, were sampled as controls. Significantly lower...
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Changes in precipitation patterns and inputs have the potential to cause major changes in productivity, composition, and diversity of terrestrial plant communities. Vegetation response to altered timing of precipitation was assessed during a 7-year experiment in an Artemisia tridentata spp. wyomingensis community in the northern Great Basin, USA. Four permanent rainout shelters excluded natural rainfall, with seasonal distribution of precipitation controlled with the use of an overhead sprinkler system. Precipitation treatments under each shelter were WINTER, SPRING, and CURRENT. The WINTER treatment received 80% of its water between October and March; in the SPRING treatment 80% of total water was applied between...
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We evaluated the potential for restoring riparian grass and sedge meadows currently dominated by Artemisia tridentata var. tridentata with an experiment in which we burned sites with low, intermediate, and high water tables, i.e., dry, intermediate, and wet sites. To define the alternative states and thresholds for these ecosystems, we examined burning and water table effects on both abiotic variables and establishment of grasses adapted to relatively high (Poa se-cunda ssp. juncifolia), intermediate (Leymus triticoides), or low (L. cinereus) water tables. Wet sites had lower soil temperatures and higher soil water contents than dry sites. Burning increased soil temperatures on all sites. Undershrub microsites on...
Mortality of shadscale (Atriplex confertifolia [Torr. & Frem.] Wats.) was severe in Great Basin valley bottoms between 1983 and 1988. Puddle Valley, Utah, just west of the Great Salt Lake, typifies areas of extensive shrub loss in which density decreased from over to less than . We analyzed vegetation along a radial transect established in the bottom of Puddle Valley in 1987. Mortality was greatest at the lowest elevations where shrubs were initially most dense. These sites occurred where soil moisture, fine-textured soils, and bulk density were greatest of all sites evaluated. Soil was most saline at the margins of the valley bottom. Higher densities of live shadscale occurred where slopes are greater, soil is...
We examined the relationship of breeding birds to elevation across and within four adjacent mountain ranges in the central Great Basin, a cold desert in western North America. Data came from 7 years of point counts at elevations from 1,915 to 3,145 m. We focused on eight passerine species that in this region are associated frequently with Pinus monophylla–Juniperus spp. (pinyon–juniper) woodland. Mean elevation of species' presence differed significantly among mountain ranges for all species except Spizella passerina (Chipping Sparrow); all species except Spizella breweri (Brewer's Sparrow) occurred at the highest mean elevation in the Toquima Range. Observed patterns were consistent with the elevational distribution...
    map background search result map search result map The effects of precipitation timing on sagebrush steppe vegetation High apoplastic solute concentrations in leaves alter water relations of the halophytic shrub, Sarcobatus vermiculatus Restoring riparian meadows currently dominated by Artemisia using alternative state concepts - the establishment component High apoplastic solute concentrations in leaves alter water relations of the halophytic shrub, Sarcobatus vermiculatus Restoring riparian meadows currently dominated by Artemisia using alternative state concepts - the establishment component The effects of precipitation timing on sagebrush steppe vegetation