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Historical disturbance regimes are often considered a critical element in maintaining native plant communities. However, the response of plant communities to disturbance may be fundamentally altered as a consequence of invasive plants, climate change, or prior disturbances. The appropriateness of historical disturbance patterns under modern conditions and the interactions among disturbances are issues that ecologists must address to protect and restore native plant communities. We evaluated the response of Artemisia tridentata ssp. wyomingensis (Beetle & A. Young) S.L. Welsh plant communities to their historical disturbance regime compared to other disturbance regimes. The historical disturbance regime of these...
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Resource specialists at Dinosaur National Monument utilize both planned and unplanned wildland ignitions in big sagebrush (Artemisia tridentata)--dominated plant communities to restore successional processes, maintain vegetation vigor, and promote diversified landscapes. Short- and long-term effects of prescribed burning on small mammal populations are not well understood. The objectives of this study were to (1) compare small mammal species richness, similarity, and diversity between paired burned and unburned treatment plots, and (2) assess long-term trends of small mammal community responses to burning. Five paired burned/unburned sites having similar vegetation, soils, elevation, and annual precipitation were...
We surveyed for pygmy rabbits, Brachylagus idahoensis, in Summer 2003 in Nevada (USA) to better determine the distribution, habitat, and soil patterns of this potentially threatened species. Pygmy rabbits and/or their sign (burrows and fecal pellets) were observed at 261 of 643 survey sites and their known distribution was extended 12 km to the south. Data on topography, soil, lithology, and hydrology were compared between sagebrush habitats where pygmy rabbits and/or their sign was present and absent. A predictive equation was produced and used as a model for characterizing habitats where pygmy rabbits were present. This model successfully explained the occurrence of pygmy rabbits and/or their sign on 56.7% of...
Greater sage-grouse (Centrocercus urophasianus) populations throughout much of their range have been declining. These declines have largely been attributed to the loss or deterioration of sagebrush (Artemisia spp.) habitat. In response government agencies such as the United States Department of Agriculture, Natural Resources Conservation Service are cost-sharing on management practices designed to improve habitat conditions for sage-grouse. Little is known regarding sage-grouse response to various sagebrush management techniques. We studied the effects of reducing sagebrush canopy cover using 2 mechanical (Dixie harrow and Lawson aerator) treatments and 1 chemical (Tebuthiuron) treatment on greater sage-grouse use...
Pathogens and herbivores can severely reduce host fitness, potentially leading to altered succession rates and changes in plant community composition. Thus, to predict vegetation dynamics under climate change, it is necessary to understand how plant pathogens and herbivores will respond. Pathogens and herbivores are predicted to increase under climate warming because the amount of time available for growth and reproduction will increase. To test this prediction, we used a warming experiment in which heaters were suspended over a natural montane meadow for 12 years. In the summer of 2002, we quantified damage by all the observable (aboveground) pathogens and herbivores on six of the most common plant species (Artemisia...
Sagebrush (Artemisia tridentata) comprises up to 99% of the winter and 50% of the summer diets of pygmy rabbits (Brachylagus idahoensis). Few animals specialize on such plants as sagebrush, which contain high levels of plant chemicals that can be toxic. We investigated the nutritional requirements of pygmy rabbits and their ability and propensity to consume sagebrush alone and as part of a mixed diet. We compared diet choices of pygmy rabbits with that of a generalist forager, the eastern cottontail (Sylvilagus floridanus). Pygmy rabbits had a moderately low nitrogen requirement (306.5 mg N/kg0.75/d), but a relatively high energy requirement, needing 750.8 kJ digestible energy/kg0.75/d to maintain their body mass...
Aim: Greater sage-grouse (Centrocercus urophasianus), a shrub-steppe obligate species of western North America, currently occupies only half its historical range. Here we examine how broad-scale, long-term trends in landscape condition have affected range contraction. Location: Sagebrush biome of the western USA. Methods: Logistic regression was used to assess persistence and extirpation of greater sage-grouse range based on landscape conditions measured by human population (density and population change), vegetation (percentage of sagebrush habitat), roads (density of and distance to roads), agriculture (cropland, farmland and cattle density), climate (number of severe and extreme droughts) and range periphery....
Nitric oxide (NO) is a relatively short-lived trace gas that reacts with oxygen in the troposphere to produce the air pollutant ozone. It also reacts with water vapor to form nitric and nitrous acids, which acidify precipitation and increase N deposition. Models currently used to predict soil NO fluxes are based on the assumption that NO flux is proportional to the gross rate of nitrification or N mineralization; however, this assumption has not been tested because of the difficulty in measuring gross N-cycling rates in situ. We measured soil NO fluxes, gross and net N-cycling rates, and a variety of other soil characteristics in the forest floor and intact soil cores at nine undisturbed forest and rangeland ecosystems...
Bromus tectorum is a dominant winter annual weed in cold deserts of western North America. We followed patterns of seed carry-over and abundance of the pathogen Pyrenophora semeniperda over 5 years at B. tectorum-dominated shadscale (Atriplex confertifolia) and sagebrush (Artemisia tridentata) sites in southern Idaho. We hypothesised that more seeds could potentially carry over at the drier shadscale site because of minimal autumn precipitation, but that P. semeniperda, a pathogen that primarily kills dormant seeds, would have more impact at the drier site, where a higher density of dormant seeds would likely be present in the early spring seedbank. Successful first-year seed carry-over was higher in years with...
For much of the western USA, precipitation occurs in pulses, the nature of which determine soil water potential and plant physiological performance. This research utilized three experiments to examine the sensitivity of photosynthesis and water relations for two widespread Great Basin Desert shrub species, Artemisia tridentata (which has both deep and shallow roots) and Purshia tridentata (which reportedly has only deep roots), to (1) variation in pulse magnitude size, (2) the kinetics of responses to pulses, and (3) the relationship between pulse-size and antecedent soil water content. At the study site in the southwestern Great Basin Desert, USA, summer rainfall exhibits a greater frequency of larger-sized events,...
Modification of landscapes due to energy development may alter both habitat use and vital rates of sensitive wildlife species. Greater sage-grouse (Centrocercus urophasianus) in the Powder River Basin (PRB) of Wyoming and Montana, USA, have experienced rapid, widespread changes to their habitat due to recent coal-bed natural gas (CBNG) development. We analyzed lek-count, habitat, and infrastructure data to assess how CBNG development and other landscape features influenced trends in the numbers of male sage-grouse observed and persistence of leks in the PRB. From 2001 to 2005, the number of males observed on leks in CBNG fields declined more rapidly than leks outside of CBNG. Of leks active in 1997 or later, only...
Prolonged use of broad-spectrum antibiotics has led to the emergence of drug-resistant pathogens, both in medicine and in agriculture. New threats such as biological warfare have increased the need for novel and efficacious antimicrobial agents. Natural habitats not previously examined as sources of novel antibiotic-producing microorganisms still exist. One such habitat is the rhizosphere of desert shrubs. Here, we show that one desert shrub habitat, the rhizosphere of desert big sagebrush (Artemisia tridentata) is a source of actinomycetes capable of producing an extensive array of antifungal metabolites. Culturable microbial populations from both the sagebrush rhizosphere and nearby bulk soils from three different...
The ecological integrity of Sagebrush (Artemisia spp.) ecosystems in the Intermountain West (U.S.A.) has been diminished by synergistic relationships among human activities, spread of invasive plants, and altered disturbance regimes. An aggressive effort to restore Sagebrush habitats is necessary if we are to stabilize or improve current habitat trajectories and reverse declining population trends of dependent wildlife. Existing economic resources, technical impediments, and logistic difficulties limit our efforts to a fraction of the extensive area undergoing fragmentation, degradation, and loss. We prioritized landscapes for restoring Sagebrush habitats within the intermountain western region of the United States...
Mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana) covers large areas in arid regions of western North America. Climate-change models predict a decrease in the range of sagebrush, but few studies have examined details of predicted changes on sagebrush growth and the potential impacts of these changes on the community. We analyzed effects of temperature, precipitation, and snow depth on sagebrush annual ring width for 1969 to 2007 in the Gunnison Basin of Colorado. Temperature at all times of year except winter had negative correlations with ring widths; summer temperature had the strongest negative relationship. Ring widths correlated positively with precipitation in various seasons except summer;...
Detailed empirical models predicting both species occurrence and fitness across a landscape are necessary to understand processes related to population persistence. Failure to consider both occurrence and fitness may result in incorrect assessments of habitat importance leading to inappropriate management strategies. We took a two-stage approach to identifying critical nesting and brood-rearing habitat for the endangered Greater Sage-Grouse (Centrocercus urophasianus) in Alberta at a landscape scale. First, we used logistic regression to develop spatial models predicting the relative probability of use (occurrence) for Sage-Grouse nests and broods. Secondly, we used Cox proportional hazards survival models to identify...
It is widely believed that wild and domestic herbivores have modified the structure and composition of arid and semi-arid plant communities of western North America, but these beliefs have rarely been tested in long-term, well-replicated studies. We examined the effects of removing large herbivores from semi-arid shrublands for 40-50 years using 17 fenced exclosures in western Colorado, USA. Shrub cover was greater (F=5.87, P=0.0020) and cover (F=3.01, P=0.0601) and frequency (F=3.89, P=0.0211) of forbs was less inside the exclosures (protected) relative to grazed plots. However, we found no significant effects (minimum P=0.18) of protection from grazing on cover or frequency of grasses, biotic crusts, or bare soil....
Recent energy development has resulted in rapid and large-scale changes to western shrub-steppe ecosystems without a complete understanding of its potential impacts on wildlife populations. We modeled winter habitat use by female greater sage-grouse (Centrocercus urophasianus) in the Powder River Basin (PRB) of Wyoming and Montana, USA, to 1) identify landscape features that influenced sage-grouse habitat selection, 2) assess the scale at which selection occurred, 3) spatially depict winter habitat quality in a Geographic Information System, and 4) assess the effect of coal-bed natural gas (CBNG) development on winter habitat selection. We developed a model of winter habitat selection based on 435 aerial relocations...
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...
Semi-arid ecosystems cover tens of millions of hectares in the Intermountain West of the United States, and most have altered plant communities due to land use, especially livestock grazing. Thus, relatively unaltered ?reference? plant community information is needed to guide restoration. Plant communities were sampled over a large (600 000 ha) semi-arid landscape in western Colorado, within pi�on?juniper woodlands, sagebrush shrublands, and grasslands, and over conditions ranging from relict areas without livestock grazing to heavily utilized areas. Ordination was used to group samples into ranked categories of ecological condition within 18 communities, and means?tests and other techniques were used to identify...
Relative water content (RWC) and water potential were compared for leaves of several plant species exposed to a warming manipulation at the Rocky Mountain Biological Laboratory, near Crested Butte, Colorado, USA, to test the hypothesis that species-specific changes in water relations parameters will occur in response to future increases in planetary air temperatures. Leaves of Artemisia tridentata, Erigeron speciosus, Festuca thurberi, Helianthella quinquinervis, Potentilla fruticosa, Potentilla gracilis and Rhodiola integrifolia were collected from plants growing in situ in control and infrared (IR)-heated (22 W m−2) plots in a meadow near the upper elevational distribution limit for A. tridentata. For six of...
map background search result map search result map Interaction of historical and nonhistorical disturbances maintains native plant communities Fire effects on small mammal communities in Dinosaur National Monument Fire effects on small mammal communities in Dinosaur National Monument Interaction of historical and nonhistorical disturbances maintains native plant communities