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Shrub encroachment in arid and semiarid rangelands, a worldwide phenomenon, results in a heterogeneous landscape characterized by a mosaic of nutrient-depleted barren soil bordered by nutrient-enriched shrubby areas known as “fertile islands.� Even though shrub encroachment is considered as a major contributor to rangeland degradation, little is known about mechanisms favoring the reversibility of the early stages of this process. Here we synthesize the interactions between fires and soil erosion processes, and the implications of these interactions for management of rangelands. The burning of shrub vegetation develops relatively high levels of soil hydrophobicity. This fire-induced water repellency was shown...
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Historically, ecosystems in the southwestern United States derived much of their nitrogen (N) from N-fixation in biological soil crusts. Today, these regions have highly reduced crust cover, and atmospheric deposition may be the dominant source of N. This study investigates the effects of increased nitrogen deposition on nitrogen uptake, photosynthesis, and growth of the two main forage grasses on the Colorado Plateau, galleta (Hilaria jamesii [Torr.] Benth.) and Indian ricegrass (Oryzopsis hymenoides, [Roemer & J.S. Schultes] Ricker ex Piper). Plots were fertilized for 2 years with 0, 10, 20, and 40 kg nitrogen ha?1 annually, up to 4� the estimated current annual deposition rate, in 2 applications per year (spring...
Sage-grouse (Centrocercus urophasianus and C. minimus) historically inhabited much of the sagebrush-dominated habitat of North America. Today, sage-grouse populations are declining throughout most of their range. Population dynamics of sage-grouse are marked by strong cyclic behavior. Adult survival is high, but is offset by low juvenile survival, resulting in low productivity. Habitat for sage-grouse varies strongly by life-history stage. Critical habitat components include adequate canopy cover of tall grasses (? 18 cm) and medium height shrubs (40?80 cm) for nesting, abundant forbs and insects for brood rearing, and availability of herbaceous riparian species for late-growing season foraging. Fire ecology of...
Broom snakeweed (Gutierrezia sarothrae [Pursh] Britton & Rusby) increases and dominates rangelands following disturbances, such as overgrazing, fire, and drought. However, if cattle can be forced to graze broom snakeweed, they may be used as a biological tool to control it. Cattle grazed broom snakeweed in May and August 2004–2007. Narrow grazing lanes were fenced to restrict availability of herbaceous forage to force cattle to graze broom snakeweed. They used 50–85% of broom snakeweed biomass. Mature broom snakeweed plant density declined because of prolonged drought, but the decline was greater in grazed lanes. At the end of the study, density of mature plants in grazed lanes was 0.31 plants ?m22, compared...
We assessed plant interspaces in July 2007 using continuous line intercepts in twice-replicated pastures of northern mixed-grass prairie with contrasting grazing treatments: 1) long-term (25 yr) heavily grazed, dominated by the bunchgrass blue grama (Bouteloua gracilis), and 2) ungrazed, dominated by the rhizomatous grass western wheatgrass (Pascopyrum smithii). The number of plant interspaces was 26% higher in pastures heavily grazed, but the amount of soil surface occupied by plant interspaces was 27% greater without grazing. Plant interspaces were larger without grazing (14.8�1.2 cm, mean�1 SE) than heavily grazed (8.9�0.4 cm). Plant interspaces represented 87% and 68% of the total soil surface in the ungrazed...
The invasion of 40 million hectares of the American West by cheatgrass (Bromus tectorum L.) has caused widespread modifications in the vegetation of semi-arid ecosystems and increased the frequency of fires. In addition to well-understood mechanisms by which cheatgrass gains competitive advantage, it has been implicated in reducing arbuscular mycorrhizal fungi (AMF) abundance and taxa diversity. We evaluated this possibility at a high elevation site in a two-pronged approach. To test whether cheatgrass changed native AMF communities in ways that affected subsequent native plant growth, we grew cheatgrass and native plants in native soils and then planted native plants into these soils in a greenhouse experiment....
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Over a 3-yr period, the qualitative assessment protocol “Interpreting Indicators of Rangeland Health” was used to evaluate the status of three ecosystem attributes (soil/site stability, hydrologic function, and biotic integrity) at over 500 locations in and adjacent to Grand Staircase–Escalante National Monument (Utah). Objectives were to provide data and interpretations to support the development of site-specific management strategies and to investigate broad-scale patterns in the status of different rangeland ecological sites. Quantitative data on ground cover, plant community composition, and soil stability were collected to aid the evaluation of qualitative attributes and improve consistency of the assessment...
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Biological soil crusts are a diverse soil surface community, prevalent in semiarid regions, which function as ecosystem engineers and perform numerous important ecosystem services. Loss of crusts has been implicated as a factor leading to accelerated soil erosion and other forms of land degradation. To support assessment and monitoring efforts aimed at ensuring the sustainability of rangeland ecosystems, managers require spatially explicit information concerning potential cover and composition of biological soil crusts. We sampled low disturbance sites in Grand Staircase?Escalante National Monument (Utah, USA) to determine the feasibility of modeling the potential cover and composition of biological soil crusts...
Broom snakeweed (Gutierrezia sarothrae [Pursh] Britt. & Rusby) is an aggressive native invasive species that thrives after disturbance in semiarid rangelands of the western United States. A 5-yr (2002?2006) study was initiated following grazing and fire disturbances on an Upland Gravelly Loam ecological site in the sagebrush steppe of northern Utah, to evaluate broom snakeweed invasion in different plant communities. The study site originally had two plant communities: a sagebrush/ bunchgrass community that received alternate-year, fall cattle grazing, and was dominated by bluebunch wheatgrass (Elymus spicatus) and an open stand of Wyoming big sagebrush (Artemisia tridentata subsp. wyomingensis), and a sagebrush...
Cheatgrass (Bromus tectorum L.) is a winter annual weed that presents a serious obstacle to rangeland restoration in the Intermountain West. The objective of this study was to evaluate factors regulating the size and persistence of cheatgrass carryover seed banks on semiarid sites in western Utah. We prevented current-year seed production in each of four habitats, then tallied emerging seedlings over the next 4 yr. Two iterations of the study were conducted during consecutive years. One year before initiation of each iteration, we estimated seed rain at each site. Above-average precipitation in 1998–1999 resulted in relatively high seed rain (13942 seeds·m−2) for the first iteration, whereas seed rain for the...
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Over the last century there has been marked expansion and infilling of pinyon (Pinus spp.)–juniper (Juniperus spp.) woodlands into grassland and shrubland ecosystems across the western United States. Although range expansions in pinyon-juniper populations have been documented with changing climate throughout the Holocene, over the last century, local scale impacts such as livestock grazing, changes in fire regimes, and increasing atmospheric CO2 concentrations are thought to be more recent drivers of pinyon-juniper woodland distribution. Our objective was to examine the role of historical livestock grazing relative to past climate in regulating pinyon (Pinus edulis Engelm.) recruitment and growth over the last...
The resilience of willow (Salix monticola Bebb, Salix geyeriana Anderss., Salix planifolia Pursh) stems released from intense elk (Cervus elaphus) browsing in Rocky Mountain National Park, Colorado, was quantified in 1998 with a retrospective study that compared biomass, number, and length of segments on willow stems located inside (protected) and outside (browsed) elk exclosures. Segment biomass increased each year after protection by about 3?12 g year?1 on browsed stems and 10?27 g year?1 on protected stems. The number of segments on stems was similar for browsed and protected stems in the first 2 years after exclusion but differed in the next 3 years, when they increased exponentially on protected stems. Nearly...
It is hypothesized that Utah beef producers in certain locations could intensify private land use via improved forages and irrigation. Although intensification could increase ranch productivity and help compensate for any future restrictions in public grazing, is the approach profitable and sustainable in a dynamic environment? We investigated the efficacy of intensification using linear programming for three size-classes of model ranches. Model solutions maximize returns net of forage costs; outputs include brood-herd dynamics, optimal forage mixes, and net returns. The model is driven by 11-year risk scenarios combining high or low precipitation with high or low beef prices. We then consider current or no access...
Scattering slash (downed woody materials) after tree removal is increasingly prescribed by land managers as a treatment to promote the establishment and growth of understory vegetation in pinyon–juniper woodlands. However, the effects of scattering slash on soil resources and plant communities are poorly understood and often confounded with the release from tree competition. In order to examine how slash affects plant establishment, soil stability, soil nutrients, and soil microbiota, we initiated a 2 3 2 full factorial experiment with two levels of seeding and two levels of slash additions within 30 intercanopy spaces, repeated at two intact pinyon–juniper woodland sites with different soil characteristics...
Vegetative differences and changes were evaluated over a 6-year period (1999-2004) on adjoining conservatively grazed and grazing-excluded (22 years) shortgrass rangelands in northwestern New Mexico. Autumn total perennial grass and blue grama (Bouteloua gracilis [Willd. ex Kunth] Lag. Griffiths) standing crop did not differ on grazed and grazing-excluded areas when data were averaged across years. There were no long-term differences in vegetation basal cover or composition between the grazed and grazing-excluded areas. Plant community similarity values between the grazed and grazing-excluded areas were 80% and 93% during the first 2 years (1999-2000) and last 2 years (2003-2004) of study, respectively. Climatic...
We investigated soil compaction and hydrologic responses from mechanically shredding Utah juniper (Juniperus ostesperma [Torr.] Little) to control fuels in a sagebrush/bunchgrass plant community (Artemisia nova A. Nelson, Artemisia tridentata Nutt. subsp. wyomingensis Beetle & Young/Pseudoroegneria spicata [Pursh] A. L�ve, Poa secunda J. Presl) on a gravelly loam soil with a 15% slope in the Onaqui Mountains of Utah. Rain simulations were applied on 0.5-m2 runoff plots at 64 mm � h?1 (dry run: soil initially dry) and 102 mm � h?1 (wet run: soil initially wet). Runoff and sediment were collected from runoff plots placed in five blocks, each containing four microsites (juniper mound, shrub mound, vegetation-free or...
In light of the continuing debate regarding overcompensation we studied the responses of above-ground biomass in a high-elevation, semi-arid grassland to defoliation, defoliation history, and livestock grazing. The above-ground annual net primary productivity (ANPP) was measured over 2 years in one-hundred twenty, 1-m2 plots that were exposed to single- and multi-year defoliation and grazing treatments. Plant communities showed an average increase in ANPP of 31%?45% due to a single defoliation event. The most conservative estimate of average ANPP of defoliated subplots was 29.4 g m?2 greater than the non-defoliated controls. A history of defoliation, due to clipping or grazing, lessened the magnitude of the compensatory...
Cheatgrass (Bromus tectorum L.) is an invasive annual grass that creates near-homogenous stands in areas throughout the Intermountain sagebrush steppe and challenges successful native plant restoration in these areas. A clipping experiment carried out at two cheatgrass-dominated sites in eastern Oregon (Lincoln Bench and Succor Creek) evaluated defoliation as a potential control method for cheatgrass and a seeding preparation method for native plant reseeding projects. Treatments involved clipping plants at two heights (tall=7.6 cm, and short=2.5 cm), two phenological stages (boot and purple), and two frequencies (once and twice), although purple-stage treatments were clipped only once. Treatments at each site were...
Soil nutrient availability influences plant invasions. Resin capsules were used to examine soil nutrient bioavailability along 2 sagebrush–grassland elevation transects in the east Tintic Range (Utah) and Shoshone Range (Nevada). In the fall of 2001, treatments were applied to 3 replicate plots at each site, which included prescribed burning, herbaceous vegetation removal, and controls. Cheatgrass (Bromus tectorum L.) was overseeded in small subplots within each treatment. Following treatments in each plot, resin capsules were installed at 15-cm depth in a shrub interspace and a B. tectorum–overseeded area. Nutrient availability was integrated during late fall to spring and spring to late fall for 2 years. Herbaceous...
Cheatgrass (Bromus tectorum L.) is the most widespread invasive weed in sagebrush ecosystems of North America. Restoration of perennial vegetation is difficult and land managers have often used introduced bunchgrasses to restore degraded sagebrush communities. Our objective was to evaluate the potential of ‘Vavilov’ Siberian wheatgrass (Agropyron fragile [Roth] P. Candargy) to establish on cheatgrass-dominated sites. We examined Vavilov establishment in response to different levels of soil nitrogen availability by adding sucrose to the soil to promote nitrogen (N) immobilization and examined cheatgrass competition by seeding different levels of cheatgrass. We used a blocked split-split plot design with two sucrose...
map background search result map search result map Influence of Livestock Grazing and Climate on Pinyon Pine (Pinus edulis) Dynamics - Rangeland Ecology & Management Effects of Nitrogen Deposition on an Arid Grassland in the Colorado Plateau Cold Desert Spatial Modeling of Biological Soil Crusts to Support Rangeland Assessment and Monitoring Plant Interspaces Resulting From Contrasting Grazing Management in Northern Mixed-Grass Prairie: Implications for Ecosystem Function Broad-Scale Assessment of Rangeland Health, Grand Staircase-Escalante National Monument, USA Effects of Nitrogen Deposition on an Arid Grassland in the Colorado Plateau Cold Desert Influence of Livestock Grazing and Climate on Pinyon Pine (Pinus edulis) Dynamics - Rangeland Ecology & Management Broad-Scale Assessment of Rangeland Health, Grand Staircase-Escalante National Monument, USA Spatial Modeling of Biological Soil Crusts to Support Rangeland Assessment and Monitoring