Sagebrush Steppe Communities Research Articles

Modelling plant growth dynamics in sagebrush steppe communities affected by fire

The EDYS model was used to simulate plant production in burned and unburned communities dominated by Bromus tectorum at the US Army Yakima Training Centre, Washington. Model results were validated with 4 years of field data obtained in experiments designed specifically for this study. Subsequently, 50-year simulations of plant production were conducted with normal precipitation for the area and with no disturbances such as grazing or military training. Our simulations of plant production were not significantly different ( p>0.05) from observed results of burned and unburned communities in 90% of the comparisons, indicating that EDYS adequately simulated the dynamics of this system. Long-term simulations indicated that annual species, primarily B. tectorum, dominated burned and unburned plant communities for 13–15 years, after which, annuals were replaced by perennials. B. tectorum, however, remained five years longer in the burned than in the unburned community, suggesting that fire favors the persistence of this species in invaded areas. Although B. tectorum dominated both plant communities during the initial simulation period, its production fluctuated greatly. The main perennials that replaced B. tectorum were Chrysothamnus nauseosus, Artemisia tridentata, and Agropyron cristatum. Our long-term modelling results are supported by previous field observations in which annual species are replaced by perennials in the absence of disturbances.

Leaf‐to‐aircraft measurements of net CO2 exchange in a sagebrush steppe ecosystem

Measurements of net CO2 flux density (μmol m−2 s−1) from a high elevation, sagebrush steppe community in southeastern Wyoming (USA) were compared quantitatively among four different instrument systems (leaf cuvette and 1 m2 community chamber for gas exchange measurements; tower and aircraft eddy covariance systems) by minimizing spatial and temporal variability. Ground‐based flux measurements were recorded at an intensive site located near the midpoint and directly beneath an approximate 20‐km flight transect. A high degree of homogeneity in plant species composition, density, cover, and the amount of leaf area per unit ground area, as well as little topographic variability, was measured at the intensive site and along the flight transect. Flux measurements were compared on days with relatively high and low soil moisture availability (predawn plant water potentials >−0.8 MPa and <−2.0 MPa, respectively). Same‐day, mean flux values between the four measurement systems (4.0–4.6 μmol m−2 s−1) over identical time intervals (0900–1100 hours) varied by a maximum of ±9% (maximum range 23%). Ground‐level measurements taken within ±1 day of flight measurements, varied by a minimum of ±7% (25% maximum range) of aircraft values. This difference increased curvilinearly to a maximum of ±31% (38% maximum range) for a 2‐week separation between flight and ground‐based measurements. Thus, under near‐ideal conditions of topographic and vegetative homogeneity, temporal heterogeneity in the measurement regime of only a few days resulted in greater disparity in measured CO2 flux density than occurred among the four instrument types.

Restoration of degraded lands in the interior Columbia River basin: passive vs. active approaches

Evidence for success of passive and active restoration is presented for interior conifer forest, sagebrush steppe, and riparian ecosystems, with a focus on the Columbia River basin. Passive restoration, defined as removal of the stresses that cause degradation, may be most appropriate for higher elevation forests, low-order riparian ecosystems, and for sagebrush steppe communities that are only slightly impaired. More active approaches, in which management techniques such as planting, weeding, burning, and thinning are applied, have been successful in forests with excessive fuels and in some riparian systems, and may be necessary in highly degraded sagebrush steppe communities. There is general agreement that true restoration requires not only reestablishment of more desirable structure or composition, but of the processes needed to sustain these for the long term. The challenge for the restorationist is to find a way to restore more desirable conditions within the context of social constraints that limit how processes are allowed to operate, and economic constraints that determine how much effort will be invested in restoration.

Point Sampling for Leaf Area Index in Sagebrush Steppe Communities

Although point sampling has been used for more than 30 years to quantify leaf area index (LAI), this field technique has not been rigorously evaluated in sagebrush steppe plant communities. Leaf area index estimates obtained using different sampling pin inclinations or combinations of pin inclinations were evaluated in Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle and Young), low sagebrush (Artemisia arbuscula Nutt.), and mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana [Rydb.] Beetle) communities within the Reynolds Creek Experimental Watershed near Boise, Ida. Leaf area index values determined by clipping and processing green foliage through a leaf area meter were used as evaluation standards. Pins inclined at 13 degrees from the horizontal, used alone or in combination with pins of 52 degrees and/or 90 degrees inclinations, performed poorly for estimating LAI in the Wyoming big sagebrush and low sagebrush communities. Estimating total LAI with either the combination of 52 degrees and 90 degrees angle pins or with 52 degrees or 90 degrees pins alone explained at least 96% of the variability in LAI standard values from the Wyoming big sagebrush and mountain big sagebrush communities. Using 52 degrees angle pins alone produced model fits similar to those obtained when the combination of 52 degrees and 90 degrees angle pins were used to estimate shrub, graminoid, and forb LAI across all 3 communities (P > 0.1). Collecting point data using 52 degrees angle pins often provided better or similar model fits with LAI standards compared to other pin angles but using 90 degrees angle pins offers a better compromise between practicality, efficiency, and accuracy. DOI:10.2458/azu_jrm_v54i5_clark

Bowen ratio and closed chamber carbon dioxide flux measurements over sagebrush steppe vegetation

Measurement of carbon dioxide (CO 2) fluxes over sagebrush steppe ecosystems has received little attention, and seasonal dynamics of CO 2 uptake are not known for most portions of this expansive ecosystem. We utilized two techniques — Bowen ratio/energy balance (BREB) and closed chamber (CC) — to measure CO 2 fluxes during eight 24 h sampling periods throughout the 1997 growing season on ungrazed sagebrush steppe communities at the US Sheep Experiment Station near Dubois, ID and the Northern Great Basin Experimental Range near Burns, OR. Instantaneous CC measurements generally agreed with 20 min average CO 2 fluxes measured by BREB instrumentation, except later in the season at Burns when soil moisture was depleted. Maximum mid-day CO 2 assimilation occurred in June at both locations, with rates up to 0.4 and 0.5 mg CO 2 m −2 s −1 at Burns and Dubois, respectively. In August, mid-day assimilation was low, at about 0.1 mg m −2 s −1 at both locations. Slopes of CC fluxes as a function of BREB were not different between locations, so data were combined across locations. A significant, positive correlation was observed between CC and BREB ( R=0.82, n=190). These two independent measurements of CO 2 flux showed good agreement, except during extremely hot and dry periods in late summer. This suggests that both BREB and CC are valid techniques and can be used in concert to obtain reliable estimates of CO 2 flux on these shrub-dominated communities, although caution is advised for CC during periods when temperatures are high and soil moisture is low. The BREB technique is appropriate for large-scale, continuous measurements of CO 2 flux, and compares well with the CC technique, which can partition flux estimates between shrub canopy and interspace, thereby providing a measure of spatial variability.

Point sampling for leaf area index in sagebrush steppe communities

Although point sampling has been used for more than 30 years to quantify leaf area index (LAI), this field technique has not been rigorously evaluated in sagebrush steppe plant communities. Leaf area index estimates obtained using different sampling pin inclinations or combinations of pin inclinations were evaluated in Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle and Young), low sagebrush (Artemisia arbuscula Nutt.), and mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana [Rydb.] Beetle) communities within the Reynolds Creek Experimental Watershed near Boise, Ida. Leaf area index values determined by clipping and processing green foliage through a leaf area meter were used as evaluation standards. Pins inclined at 13 degrees from the horizontal, used alone or in combination with pins of 52 degrees and/or 90 degrees inclinations, performed poorly for estimating LAI in the Wyoming big sagebrush and low sagebrush communities. Estimating total LAI with either the combination of 52 degrees and 90 degrees angle pins or with 52 degrees or 90 degrees pins alone explained at least 96% of the variability in LAI standard values from the Wyoming big sagebrush and mountain big sagebrush communities. Using 52 degrees angle pins alone produced model fits similar to those obtained when the combination of 52 degrees and 90 degrees angle pins were used to estimate shrub, graminoid, and forb LAI across all 3 communities (P > 0.1). Collecting point data using 52 degrees angle pins often provided better or similar model fits with LAI standards compared to other pin angles but using 90 degrees angle pins offers a better compromise between practicality, efficiency, and accuracy.

Cheatgrass ( Bromus tectorum L) dominance in the Great Basin Desert : History, persistence, and influences to human activities

Cheatgrass ( Bromus tectorum L), an exotic annual, is a common, and often dominant, species in both the shadscale and sagebrush-steppe communities of the Great Basin Desert. Approximately 20% of the sagebrush-steppe vegetation zone is dominated by cheatgrass to the point where the establishment of native perennial species is nearly Impossible. This paper discusses the historical factors that led to the establishment and dissemination of cheatgrass in the Great Basin, examines the processes that further cheatgrass dominance, provides examples of subsequent influences of the grass to human activities, and links the ecological history with range condition models. Evidence suggests that cheatgrass was introduced accidentally to the Great Basin as a grain contaminant at the end of the 19th century at the same time that largescale domestic grazing was occurring. Imported from Mediterranean Europe and central and south-western Asia, seeds of cheatgrass exploited an ecological niche, as no native annual was dominant in the Great Basin. Cattle, sheep, and feral horses facilitated establishment, for they spread the seeds in the same areas that they disturbed. Once established, cheatgrass promoted the likelihood of fire to the detriment of the native species. in addition, other factors, such as the effects of the lack of vesicular arbuscular mycorrhizae and selective lagomorph grazing have worked in concert to further establish cheatgrass dominance. The ecological consequences of cheatgrass establishment have been an increase in fire frequency and intensity, a decrease in species diversity, and a landscape susceptible to severe erosion. Bunchgrasses interspersed with longlived perennial shrubs now are replaced with either nearly pure patches of cheatgrass or swaths of cheatgrass and shortlived perennial shrubs. Some consequences to human activities involve the numerous ramifications of rangeland fires with costs of approximately US$20 million annually, the undependability of cheatgrass as a source of forage for cattle and sheep, and the value of biotic diversity as numerous plant and animals species undergo high amplitude population fluctuations. Management of these Great Basin vegetation communities should be approached using the state and threshold range condition model.

Growth and elemental content of several sagebrush-steppe species in unburned and post-wildfire soil and plant effects on soil attributes

Fire is the principal means of stand renewal in big sagebrush-steppe communities of western North America. Plant growth following fire may be influenced by heat-induced changes in the nutrient status of the soil. Moreover, post-wildfire pioneer plant species may alter soil properties, and thereby, impact subsequent plant recruitment. Our study compared the growth and elemental content of big sagebrush (Artemisia tridentata), squirreltail (Elymus elymoides), cheatgrass (Bromus tectorum), and Indian ricegrass (Achnatherum hymenoides), grown under greenhouse conditions in post-wildfire and similar unburned soil. We also examined soil attributes following plant growth. Cheatgrass and squirreltail, grown in post-wildfire soil, had significantly (p≤0.05) greater aboveground mass than plants grown in unburned soil. As compared with unburned soil, post-wildfire soil engendered the following significant (p≤0.05) differences in leaf elemental content: 1) big sagebrush had higher levels of P and lower levels of Mn; 2) squirreltail accumulated more P and N; and 3) all grass species had higher SiO2 content. Following harvest of plants, post-wildfire soil generally contained significantly (p≤0.05) more KCl-extractable ortho-P, NH inf4 + , and SO 4 − , than unburned soil. Plant growth in both burned and unburned soils fostered a significant (p≤0.05) increase in the bicarbonate-extractable pool of P as compared with unplanted controls. Soil Kjeldahl-N was significantly (p≤0.05) greater after plant growth in burned treatments as compared with the control. This study demonstrates that post-wildfire soil can have a stimulatory effect on plant growth for some species. Squirreltail deserves consideration as a post-wildfire revegetation species. Furthermore, pioneer plant growth following wildfires can attenuate soil properties and therefore influence plant succession.

Nitrogen and Phosphorus Effects on Secondary Succession Dynamics on a Semi‐Arid Sagebrush Site

A sagebrush steppe community in northwestern Colorado was disturbed in 1984 and subjected to annual applications of nitrogen and phosphorus, and successional responses were studied over a 5—yr period. Phosphorus was not found to be significant but nitrogen did significantly affect succession for all years except the first. Three seral groups developed on the non—fertilized plots, the first two dominated by annuals and lasting 3 yr, the third transitional and dominated by perennials. The addition of N altered this successional pattern by allowing annuals to remain as site dominants through the 5th yr. Results of this study suggest that dominance of a site by annuals in early stages of secondary succession is related to high nutrient availability.

Birth and Fawn Bed Site Selection by Pronghorns in a Sagebrush-Steppe Community

In a sagebrush-steppe community in southcentral Wyoming, we measured shrub canopy cover and height at 13 pronghorn (Antilocapra americana) fawn birth sites and 50 fawn bedding sites and compared them to measurements we made at 47 random points in areas infrequently used by parturient pronghorn. Birth sites and bed sites were similar (P=0.96) in shrub cover but differed from random points (P=0.015 and P=0.002, respectively). Plant height was not significantly different between birth sites, bedding sites, or random points measured in low use areas. In a second study, we fitted 7 pronghorn fawns (3-5 days old) with solar-powered radio transmitters and relocated them daily for 3 weeks

Succession patterns following soil disturbance in a sagebrush steppe community.

A study was begun in 1976 to measure succession patterns following soil disturbance within a sagebrush community in northwestern Colorado. The principal hypothesis was that type of disturbance affects the direction of succession, resulting in different plant communities over time. Successional dynamics were studied through 1988. Four types of soil disturbance resulted in 3 early seral communities: one dominated by grasses, one by annuals, and one intermediate. The annual-dominated communities were opportunistic on these sites, lasting 3-5 years and not determining the direction in which succession proceeded following their replacement. Twelve years after disturbance, 3 communities (one grass-dominated, one shrub-dominated, and one intermediate) occupied the site, the characteristics of which were functions of type of initial soil disturbance. For the period of time covered by this study (12 years), degree of disturbance was found to affect the direction of succession, resulting in different plant communities over time. There were, however, successional characteristics toward the end of the study that suggest that over a longer time period, succession might progress to a single community regardless of type of disturbance.

Short-lived phosphorescent components in CsI(T1) scintillation crystals

Cheatgrass (Bromus tectorum L), an exotic annual, is a common, and often dominant, species in both the shadscale and sagebrush-steppe communities of the Great Basin Desert. Approximately 20% of the sagebrush-steppe vegetation zone is dominated by cheatgrass to the point where the establishment of native perennial species is nearly Impossible. This paper discusses the historical factors that led to the establishment and dissemination of cheatgrass in the Great Basin, examines the processes that further cheatgrass dominance, provides examples of subsequent influences of the grass to human activities, and links the ecological history with range condition models.Evidence suggests that cheatgrass was introduced accidentally to the Great Basin as a grain contaminant at the end of the 19th century at the same time that largescale domestic grazing was occurring. Imported from Mediterranean Europe and central and south-western Asia, seeds of cheatgrass exploited an ecological niche, as no native annual was dominant in the Great Basin. Cattle, sheep, and feral horses facilitated establishment, for they spread the seeds in the same areas that they disturbed. Once established, cheatgrass promoted the likelihood of fire to the detriment of the native species. in addition, other factors, such as the effects of the lack of vesicular arbuscular mycorrhizae and selective lagomorph grazing have worked in concert to further establish cheatgrass dominance.The ecological consequences of cheatgrass establishment have been an increase in fire frequency and intensity, a decrease in species diversity, and a landscape susceptible to severe erosion. Bunchgrasses interspersed with longlived perennial shrubs now are replaced with either nearly pure patches of cheatgrass or swaths of cheatgrass and shortlived perennial shrubs. Some consequences to human activities involve the numerous ramifications of rangeland fires with costs of approximately US$20 million annually, the undependability of cheatgrass as a source of forage for cattle and sheep, and the value of biotic diversity as numerous plant and animals species undergo high amplitude population fluctuations. Management of these Great Basin vegetation communities should be approached using the state and threshold range condition model.