Sagebrush Steppe Communities Research Articles

A realized facilitation cascade mediated by biological soil crusts in a sagebrush steppe community

Biological soil crusts can have strong effects on vascular plant communities which have been inferred from short-term germination and early establishment responses. However, biocrusts are often assumed to function as an “organizing principle” in communities because their effects can “cascade” to interactions among crust-associated plant species. We conducted surveys and experiments to explore these cascades and found that biocrusts were positively associated with large patches (> 10 m diameter) of a dominant shrub Artemisia tridentata. At the smaller scale of individual shrubs and the open matrices between shrubs, biocrusts were negatively associated with Artemisia. Juveniles of Artemisia were found only in biocrusts in intershrub spaces and never under shrubs or in soil without biocrusts. In two-year field experiments, biocrusts increased the growth of Festuca and the photosynthetic rates of Artemisia. Festuca planted under Artemisia were also at least twice as large as those planted in open sites without crusts or where Artemisia were removed. Thus, biocrusts can facilitate vascular plants over long time periods and can contribute to a “realized” cascade with nested negative and positive interactions for a range of species, but unusual among documented cascades in that it includes only autotrophs.

The Clean Water Act and biosolids: A 45‐year chronological review of biosolids land application research in Colorado

The 1972 U.S. Clean Water Act set forth the generation of biosolids. In Colorado, biosolids land application research began in 1976 and continues today. Pastureland research suggested that sewage effluent could effectively be land applied to benefit aboveground plant growth and to polish water prior to reaching receiving waters. Forest wildfire-affected ecosystems can also benefit from biosolids applications; application rates of up to 80 Mg ha-1 can lead to greater plant establishment, soil microbial activity, and nutrient turnover and reduced nutrient and heavy metal concentrations in runoff below livestock and USEPA drinking water standards. Long-term (24-yr) observations in oil shale-mined lands showed that biosolids (up to 224 Mg ha-1 ) can have a positive effect on microbial-mediated nutrient cycling and, in turn, on aboveground plant community structure. Biosolids applications of up to 40 Mg ha-1 in high-elevation shrubland ecosystems, dominated by Mo-containing shale deposits, can aid in reducing imbalances between Mo and Cu in soils and plants; excessive plant Mo, when consumed by ruminants, can lead to molybdenosis. Biosolids and lime applications (both at 224 Mg ha-1 ) have been shown to improve long-term reclamation success on acid-generating, heavy metal-containing fluvial mine tailings. Thirty years of grazing land research, focused on soil and aboveground plant benefits, illustrate that soil health and plant productivity can be improved to the greatest extent at biosolids application rates close to 10 Mg ha-1 . Finally, 40 yr of dryland agroecosystem research (a) have helped identify biosolids N fertilizer equivalency (∼8kg N Mg-1 ) and thus dryland winter wheat application rates (e.g., 4.5-6.7 dry Mg ha-1 ); (b) have identified first-year mineralization rates of 25-32%; (c) dispute the "time bomb" theory by showing that plant metal uptake follows an exponential rise to a maximum; (d) showcase economic return to producers via increased wheat grain protein content; (e) suggest that biosolids-borne proteins and their degradation products are labile C and N sources; (f) have led to long-term tracking of micronutrients and heavy metals in soils and revealed that plants-soil concentrations will not lead to groundwater degradation and that plants are safe for human consumption; and (g) have shown that biosolids provide Zn, helping to overcome soil deficiencies and enhancing Zn biofortification in wheat grain. This latter point is important because ∼2 billion people globally suffer from Zn deficiencies. Forty-five years of research in Colorado have proven that biosolids can enhance environmental quality, improve soil health, and produce healthy food products.

Grazing effects on shrub-induced resource islands and herbaceous vegetation heterogeneity in sagebrush-steppe communities

Spatial heterogeneity in plant communities promotes coexistence and diversity by providing a variety of niches for different species. In shrub-steppe communities, shrubs create distinct microsites under their canopies (canopy microsites) compared to areas between their canopies (interspace microsites). This creates spatial heterogeneity in soil nutrient availability and herbaceous vegetation. Grazing can influence spatial heterogeneity, but the effect of grazing on shrub-induced spatial heterogeneity is largely unknown. We investigated the long-term (+80 yrs.) effects of moderate grazing by cattle on sagebrush ( Artemisia )-induced spatial heterogeneity in soil nutrients, herbaceous vegetation, and ground cover in sagebrush-bunchgrass steppe communities at eight sites in southeastern Oregon. Each site consisted of a long-term grazing exclosure and an adjacent grazed area. Almost all measured herbaceous vegetation (cover, density, diversity, and evenness) and ground cover variables differed between canopy and interspace microsites. Grazing did not influence the effects of microsites on most measured herbaceous vegetation characteristics and ground cover variables. Available soil nutrients were not influenced by grazing, but the majority differed between microsites. The limited effect of moderate grazing on shrub-induced spatial heterogeneity provides evidence that sagebrush exerts a strong influence on patterns of soil nutrients and herbaceous vegetation in sagebrush-bunchgrass communities. These results also demonstrate that moderate grazing by cattle can be compatible with maintaining spatial heterogeneity within shrub-steppe communities. In these ecosystems, maintaining and restoring shrubs is critical to promoting spatial heterogeneity, thereby encouraging coexistence and diversity.

Flowering time advances since the 1970s in a sagebrush steppe community: Implications for management and restoration.

Climate change is widely known to affect plant phenology, but little is known about how these impacts manifest in the widespread sagebrush ecosystem of the Western United States, which supports a number of wildlife species of concern. Shifts in plant phenology can trigger consequences for the plants themselves as well as the communities of consumers that depend upon them. We assembled historical observations of first-flowering dates for 51 species collected in the 1970s and 1980s in a montane sagebrush community in the Greater Yellowstone Ecosystem and compared these to contemporary phenological observations targeting the same species and locations (2016-2019). We also assembled regional climate data (average spring temperature, day of spring snowmelt, and growing degree days) and tested the relationship between first-flowering time and these variables for each species. We observed the largest change in phenology in early-spring flowers, which, as a group, bloomed on average 17 days earlier, and as much as 36 days earlier, in the contemporary data set. Mid-summer flowers bloomed on average 10 days earlier, nonnative species 15 days earlier, and berry-producing shrubs 5 days earlier, while late summer flowering plants did not shift. The greatest correlates of early-spring and mid-summer flowering were average spring temperature and day of snowmelt, which was 21 days earlier, on average, in 2016-2019 relative to the 1973-1978 observations. The shifts in flowering phenology that we observed could indicate developing asynchronies or novel synchronies of these plant resources and wildlife species of conservation concern, including Greater Sage-grouse, whose nesting success is tied to availability of spring forbs; grizzly bears, which rely heavily on berries for their fall diet; and pollinators. This underscores the importance of maintaining a diverse portfolio of native plants in terms of species composition, genetics, phenological responsiveness to climatic cues, and ecological importance to key wildlife and pollinator species. Redundancy within ecological niches may also be important considering that species roles in the community may shift as climate change affects them differently. These considerations are particularly relevant to restoration and habitat-enhancement projects in sagebrush communities across western North America.

Plant community context controls short‐ versus medium‐term effects of pre‐emergent herbicides on target and non‐target species after fire

AbstractQuestionsSelective herbicide application is a common restoration strategy to control exotic invaders that interfere with native plant recovery after wildfire. Whether spraying with pre‐emergent or bio‐herbicides releases native plants from competition with exotics (“spray‐and‐release” strategy) and makes communities resistant to reinvasion by exotic annual grasses (e.g. cheatgrass, medusahead), without risks to non‐target native plants or secondary invasion, is a major question for land managers of semiarid plant communities.LocationSagebrush steppe of southwest Idaho, USA.MethodsWe applied chemical herbicides (imazapic, rimsulfuron) and weed‐suppressive bacteria (Pseudomonas fluorescens strains MB906 and D7) to three sagebrush steppe communities after fire. We measured plant cover prior to burning and for four years (five for exotic annual grasses) post treatment.ResultsBoth chemical herbicides significantly reduced exotic annual grass cover in all communities in the first post‐spraying year, but rimsulfuron plots were re‐invaded after 1–2 years, while imazapic plots continued to resist reinvasion four and even five years post spraying, well after the herbicide should have degraded. We did not detect any increase in native perennial grass cover with either herbicide, and herbicides had both positive and negative effects on individual bunchgrass basal diameter, depending on species and plant community. Rimsulfuron was more damaging than imazapic to shallow‐rooted perennial bunchgrasses. Moss and lichen cover, key components of soil integrity, increased with chemical herbicide treatments in some communities. Both herbicides increased secondary invaders (exotic forbs or grasses), which varied by plant community and herbicide. Weed‐suppressive bacteria treatments had no significant effects on cover of any functional group.ConclusionsWhile short‐term effects of chemical herbicides that target exotic annual grasses were relatively consistent and predictable, longer‐term effects were specific to the herbicide and plant community. The “spray‐and‐release” strategy may confer resistance to re‐invasion by exotic annual grasses if herbicides prevent re‐invasion for an extended period.

Bridging the Gap Between Spatial Modeling and Management of Invasive Annual Grasses in the Imperiled Sagebrush Biome

Invasions of native plant communities by non-native species present major challenges for ecosystem management and conservation. Invasive annual grasses such as cheatgrass, medusahead, and ventenata are pervasive and continue to expand their distributions across imperiled sagebrush-steppe communities of the western United States. These invasive grasses alter native plant communities, ecosystem function, and fire regimes, threatening sagebrush ecosystem persistence. Spatial data describing the distribution and abundance of invasive species are often used by resource managers to identify, target, and determine needed interventions. However, there are challenges associated with translating these datasets into management actions. We conducted a review of available spatial products to assess advances in, and barriers to, applying contemporary model-based maps to support rangeland management. We found dozens of regional data products describing cheatgrass or annual herbaceous cover and few maps describing ventenata or medusahead. Over the past decade, IAG spatial data increased in spatial and temporal resolution and increasingly used response variables that indicate the severity of infestation such as percent cover. Despite improvements, use of such data is limited by the time required to find, compare, understand, and translate model-based maps into management strategy. There is also a need for products with higher spatial resolution and accuracy. In collaboration with a multipartner stakeholder group, we identified key considerations that guide selection of IAG spatial data products for use by land managers and other users. On the basis of these considerations, we discuss issues that contribute to a research-implementation gap between users and product developers and suggest future directions for improved development of management-ready spatial products.

Drought and shrub cover differentially affect seed bank composition within two sagebrush steppe communities

Soil seed banks are critical biodiversity repositories for dryland plant communities. Understanding how environmental factors alter seed bank composition provides valuable information on ecological processes within a community and can be useful for creating land management strategies. We assessed seed bank response to drought and microsite within an Artemisia arbuscula dominated community and a directly adjacent (∼60m apart) A. cana dominated community, and characterized the similarity between these two seed banks and the corresponding aboveground vegetation. We found that drought increased exotic grass seed density and decreased seed species diversity and evenness within the A. arbuscula community, whereas shrub microsites enhanced seed species diversity and native forb seed density. In contrast, there were only minor drought effects within the A. cana community. Within both plant communities, there was low similarity between the seed bank and existing vegetation (<28%), and both seed banks were comprised of over 50% exotic annual grass seeds. Our study suggests that seed banks of drylands similar to A. arbuscula dominated plant communities (with heterogenous landscapes and low soil moisture availability) may experience more drought induced impacts than adjacent sagebrush communities, and highlights the role of shrub canopies as beneficial microsites for seeds in some drylands.

Assessing commercial and early-seral arbuscular mycorrhizal fungi inoculation to aid in restoring sagebrush steppe shrubs

Arbuscular mycorrhizal fungi (AMF) are drivers of plant communities as they influence plant competition by increasing plants’ root absorptive surface. As such, AMF could be an important tool for ecological restoration. However, a lack of research using AMF in sagebrush steppe communities implies a need for more assessments of its efficacy. Here, we assessed the ability of a commercial inoculum to colonize and influence growth of three native Artemisia spp. (sagebrush) shrubs and the exotic Taeniatherum caput-medusae (medusahead). We expected to increase colonization and biomass production with the addition of the inoculum. Before testing the inoculum, its viability was examined using Trifolium incarnatum (crimson clover) in autoclaved soil. Next, a factorial greenhouse experiment was conducted to evaluate the target species when grown in live or autoclaved field soil from a disturbed (early seral) site. Inoculation resulted in an average root colonization of 24.82% ± 4.86% for T. incarnatum but failed to colonize any of the sagebrush steppe species in autoclaved soil and had little to no influence on colonization in live soil. All sagebrush steppe species were colonized by AMF in live soil, and biomass production averaged 889 mg, 530 mg, 323 mg, and 1 852 mg, respectively; however, average biomass for all species was greater when grown in autoclaved soils (1 620 mg, 706 mg, 371 mg, and 3 902 mg, respectively). Our results reveal differential effects of a commercial AMF inoculum on root colonization of Artemisia spp. and T. incarnatum and highlight the need to assess the efficacy of AMF inoculum before field application.

Seed and seedling traits have strong impacts on establishment of a perennial bunchgrass in invaded semi‐arid systems

Abstract Many restoration projects use seeds to found new populations, and understanding phenotypic traits associated with seedling establishment in disturbed and invaded communities is important for restoration efforts world‐wide. Focusing on the perennial grass Elymus elymoides, a native species common to sagebrush steppe communities in the Western United States, we asked if seed and seedling traits could predict field establishment. We collected seeds from 34 populations from the western Great Basin. In greenhouse studies, we measured variation in seed and seedling characteristics of wild populations and one cultivar. We also quantified abiotic conditions at the collection location and asked if these characteristics predicted survival and other fitness metrics at five planting sites. Planting sites were all near‐monocultures of the invasive annual grass Bromus tectorum, and all sites experienced similar, below‐average precipitation during the experiment. Phenotypic traits were strongly correlated with performance across all sites, with remarkably high predictive power. Seeds from populations with longer roots, larger seeds and earlier emergence were significantly more likely to survive the first growing season (R2 = 0.66, p &lt; 0.0001). In contrast, while some abiotic variables at the collection location (e.g. 30‐year average summer precipitation and fall minimum temperatures) were associated with field performance at some sites, abiotic variables explained less variation in performance than traits (average R2 = 0.22). Despite the low predictive power of abiotic variables, populations that performed best at each field site were from locations with climate variables similar to planting sites. Synthesis and applications. The best seed sources for restoration of Elymus elymoides in invaded sites were populations with longer roots, larger seeds and earlier emergence. These easily measured traits were strong predictors of survival in disturbed field sites. While the most successful populations were found in areas with similar abiotic conditions as planting sites, there was phenotypic variation even among populations originating from locations with similar conditions. Thus, our results indicate that abiotic conditions are important considerations when selecting seeds, but these conditions may not sufficiently predict which populations will establish. Understanding population differences in seedling functional traits can improve predictions of restoration success.

Longer-Term Evaluation of Revegetation of Medusahead-Invaded Sagebrush Steppe

Medusahead (Taeniatherum caput-medusae [L.] Nevski) and other exotic annual grasses have invaded millions of hectares of sagebrush (Artemisia L.) steppe. Revegetation of medusahead-invaded sagebrush steppe with perennial vegetation is critically needed to restore productivity and decrease the risk of frequent wildfires. However, it is unclear if revegetation efforts provide long-term benefits (fewer exotic annuals and more perennials). The limited literature available on the topic questions whether revegetation efforts reduce medusahead abundance beyond 2 or 3 yr. We evaluated revegetation of medusahead-invaded rangelands for 5 yr after seeding introduced perennial bunchgrasses at five locations. We compared areas that were fall-prescribed burned immediately followed by an imazapic herbicide treatment and then seeded with bunchgrasses 1 yr later (imazapic-seed) with untreated controls (control). The imazapic-seed treatment decreased exotic annual grass cover and density. At the end of the study, exotic annual grass cover and density were 2-fold greater in the control compared with the imazapic-seed treatment. The imazapic-seed treatment had greater large perennial bunchgrass cover and density and less annual forb (predominately exotic annuals) cover and density than the untreated control for the duration of the study. At the end of the study, large perennial bunchgrass density average 10 plant∙m−2 in the imazapic-seed treatment, which is comparable with intact sagebrush steppe communities. Plant available soil nitrogen was also greater in the imazapic-seed treatment compared with the untreated control for the duration of the study. The results of this study suggest that revegetation of medusahead-invaded sagebrush steppe can provide lasting benefits, including limiting exotic annual grasses.

Indicators of Ventenata (Ventenata dubia) Invasion in Sagebrush Steppe Rangelands

AbstractVentenata [Ventenata dubia(Leers) Coss.], an invasive winter annual grass, significantly reduces forage production in grassland systems and displaces species within both perennial- and annual-dominated grasslands within the Inland Northwest. The range ofV. dubiais expanding into sagebrush steppe communities, an expansive habitat critical for forage production, wildlife, and recreation. Currently, there is limited knowledge ofV. dubia’s distribution and abundance within sagebrush steppe communities. We performed field surveys at 15 locations in sagebrush steppe rangelands in southern Idaho and eastern Oregon to assess whereV. dubiaoccurs, with the aim of providing insight about its niche in this new habitat. Specifically, we evaluated biotic and abiotic factors of the plant community as indicators ofV. dubiapresence. We also correlated species diversity measures with no, low (&lt;12.5%), and high (&gt;12.5%)V. dubiacover. Though widely distributed throughout the study region,V. dubiaonly appeared in 45% of the 225 plots, and foliar cover was typically less than 50%. It was primarily found in ephemerally wet microhabitats. Species richness and the Shannon diversity index were lowest in plots with highV. dubiacover. Nonmetric multidimensional scaling analysis revealed thatV. dubiaand medusahead [Taeniatherum caput-medusae(L.) Nevski] were closely associated. Furthermore, chi-square indicator analysis showed thatT. caput-medusaewas more prevalent, while mountain big sagebrush [Artemisia tridentataNutt. spp.vaseyana(Rydb.) Beetle] was less prevalent, in plots containingV. dubia. Abiotic factors that explained variation inV. dubiaabundance included rock cover, soil depth, and a north/south aspect. HigherV. dubiacover also correlated with higher clay content and lower phosphorus and potassium concentrations in the soil. We suggest that at this point, detection survey efforts to locate incipient infestations ofV. dubiain sagebrush steppe communities should focus on moist areas and sites susceptible to invasion byT. caput-medusae.

Floral Guilds of Bees in Sagebrush Steppe: Comparing Bee Usage of Wildflowers Available for Postfire Restoration

ABSTRACT: Healthy plant communities of the American sagebrush steppe consist of mostly wind-pollinated shrubs and grasses interspersed with a diverse mix of mostly spring-blooming, herbaceous perennial wildflowers. Native, nonsocial bees are their common floral visitors, but their floral associations and abundances are poorly known. Extrapolating from the few available pollination studies, bees are the primary pollinators needed for seed production. Bees, therefore, will underpin the success of ambitious seeding efforts to restore native forbs to impoverished sagebrush steppe communities following vast wildfires. This study quantitatively characterized the floral guilds of 17 prevalent wildflower species of the Great Basin that are, or could be, available for restoration seed mixes. More than 3800 bees representing >170 species were sampled from >35,000 plants. Species of Osmia, Andrena, Bombus, Eucera, Halictus, and Lasioglossum bees prevailed. The most thoroughly collected floral guilds, at Balsamorhiza...

How to quantify the temporal storage effect using simulations instead of math.

The storage effect has become a core concept in community ecology, explaining how environmental fluctuations can promote coexistence and maintain biodiversity. However, limitations of existing theory have hindered empirical applications: the need for detailed mathematical analysis whenever the study system requires a new model, and restricted theory for structured populations. We present a new approach that overcomes both these limitations. We show how temporal storage effect can be quantified by Monte Carlo simulations in a wide range of models for competing species. We use the lottery model and a generic integral projection model (IPM) to introduce ideas, and present two empirical applications: (1) algal species in a chemostat with variable temperature, showing that the storage effect can operate without a long-lived life stage and (2) a sagebrush steppe community IPM. Our results highlight the need for careful modelling of nonlinearities so that conclusions are not driven by unrecognised model constraints.

Vegetation Response to Piñon and Juniper Tree Shredding

Piñon (Pinus spp.) and juniper (Juniperus spp.) expansion and infilling in sagebrush (Artemisia L.) steppe communities can lead to high-severity fire and annual weed dominance. To determine vegetation response to fuel reduction by tree mastication (shredding) or seeding and then shredding, we measured cover for shrub and herbaceous functional groups on shredded and adjacent untreated areas on 44 sites in Utah. We used mixed model analysis of covariance to determine significant differences among ecological site type (expansion and tree climax) and treatments across a range of pretreatment tree cover as the covariate. Although expansion and tree climax sites differed in cover values for some functional groups, decreasing understory cover with increasing tree cover and increased understory cover with tree reduction was similar for both ecological site types. Shrub cover decreased by 50% when tree cover exceeded 20%. Shredding trees at ≤ 20% cover maintained a mixed shrub (18.6% cover)−perennial herbaceous (17.6% cover) community. Perennial herbaceous cover decreased by 50% when tree cover exceeded 40% but exceeded untreated cover by 11% (20.1% cover) when trees were shredded at 15−90% tree cover. Cheatgrass (Bromus tectorum L.) cover also increased after tree shredding or seeding and then shredding but was much less dominant (<10% cover) where perennial herbaceous cover exceeded 42%. Sites with high cheatgrass cover on untreated plots had high cheatgrass cover on shredded and seeded-shredded plots. Seeding and then shredding decreased cheatgrass cover compared with shredding alone when implemented at tree cover ≥ 50%. Vegetation responses to shredding on expansion sites were generally similar to those for tree cutting treatments in the SageSTEP study. Shredding or seeding and then shredding should facilitate wildfire suppression, increase resistance to weed dominance, and lead toward greater resilience to disturbance by increasing perennial herbaceous cover.

Linking demography with drivers: climate and competition

SummaryIn observational demographic data, the number of measured factors that could potentially drive demography (such as daily weather records between two censuses) can easily exceed the number of independent observations. Thus, identifying the important drivers requires alternatives to standard model selection and variable selection methods.Spline methods that estimate smooth functions over continuous domains (such as space or time) have the potential to resolve high‐dimensional problems in ecological systems. We consider two examples that are important for many plant populations: competition with neighbours that vary in size and distance from the focal individual and climate variables during a window of time before a response (growth, survival, etc.) is measured.For competition covariates, we use a simulation study based on empirical data to show that a monotone spline estimate of competition kernels via approximate AIC returns very accurate estimates. We then apply the method to long‐term, mapped quadrat data on the four dominant species in an Idaho (US) sagebrush steppe community.For climate predictors and their temporal lags, we use simulated data sets to compare functional smoothing methods with competing linear (LASSO) or machine learning (random forests) methods. Given sufficient data, functional smoothing methods outperformed the other two methods.Functional smoothing methods can advance data‐driven population modelling by providing alternatives to specifying competition kernelsa prioriand to arbitrarily aggregating continuous environmental covariates. However, there are important open questions related to modelling of nonlinear climate responses and size × climate interactions.

Influence of Habitat and Intrinsic Characteristics on Survival of Neonatal Pronghorn.

Increased understanding of the influence of habitat (e.g., composition, patch size) and intrinsic (e.g., age, birth mass) factors on survival of neonatal pronghorn (Antilocapra americana) is a prerequisite to successful management programs, particularly as they relate to population dynamics and the role of population models in adaptive species management. Nevertheless, few studies have presented empirical data quantifying the influence of habitat variables on survival of neonatal pronghorn. During 2002–2005, we captured and radiocollared 116 neonates across two sites in western South Dakota. We documented 31 deaths during our study, of which coyote (Canis latrans) predation (n = 15) was the leading cause of mortality. We used known fate analysis in Program MARK to investigate the influence of intrinsic and habitat variables on neonatal survival. We generated a priori models that we grouped into habitat and intrinsic effects. The highest-ranking model indicated that neonate mortality was best explained by site, percent grassland, and open water habitat; 90-day survival (0.80; 90% CI = 0.71–0.88) declined 23% when grassland and water increased from 80.1 to 92.3% and 0.36 to 0.40%, respectively, across 50% natal home ranges. Further, our results indicated that grassland patch size and shrub density were important predictors of neonate survival; neonate survival declined 17% when shrub density declined from 5.0 to 2.5 patches per 100 ha. Excluding the site covariates, intrinsic factors (i.e., sex, age, birth mass, year, parturition date) were not important predictors of survival of neonatal pronghorns. Further, neonatal survival may depend on available land cover and interspersion of habitats. We have demonstrated that maintaining minimum and maximum thresholds for habitat factors (e.g., percentages of grassland and open water patches, density of shrub patches) throughout natal home ranges will in turn, ensure relatively high (>0.50) neonatal survival rates, especially as they relate to coyote predation. Thus, landscape level variables (particularly percentages of open water, grassland habitats, and shrub density) should be incorporated into the development or implementation of pronghorn management plans across sagebrush steppe communities of the western Dakotas, and potentially elsewhere within the geographic range of pronghorn.

Estimating pinyon and juniper cover across Utah using NAIP imagery

Expansion of Pinus L. (pinyon) and Juniperus L. (juniper) (P-J) trees into sagebrush ( Artemisia L.) steppe communities can lead to negative effects on hydrology, loss of wildlife habitat, and a decrease in desirable understory vegetation. Tree reduction treatments are often implemented to mitigate these negative effects. In order to prioritize and effectively plan these treatments, rapid, accurate, and inexpensive methods are needed to estimate tree canopy cover at the landscape scale. We used object based image analysis (OBIA) software (Feature Analyst TM for ArcMap 10.1 ® , ENVI Feature Extraction ® , and Trimble eCognition Developer 8.2 ® ) to extract tree canopy cover using NAIP (National Agricultural Imagery Program) imagery. We then compared our extractions with ground measured tree canopy cover (crown diameter and line point intercept) on 309 plots across 44 sites in Utah. Extraction methods did not consistently over- or under-estimate ground measured P-J canopy cover except where tree cover was >45%. Estimates of tree canopy cover using OBIA techniques were strongly correlated with estimates using the crown diameter method (r = 0.93 for ENVI, 0.91 for Feature Analyst TM , and 0.92 for eCognition). Tree cover estimates using OBIA techniques had lower correlations with tree cover measurements using the line-point intercept method (r = 0.85 for ENVI, 0.83 for Feature Analyst TM , and 0.83 for eCognition). All software packages accurately and inexpensively extracted P-J canopy cover from NAIP imagery when the imagery was not blurred, and when P-J cover was not mixed with Amelanchier alnifolia (Utah serviceberry) and Quercus gambelii (Gambel’s oak), which had similar spectral values as P-J.

Canid Social Structure and Density Dependence Improve Predator-Prey Models of &amp;lt;i&amp;gt;Canis latrans&amp;lt;/i&amp;gt; and &amp;lt;i&amp;gt;Lepus californicus&amp;lt;/i&amp;gt; in Curlew Valley, UT

Prominent examples of predator-prey oscillations between prey-specific predators exist, but long-term data sets showing these oscillations are uncommon. We explored various models to describe the oscillating behavior of coyote (Canis latrans) and black-tailed jackrabbits (Lepus californicus) abundances in a sagebrush-steppe community in Curlew Valley, UT over a 31-year period between 1962 and 1993. We tested both continuous and discrete models which accounted for a variety of mechanisms to discriminate the most important factors affecting the time series. Both species displayed cycles in abundance with three distinct peaks at ten-year intervals. The coupled oscillations appear greater in the mid-seventies and a permanent increase in the coyote density seems apparent. Several factors could have influenced this predator-prey system including seasonality, predator satiation, density dependence, social structure among coyotes, and a change in the coyote bounty that took place during the course of data collection. Maximum likelihood estimation was used to obtain parameter values for the models, and Akaike Information Criterion (AIC) values were used to compare models. Coyote social structure and limiting resources in the form of density-dependence and satiation seemed to be important factors affecting population dynamics.

Post-fire vegetation dynamics of a sagebrush steppe community change significantly over time

Sagebrush steppe ecosystems of the Intermountain West have experienced a decline over the past 150 years due to changing fire regimes, invasive species and conifer encroachment. Prescribed fire is a common and cost-effective tool used in sagebrush restoration and fuels management. We examined the post-fire succession of a sagebrush steppe community over a nearly 30-year period at two study sites in northeastern California. The long-term nature of this study was particularly significant, as invasive annual grasses dominated the plant community in the years immediately following fire, but native perennial grasses and shrubs successfully out-competed them in the long term. Shrubs were slow to recover but had returned to pre-fire levels by the end of the study period. There was also notable increase in western juniper throughout the study sites, particularly in areas that had not been burned. Our results indicate that mean fire return intervals of 50 years or less would help reduce western juniper encroachment and preserve sagebrush habitat, especially for potentially threatened species such as the sage grouse.

Response of Conifer-Encroached Shrublands in the Great Basin to Prescribed Fire and Mechanical Treatments

In response to the recent expansion of piñon and juniper woodlands into sagebrush-steppe communities in the northern Great Basin region, numerous conifer-removal projects have been implemented, primarily to release understory vegetation at sites having a wide range of environmental conditions. Responses to these treatments have varied from successful restoration of native plant communities to complete conversion to nonnative invasive species. To evaluate the general response of understory vegetation to tree canopy removal in conifer-encroached shrublands, we set up a region-wide study that measured treatment-induced changes in understory cover and density. Eleven study sites located across four states in the Great Basin were established as statistical replicate blocks, each containing fire, mechanical, and control treatments. Different cover groups were measured prior to and during the first 3 yr following treatment. There was a general pattern of response across the wide range of site conditions. There was an immediate increase in bare ground and decrease in tall perennial grasses following the fire treatment, but both recovered by the second or third growing season after treatment. Tall perennial grass cover increased in the mechanical treatment in the second and third year, and in the fire treatment cover was higher than the control by year 3. Nonnative grass and forb cover did not increase in the fire and mechanical treatments in the first year but increased in the second and third years. Perennial forb cover increased in both the fire and mechanical treatments. The recovery of herbaceous cover groups was from increased growth of residual vegetation, not density. Sagebrush declined in the fire treatment, but seedling density increased in both treatments. Biological soil crust declined in the fire treatment, with no indications of recovery. Differences in plant response that occurred between mechanical and fire treatments should be considered when selecting management options.