Mixed-grass Prairie Research Articles

Effects of Feral Horse Herds on Rangeland Plant Communities across a Precipitation Gradient

Feral horses are widespread in the western United States, with the majority of feral horse herds found in the Great Basin. There is a federal mandate to manage these herds in order to maintain “ecological balance”; however, understanding of the specific effects of feral horse grazing on rangeland plant communities in this region is incomplete. To address this research gap, we utilized long-term grazing exclosures and fenceline contrasts to evaluate the impacts of feral horses on several plant community variables (diversity, richness, dominance, and biomass) and species composition. Because the effects of grazing can vary with site precipitation and productivity, we selected 5 sites from 4 different rangeland types (Great Basin Desert, Colorado Plateau, Rocky Mountain grassland, and mixed grass prairie) that spanned a mean annual precipitation gradient of 229 to 413 mm. Our results did not reveal a significant effect of feral horse grazing on plant community composition, species richness, diversity, evenness, or dominance. In contrast, total aboveground herbaceous biomass and grass biomass were significantly reduced with feral horse grazing, but these effects did not vary with mean annual precipitation. Our results suggest that, at least at the sites we studied, feral horses have affected the plant community by reducing herbaceous biomass but have not caused plant community shifts. Additional multisite studies, preferably with standardized exclosures and larger sample sizes, would increase our understanding of feral horse grazing effects and inform management of feral horse herds in the western United States.

Divergent effects of defoliation intensity and frequency on tiller growth and production dynamics ofPascopyrum smithiiandHesperostipa comata

Rotational stocking theoretically enables regrazing of regrowth, but regrowth may be limited in xerophytic vegetation. We tested the hypothesis that regrowth would be slow and fixed in Hesperostipa comata (a caespitose, drought-tolerant grass), while growth would be flexible in Pascopyrum smithii (a rhizomatous, less drought-tolerant grass) under increasing defoliation and moisture, by assessing tiller growth rates, population dynamics and plant yield on marked plants in a Dry Mixed Grass prairie. Plots were clipped in late summer to simulate a deferred control, or intermittently during the growing season (May–August) at high intensity–low frequency (HILF), low intensity–high frequency (LIHF) or high intensity–high frequency and crossed with two water treatments (ambient and addition) in both a xeric upland and a mesic lowland. Growing season defoliation increased tiller growth rates of P. smithii in the upland, whereas HILF and LIHF reduced growth in the lowland. All defoliation regimes increased tiller growth for H. comata. Tiller populations of H. comata increased with frequent defoliation, while tiller populations of P. smithii decreased regardless of defoliation regime. Frequent defoliation, regardless of intensity, reduced yield relative to the deferred control for both grasses. While water addition consistently increased growth rates and reduced differences in tiller number among defoliation treatments, the regrowth of both grasses remained similar under varied defoliation with ambient moisture. High moisture conditions also promoted regrowth more in P. smithii compared to H. comata. In summary, neither grass species displayed an inherently fixed or flexible tiller or plant yield response in response to defoliation or moisture.

Soils Determine Early Revegetation Establishment with and without Cover Crops in Northern Mixed Grass Prairie after Energy Development

Cover crops have been used to build soil health and improve ecosystem services in agricultural fields and pastures, but they have not been tested in restoration contexts. We conducted two experiments in interim oilfield reclamations at Ft. Berthold Indian Reservation in North Dakota: in 2014 two different perennial grass mixes, with and without an oat cover crop and, in 2015, a single grass mix with and without a cover crop cocktail. To determine whether cover crops speeded site recovery or whether they competed with perennial grasses, all sites were assessed for plant establishment and rangeland health in August 2015. Sites planted in 2014 ranged from 20 (± 10 SD) to 38 (± 0.5) perennial grass plants/m2. Sites planted in 2015 ranged from 6 (± 1.8) to 29 (± 11) plants/m2. Cover crop treatment and grass mix treatments were not significant determinants of perennial grass establishment ( p 0.05). Soil nutrients appeared to drive early revegetation establishment: sites with poor perennial grass establishment had lower levels of phosphorous and higher levels of calcium, iron and manganese. Rangeland health trended towards being greater when a cover crop was planted, but the effect was very small. We will eventually test whether the long-term benefits of cover crops in agricultural systems transfer to restoration, but when cover crops establish at low densities, as we observed in these studies, they may only have small effects in reclamations.

Weed Establishment and Persistence after Water Pipeline Installation and Reclamation in the Mixed Grass Prairie of Western North Dakota

Erin K. Espeland Corresponding author, Research Ecologist, USDA ARS NPARL Pest Management Research Unit, Sidney MT 59270, erin.espeland{at}ars.usda.gov.

Grazing Preferences and Vegetation Feedbacks of the Fire-Grazing Interaction in the Northern Great Plains

The fire-grazing interaction is well studied in mesic grasslands worldwide, but research is limited in semiarid systems. We examined the principal drivers and feedbacks of the fire-grazing interaction on the strength of cattle grazing selection, herbaceous biomass, crude protein, and vegetation structure and composition in two pastures in the Northern Great Plains. Cattle showed significant preference, use, and grazing utilization in recently burned patches that declined as time since fire increased. Cattle selection was driven by significantly increased crude protein in recent burns. Grazing utilization of 70% in patches with < 1 yr after fire established low herbaceous biomass, but the extent to which it was maintained varied with precipitation. Herbaceous biomass increased to nonburned levels 2 yr after fire, and crude protein decreased to nonburned levels 120 d after fire. Species composition was influenced primarily by site and year, though bare ground and litter were influenced by the fire-grazing interaction. Our data indicate that mixed-grass prairies of the Northern Great Plains are resilient to the fire-grazing interaction and that rest from grazing following fire is likely ecologically unnecessary. The use of the fire-grazing interaction is an alternative management strategy suitable for the Northern Great Plains, effectively increasing heterogeneity of grassland habitat.

An Extremely Rich Fen on the Plains of the Blackfeet Indian Reservation, Montana

ABSTRACT: An 8-ha, extremely rich fen, surrounded by saline wet meadows, occurs on the western edge of mixed-grass prairie in the northwestern Great Plains, 47 km east of the Montana Rocky Mountain Front. The site occurs on an outwash plain near the junction of Pleistocene-age continental and mountain glaciers and on the western edge of former glacial Cut Bank Lake. Five wetland plant communities are described from this site. A total of 93 vascular plant and 65 diatom species have been found. Twelve diatom taxa could not be identified with available floras and one has been confirmed as new to science. Both diatoms and vascular plants indicate a locally disjunct, post-glacial assemblage similar to those found in boreal and mountainous habitats, adapted to alkaline waters. Saline-influenced, extremely rich fens are a rare sub-type of peatland in the northern Great Plains, and contain high diatom and vascular plant species richness as well as rare taxa.

Restoring Industrial Disturbances with Native Hay in Mixedgrass Prairie in Alberta

Native grassland restorations are often unsuccessful as a consequence of unreliable seed sources and competition from weeds and agronomic species. To improve on conventional approaches, we tested whether native hay can be used as a seed source for restoring native mixedgrass prairie on oil and gas well sites and associated disturbed areas. We also assessed the recovery of grassland that had been cut to harvest native hay. We assessed three wellsites seeded with native hay seven years earlier to evaluate longer term recovery, and they showed significant similarity to controls in adjacent grassland. Additionally, in 2012, five wellsites and an access road were seeded with native hay cut from grassland close to the sites. Grassland cut for native hay recovered within one year, showing similar species composition. In the second year, native hay restored wellsites had significant weedy annual cover; nevertheless, native grasses and forbs germinated, particularly needle grasses, wheatgrasses, and bluegrasses. Three of the native hay restored wellsites were sprayed with a non-selective herbicide in the third year; however, the remaining sites showed good recovery in the third year, with native grasses replacing most of the original weedy species. Collectively, results from this research suggest seeding from native hay is a successful and sustainable technique for restoring native vegetation cover and diversity on industrial disturbances in native grasslands.

Vulnerability of grazing and confined livestock in the Northern Great Plains to projected mid- and late-twenty-first century climate

The Northern Great Plains (NGP) region of the USA—which comprises Montana, Wyoming, Colorado, North Dakota, South Dakota, and Nebraska—is a largely rural area that provides numerous ecosystem services, including livestock products, cultural services, and conservation of biological diversity. The region contains 25% of the Nation’s beef cattle and approximately one-third of the confined beef cattle, as well as the largest remaining native prairie in the US—the Northern Mixedgrass Prairie. With rising atmospheric CO2, the NGP is projected to experience warmer and longer growing seasons, greater climatic variability, and more extreme events (e.g., increased occurrence of large precipitation events). These climatic changes may affect livestock production both directly via physiological impacts on animals and indirectly via modifications to forage, invasion of undesirable plants, and increased exposure to parasites. This raises concerns about the vulnerability of grazing livestock operations and confined livestock operations to projected changes in mid- (2050) and late- (2085) twenty-first century climate. Our objectives are to (1) describe the NGP’s exposure to temperature and precipitation trends, inter-annual variability, and extreme events; (2) evaluate the sensitivity of beef cattle production to direct and indirect effects imposed by these projected climatic changes; and (3) provide a typology of adaptation strategies to minimize adverse consequences of projected changes and maximize beneficial consequences. Agricultural managers have developed considerable adaptive capacity to contend with environmental and economic variability. However, projected climatic changes, especially the increased frequency and magnitude of weather extremes, will require even greater adaptive capacity to maintain viable production systems. Consequently, regional vulnerability to projected climatic changes will be determined not only by ecological responses but also by the adaptive capacity of individual managers. Adaptive capacity in the NGP will differ from other regions, in part because projections suggest some opportunities for increased livestock production. Adaptations in both grazing and confined beef cattle systems will require enhanced decision-making skills capable of integrating biophysical, social, and economic considerations. Social learning networks that support integration of experimental and experiential knowledge—such as lessons learned from early adopters and involvement with science-based organizations—can help enhance decision-making and climate adaptation planning. Many adaptations have already been implemented by a subset of producers in this region, providing opportunities for assessment, further development, and greater adoption. Context-specific decision-making can also be enhanced through science-management partnerships, which aim to build adaptive capacity that recognizes multiple production and conservation/environmental goals.

Conventional oil and natural gas infrastructure increases brown-headed cowbird (Molothrus ater) relative abundance and parasitism in mixed-grass prairie.

The rapid expansion of oil and natural gas development across the Northern Great Plains has contributed to habitat fragmentation, which may facilitate brood parasitism of ground-nesting grassland songbird nests by brown-headed cowbirds (Molothrus ater), an obligate brood parasite, through the introduction of perches and anthropogenic edges. We tested this hypothesis by measuring brown-headed cowbird relative abundance and brood parasitism rates of Savannah sparrow (Passerculus sandwichensis) nests in relation to the presence of infrastructure features and proximity to potential perches and edge habitat. The presence of oil and natural gas infrastructure increased brown-headed cowbird relative abundance by a magnitude of four times, which resulted in four times greater brood parasitism rates at infrastructure sites. While the presence of infrastructure and the proximity to roads were influential in predicting brood parasitism rates, the proximity of perch sites was not. This suggests that brood parasitism associated with oil and natural gas infrastructure may result in additional pressures that reduce productivity of this declining grassland songbird.

Phenology of perennial, native grass, belowground axillary buds in the northern mixed-grass prairie.

Vegetative reproduction from belowground bud banks is the primary driver of grassland systems. Despite the importance of bud banks, the timing of recruitment and the crucial link between formation and maintenance is unknown. We assessed patterns of belowground bud development, dormancy, and mortality associated with three perennial native grasses in the northern Great Plains. Temperature and soil moisture were measured below the soil surface to determine relationships with belowground bud development. Blue grama (Bouteloua gracilis) generated more buds over winter that remained dormant; whereas, C3 species needle-and-thread (Hesperostipa comata) and western wheatgrass (Pascopyrum smithii), maintained limited dormant buds throughout winter. Soil temperature was a good predictor for C4 species bud production; whereas, soil moisture was a reliable predictor for C3 buds. Distinct differences existed between C4 species blue grama and C3 species needle-and-thread, whereas C3 species western wheatgrass (Pascopyrum smithii) was intermediate, indicating there is likely a species-specific continuum between the C3 and C4 extremes rather than a stark difference. The ability to predict belowground bud development is a novel insight to native perennial grasses. Native grass species' strategies and adaptability regarding belowground bud bank size and bud phenology are important factors optimizing tiller recruitment given the variable growing conditions. Patterns of bud dormancy and development will provide insight to the underlying mechanisms by which management practices and fluctuations in precipitation amount and growing season length can alter mixed-grass prairie plant community dynamics.

Power and limitation of soil properties as predictors of variation in peak plant biomass in a northern mixed-grass prairie

Soil properties are thought to affect annual plant productivity in rangelands, and thus soil variables that are consistently correlated with plant biomass may be general indicators of rangeland health. Here we measured several soil properties (e.g. aggregate stability, organic carbon, total nitrogen) and tested each as a would-be predictor of local variation in peak aboveground grassland biomass. Individual properties explained a slight (≤10%) amount of variation in plant biomass. Plant biomass was mainly (negatively) associated with two soil properties, subsurface soil carbonate concentration and the stability of soil macroaggregates near the soil surface. Less important predictive variables included: elevation, plant community composition, surface soil organic carbon, and soil carbon:nitrogen. Plot-to-plot variation in plant biomass is seemingly difficult to predict based on soil properties, including popular indicators of soil and rangeland health and even root biomass. While protection of soil is critical to overall rangeland ecosystem function, our findings suggest that the relationship between soil properties and plant biomass in natural grasslands is complex. Thus, there may not be one or even several soil properties that consistently predict appreciable variation in peak grassland biomass, especially variation within an ecosystem independent of precipitation.

Flea and Small Mammal Species Composition in Mixed-Grass Prairies: Implications for the Maintenance ofYersinia pestis

Maintenance of sylvatic plague in prairie dogs (Cynomis spp.) was once thought unlikely due to high mortality rates; yet more recent findings indicate that low-level enzootic plague may be maintained in susceptible prairie dog populations. Another hypothesis for the maintenance of sylvatic plague involves small mammals, other than prairie dogs, as an alternative reservoir in the sylvatic plague system. These hypotheses, however, are not mutually exclusive, as both prairie dogs and small mammals could together be driving sylvatic cycles of plague. The concept of a bridging vector has been used to explain the transmission of pathogens from one host species to another. In the case of sylvatic plague, this would require overlap in fleas between small mammals and prairie dogs, and potentially other species such as carnivores. Our goal was to evaluate the level of flea sharing between black-tailed prairie dogs (Cynomis ludovicianus) and other small mammals in a mixed-grass prairie in South Dakota. We investigated the species richness of small mammals and small-mammal fleas in a mixed-grass prairie system and compared findings with previous studies from a short-grass ecosystem in Colorado. Over the summer field seasons 2014-2016 we live-trapped small mammals, collected fleas, and showed differences between both the flea and small mammal composition of the two systems. We also recorded higher densities of deer mice and lower densities of northern grasshopper mice in mixed versus shortgrass prairies. We confirmed, as is the case in shortgrass prairies, a lack of substantial flea species overlap on small mammal hosts and fleas from prairie dogs and their burrows. Moreover this study demonstrates that although small mammals may not play a large part in interepizootic plague cycling in shortgrass prairie ecosystems, their role in mixed-grass prairies requires further evaluation.

Targeting Introduced Species to Improve Plant Community Composition on USFWS-Managed Prairie Remnants

The quality of plant community composition on US Fish and Wildlife Service (USFWS) lands in North Dakota and South Dakota has declined over the past several decades—the abundance of native species has decreased while the abundance of introduced species has rapidly increased. Extensive efforts have been made to improve plant community composition on USFWS prairies; however, there was not a unified approach to this end in North Dakota and South Dakota until the advent of the Native Prairie Adaptive Management (NPAM) program. The NPAM program provides decision support for the selection of management actions to improve plant community composition of tallgrass and mixed-grass prairies in the Northern Great Plains. We evaluated plant community composition on USFWS native tallgrass and mixed-grass prairie remnants enrolled in the NPAM program in North Dakota and South Dakota to examine effects of management on plant community composition. Our analysis suggests that incorporating certain management actions can improve plant community characteristics on the agency's tallgrass and mixed-grass prairies. We documented increased native species richness and decreased Bromus inermis (smooth brome) relative cover at sites that had been burned two or more times during a four-year period. In contrast, smooth brome relative cover was higher at sites managed by the exclusion of fire and intermittent light grazing or rest. Smooth brome is extremely invasive in native prairie remnants throughout the Northern Great Plains. Thus, our results have marked implications for managers working to reduce the prevalence of smooth brome on public and private lands.

Effects of shallow natural gas well structures and associated roads on grassland songbird reproductive success in Alberta, Canada.

Grassland songbird populations across North America have experienced dramatic population declines due to habitat loss and degradation. In Canada, energy development continues to fragment and disturb prairie habitat, but effects of oil and gas development on reproductive success of songbirds in North American mixed-grass prairies remains largely unknown. From 2010–2012, in southeastern Alberta, Canada, we monitored 257 nests of two ground-nesting grassland songbird species, Savannah sparrow (Passerculus sandwichensis) and chestnut-collared longspur (Calcarius ornatus). Nest locations varied with proximity to and density of conventional shallow gas well structures and associated roads in forty-two 258-ha mixed-grass prairie sites. We estimated the probabilities of nest success and clutch size relative to gas well structures and roads. There was little effect of distance to or density of gas well structure on nest success; however, Savannah sparrow experienced lower nest success near roads. Clutch sizes were lower near gas well structures and cattle water sources. Minimizing habitat disturbance surrounding gas well structures, and reducing abundance of roads and trails, would help minimize impacts on reproductive success for some grassland songbirds.

Native Forb Establishment following Application of Aminopyralid or Clopyralid

Interest exists in planting mixed forb–grass prairies in the midwestern United States. Aminopyralid or clopyralid can be used to suppress competition from invasive plants prior to seeding prairies. As these active ingredients are known to persist, concern exists that reductions in forb establishment could occur. We tested whether common midwestern forb species could tolerate an application of aminopyralid or clopyralid alone or in combination the summer prior to seeding, and whether fall dormant or spring seeding date influenced establishment. This experiment was performed in Beresford, SD, and Arlington, WI, where aminopyralid (54 or 123 g ae ha−1), clopyralid (237 and 420 g ae ha−1), or aminopyralid+clopyralid (54+237 g ae ha−1) were applied to a prepared seedbed in July of 2009. Ten forbs were seeded in November 2009 as a dormant seeding and in April 2010 as a spring seeding at both locations, and establishment was assessed 12 and 24 mo after treatment (MAT). Results were site and species specific. Time of seeding was an important driver of plant counts at both locations 12 and 24 MAT. In Wisconsin at 12 MAT, 60% of species studied exhibited higher counts in the spring seeding. This trend persisted in some, but was not consistent across all 10 species. In South Dakota, 80% of species studied had higher counts at 12 and 24 MAT, but differences were species specific and often differed from those studied in Wisconsin. Those species that had higher counts in spring seeding at 12 MAT, maintained higher counts at 24 MAT. Forbs planted in plots treated with herbicides did not differ from plots left untreated at either location. Results suggest native forbs typically seeded in the upper Midwest can tolerate these herbicides when applied at least 4 mo prior to seeding.

Kentucky Bluegrass Invasion Alters Soil Carbon and Vegetation Structure on Northern Mixed-Grass Prairie of the United States

Invasive nonnative grasses pose a significant threat to rangelands of the Northern Great Plains. Long-term data from a grazing experiment near Mandan, ND (46°46′11.43″N, 100°54′55.16″W) revealed the invasion of native prairie by Kentucky bluegrass, an exotic grass. We hypothesized that bluegrass invasion altered soil13C and15N levels, tracking the increased abundance of invasive cool-season grass aboveground. In 2014, soil samples were collected to depths of 0 to 7.6 cm and 7.6 to 15.2 cm in pastures grazed similarly since 1916. Samples were analyzed for total carbon (C) and nitrogen (N) and13C and15N isotopes and compared against archived samples from 1991. Vegetation change from native to exotic grasses changed the isotopic composition of soil C. The soil δ13C at the 0- to 7.6-cm depth became more negative between 1991 and 2014. Soil δ13C became less negative with increasing stocking rate at both soil depths. Soil δ15N values at the 0- to 7.6-cm depth decreased between 1991 and 2014. Soil δ15N increased with increasing stocking rate at the 0- to 7.6-cm depth in 2014. Soil C and N concentrations at 0 to 7.6 cm increased by 35% (12 g C kg−1) and 27% (0.9 g N kg−1), respectively, from 1991 to 2014; however, concentrations at the 7.6- to 15.2-cm depth did not change. The shift from native C4to invasive C3grass did not reduce soil C storage in the long-term prairie pastures. The more deleterious effect of invasion, however, may have been the buildup of dead biomass, which alters vegetation structure and may reduce native species’ diversity and abundance.

Fire and Season of Postfire Defoliation Effects on Biomass, Composition, and Cover in Mixed-Grass Prairie

North American prairies are acknowledged to have evolved with grazing following fire. Given this evolutionary fire-grazing interaction, our objective was to determine whether seasonal timing of defoliation following fire alters subsequent productivity and species composition. Following the April 2013 Pautre wildfire in the Grand River National Grasslands of South Dakota, we installed exclosures in three locations along the border of the fire. Grazing exclosures were paired across the fire line to create a burned and nonburned exclosure at each location. Four plots were demarcated in each exclosure. Three plots were defoliated via mowing to 6 cm either 2, 4, or 6 mo following fire, with the fourth maintained as a control. Productivity and species composition data were collected in November 2013, June 2014, August 2014, and July 2015. Fire increased productivity 56% during the 2013 growing season following fire. During the 2014 growing season, there was a tendency for burned sites to maintain greater production. June defoliation resulted in the greatest current-year productivity in 2014 regardless of fire treatment, whereas all other treatments resulted in similar productivity. Fire and defoliation effects on productivity were undetectable in 2015. Community composition was not affected by fire in 2013. Melilotus officinalis was increased by spring defoliation in 2014 and by fire in 2015. Litter was initially reduced by fire but was similar to nonburned levels by 2015. Results indicate that positive fire effects on productivity are limited to the first two growing seasons following fire, whereas defoliation effects manifest the second growing season following fire (first growing season after defoliation). With the exception of old dead material, fire and timing of defoliation affected biomass and community composition independently. Postfire rest from grazing appears unnecessary for the maintenance of plant productivity and species composition in northern mixed-grass prairie.

Reconsidering rest following fire: Northern mixed-grass prairie is resilient to grazing following spring wildfire

Current federal post-fire land management recommendations in the United States suggest that rangelands be rested from grazing for two growing seasons following fire to allow for proper recovery, despite the lack of empirical literature supporting this recommendation. This project was designed to determine if grazing the first growing season following a spring wildfire alters subsequent productivity and species composition of northern mixed-grass prairie. Following the April 2013 Pautre wildfire in northwestern South Dakota, 100m2 exclosures were erected in three burned pastures to simulate two growing seasons of rest. Grazing exclosures were paired with sites grazed both the first and second growing seasons following the fire and replicated across loamy and sandy ecological sites. Prior to grazing the second growing season, five 2m2 cages were placed at each grazed site to assess first-year grazing effects. Following the second growing season, productivity and species composition were determined for exclosures and cages. Productivity was greater for loamy than sandy ecological sites (loamy=2764kgha−1, sandy=2356kgha−1; P=0.0271), but was similar between grazing treatments (rested=2556kgha−1, grazed=2564kgha−1; P=0.9550). Ecological site strongly determined species composition. Loamy sites consistently contained more Pascopyrum smithii, Bouteloua gracilis and Carex duriuscula than sandy sites (30 v 0%, 18 v 8%, 4 v 1%; P=0.0004, 0.0457 and 0.0382 respectively). The effects of grazing exclusion were limited to Hesperostipa comata and the non-native Agropyron cristatum composition. H. comata was more prevalent on rested sites (22 v 15%, P=0.0096). A. cristatum experienced a grazing treatment by ecological site interaction as it was reduced by grazing on sandy sites, but was not affected on loamy sites (P=0.0226). Results do not support the notion that a two growing season rest period following fire is required in the northern mixed-grass prairie.

Nesting ecology of grassland birds following a wildfire in the southern Great Plains

We studied the response of nesting grassland birds occupying short-grass and mixed-grass prairie sites 2 and 3 y following two, large-scale wildfires that burned ≥360,000 ha in the Texas Panhandle in March 2006. Nest success was greater on burned plots compared to unburned plots, though this varied by species and year. Woody vegetation cover was greater around nests on unburned plots compared to burned plots for Cassin's sparrow (Peucaea cassinii) and lark sparrow (Chondestes grammacus). Cassin's sparrows and lark sparrows nested in more-woody vegetation than did grasshopper sparrows (Ammodramus savannarum), and woody vegetation was reduced following the wildfires. The wildfires appear to have had few if any negative influences on the avian community 3 years postfire. This may be due to grassland breeding birds being adapted to landscapes in which, historically, periodic disturbance (e.g., wildfire, intensive grazing by bison [Bison bison]) resulted in vegetation heterogeneity.

Changing edaphic conditions and exploitation of an expanded phenological niche allows for increased exotic (introduced) plant species dominance

Aims Global change agents are creating novel climatic and edaphic conditions that may favor introduced species. We attempted to identify mechanisms and impacts of Bromus tectorum invasion in the Colorado Front Range mixed-grass prairie under changing conditions.