Mixed-grass Prairie Research Articles

Leaf Photosynthesis and Plant Competitive Success in a Mixed-grass Prairie: With Reference to Exotic Grasses Invasion

The widespread invasion of exotic cool-season grasses in mixed-grass rangeland is diminishing the hope of bringing back the natural native plant communities. However, ecophysiological mechanisms explaining the relative competitiveness of these invasive grasses over the native species generally are lacking. We used experimental data collected in south-central North Dakota, USA to address this issue. Photosynthetic potential was obtained from the net assimilation (A) vs. internal CO2 (Ci) response curves from plants grown in a greenhouse. Plant success was defined as the average frequency measured over 25 years (1988 to 2012) on overflow range sites across five levels of grazing intensity. Also, estimated leaf area index of individual species under field conditions was used to indicate plant success. The correlation between photosynthetic potential based on A/Ci curves and plant frequency was negative. The correlation between leaf photosynthesis and plant success (defined as leaf area within a unit land area) was also negative, although statistically weak. These results suggest that the two cool-season grasses, Poa pratensis and Bromus inermis, do not rely on superior leaf-level photosynthesis for competitive success. Instead, some other traits, such as early and late-season growth, may be more important for them to gain dominance in the mixed-grass prairie. We propose that the negative photosynthesis-frequency relation as observed in this study results from a strong competition for limited soil nutrients in the mixed-grass prairie. It has implications for the stability and productivity of the grassland under various human disruptions influencing the soil nutrient status.

Detecting the Influence of Best Management Practices on Vegetation Near Ephemeral Streams With Landsat Data

Various best management practices (BMPs) have been implemented on rangelands with the goals of controlling nonpoint source pollution, reducing the impact of livestock in ecologically important riparian areas, and improving grazing distribution. Providing off-stream water sources to livestock in pastures, cross-fencing, and rotational grazing are common rangeland BMPs that have demonstrated success in drawing livestock grazing pressure away from streams. We evaluated the effects of rangeland BMP implementation with six commercial-scale pastures in the northern mixed-grass prairie. Four pastures received a BMP suite consisting of off-stream water, cross-fencing, and deferred-rotation grazing, and two pastures did not receive BMPs. We hypothesized that the BMPs increased the quantity of riparian vegetation cover relative to the conditions in these pastures during the pre-BMP period and to the two pastures that did not receive BMPs. We used a series of 30-m Landsat normalized difference vegetation index (NDVI) images to track the spatial and temporal changes (1984–2010, n = 24) in vegetation cover, to which NDVI has been well correlated. Validation indicated that the remotely sensed signal from in-channel vegetation was representative of ground conditions. The BMP suite was associated with a 15% increase in the in-channel NDVI (0–30 m from stream centerline) and 18% increase in the riparian NDVI (30–180 m from stream center line). Conversely, the in-channel and riparian NDVI of non-BMP pastures declined 30% and 18% over the study period. The majority of change occurred within 2 yr of BMP implementation. The patterns of in-channel NDVI among pastures suggested that BMP implementation likely altered grazing distribution by decreasing the preferential use of riparian and in-channel areas. We demonstrated that satellite imagery time series are useful in retrospectively evaluating the efficacy of conservation practices, providing critical information to guide adaptive management and decision makers.

Interactions between ecological disturbances: burning and grazing and their effects on songbird communities in northern mixed-grass prairies

Historically, North American prairies were strongly influenced by two natural disturbances, fire and grazing, and their interaction. However, the frequency and size of fires has been greatly altered over time, while native ungulates have been replaced by livestock; this may have had strong ecological influences on modern prairies. The feedback hypothesis proposes that grazing by ungulates will increase the duration of fire effects because ungulates will be attracted to burned patches. We conducted point-count surveys in burned-grazed, burned-ungrazed, unburned-grazed, and unburned-ungrazed sites over a 5-year period following fires that occurred naturally in 2006 in southern Saskatchewan, Canada, to test predictions related to avian community composition related to the feedback hypothesis. Generalized linear mixed models were used to analyze interactions among burning, grazing, and time since burning. Six of the nine avian species we studied responded positively or negatively to burning or grazing, although there were few statistically significant effects on the vegetation structure variables we measured. We found mixed evidence that grazing increased the duration of effects of burning, cumulatively providing little evidence for the feedback hypothesis. Nonetheless, effects of burning and grazing differed from and interacted with one another; for example, short-term effects of burning on Sprague’s Pipits (Anthus spragueii) and Baird’s Sparrows (Ammodramus bairdii) were greater than effects of grazing, and effects of grazing and burning in combination were frequently greater than effects of a single disturbance. Therefore, both should be integrated into management for the conservation of grassland songbirds. Interactions entre des perturbations ecologiques : les feux, le broutement et leurs effets sur les communautes de passereaux dans des prairies mixtes septentrionales RESUME. Historiquement, les prairies d’Amerique du Nord etaient fortement influencees par deux perturbations naturelles, soit le feu et le broutement, et leurs interactions. Cependant, la frequence et la taille des feux ont beaucoup change depuis ce temps, et les ongules indigenes ont ete remplaces par le betail; or, ces changements ont peut-etre eu une grande influence ecologique sur les prairies contemporaines. L’hypothese de retroaction sous-tend que le broutement par les ongules augmentera la duree de l’effet des feux parce que les ongules vont etre attires par les ilots brules. Nous avons effectue des denombrements par points d’ecoute dans des sites brulesbroutes, brules-non broutes, non brules-broutes et non brules-non broutes, au cours des cinq annees qui ont suivi les feux s’etant produits naturellement en 2006 dans le sud de la Saskatchewan, Canada, afin de tester les predictions relatives a la composition des communautes aviaires selon l’hypothese de retroaction. Des modeles lineaires generalises a effets mixtes ont ete utilises pour analyser les interactions entre les feux, le broutement et le temps ecoule depuis les feux. Six des neuf especes d’oiseaux que nous avons examinees ont reagi positivement ou negativement aux feux ou au broutement, bien qu’il y ait eu peu d’effets statistiquement significatifs sur les variables touchant la structure de la vegetation que nous avons mesurees. Nous avons obtenu des resultats contradictoires pour ce qui est de l’augmentation de la duree de l’effet des feux par le broutement; ces resultats supportent ainsi tres peu l’hypothese de retroaction dans l’ensemble. Neanmoins, les effets des feux et du broutement etaient differents et interagissaient entre eux; par exemple, les effets a court terme des feux sur les Pipits de Sprague (Anthus spragueii) et les Bruants de Baird (Ammodramus bairdii) etaient superieurs aux effets du broutement, et les effets combines des feux et du broutement etaient souvent plus eleves que les effets d’une des deux perturbations prise seule. Par consequent, les deux types de perturbation devraient etre integres dans les mesures de gestion destinees a la conservation des passereaux de milieux de prairie.

Patterns of spatio-temporal distribution, abundance, and diversity in a mosquito community from the eastern Smoky Hills of Kansas

Nearly 30% of emerging infectious disease events are caused by vector-borne pathogens with wildlife origins. Their transmission involves a complex interplay among pathogens, arthropod vectors, the environment and host species, and they pose a risk for public health, livestock and wildlife species. Examining habitat associations of vector species known to transmit infectious diseases, and quantifying spatio-temporal dynamics of mosquito vector communities is one aspect of the holistic One Health approach that is necessary to develop effective control measures. A survey was conducted from May to August, 2010 of the abundance and diversity of mosquito species occurring in the mixed-grass prairie habitat of the Smoky Hills of Kansas. This region is an important breeding ground for North America's grassland nesting birds and, as such, it could represent an important habitat for the enzootic amplification cycle of avian malaria and infectious encephalitides, as well as spill-over events to humans and livestock. A total of 11 species, belonging to the three genera Aedes, Anopheles, and Culex, was collected during this study. Aedes nigromaculis, Ae. sollicitans, Ae. taeniorhynchus, Culex salinarius, and Cx. tarsalis accounted for 98% of the collected species. Multiple linear regression models suggested that mosquito abundances in the grasslands of the central Great Plains were explained by meteorological and environmental variables. Temporal dynamics in mosquito abundances were well supported by models that included maximum and minimum temperature indices (adjusted R(2) = 0.73). Spatial dynamics of mosquito abundances were best explained by a model containing the following environmental variables (adjusted R(2) =0.37): ground curvature, topographic wetness index, distance to woodland, and distance to road. The mosquito species we detected are known vectors for infectious encephalitides, including West Nile virus. Understanding the microhabitat characteristics of these mosquito species in a grassland ecosystem will aid in the control and management of these disease vectors.

Leafy Spurge (Euphorbia esula) Affects Vegetation More Than Seed Banks in Mixed-Grass Prairies of the Northern Great Plains

AbstractExotic plants have the ability to modify soil seed banks in habitats they invade, but little is known about the legacy of invasion on seed banks once an exotic plant has successfully been controlled. Natural areas previously invaded by leafy spurge in the northern Great Plains typically have one of two fates following its removal: a return of native plants, or a secondary invasion of other exotic plants. It is unknown, however, if this difference in plant communities following leafy spurge control is due to seed bank differences. To answer this question, we monitored seed banks and standing vegetation for 2 yr in mixed-grass prairies that were previously invaded by leafy spurge but controlled within 5 yr of our study. We found that native plant seed banks were largely intact in areas previously invaded by leafy spurge, regardless of the current living plant community, and leafy spurge invasion history had a larger impact on cover and diversity of the vegetation than on the seed banks. Differences in plant communities following leafy spurge control do not appear to be related to the seed banks, and soil conditions may be more important in determining trajectories of these postinvasion communities.

Linking Phenology and Biomass Productivity in South Dakota Mixed-Grass Prairie

Assessing the health of rangeland ecosystems based solely on annual biomass production does not fully describe the condition of the plant community; the phenology of production can provide inferences about species composition, successional stage, and grazing impacts. We evaluated the productivity and phenology of western South Dakota mixed-grass prairie in the period from 2000 to 2008 using the normalized difference vegetation index (NDVI). The NDVI is based on 250-m spatial resolution Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery. Growing-season NDVI images were integrated weekly to produce time-integrated NDVI (TIN), a proxy of total annual biomass production, and integrated seasonally to represent annual production by cool- and warm-season species (C3 and C4, respectively). Additionally, a variety of phenological indicators including cool-season percentage of TIN were derived from the seasonal profiles of NDVI. Cool-season percentage and TIN were combined to generate vegetation classes, which served as proxies of the conditions of plant communities. TIN decreased with precipitation from east to west across the study area. However, the cool-season percentage increased from east to west, following patterns related to the reliability (interannual coefficient of variation [CV]) and quantity of midsummer precipitation. Cool-season TIN averaged 76.8% of the total TIN. Seasonal accumulation of TIN corresponded closely (R2 > 0.90) to that of gross photosynthesis data from a carbon flux tower. Field-collected biomass and community composition data were strongly related to TIN and cool-season percentage. The patterns of vegetation classes were responsive to topographic, edaphic, and land management influences on plant communities. Accurate maps of biomass production, cool- and warm-season composition, and vegetation classes can improve the efficiency of land management by facilitating the adjustment of stocking rates and season of use to maximize rangeland productivity and achieve conservation objectives. Further, our results clarify the spatial and temporal dynamics of phenology and TIN in mixed-grass prairie.

Interactive Effects of Simulated Nitrogen Deposition and Altered Precipitation Patterns on Plant Allelochemical Concentrations

Global environmental change alters the supply of multiple limiting resources that regulate plant primary and secondary metabolism. Through modifications in resource availability, acquisition, and allocation, global change is likely to influence plant chemical defenses, and consequently species interactions that are mediated by these compounds. While many studies focus on individual global change factors, simultaneous changes in abiotic factors may interact to influence plant allelochemicals. In this study, we examined the individual and interactive effects of nitrogen enrichment and altered precipitation patterns on chemical defense compounds (iridoid glycosides) of an invasive plant, Linaria dalmatica. Plants were grown from seed in native mixed-grass prairie for 2 years. Nitrogen and water treatments were applied in each growing season over this period. Results indicate that soil water and nitrogen availability interact to shape plant chemical defense concentrations in L. dalmatica. Nitrogen addition decreased iridoid glycoside concentrations by approximately 25% under reduced water availability, increased concentrations by 37% in ambient water plots, and had no effect on these chemical defenses for plants growing under augmented water supply. Thus, results show differing patterns of allelochemical response to nitrogen enrichment, with respect to both the magnitude and direction of change, depending on water availability. Our study demonstrates the importance of examining multiple environmental factors in order to predict potential changes in plant chemical defenses with climate change.

Fire and Nitrogen Effects on Purple Threeawn (Aristida purpurea) Abundance in Northern Mixed-Grass Prairie Old Fields

Purple threeawn (Aristida purpurea Nutt. varieties) is a native grass capable of increasing on rangelands, forming near monocultures, and creating a stable state. Productive rangelands throughout the Great Plains and Intermountain West have experienced increases in purple threeawn abundance, reducing overall forage quality. Our objectives were to 1) reveal the effects of prescribed fire and nitrogen amendments on purple threeawn abundance and 2) assess nontarget plant response posttreatment. Season of fire (no fire, summer fire, fall fire) and nitrogen addition (0kg N · ha−1, 46kg N · ha−1, and 80kg N · ha−1) were factorially arranged in a completely randomized design and applied to two similar sites in southeastern Montana. We evaluated fire and nitrogen effects on purple threeawn basal cover, relative composition, and current-year biomass one growing season postfire at two sites treated during different years. Spring weather following fire treatments was very different between years and subsequently impacted community response. Initial purple threeawn biomass at both sites was 1 214 ± 46kg · ha−1 SEc. When postfire growing conditions were wet, current-year biomass of purple threeawn was reduced 90% and 73% with summer and fall fire, respectively. Under dry postfire growing conditions, purple threeawn current-year biomass was reduced 73% and 58% with summer and fall fire, respectively. Nitrogen additions had no effect on purple threeawn current-year biomass at either site. Current-year biomass of C3 perennial grass doubled with nitrogen additions and was not impacted by fire during a wet spring. Nitrogen additions and fire had no effect on C3 perennial grass current-year biomass following a dry spring. Prescribed fire appears to be a highly effective tool for reducing purple threeawn abundance on semiarid rangelands, with limited detrimental impacts to nontarget species.

Effects of Disturbance on Silver Sagebrush Communities in Dry Mixed-Grass Prairie

Restoration specialists are increasingly interested in re-establishing silver sagebrush ( Artemisia cana ) communities due to the large number of wildlife species that are partial sagebrush obligates. Energy development within native grasslands can contribute to habitat loss through introduction of invasive species. In this study, pipeline and reclaimed well site footprints were assessed relative to undisturbed sample units to identify management practices that achieve effective restoration of silver sagebrush communities on disturbed sites. Our objectives were to compare silver sagebrush communities on energy disturbances with undisturbed areas in two ecological range sites in dry mixed-grass prairie: blowouts (hard-packed bare ground) and overflows (mesic sedimentation). Our hypothesis was that moisture, greater nutrient values, and potential seed banks found in overflows may benefit silver sagebrush growth. We were also interested in plant communities resulting from of various seeding treatments, hypothesizing that silver sagebrush may be negatively impacted by some seeding treatments. We used a paired transect design to measure variations in plant species cover in each ecological range type. We found similar silver sagebrush cover values to adjacent undisturbed areas following disturbances on both overflow and blowout ecological range types; however, silver sagebrush was significantly reduced in disturbed areas that were seeded with grass species compared to sites that were allowed to recover naturally. We recommend minimum disturbance practices with natural recovery, avoidance of seeding agronomic cultivars, and in particular preventing introduction of invasive species such as crested wheatgrass.

Invasive forb benefits from water savings by native plants and carbon fertilization under elevated CO2 and warming

As global changes reorganize plant communities, invasive plants may benefit. We hypothesized that elevated CO2 and warming would strongly influence invasive species success in a semi-arid grassland, as a result of both direct and water-mediated indirect effects. To test this hypothesis, we transplanted the invasive forb Linaria dalmatica into mixed-grass prairie treated with free-air CO2 enrichment and infrared warming, and followed survival, growth, and reproduction over 4 yr. We also measured leaf gas exchange and carbon isotopic composition in L. dalmatica and the dominant native C3 grass Pascopyrum smithii. CO2 enrichment increased L. dalmatica biomass 13-fold, seed production 32-fold, and clonal expansion seven-fold, while warming had little effect on L. dalmatica biomass or reproduction. Elevated CO2 decreased stomatal conductance in P. smithii, contributing to higher soil water, but not in L. dalmatica. Elevated CO2 also strongly increased L. dalmatica photosynthesis (87% versus 23% in P. smithii), as a result of both enhanced carbon supply and increased soil water. More broadly, rapid growth and less conservative water use may allow invasive species to take advantage of both carbon fertilization and water savings under elevated CO2 . Water-limited ecosystems may therefore be particularly vulnerable to invasion as CO2 increases.

Phenology-assisted classification of C3 and C4 grasses in the U.S. Great Plains and their climate dependency with MODIS time series

Grassland ecosystems in the North America are primarily composed of C3 and C4 plant functional types (PFTs) that have different responses to the changing climate. Knowledge of their spatial distributions and temporal variations helps us better understand the ecological functions and climate dependencies of grasslands. This study used the 500-m MODIS surface reflectance products (MOD09A1) from 2000 to 2009 to extract NDVI time series of C3 and C4 grass PFTs in different floristic regions (tallgrass, shortgrass, and mixed-grass prairies.) A set of phenology metrics, including Start of Season, End of Season, Season Length, Peak NDVI, Peak Date, and ∑NDVI, were found useful in delineating these grass types. A phenology-assisted decision tree classifier was developed to map the four grass PFTs in the Great Plains. The relative abundance of C3 and C4 PFTs generally showed the expected latitudinal shifts. Longitudinal shifts of tallgrass and shortgrass PFTs were also in agreement with the distributions of floristic prairie regions. In shortgrass and northern mixed prairies, shortgrass C3 was located in the north while shortgrass C4 was in the south. The native tallgrass C4 remained in prairie remnants, although other native grasslands had been mostly converted to croplands or tallgrass C3-dominated pastures. The inter-annual spatial variations of PFTs were statistically correlated with climate factors over a 10-year study period. The preliminary findings revealed that the strength and direction of correlations varied geographically and seasonally for different PFTs. This spatio-temporally explicit information may provide quantitative inputs in ecological forecasting for various climate change scenarios.

A meta-analysis of lesser prairie-chicken nesting and brood-rearing habitats: Implications for habitat management

The distribution and range of lesser prairie-chicken (Tympanuchus pallidicinctus) has been reduced by >90% since European settlement of the Great Plains of North America. Currently, lesser prairie-chickens occupy 3 general vegetation communities: sand sagebrush (Artemisia filifolia), sand shinnery oak (Quercus havardii), and mixed-grass prairies juxtaposed with Conservation Reserve Program grasslands. As a candidate for protection under the Endangered Species Act, there is a need for a synthesis that characterizes habitat structure rangewide. Thus, we conducted a meta-analysis of vegetation characteristics at nest sites and brood habitats to determine whether there was an overall effect (Hedges' d) of habitat selection and to estimate average (95% CI) habitat characteristics at use sites. We estimated effect sizes (di) from the difference between use (nests and brood sites) and random sampling sites for each study (n = 14), and derived an overall effect size (d++). There was a general effect for habitat selection as evidenced by low levels of variation in effect sizes across studies and regions. There was a small to medium effect (d++ = 0.20–0.82) of selection for greater vertical structure (visual obstruction) by nesting females in both vegetation communities, and selection against bare ground (d++ = 0.20–0.58). Females with broods exhibited less selectivity for habitat components except for vertical structure. The variation of d++ was greater during nesting than brooding periods, signifying a seasonal shift in habitat use, and perhaps a greater range of tolerance for brood-rearing habitat. The overall estimates of vegetation cover were consistent with those provided in management guidelines for the species. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Soil mineral nitrogen responses following liquid hog manure application to semiarid forage lands

Bork, E. W., Lambert, B. D., Banerjee, S. and Blonski, L. J. 2013. Soil mineral nitrogen responses following liquid hog manure application to semiarid forage lands. Can. J. Soil Sci. 93: 369–378. Expansion of intensive livestock operations into semiarid regions lacking cultivated lands requires consideration of perennial forages for the efficient and sustainable disposal of manure. Little information exists on the nutrient dynamics associated with the application of manure to these areas. We examined soil mineral nitrogen (N) responses in four sites of the mixed-grass prairie, including two native grasslands and two introduced pastures, following different seasons (fall vs. spring), methods (dribble broadcast vs. coulter injected) and rates of liquid hog manure application (9.4, 18.8, 37.5, 75 and 150 kg ha−1available N). Soil mineral N, including NO3-N, NH4-N and total mineral N, were assessed after application but prior to plant growth in April 1999, and again one growing season later in April 2000. Initial soil N did not vary with season of application. Soil mineral N predictably increased with application rate, but only in the upper soil profile (0–20 cm). Decreases in soil mineral N after one growing season in all treatments highlighted the ability of these perennial forage lands to immobilize large amounts of soil N, a significant portion of which was related to N uptake by vegetation. Compared with broadcast application, manure injection led to 35% greater soil mineral N (both NO3and NH4) prior to plant growth, a response that persisted 1 yr later (+12%), thus demonstrating the N conserved benefits of manure incorporation. Overall, increases in soil mineral N within these forage lands appeared to be relatively short-term in nature, largely depleting over the course of a single growing season, suggesting one-time liquid hog manure application at low to moderate rates may be sustainable in this region of the mixed-grass prairie.

Influence of management and precipitation on carbon fluxes in great plains grasslands

Suitable management and sufficient precipitation on grasslands can provide carbon sinks. The net carbon accumulation of a site from the atmosphere, modeled as the Net Ecosystem Productivity (NEP), is a useful means to gauge carbon balance. Previous research has developed methods to integrate flux tower data with satellite biophysical datasets to estimate NEP across large regions. A related method uses the Ecosystem Performance Anomaly (EPA) as a satellite-derived indicator of disturbance intensity (e.g., livestock stocking rate, fire, and insect damage). To better understand the interactions among management, climate, and carbon dynamics, we evaluated the relationship between EPA and NEP data at the 250m scale for grasslands in the Central Great Plains, USA (ranging from semi-arid to mesic). We also used weekly estimates of NEP to evaluate the phenology of carbon dynamics, classified by EPA (i.e., by level of disturbance impact). Results show that the cumulative carbon balance over these grasslands from 2000 to 2008 was a weak net sink of 13.7gCm−2yr−1. Overall, NEP increased with precipitation (R2=0.39, P<0.05) from west to east. Disturbance influenced NEP phenology; however, climate and biophysical conditions were usually more important. The NEP response to disturbance varies by ecoregion, and more generally by grassland type, where the shortgrass prairie NEP is most sensitive to disturbance, the mixed-grass prairie displays a moderate response, and tallgrass prairie is the least impacted by disturbance (as measured by EPA). Sustainable management practices in the tallgrass and mixed-grass prairie may potentially induce a period of average net carbon sink until a new equilibrium soil organic carbon is achieved. In the shortgrass prairie, management should be considered sustainable if carbon stocks are simply maintained. The consideration of site carbon balance adds to the already difficult task of managing grasslands appropriately to site conditions. Results clarify the seasonal and interannual dynamics of NEP, specifically the influence of disturbance and moisture availability.

Net primary productivity and rain‐use efficiency as affected by warming, altered precipitation, and clipping in a mixed‐grass prairie

Grassland productivity in response to climate change and land use is a global concern. In order to explore the effects of climate change and land use on net primary productivity (NPP), NPP partitioning [fBNPP , defined as the fraction of belowground NPP (BNPP) to NPP], and rain-use efficiency (RUE) of NPP, we conducted a field experiment with warming (+3°C), altered precipitation (double and half), and annual clipping in a mixed-grass prairie in Oklahoma, USA since July, 2009. Across the years, warming significantly increased BNPP, fBNPP , and RUEBNPP by an average of 11.6%, 2.8%, and 6.6%, respectively. This indicates that BNPP was more sensitive to warming than aboveground NPP (ANPP) since warming did not change ANPP and RUEANPP much. Double precipitation stimulated ANPP, BNPP, and NPP but suppressed RUEANPP , RUEBNPP , and RUENPP while half precipitation decreased ANPP, BNPP, and NPP but increased RUEANPP , RUEBNPP , and RUENPP . Clipping interacted with altered precipitation in impacting RUEANPP , RUEBNPP , and RUENPP , suggesting land use could confound the effects of precipitation changes on ecosystem processes. Soil moisture was found to be a main factor in regulating variation in ANPP, BNPP, and NPP while soil temperature was the dominant factor influencing fBNPP . These findings suggest that BNPP is critical point to future research. Additionally, results from single-factor manipulative experiments should be treated with caution due to the non-additive interactive effects of warming with altered precipitation and land use (clipping).

Grazing and Songbird Nest Survival in Southwestern Saskatchewan

Grassland songbird populations are declining, and one reason for this might be livestock management practices in native prairies. Although cattle grazing is a common practice in native mixed-grass prairie, little research has been conducted to date to determine its impact on prairie songbird nest survival. During the summers of 2006–2007, we examined the effects of low- to moderate-intensity cattle grazing typical of the region and nest site vegetation structure on nest survival of five species of ground-nesting songbirds in native mixed-grass prairie in southwestern Saskatchewan, Canada. There was no significant effect of grazing (P > 0.10) on Sprague’s pipit (Anthus spragueii), Baird’s sparrow (Ammodramus bairdii), vesper sparrow (Pooecetes gramineus), lark bunting (Calamospiza melanocorys), or chestnut-collared longspur (Calcarius ornatus) nest survival. All five species used denser vegetation than was generally available (P ≤ 0.001). Sprague’s pipit nest survival was negatively correlated with vegetation density (P = 0.055) and litter depth (P = 0.033), and vesper sparrow nest survival was positively correlated with increased visibility from above (P = 0.056), but nest survival of the other species was independent of vegetation structure. Our results suggest that low- to moderate-intensity grazing is consistent with the conservation needs of ground-nesting songbirds in mixed-grass prairies of southwestern Saskatchewan.

Bison Selection of Prairie Dog Colonies on Shortgrass Steppe

American bison (Bison bison L.) preferentially use black-tailed prairie dog (Cynomys ludovicianus L.) colonies over uncolonized range in the mixed-grass prairie of North America. To assess bison use of prairie dog colonies in a different ecosystem, the shortgrass steppe, this study was conducted at the Vermejo Park Ranch, New Mexico. Driving surveys were conducted in summer 2007 to determine the number of bison on and off prairie dog colonies in 2 pastures. Prairie dogs occupied 25.5% and 48.5% of the 2 pastures surveyed. Bison of both sexes used prairie dog colonies more than expected compared to a scenario of bison using colonies based on colony availability (P < 0.001). With the exception of bulls in one pasture, bison observed off-colony were more likely to be grazing than bison observed oncolony (P < 0.04). When selection of prairie dog colonies was assessed for only those bison observed grazing, bulls in both pastures and cows in one pasture used prairie dog colonies more than expected based on availability (P ≤ 0.001). Forage quality was superior on prairie dog colonies, with crude protein higher (P < 0.001) and acid detergent fiber lower (P < 0.001) in blue grama (Bouteloua gracilis [Willd. ex Kunth] Lag. ex Griffiths) collected on-colony than offcolony. Further studies under a variety of conditions are still needed, but selection for prairie dog colonies by bison at Vermejo, combined with findings from previous studies, suggests that during the growing season, bison and cattle (Bos taurus L.) might select prairie dog colonies over uncolonized range in both the northern and southern extents of North American grasslands.

Optimal Placement of Off-Stream Water Sources for Ephemeral Stream Recovery

Uneven and/or inefficient livestock distribution is often a product of an inadequate number and distribution of watering points. Placement of off-stream water practices (OSWP) in pastures is a key consideration in rangeland management plans and is critical to achieving riparian recovery by improving grazing evenness, while improving livestock performance. Effective OSWP placement also minimizes the impacts of livestock use radiating from OSWP, known as the “piosphere.” The objective of this study was to provide land managers with recommendations for the optimum placement of OSWP. Specifically, we aimed to provide minimum offset distances of OSWP to streams and assess the effective range of OSWP using Normalized Difference Vegetation Index (NDVI) values, an indicator of live standing crop. NDVI values were determined from a time-series of Satellite Pour l'Observation de la Terre (SPOT) 20-m images of western South Dakota mixed-grass prairie. The NDVI values in ephemeral stream channels (in-channel) and uplands were extracted from pre- and post-OSWP images taken in 1989 and 2010, respectively. NDVI values were normalized to a reference imagine and subsequently by ecological site to produce nNDVI. Our results demonstrate a significant (P < 0.05) increase in the nNDVI values of in-channel vegetation within 1 250m of OSWP following their implementation. The area of piospheres (n = 9) increased with pasture size (R2 = 0.49, P = 0.05) and increased with average distance to OSWP in a pasture (R2 = 0.43, P = 0.07). Piospheric reduction in nNDVI was observed within 200m of OSWP, occasionally overlapping in-channel areas. The findings of this study suggest placement of OSWP 200 to 1 250m from streams to achieve optimal results. These results can be used to increase grazing efficiency by effectively placing OSWP and insure that piospheres do not overlap ecologically important in-channel areas.

Temperature and Precipitation Affect Steer Weight Gains Differentially by Stocking Rate in Northern Mixed-Grass Prairie

Cattle weight gain responses to seasonal weather variability are difficult to predict for rangelands because few long-term (>20 yr) studies have been conducted. However, an increased understanding of temperature and precipitation influences on cattle weight gains is needed to optimize stocking rates and reduce enterprise risk associated with climatic variability. Yearling steer weight gain data collected at the USDA-ARS High Plains Grasslands Research Station at light, moderate, and heavy stocking rates for 30 years (1982–2011) were used to examine the effects of spring (April–June) and summer (July–September) temperature and precipitation, as well as prior-growing-season (prior April–September) and fall/winter (October–March) precipitation, on beef production (kg · ha−1). At heavier stocking rates, steer production was more sensitive to seasonal weather variations. A novel finding was that temperature (relatively cool springs and warm summers) played a large predictive role on beef production. At heavier stocking rates, beef production was highest during years with cool, wet springs and warm, wet summers, corresponding to optimum growth conditions for this mixed C3–C4 plant community. The novelty and utility of these findings may increase the efficacy of stocking rate decision support tools. The parsimonious model structure presented here includes three-month seasonal clusters that are forecasted and freely available from the US National Oceanic and Atmospheric Administration up to a year in advance. These seasonal weather forecasts can provide ranchers with an increased predictive capacity to adjust stocking rates (in advance of the grazing season) according to predicted seasonal weather conditions, thereby reducing enterprise risk.

Restoring Mixed Grass Prairie in Southeastern Alberta, Canada

On the Ground Between 2008 and 2010 a cultivated field of 57 ha within the mixed grass prairie of southeastern Alberta was restored with native grasses and silver sagebrush plugs. Wildlife occupying the site increased from being dominated by horned larks to 13 species using the land within 3 years. Two of these species Sprague's pipit and chestnut-collared longspur are native grassland specialists considered “Threatened” under Canada's Species at Risk Act. Litter values on the reseed in year 3 were approaching normal values that would be expected on a loamy site within a healthy mixed grass prairie.