Mixed-grass Prairie Research Articles

Corn, Beans and Bison: Cultivated Plants and Changing Economies of the Late Prehistoric Villagers on the Plains of Oklahoma and Northwest Texas

The economies of past Native American societies on the southern Plains are often viewed as bison dependent based on historical descriptions of mobile, horse-based hunters and early excavations that recovered abundant bison bones but few plant remains. Very little historical description is available for the plants used by these people and little attention has been given to the time depth of this adaptation. Over the past 25 years, research on Plains Village and early contact sites in western Oklahoma and northwestern Texas has revealed evidence of a mixed economy with cultivated plants and bison as important elements. This paper reviews the paleobotanical data from sites covering the past 1,000 years and examines the role of cultivated and wild plants in these southern Plains societies. The importance of various cultivated plants for villagers in the wetter, eastern tall grass prairies is compared to the use of these plants by villagers in the dryer settings of the western mixed and short grass prairies. Some variations in the use of some cultivated plants are also documented through time, especially in the period after European contact.

Effects of normal and altered cattle urine on short-term greenhouse gas flux from mixed-grass prairie in the Northern Great Plains

Use of dietary amendments to reduce nitrogen (N) in excreta represents a possible strategy to decrease greenhouse gas (GHG) emissions from livestock. In this regard, ingestion of small amounts of condensed quebracho tannin has been found to reduce N concentration in livestock urine. In this study, we sought to quantify the effects of tannin-affected cattle urine, normal cattle urine, and NH 4NO 3 in solution on greenhouse gas flux. Carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2O) flux was measured using static chamber methodology from the three N treatments and a no application control over a 6-week period in a mixed grass prairie in west-central North Dakota, USA. Over the course of the study, average CO 2 emission was greatest from normal urine (335 ± 8 mg C m −2 h −1) and least from the control (229 ± 19 mg C m −2 h −1), with intermediate fluxes for the tannin urine and NH 4NO 3 treatments (290 ± 27 and 286 ± 54 mg C m −2 h −1, respectively). Methane uptake was prevalent throughout the study, as soil conditions were predominantly warm and dry. Uptake of CH 4 was greatest within the control (−30 ± 2 μg C m −2 h −1) and least in the tannin urine treatment (−12 ± 4 μg C m −2 h −1). Uptake of CH 4 was over 40% less within the tannin urine treatment as compared to normal urine, and may have been repressed by the capacity of tannin to bind monooxygenases responsible for CH 4 oxidation. Average N 2O emission from NH 4NO 3 solution was more than twice that of all other treatments. Though the tannin urine treatment possessed 34% less N than normal cattle urine, cumulative N 2O emission between the treatments did not differ. Results from this study suggest the use of condensed quebracho tannin as a dietary amendment for livestock does not yield GHG mitigation benefits in the short-term.

Functional Group and Species Responses to Precipitation in Three Semi-Arid Rangeland Ecosystems

The objective of this study was to compare forage production and foliar and basal cover responses of plant communities, plant functional groups, and individual species between years with below average (2004) and well above-average (2005) spring precipitation in three semi-arid rangeland ecosystems (shortgrass steppe, northern mixed-grass prairie, and sagebrush grassland). Foliar and basal cover at the time of a peak standing crop were visually estimated using modified Daubenmire cover categories, and forage production by species was harvested from areas that had been excluded from large herbivores. Responses of forage production to precipitation, but not foliar and basal cover, were similar for the three semi-arid ecosystems. Total forage production was more responsive (75–159%) than basal (8–35%) or foliar (2–29%) cover to increasing precipitation. Absolute (1016 kg·ha−1) and relative (159%) increases in total forage production from 2004 to 2005 were greatest for the shortgrass steppe. Forage production increases were largely attributable to greater production by C3 perennial graminoids in each ecosystem; increases in basal and foliar cover for this plant functional group were observed in shortgrass steppe and sagebrush grassland, but not in northern mixed-grass prairie. Fine-scale inputs of species and plant functional group responses to precipitation will further the accuracy of forage prediction models in predicting both total biomass production and relative proportions of plant biomass.

Registration of Southlow Michigan Little Bluestem Germplasm

Little bluestem grows in dry open areas throughout the USA. It attracts insects; provides food, nesting, and winter cover for birds and small mammals; and is a major component of tall and mixed grass prairies. Southlow Michigan little bluestem provides a genetically diverse, defi ned population for use in restoration and diversifi cation of native habitats and for ero- sion control. Moreover, it will augment seed availability in Michigan for Federal and state programs (e.g., Conservation Reserve Program, Conservation Reserve Enhancement Program, Grassland Reserve Program, and Michigan Landowner Incen- tive Program) that require or encourage the use of verifi ed, regionally-sourced native grasses. Its known area of adapta- tion is the southern half of Michigan's Lower Peninsula. Limited quantities of seeds are available on request from Dave Burgdorf (dave.burgdorf@mi.usda.gov) for fi ve years after registration with CSSA. Afterward, seeds will be made available from the National Plant Germplasm System (NPGS). Recipients of seeds are asked to make appropriate recognition of the source of germplasm if it is used in the development of a new cultivar, germplasm, parental line, or genetic stock.

Spatiotemporal dynamics of black-tailed prairie dog colonies affected by plague

Black-tailed prairie dogs (Cynomys ludovicianus) are a key component of the disturbance regime in semi-arid grasslands of central North America. Many studies have compared community and ecosystem characteristics on prairie dog colonies to grasslands without prairie dogs, but little is known about landscape-scale patterns of disturbance that prairie dog colony complexes may impose on grasslands over long time periods. We examined spatiotemporal dynamics in two prairie dog colony complexes in southeastern Colorado (Comanche) and northcentral Montana (Phillips County) that have been strongly influenced by plague, and compared them to a complex unaffected by plague in northwestern Nebraska (Oglala). Both plague-affected complexes exhibited substantial spatiotemporal variability in the area occupied during a decade, in contrast to the stability of colonies in the Oglala complex. However, the plague-affected complexes differed in spatial patterns of colony movement. Colonies in the Comanche complex in shortgrass steppe shifted locations over a decade. Only 10% of the area occupied in 1995 was still occupied by prairie dogs in 2006. In 2005 and 2006 respectively, 74 and 83% of the total area of the Comanche complex occurred in locations that were not occupied in 1995, and only 1% of the complex was occupied continuously over a decade. In contrast, prairie dogs in the Phillips County complex in mixed-grass prairie and sagebrush steppe primarily recolonized previously occupied areas after plague-induced colony declines. In Phillips County, 62% of the area occupied in 1993 was also occupied by prairie dogs in 2004, and 12% of the complex was occupied continuously over a decade. Our results indicate that plague accelerates spatiotemporal movement of prairie dog colonies, and have significant implications for landscape-scale effects of prairie dog disturbance on grassland composition and productivity. These findings highlight the need to combine landscape-scale measures of habitat suitability with long-term measures of colony locations to understand the role of plague-affected prairie dogs as a grassland disturbance process.

LONG-TERM MAPPED QUADRATS FROM KANSAS PRAIRIE: DEMOGRAPHIC INFORMATION FOR HERBACEOUS PLANTS

Demographic data will play a central role in testing current theories in plant ecology and forecasting the effects of global change. However, long-term data on vital rates are very limited, especially for species in herbaceous plant communities. Here we present a data set that has great potential to increase our understanding of plant demographic processes. Every year from 1932 to 1972, researchers in Hays, Kansas (USA), mapped all individual plants in a series of 1-m2 quadrats in a mixed grass prairie. The rare combination of temporal extent and fine spatial resolution makes it possible to follow individual herbaceous plants (or genets) through time and to answer questions such as: How does individual survival and recruitment vary with precipitation and temperature? How are these relationships modified by interactions with neighboring conspecifics and heterospecifics? The data set includes the digitized maps in Arc Export format, a tabular, nonspatial version of the entire data set, descriptive informati...

Effect of controlled fire frequency on grassland bird abundance during the breeding season at Cheyenne Bottoms Wildlife Area, Kansas

Abstract Cheyenne Bottoms Wildlife Area (CBWA) is an internationally recognized wetland surrounded by mixed-grass prairie. Because habitat management historically has been focused on the marsh, this study was initiated to determine the effects of spring burning on abundance and species richness of grassland-nesting birds. The effects of years since last burn and location on abundance and species richness were inconsistent among years. Unless additional bird surveys show consistent patterns in bird response to burning, frequency of burns will be determined based on vegetation characteristics rather than abundance of nesting birds.

Large-scale Aerial Images Capture Details of Invasive Plant Populations

Satellite and high-altitude aerial remote sensing have been used to measure dense infestations of invasive weeds over very large areas but have limited resolution and cannot be used to detect sparsely distributed weeds. Ground-based methods have provided detailed measurements of invasive weeds but can measure only limited areas. Here we test a novel approach that uses a lightweight airplane, flying at 72 km ṡ h−1 and 100-m altitude, to rapidly collect high-resolution images over relatively large areas. We obtained 1 987 images, each representing 48.5 m2 of mixed-grass prairie with 2-mm resolution (ground sample distance). From these images we were able to reliably measure small patches and even individual plants of the invasive forb Dalmatian toadflax (Linaria dalmatica [L.] P. Mill.). Ground-based measurements of aboveground toadflax biomass were highly correlated (R2 > 0.93) with point-intercept and visual-estimate cover measurements from aerial images. The time required to analyze images ranged from 4 to 45 seconds for presence/absence data and from 1 to 6 minutes for cover data. Toadflax was present in 795 of 1 987 images but exceeded 1% cover in only 99 images. Given the observed variation among images in toadflax cover, at least 400 images were needed to precisely estimate the mean toadflax cover of 0.2%. These results suggest that such high-resolution aerial imagery could be used to obtain detailed measurements of many invasive weed populations. It may be most useful for identifying incipient weed infestations and expanding the scale at which population-level attributes of weed populations can be effectively measured.

Demographic Response of a Grassland Rodent to Environmental Variability

We used stage-structured matrix population models, derived from 3 years with disparate levels of precipitation, to assess the potential effects of climate change on annual population growth (k) of deer mice (Peromyscus maniculatus). Populations of deer mice increased during a year of normal precipitation (k ¼ 1.69 6 0.02 SE) and a wet year (k ¼ 1.03 6 0.02), but declined in a dry year (k ¼ 0.34 6 0.02). Life-table response experiment analyses indicated that reduced survival of adults in the dry year, and reduced survival of pups and juveniles in the wet year, exerted the greatest influence on variation in population growth. Stochastic models that projected populations of deer mice for a 50-year period predicted that populations would not be able to persist if mean annual precipitation was reduced � 11% by increasing the frequency of dry years. Furthermore, the stochastic population growth rate declined more quickly when the probability of a normal year was reduced, simulating increased variability in rainfall, relative to other scenarios examined. Our stochastic models indicate that a relatively small reduction in mean precipitation could result in substantial population declines of P. maniculatus in the mixed-grass prairie of central North America.

Soil modification by invasive plants: effects on native and invasive species of mixed-grass prairies

Invasive plants are capable of modifying attributes of soil to facilitate further invasion by conspecifics and other invasive species. We assessed this capability in three important plant invaders of grasslands in the Great Plains region of North America: leafy spurge (Euphorbia esula), smooth brome (Bromus inermis) and crested wheatgrass (Agropyron cristatum). In a glasshouse, these three invasives or a group of native species were grown separately through three cycles of growth and soil conditioning in both steam-pasteurized and non-pasteurized soils, after which we assessed seedling growth in these soils. Two of the three invasive species, Bromus and Agropyron, exhibited significant self-facilitation via soil modification. Bromus and Agropyron also had significant facilitative effects on other invasives via soil modification, while Euphorbia had significant antagonistic effects on the other invasives. Both Agropyron and Euphorbia consistently suppressed growth of two of three native forbs, while three native grasses were generally less affected. Almost all intra- and interspecific effects of invasive soil conditioning were dependent upon presence of soil biota from field sites where these species were successful invaders. Overall, these results suggest that that invasive modification of soil microbiota can facilitate plant invasion directly or via ‘cross-facilitation’ of other invasive species, and moreover has potential to impede restoration of native communities after removal of an invasive species. However, certain native species that are relatively insensitive to altered soil biota (as we observed in the case of the forb Linum lewisii and the native grasses), may be valuable as ‘nurse’species in restoration efforts.

Grazing-Induced Modifications to Peak Standing Crop in Northern Mixed-grass Prairie

Selective grazing can modify the productive capacity of rangelands by reducing competitiveness of productive, palatable species and increasing the composition of more grazing-resistant species. A grazing system (season-long and short-duration rotational grazing) × stocking rate (light: 16 steers · 80 ha−1, moderate: 4 steers · 12 ha−1, and heavy: 4 steers · 9 ha−1) study was initiated in 1982 on northern mixed-grass prairie. Here, we report on the final 16 years of this study (1991–2006). Spring (April May June) precipitation explained at least 54% of the variation in peak standing crop. The percentage of variation explained by spring precipitation was similar between stocking rates with short-duration grazing but decreased with increasing stocking rate for season-long grazing. April precipitation explained the greatest percentage of the variation in peak standing crop for the light stocking rate (45%), May precipitation for the moderate stocking rate (49%), and June precipitation for the heavy stocking rate (34%). Peak standing crop was 23%–29% greater with light (1 495 ± 66 kg · ha−1, mean ± 1 SE) compared to moderate (1 218 ± 64 kg · ha−1) and heavy (1 156 ± 56 kg · ha−1) stocking rates, which did not differ. Differences in peak standing crop among stocking rates occurred during average and wet but not dry springs. Neither the interaction of grazing system and stocking rate nor grazing system alone affected standing crop across all years or dry, average, or wet springs. Grazing-induced modification of productive capacity in this northern mixed-grass prairie is attributed to changes in species composition with increasing stocking rate as the less productive, warm-season shortgrass blue grama (Bouteloua gracilis [H.B.K.] Lag. ex Griffiths) increases at the expense of more productive, cool-season midheight grasses. Land managers may need to substantially modify management to offset these losses in productive capacity.

Estimating forage quantity and quality using aerial hyperspectral imagery for northern mixed-grass prairie

Sustainable rangeland stewardship calls for synoptic estimates of rangeland biomass quantity (kg dry matter ha − 1 ) and quality [carbon:nitrogen (C:N) ratio]. These data are needed to support estimates of rangeland crude protein in forage, either by percent (CP c) or by mass (CP m). Biomass derived from remote sensing data is often compromised by the presence of both photosynthetically active (PV) and non-photosynthetically active (NPV) vegetation. Here, we explicitly quantify PV and NPV biomass using HyMap hyperspectral imagery. Biomass quality, defined as plant C:N ratio, was also estimated using a previously published algorithm. These independent algorithms for forage quantity and quality (both PV and NPV) were evaluated in two northern mixed-grass prairie ecoregions, one in the Northwestern Glaciated Plains (NGGP) and one in the Northwestern Great Plains (NGP). Total biomass (kg ha − 1 ) and C:N ratios were mapped with 18% and 8% relative error, respectively. Outputs from both models were combined to quantify crude protein (kg ha − 1 ) on a pasture scale. Results suggest synoptic maps of rangeland vegetation mass (both PV and NPV) and quality may be derived from hyperspectral aerial imagery with greater than 80% accuracy.

Growth of White Spruce, <em>Picea glauca</em>, Seedlings in Relation to Microenvironmental Conditions in a Forest-Prairie Ecotone of Southwestern Manitoba

The influence of microenvironmental conditions on the growth performance (i.e., diameter and height growth) of White Spruce [Picea glauca (Moench) Voss] seedlings was examined within three contrasting habitats: White Spruce tree islands, open prairies and Trembling Aspen (Populus tremuloides Michx.) groves. These habitats exist within a disjunct occurrence of White Spruce at its southern limit of distribution in three mixed-grass prairie preserves in the Spruce Woods Provincial Park within the forest-prairie ecotone of southwestern Manitoba. Microenvironmental measurements (i.e., light, temperature, relative humidity, soil moisture) were obtained on 10 sites in each of the three habitats and growth characteristics of 60 White Spruce seedlings were measured in each of three habitats. Higher light and soil temperature conditions occurred within the open prairie. In contrast, lower light and soil temperature conditions occurred under the tree canopy of aspen groves and the northern aspect of spruce islands, which moderated the effect of the dry regional climate. Height growth did not vary significantly among the three habitats. The greater diameter growth and decreased slenderness of White Spruce seedlings in the open versus the shaded habitats appears to be a result of increased photosynthesis at higher light intensity and may also represent a morphological adaptation to withstand the effect of increased wind exposure. The increased slenderness of White Spruce in the shaded habitats appears to be a morphological adaptation of increasing carbon allocation towards height growth and thus maximizing effective competition for light.

One Hundred Years of Echinacea angustifolia Harvest in the Smoky Hills sof Kansas, USA

Abstract Echinacea angustifolia DC. (Asteraceae) is a major North American medicinal plant that has been harvested commercially in north-central Kansas for 100 years, making it one of the longest documented histories of large-scale commercial use of a native North American medicinal herb. We have compiled historical market data and relate it to harvest pressure on wild Echinacea populations. Interviews with local harvesters describe harvesting methods and demonstrate the species' resilience. Conservation measures for E. angustifolia also should address the other threats faced by the species and may include restoration and management of its mixed-grass prairie habitat and protection by private landowners.

ANNUAL RETURN RATES OF BREEDING GRASSLAND SONGBIRDS

Abstract We used reobservation of color-banded birds to index annual breeding site fidelity of four species of songbirds that nest in the northern mixed-grass prairie of northcentral Montana (1996–2005). Territorial males of Sprague's Pipits (Anthus spragueii), and Savannah (Passerculus sandwichensis), Grasshopper (Ammodramus savannarum), and Baird's (A. bairdii) sparrows were located on five permanent study sites (1998– 2004) and lured into mist-nets using tape broadcasts of conspecific songs and calls. The proportion reobserved was 5.3% (n = 247) across all banded adult males. Grasshopper Sparrows had the highest proportion of returns (8.9%), followed by Savannah Sparrows (5.4%), Baird's Sparrows (5.1%), and Sprague's Pipits (2.1%). Three nestling Savannah Sparrows were reobserved in subsequent years (n = 193), while no nestlings of the other species were reobserved (n = 401). Our return rates were low for all adults in comparison with typical reports of return rates for songbird species of woodland and...

Soil nitrogen mineralization not affected by grass species traits

Species N use traits was evaluated as a mechanism whereby Bromus inermis ( Bromus), an established invasive, might alter soil N supply in a Northern mixed-grass prairie. We compared soils under stands of Bromus with those from three representative native grasses of different litter C/N: Andropogon gerardii ( Andropogon), Nassella viridula ( Nassella) and Pascopyrum smithii ( Pascopyrum); in ascending order of litter quality. Net mineralization (per g soil N) measured in year-long laboratory incubations showed no differences in comparisons of Bromus with two of the three native grasses: Andropogon and Nassella. Higher mineralization in Pascopyrum stands relative to Bromus was consistent with its higher litter quality. However, an unusually high occurrence of an N-fixing legume in Pascopyrum stands, potentially favoring high mineralization rates, confounded any conclusions regarding the effects of plant N use on N mineralization. Instead of an initial flush of net mineralization, as would be expected in laboratory incubation, we observed an initial lag phase. This lag in net N mineralization coincided with high microbial activity (respiration) that suggests strong N limitation of the microbial biomass. Further support for the importance of immobilization initially came from modeling mineralization dynamics, which was explained better when we accounted for microbial growth in our model. The absence of strong differences in net mineralization beneath these grasses suggests that differences in plant N use alone were unlikely to influence soil N mineralization through substrate quality, particularly under strong N control of the microbial biomass.

Strategic and Tactical Prediction of Forage Production in Northern Mixed-Grass Prairie

Predictions of forage production derived from site-specific environmental information (e.g., soil type, weather, plant community composition, and so on) could help land managers decide on appropriate stocking rates of livestock. This study assessed the applicability of the Great Plains Framework for Agricultural Resource Management (GPFARM) forage growth model for both strategic (long-term) and tactical (within-season) prediction of forage production in northern mixed-grass prairie. An improved version of the model was calibrated for conditions at the USDA‐ARS High Plains Grasslands Research Station in Cheyenne, Wyoming. Long-term (1983‐2001) simulations of peak standing crop (PSC) were compared to observations. Also, within-season (1983) forecasts of total aboveground biomass made for 1 March onward, 1 April onward, 1 May onward, and 1 June onward were compared to observations. The normal, driest, and wettest weather years on record (1915‐1981) were used to simulate expected values, lower bounds, and upper bounds of biomass production, respectively. The forage model explained 66% of the variability in PSC from 1983 to 2001. The cumulative distribution function (CDF) derived from long-term simulated PSC overestimates cumulative probabilities for PSC . 1 500 kg � ha � 1 . The generated CDF could be used strategically to estimate long-term forage production at various levels of probability, with errors in cumulative probability ranging from 0.0 to 0.16. Within-season forecasts explained 77%‐94% of biomass variability in 1983. It was shown that monthly updating of the forage forecast, with input of actual weather to date, improves accuracy. Further development and testing of the forage simulation model will focus on the interactions between forage growth, environmental perturbations (especially drought), and grazing.

A multi-scaled analysis of avian response to habitat amount and fragmentation in the Canadian dry mixed-grass prairie

Previous research has suggested that ducks and songbirds may benefit from prairie landscapes that consist primarily of contiguous grasslands. However, the relative importance of landscape-level vs. local characteristics on mechanisms underlying observed patterns is unclear. We measured effects of grassland amount and fragmentation on upland and wetland songbird and duck density and nest success, and on some nest predators, across 16 landscapes in southern Alberta, Canada. We compared these landscape-level effects with local-scale responses, including distance to various edges and vegetation characteristics. We also evaluated several statistical approaches to comparing effects of habitat characteristics at multiple spatial scales. Few species were influenced by grassland amount or fragmentation. In contrast, distance to edge and local vegetation characteristics had significant effects on densities and nest success of many species. Previous studies that reported effects of landscape characteristics may have detected patterns driven by local mechanisms. As a corollary, results were very sensitive to statistical model structure; landscape level effects were much less apparent when local characteristics were included in the models.

Stable-carbon isotope composition of Poaceae pollen: an assessment for reconstructing C3 and C4 grass abundance

Plants using the C3 and C4 photosynthetic pathways differ in carbon-isotope composition, and this difference offers a means to estimate the relative abundance of these two functional groups in the palaeorecord. We report here results of a study aiming to evaluate pollen d 13 C( d 13 Cp) of Poaceae (the grass family) as a proxy indicator for palaeoecological studies. On average d 13 Cp differs by � /13 between modern C3 (� / 22.6 to � /) and C4 (� /9.2 to � /) grass species. d 13 Cp is 1.2 � 3.7 more negative for modern grass pollen treated with the same protocol as for fossil samples than for untreated modern samples. d 13 Cp ranges from � / to � / for grass pollen in the middle-Holocene sediments from West Olaf Lake, located near the modern tallgrass prairieforest ecotone in western Minnesota. We applied a two end-member mixing model to estimate fluctuations in C3 and C4 grass abundance around this lake. Both C3 and C4 grasses expanded relative to Ambrosia and Artemisia with the decline of aridity from 8000 to 4000 BP. C3 grasses were generally more abundant than C4 grasses throughout the middle Holocene, suggesting the presence of mixed-grass prairie around West Olaf Lake. The grass d 13 Cp-based estimates of C4 plant abundance were lower than charcoal d 13 C-based estimates, probably reflecting different source areas of pollen and charcoal. Grass d 13 Cp also revealed greater submillennial-scale variability in C3 and C4 abundance than charcoal d 13 C. These results suggest that grass d 13 Cp can provide

Mixed-Grass Prairie Passerines Exhibit Weak and Variable Responses to Patch Size

AbstractMuch of our current understanding of the demographic effects of habitat fragmentation on bird populations is derived from studies of passerines in forests and tallgrass prairie surrounded by woody vegetation. We quantified grassland bird density, nest survival, and productivity in 41 native mixed-grass prairie pastures during 1997-2000 in southern Saskatchewan, Canada. Pastures ranged in size from 18 ha to 11,600 ha and were typically surrounded by agriculture (i.e., ranching and annual cropping). Grassland passerines did not respond strongly or uniformly to patch size. Sprague's Pipit (Anthus spragueii) was the only species whose density increased with pasture size. Patch size had minimal influence on nest survival of Sprague's Pipit or Clay-colored Sparrow (Spizella pallida); whereas nest survival increased with patch size for Savannah Sparrow (Passerculus sandwichensis) and declined for Baird's Sparrow (Ammodramus bairdii), Chestnut-collared Longspur (Calcarius ornatus), and Western Meadowlark (Sturnella neglecta). Time-specific factors (i.e., nest age, date, and year) were more important predictors of nest survival than patch size. Exploratory analyses indicated that effects of edge distance, pasture shape, or landscape on nest survival were just as likely as patch-size effects. However, effects of edge on Chestnut-collared Longspurs may be governed by landscape-level factors, because nest survival decreased with distance to edge in landscapes with increased amounts of cropland. Our results indicate that mixed-grass prairie parcels ≥18 ha play a role in the conservation of several grassland passerine species currently in decline, but the conservation of Sprague's Pipit likely depends on maintaining larger tracts of native prairie.Les Passereaux des Prairies Herbacées Montrent des Réponses Faibles et Variables en Réponse à la Taille des Parcelles d'Habitats