Native Prairie Sites Research Articles

Influence of Livestock Grazing History on Plant Community Composition on Native Prairies of the Southern Prairie Pothole Region

The southern Prairie Pothole Region (PPR) of central North America is a highly modified landscape where remnant unplowed prairies could serve as repositories of native plant biodiversity. A previous study paired two historically idle US Fish and Wildlife Service (USFWS) National Wildlife Refuges with nearby privately owned grazing lands in North Dakota and found differences in invasive grass frequency, notably that smooth brome (Bromus inermis Leyss.) was less prevalent on annually grazed lands. A broader assessment, conducted over a wider geographic area, was warranted to investigate whether this relationship held across the southern extent of PPR in North Dakota and South Dakota. To this end, we selected 26 USFWS native prairie sites paired with adjacent/nearby native prairie sites with a history of livestock grazing in the PPR of North Dakota and South Dakota. We estimated plant species’ cover in five 10 × 10 m plots at each paired site in June or July of 2021. Plant community composition on USFWS sites was distinct from paired sites under private or state ownership (permutational analysis of variance (P = 0.021, F = 1.935). Additionally, paired t-tests revealed that sites under private or state ownership (with a long-term history of grazing) had higher total species richness (P = 0.006) and floristic quality index (a measure of species richness and disturbance tolerance) values (P = 0.042) than USFWS sites (without a long-term history of grazing). Smooth brome relative cover was lower (P = 0.019) at sites with a long-term history of grazing (13.4% mean relative cover) than paired USFWS sites (23.3% mean relative cover). Given these differences, remnant native prairies with long-term histories of annual grazing may provide unique opportunities for conserving native plant diversity and impeding smooth brome spread in the southern PPR.

Grassland bird population declines at three Breeding Bird Survey spatial scales in contrast to a large native prairie

AbstractGrassland biomes in North America are threatened by agricultural intensification with implications for grassland‐associated bird populations via habitat loss, alteration, pesticide use, and declining landscape heterogeneity. Despite decades of conservation concern, steep declines of grassland birds continue. Key to optimizing conservation effort is understanding how land‐use practices, such as agriculture, across the annual cycle affect population status. Determining the relative influence of impacts on grassland bird declines is difficult given that the most robust estimate of trends, the North American Breeding Bird Survey (BBS), is conducted throughout agriculturally dominated regions. Our goal was to explore whether agriculture during the breeding season is a major driver of grassland bird declines, by evaluating population trends in regions with different amounts of agricultural development. We derived trends for 16 bird species spanning 23 years (1994–2016) at a large (459 km2), native prairie site, Suffield National Wildlife Area (SNWA) in Alberta, Canada. We compared those trends with the BBS across three spatial scales, a regional monitoring scheme with higher than average native grass cover (Grassland Bird Monitoring [GBM]), Bird Conservation Region 11 Canada (Canada), and all of Bird Conservation Region 11 (BCR 11). Trends measured as annual percent change and credible interval varied greatly among species and survey strata. Across all species, declines were greatest for Canada (−1.3%, CI: −2.8, 0.0) and BCR 11 (−1.9%, CI: −3.2, −0.6). This contrasts with positive trends for GBM routes (1.0%, CI: −0.4, 2.3) and the SNWA data (1.7%, CI: 0.3, 3.3). Six of 16 species at SNWA were increasing with one decreasing. Five species increased at GBM and four declined. Canada had 10 species declines and 3 increases and BCR 11 had 10 declines and no increases. None of the six grassland obligate species declined at SNWA, two declined at GBM, and all six declined over the two larger BBS strata. Our results showing fewer negative population trends at a large native grassland site compared with BBS at three spatial scales across the North American prairies support the prediction that agricultural intensification on breeding grounds may be driving population declines and protection of native grasslands is a key component of grassland bird conservation efforts.

Microbial Dispersal, Including Bison Dung Vectored Dispersal, Increases Soil Microbial Diversity in a Grassland Ecosystem.

Microbial communities display biogeographical patterns that are driven by local environmental conditions and dispersal limitation, but the relative importance of underlying dispersal mechanisms and their consequences on community structure are not well described. High dispersal rates can cause soil microbial communities to become more homogenous across space and therefore it is important to identify factors that promote dispersal. This study experimentally manipulated microbial dispersal within different land management treatments at a native tallgrass prairie site, by changing the relative openness of soil to dispersal and by simulating vector dispersal via bison dung addition. We deployed experimental soil bags with mesh open or closed to dispersal, and placed bison dung over a subset of these bags, to areas with three different land managements: active bison grazing and annual fire, annual fire but no bison grazing, and no bison grazing with infrequent fire. We expected microbial dispersal to be highest in grazed and burned environments, and that the addition of dung would consistently increase overall microbial richness and lead to homogenization of communities over time. Results show that dispersal rates, as the accumulation of taxa over the course of the 3-month experiment, increase taxonomic richness similarly in all land management treatments. Additionally, bison dung seems to be serving as a dispersal and homogenization vector, based on the consistently higher taxon richness and increased community similarity across contrasting grazing and fire treatments when dung is added. This finding also points to microbial dispersal as an important function that herbivores perform in grassland ecosystems, and in turn, as a function that was lost at a continental scale following bison extermination across the Great Plains of North America in the nineteenth century. This study is the first to detect that dispersal and vector dispersal by grazing mammals promote grassland soil microbial diversity and affect microbial community composition.

Impacts of oil well drilling and operating noise on abundance and productivity of grassland songbirds

Abstract Anthropogenic noise from natural resource extraction may negatively impact many species, particularly those reliant on acoustic communication. To compare the impacts of several types of noise resulting from oil extraction operations on habitat use and productivity of grassland songbirds, we designed and implemented a novel large‐scale, spatially and temporally replicated experiment. We recreated soundscapes produced by drilling and operating oil well noise, and compared impacts of noise‐producing and quiet playback infrastructure, in twenty‐nine 64.7‐ha native prairie sites in Alberta, Canada, from 2013 to 2015. Drilling noise recordings played 24 hr/day for 10 days, twice during each breeding season, while oil well operating noise played continuously, 24 hr/day, throughout each ~90‐day breeding season. Despite the much shorter duration of drilling noise playbacks, drilling noise negatively impacted three of our four focal species, and had a much greater impact on habitat use and productivity than did well operating noise. Infrastructure also impacted Vesper Sparrows and Sprague's Pipits, even in the absence of noise. Synthesis and applications. Acute oil drilling noise had a greater negative impact on breeding migratory birds when compared to chronic oil well noise, perhaps because drilling noise is unpredictable. While this study demonstrates that noise alone can negatively impact habitat use, nesting success and nestling quality, it is also clear that effective mitigation strategies require both noise and above‐ground infrastructure management to reduce impacts on wildlife.

Mass ratio effects underlie ecosystem responses to environmental change

Abstract Random species loss has been shown experimentally to reduce ecosystem function, sometimes more than other anthropogenic environmental changes. Yet, controversy surrounds the importance of this finding for natural systems where species loss is non‐random. We compiled data from 16 multi‐year experiments located at a single native tallgrass prairie site. These experiments included responses to 11 anthropogenic environmental changes, as well as non‐random biodiversity loss either the removal of uncommon/rare plant species or the most common (dominant) species. As predicted by the mass ratio hypothesis, loss of a dominant species had large impacts on productivity that were comparable to other anthropogenic drivers. In contrast, the loss of uncommon/rare species had small effects on productivity despite having the largest effects on species richness. The anthropogenic drivers that had the largest effects on productivity nitrogen, irrigation, and fire experienced not only loss of species but also significant changes in the abundance and identity of dominant species. Synthesis. These results suggest that mass ratio effects, rather than species loss per se, are an important determinant of ecosystem function with environmental change.

Assessing a farmland set-aside conservation program for an endangered butterfly: USDA State Acres for Wildlife Enhancement (SAFE) for the Karner blue butterfly

Private lands provide critical habitat for threatened and endangered species, but only recently have farm-based conservation programs focused on at-risk, invertebrate species. The USDA Conservation Reserve Program State Acres for Wildlife Enhancement (CRP-SAFE) is one of the first federal programs to do so with a Wisconsin-based initiative for the US federally endangered Karner blue butterfly (KBB). This study is the first to evaluate how well the KBB-SAFE provides suitable habitat for the Karner and other butterflies. It also provides a critical foundation for better understanding the potential of new USDA programs that create pollinator habitat including for declining species such as the Monarch butterfly. Here we compare data (2009–2014) on assemblages of grassland communities, blooming floral resource availability, and abundance and richness of butterflies, between KBB-SAFE and native prairie sites. We found that KBB-SAFE and native sites had distinctly different forb species assemblages, with SAFE sites having fewer native blooming species available during the first flight of the KBB yet similar availability during second flight. Butterfly abundance was ultimately greater on native sites compared to SAFE sites, but richness was comparable between sites. We conclude that KBB-SAFE can provide habitat for many grassland species, and serve as surrogate KBB habitat. We provide straightforward management recommendations designed to better meet the needs of the Karner blue and other sensitive butterfly species and we provide further evidence that increased abundance and richness of native forbs and grasses on land formerly used for agriculture can provide habitat for butterflies adapted to early successional habitats.

Microsites Matter: Improving the Success of Rare Species Reintroductions.

Our study was undertaken to better understand how to increase the success rates of recovery plantings of a rare hemiparasite, golden paintbrush (Castilleja levisecta—Orobanchaceae). This species is endemic to western Washington and Oregon, USA, and southwestern British Columbia, Canada. Over 5000 golden paintbrush plants were outplanted as plugs in 2007 at six different native prairie sites that were considered to be suitable habitat, based on general evaluations of vegetation and soil conditions. Outplantings were installed at regular intervals along transects up to 1 km long to include a range of conditions occurring at each site. All plantings were re-examined five years later. The patchy distribution of surviving plugs and new recruits within each reintroduction site suggested success is strongly influenced by microsite characteristics. Indicator species analysis of taxa growing in microsites around outplanted golden paintbrush identified species that were positively or negatively associated with paintbrush survival. Species such as Festuca roemeri, Eriophyllum lanatum, and Viola adunca were strong indicators at some sites; non-natives such as Hypochaeris radicata and Teesdalia nudicaulis tended to be frequent negative indicators. Overall, higher richness of native perennial forbs was strongly correlated with both survival and flowering of golden paintbrush, a pattern that may reflect interactions of this hemiparasite with the immediately surrounding plant community. Topographic position also influenced outcomes, with greater survival occurring on mounds and in swales, where soils generally were deeper. Our findings suggest that assessments of site suitability based on vegetation alone, and coarser, site-level assessments that do not characterize heterogeneity at the microsite scale, may not be strong predictors of restoration success over the longer term and in sites with variability in vegetation and soils. By identifying suitable microsites to focus rare species plantings, survival and efficiency may be significantly enhanced.

Kentucky bluegrass (Poa pratensis) Invasion in the Northern Great Plains: A Story of Rapid Dominance in an Endangered Ecosystem

AbstractKentucky bluegrass was introduced into the present-day United States in the 1600s. Since that time, Kentucky bluegrass has spread throughout the United States and Canada becoming prolific in some areas. In the past century, Kentucky bluegrass has been a presence and often a dominant species in some prairies in the Northern Great Plains. Sometime within the past few decades, Kentucky bluegrass has become the most-common species on the untilled, native prairie sites of much of North and South Dakota. In this article, we hypothesize how Kentucky bluegrass has come to dominate one of the most endangered ecosystems in North America—the prairie—through a historical, ecological, and climatological lens. We urge others to start addressing the invasion of Kentucky bluegrass with both new research and management strategies.

Influence of drought on growing season carbon and water cycling with changing land cover

Grasslands around the world are experiencing increased woody encroachment while drought frequency and severity is expected to increase with climate change. These processes will result in changes in the local carbon, water, and energy balances. Two closely located eddy covariance towers on native prairie sites in Kansas with differing burn regimes provided a unique opportunity to investigate those changes with minimal confounding climate factors. Daytime turbulent fluxes were analyzed throughout the growing season during two wet years (2008, 2009) and one drought year (2011). The site experiencing more woody encroachment (K4B) was a greater carbon sink every year, especially in 2011, when the annually burned site (KON) became a negligible sink and potential source of carbon. K4B also had greater seasonal water use efficiency (WUE) at all times except during drought and when burned. Evidence of water loss from deeper, stored sources was shown at K4B through cumulative evaporative loss that exceeded precipitation during drought conditions. Changes in the nature of the turbulent fluxes were also investigated through deviations from similarity theory, quadrant analysis, and wavelet decomposition. Wavelet analysis determined the size of eddies primarily involved in net exchange, showing differences between sites across small to medium scales (average diameter of 4.0–108m). Increased surface heterogeneity and roughness with woody encroachment was seen through smaller eddy size of maximum transport and slightly weakened applicability of similarity theory at K4B. Eddy size decreased over the course of the growing season, in a strikingly inverse relation to grass leaf area index, likely corresponding to greater canopy height and roughness. Variance of the correlation between carbon and water, indicative of more variable plant productivity, is much greater across all scales in 2011 at KON only. Overall, results indicate woody encroachment increases resilience to drought. Though carbon sequestration remains stronger at the woody encroachment site, it comes at the cost of far increased water loss, including from deeper groundwater resources, which could prove detrimental in combination with predicted climate change.

Spring Clipping, Fire, and Simulated Increased Atmospheric Nitrogen Deposition Effects on Tallgrass Prairie Vegetation

Defoliation aimed at introduced cool-season grasses, which uses similar resources of native grasses, could substantially reduce their competitiveness and improve the quality of the northern tallgrass prairie. The objective was to evaluate the use of early season clipping and fire in conjunction with simulated increased levels of atmospheric nitrogen deposition on foliar canopy cover of tallgrass prairie vegetation. This study was conducted from 2009 to 2012 at two locations in eastern South Dakota. Small plots arranged in a split-plot treatment design were randomized in four complete blocks on a warm-season grass interseeded and a native prairie site in east-central South Dakota. The whole plot consisted of seven treatments: annual clip, biennial clip, triennial clip, annual fire, biennial fire, triennial fire, and undefoliated control. The clip plots consisted of weekly clipping in May to simulate heavy grazing. Fire was applied in late April or early May. The subplot consisted of nitrogen applied at 0 or 15 kg N · ha−1 in early June. All treatments were initially applied in 2009. Biennial and triennial treatments were reapplied in 2011 and 2012, respectively. Canopy cover of species/major plant functional groups was estimated in late August/early September. Annual clipping was just as effective as annual fire in increasing native warm-season grass and decreasing introduced cool-season grass cover. Annual defoliation resulted in greater native warm-season grass cover, less introduced cool-season grass cover, and less native cool-season grass cover than biennial or triennial defoliation applications. Low levels of nitrogen did not affect native warm-season grass or introduced cool-season cover for any of the defoliation treatments, but it increased introduced cool-season grass cover in the undefoliated control at the native prairie site. This study supports the hypothesis that appropriately applied management results in consistent desired outcomes regardless of increased simulated atmospheric nitrogen depositions.

Gross nitrogen transformations and related N2O emissions in uncultivated and cultivated black soil

A better understanding of the nitrogen (N) cycle in agricultural soils is crucial for developing sustainable and environmentally friendly N fertilizer management and to propose effective nitrous oxide (N2O) mitigation strategies. This laboratory study quantified gross nitrogen transformation rates in uncultivated and cultivated black soils in Northeast China. It also elucidated the contribution made by nitrification and denitrification to the emissions of N2O. In the laboratory, soil samples adjusted to 60 % water holding capacity (WHC) were spiked with 15NH4NO3 and NH415NO3 and incubated at 25 °C for 7 days. The size and 15N enrichment of the mineral N pools and the N2O emission rates were determined between 0 and 7 days. The results showed that the average N2O emission rate was 21.6 ng N2O-N kg−1 h−1 in cultivated soil, significantly higher than in the uncultivated soil (11.6 ng N2O-N kg−1 h−1). Denitrification was found to be responsible for 32.1 % of the N2O emission in uncultivated soil, and the ratio increased significantly to 43.2 % in cultivated soil, due to the decrease in soil pH. Most of the increase in net N2O-N emissions observed in the cultivated soil was resulting from the increased production of N2O through denitrification. Gross nitrification rate was significantly higher in the cultivated soil than in the uncultivated soil, and the ratio of gross nitrification rate/ammonium immobilization rate was 6.87 in cultivated soil, much larger than the uncultivated soil, indicating that nitrification was the dominant NH4+ consuming process in cultivated soil, and this will lead to the increased production of nitrate, whereas the increased contribution of denitrification to N2O emission promoted the larger emission of N2O. This double impact explains why the risk of N loss to the environment is increased by long-term cultivation and fertilization of native prairie sites, and controlling nitrification maybe effective to abate the negative environmental effects.

Fractal distribution of mass from the millimeter- to decimeter-scale in two soils under native and restored tallgrass prairie

Fractal models that describe the distribution of aggregate mass and the hierarchical organization of soil structure at scales relevant to hydrological processes have been tested only over a small range of aggregate sizes. The objectives of this work were to extend to the decimeter-scale the range of aggregate diameters used in mass–volume investigations, to examine the ability of a fractal model to describe the mass–volume relationship, and to assess the variability of fractal parameters obtained from individual clods sampled within the same horizon. Soils at a native prairie (NP) and a restored prairie (RP) at a formerly cultivated field site in northeastern Kansas were studied. Six clods (500–1000cm3) sampled from each of two soil horizons at the NP (A and Btss1) and RP sites (Ap and Btss1) were sequentially broken and volume measured with a combination of a multistripe laser triangulation scanner and a displacement technique using two immiscible liquids. Volumes were converted to diameters and normalized by individual aggregate/ped roundness, paired with their respective masses and fit with a power law expression to obtain Dm (fractal dimension of mass) and km (the mass of an aggregate of unit diameter). Except for the RP Btss1 horizon, the fits demonstrated two domains separated at a breakpoint, db, with values between 0.8 and 1.1cm. We found a strong relationship between db and the combination of organic carbon and silt+clay content (R2=0.95, P<0.01) suggesting that these properties interact to control aggregation in aggregates with diameters smaller than db. Dm-values for the Btss1 and A horizons were not fractal (Dm=3) for small aggregates and fractal with values between 2.79 and 2.89 for large aggregates. For the RP Ap horizon, Dm was 2.51 for the small and ~3 for the large aggregates, likely due to high concentrations of roots and organic carbon observed in this horizon. Variation of Dm and km within any given horizon was large and comparable to the variation of similar values obtained from water retention from a variety of soils of contrasting textures found in other studies, suggesting that a more thorough understanding of the horizon-scale variability of these parameters is needed in order to appropriately apply fractal models of water retention. Our results confirm that fractal models provide a theoretical framework to describe soil structure, but they should be developed from data spanning several orders of magnitude and tested critically.

Cool Season Invasive Grasses in Northern Great Plains Natural Areas

Native prairie sites within the Northern Great Plains are being invaded by cool season invasive grasses despite utilizing even the most conservation-oriented management. Native prairie sites of the Knife River Indian Villages National Historic Site, located near the confluence of the Knife and Missouri Rivers in central North Dakota, were reassessed 23 years after the first assessment. The native prairie sites were initially assessed the summer of 1984 utilizing a modified Daubenmire technique which entailed randomly placing twenty-five ¼ m2 quadrats along transects at each native prairie site. Prior to 1976, native prairie sites were grazed by livestock; and after the National Park Service took ownership, sites were not grazed by livestock and were essentially left idle. The same technique was repeated during the summer of 2007 on the same native prairie sites surveyed in 1984, and comparisons were made between species composition of those sites in 1984 and 2007. Species composition of several sites across the landscape changed from containing a high percentage of native graminoids and forbs to containing a high percentage of invasive species such as smooth brome (Bromus inermis Leyss.) and Kentucky bluegrass (Poa pratensis L.). A few of the more xeric native prairie sites maintained a high percentage of native graminoids and forbs with minor changes in coverage. This study illustrates the emergence of invasive species and species composition changes under historic land use and climatic conditions and the roles that disturbances, such as grazing processes and fire, may play in maintaining native plant communities.

Pyrenopeziza plantaginis new to North America.

Pyrenopeziza plantaginis is reported from leaves of Plantago lanceolata from remnant native prairie sites in Benton Co., Oregon which harbor the endangered Taylor's checkerspot. The butterfly uses P. lanceolata as a pre-diapause larval host. The fungus is associated with a leaf blight of P. lanceolata and may impair restoration of populations of Taylor's checkerspot.

Herbicide and Fire Effects on Smooth Brome (Bromus inermis) and Kentucky Bluegrass (Poa pratensis) in Invaded Prairie Remnants

AbstractSmooth brome and Kentucky bluegrass are introduced cool-season perennial grasses known to invade grasslands throughout North America. During the fall of 2005 and spring of 2006, we implemented a restoration study at six native prairie sites in eastern South Dakota that have been invaded by smooth brome and Kentucky bluegrass. Treatments included five herbicide combinations, a fall prescribed burn, and an untreated control to determine the potential of each for renovation of invaded native grasslands. Herbicide treatments tested were sulfosulfuron, imazapyr, imazapic + sulfosulfuron, and imazapyr + imazapic, and were applied in late September 2005 and mid-May 2006. Untreated control plots averaged 64% (± 3.1) smooth brome cover and 38% (± 5.5) Kentucky bluegrass cover after the third growing season. Smooth brome cover in herbicide treated plots ranged from 6 to 23% and Kentucky bluegrass cover ranged from 15 to 35% after the third growing season. Smooth brome cover was 20% (± 2.9) and Kentucky bluegrass cover was 19% (± 4.0) in burned plots after the third growing season. Spring and fall treatments had similar native plant cover after three growing seasons. Spring and fall application of 0.33 kg ai ha−1imazapyr and 0.10 kg ai ha−1imazapic + 0.16 kg ai ha−1imazapyr had ≤ 10% smooth brome cover and increased native species cover after three growing seasons. Herbicides were effective at reducing cover of smooth brome and Kentucky bluegrass, and can be incorporated with other management strategies to restore prairie remnants.

Effects of long-term soil and crop management on soil hydraulic properties for claypan soils

Various land management decisions are based on local soil properties. These soil properties include average values from soil characterization for each soil series. In reality, these properties might be variable due to substantially different management, even for similar soil series. This study was conducted to test the hypothesis that for claypan soils, hydraulic properties can be significantly affected by long-term soil and crop management. Sampling was conducted during the summer of 2008 from two fields with Mexico silt loam (Vertic Epiaqualfs). One field has been under continuous row crop cultivation for over 100 years (Field), while the other field is a native prairie that has never been tilled (Tucker Prairie). Soil cores (76 × 76 mm [3.0 × 3.0 in]) from six replicate locations from each field were sampled to a 60 cm (24 in) depth at 10 cm (3.9 in) intervals. Samples were analyzed for bulk density, saturated hydraulic conductivity (K_sat), soil water retention, and pore-size distributions. Values of coarse (60 to 1,000 μm [0.0024 to 0.039 in] effective diameter) and fine mesoporosity (10 to 60 μm [0.00039 to 0.0024 in] effective diameter) for the Field site (0.044 and 0.053 m³ m⁻³ [0.044 and 0.053 in³ in⁻³]) were almost half those values from the Tucker Prairie site (0.081 and 0.086 m³ m⁻³ [0.081 and 0.086 in³ in⁻³]). The geometric mean value of K_sat was 57 times higher in the native prairie site (316 mm h⁻¹ [12.4 in hr⁻¹]) than in the cropped field (5.55 mm h⁻¹ [0.219 in hr⁻¹]) for the first 10 cm (3.9 in) interval. Differences in K_sat values were partly explained by the significant differences in pore-size distributions. The bulk density of the surface layer at the Tucker Prairie site (0.81 g cm⁻³ [50.6 lb ft⁻³]) was two-thirds of the value at the Field site (1.44 g cm⁻³ [89.9 lb ft⁻³]), and was significantly different throughout the soil profile, except for the 20 to 30 cm (7.9 to 12 in) depth. These results show that row crop management and its effect on soil loss have significantly altered the hydraulic properties for this soil. Results from this study increase our understanding of the effects of long-term soil management on soil hydraulic properties.

Soil moisture and plant growth responses to litter and defoliation impacts in Parkland grasslands

Soil moisture can limit plant production in cool-temperate grasslands, particularly under recent increases in drought severity and predictions of future climate change. This necessitates research that examines moisture mitigation strategies under the dominant land use of grazing. We examined the effectiveness of plant litter in regulating soil moisture dynamics and associated plant production in a native grassland and tame pasture in the Aspen Parkland of Alberta, Canada during 2007/2008, specifically testing (1) how litter and defoliation (as a surrogate for grazing) alter the micro-environment at the soil surface, (2) whether litter, in combination with defoliation, alters forage production, and (3) whether production changes can be linked to observed micro-environmental changes created by litter modification. The full factorial randomized complete block design consisted of three litter treatments (litter removal, in situ control, and double litter) and three defoliation treatments (undefoliated control, light defoliation to 6.5 cm stubble height, and heavy defoliation to 2.5 cm). Soil moisture levels were assessed over four periods after summer precipitation to examine soil moisture depletion. Plant phenological development and canopy cover were also assessed throughout 2007, and biomass was measured in August 2007 and 2008. Abundant litter (up to 14,000 kg ha −1) improved soil moisture levels in both native and tame grasslands by either maintaining higher absolute moisture levels or reducing total moisture loss after rainfall. Both litter removal and double litter reduced total growing season production compared to in situ levels at the Native Site, despite highest vegetation cover in litter removal plots. High litter levels also improved growth of individual grass tillers at this site, but negatively impacted sexual production. Conversely litter removal improved overall production at the Tame Site, although litter did enhance grass tiller recovery following mid-season defoliation at both sites, in part due to positive influences on soil moisture. Treatment effects on plant production were less pronounced in 2008 than in 2007. Overall, high litter levels improve soil moisture retention and can improve or stabilize plant production particularly in native prairie sites, and can provide an important drought management strategy in the Aspen Parkland.

Design, rationale and methodological considerations for a long term alternative cropping experiment in the Canadian plain region

An interdisciplinary field experiment was initiated to evaluate sustainability of crop production in the Canadian Prairie region. The objective was to develop a resource that would be used to measure change over time associated with input and cropping diversity strategies. The knowledge generated would serve to provide early indications of potential problems and to guide development of improved systems. The study was located near the geographic center of the region on the transition between the semi-arid prairie and the sub-humid parkland regions. The design of the study is reported here, while later papers will report and discuss treatment responses. The study is based on three levels of inputs; organic, reduced and high combined with three levels of cropping diversity: low, diversified annual grains and diversified annual perennial to give a matrix of nine treatments. The site was uniformly cropped and characterized for one year prior to imposition of the treatments, and results used to validate the experimental design. Systems were defined by general principles that incorporate flexibility and allow systems to be changed so they could function in a near optimal state. Several grassland sites and one native prairie site located nearby were characterized as reference points for examining biodiversity and soil quality attributes of the treatments. To accommodate multidisciplinary use of the data, a central database was developed that allows all collaborating scientists to access the data, yet protects data integrity. Overall results to date provide a clear indication that the study provides a resource that is well suited to meet the objectives.

Influence of Prairie Restoration on CT‐Measured Soil Pore Characteristics

Restored prairies are expected to improve soil physical properties, yet little is known about the extent of change to soil properties and how rapidly these changes take place. The objective of this study was to compare effects of prairie restoration on computed tomography (CT)-measured pore parameters. Undisturbed soil cores (76 mm diam. by 76 mm long) from native prairie (NP), restored prairie (RP), conservation reserve program (CRP), and no-till corn (Zea mays L.)-soybean (Glycine max (L.) Merr.; CS) sites were collected with six replicates from the 0- to 40-cm depth in 10-cm increments. Five CT images were acquired from each soil core using a medical CT scanner with 0.2 by 0.2 mm pixel resolution with 0.5 mm slice thickness, and then images were analyzed. Soil bulk density and hydraulic conductivity (K(sat)) were also measured. Soils under NP, RP, CRP, and CS areas had 83, 43, 48, and 26 pores on a 2500 mm(2) area, respectively, for the 0- to 40-cm depth. The number of pores, number of macropores (>1000 microm diam.), macroporosity, mesoporosity (200-1000 microm diam.), and fractal dimension were significantly higher and pore circularity was lower for NP, RP, and CRP than the CS treatment. The CT-measured mesoporosity and macroporosity of the CS treatment were 20 and 18% of the values for the NP site. CT-measured number of pores and macropores explained 43 and 40% of the variation for K(sat). The study showed that prairie restoration improves CT-measured soil pore parameters and decreases bulk density which are related to soil water infiltration.

USING PYROLYSIS MOLECULAR BEAM MASS SPECTROMETRY TO CHARACTERIZE SOIL ORGANIC CARBON IN NATIVE PRAIRIE SOILS

The goal of this study was to test if analytical pyrolysis coupled with molecular beam mass spectrometry and multivariate statistical analyses could provide a rapid and accurate methodology to identify and quantify soil carbon fractions and understand the fundamental chemistry that distinguishes these fractions. We analyzed soil organic carbon (SOC) contained in well-characterized agricultural soils with pyrolysis molecular beam mass spectrometry (py-MBMS) and then determined correlations between the mass spectra and associated soil characterization data. Both soil carbon chemistry and the organic forms in which SOC is sequestered (soil microbial biomass (SMBC), particulate organic matter carbon (POM C), and mineral-associated carbon (Cmin C)) were assessed by multivariate statistical analyses to discover existing correlations and if they could be developed into estimative models. The sample set consisted of well-characterized soils collected from native prairie sites in the western U.S. Corn Belt and Great Plains: 11 sites located within 8 midwestern states (CO, NE, IA, ND, MT, TX, MO, and MN). Sample characterization parameters included site, depth, %SOC, POM C, Cmin C, SMBC, and SOC calendar age (determined from 14C age). Correlations were found for samples collected across this large geographic region (at or greater than 0.90) for SOC, POM C, Cmin C, and SMBC. Soil organic carbon calendar age derived from radiocarbon-14 dating could be estimated for ustollic soils from MT, NE, and CO. These soils also contained deeper and younger eolian layers, whose ages were correctly estimated with this technique. The Py-MBMS analysis additionally showed that soils developed from water-sorted sediments on a tilled-floor lake plain (lacustrine soils) were significantly different from the other samples.