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Historically, grasslands with limited tree presence were embedded in a matrix of predominantly open oak and pine forests in the eastern United States. These open ecosystems mostly have been lost to other land uses, particularly agriculture, and also to closed forests under fire exclusion because frequent surface fire prevents tree encroachment. We located the potential extent of eastern fire‐maintained grasslands by applying the random forests and C5.0 classifiers to determine the relationship between mapped areas of historical grasslands and topography and wind speed, which are proxies for surface fire frequency. A generalized ruleset was that fire‐maintained grasslands occurred at roughness values of less than 95, or flatter sites, and wind speeds ≥3.4 m s−1, which created large fire compartments. Potential grasslands covered 27 million ha, or 14% of the 200 million ha of the eastern United States, although these fire‐maintained locations also may have been savannas or open woodlands historically. Currently, potential grassland locations are 40% crops, 25% pasture, 18% forests, and 13% developed land, with about 1.5% each of herbaceous upland vegetation, herbaceous wetlands, and shrublands. According to historical accounts, fire‐maintained grasslands generally transitioned to dense young tree growth within a 20‐year interval after fire exclusion; in Kentucky, the transition transpired during the periods 1790–1810 or 1810–1830, but dates vary with Euro‐American settlement time. Finding the forgotten grasslands of the eastern United States, with this mechanistic approach to estimate fire disturbance, is an important first step for recovering and managing eastern grassland biodiversity. [ABSTRACT FROM AUTHOR]

PREMISE: Shifting phenology in response to climate is one mechanism that can promote population persistence and geographic spread; therefore, species with limited ability to phenologically track changing environmental conditions may be more susceptible to population declines. Alternatively, apparently nonresponding species may demonstrate divergent responses to multiple environmental conditions experienced across seasons. METHODS: Capitalizing on herbarium records from across the midwestern United States and on detailed botanical surveys documenting local extinctions over the past century, we investigated whether extirpated and extant taxa differ in their phenological responses to temperature and precipitation during winter and spring (during flowering and the growing season before flowering) or in the magnitude of their flowering time shift over the past century. RESULTS: Although warmer temperatures across seasons advanced flowering, extirpated and extant species differed in the magnitude of their phenological responses to winter and spring warming. Extirpated species demonstrated inconsistent phenological responses to warmer spring temperatures, whereas extant species consistently advanced flowering in response to warmer spring temperatures. In contrast, extirpated species advanced flowering more than extant species in response to warmer winter temperatures. Greater spring precipitation tended to delay flowering for both extirpated and extant taxa. Finally, both extirpated and extant taxa delayed flowering over time. CONCLUSIONS: This study highlights the importance of understanding phenological responses to seasonal warming and indicates that extirpated species may demonstrate more variable phenological responses to temperature than extant congeners, a finding consistent with the hypothesis that appropriate phenological responses may reduce species' likelihood of extinction. [ABSTRACT FROM AUTHOR]

Grazing as a management tool is often intended to alter plant community dynamics through preferential foraging. Bison diet in the western United States has been well studied, especially in short and mixed grass remnant prairies. However, there is little known about what bison consume in restored and tallgrass prairies. As bison reintroductions are used more commonly in eastern tallgrass prairies, it is important to understand their diet to predict future impacts on prairie plant communities. This study aims to understand bison diet across different seasons, and asks whether diet differs among male and female, and differently aged bison. We used stable isotope analysis to quantify δ13C and δ15N in plants and used a Bayesian isotope mixing model to estimate bison diet. We found bulls relied more heavily on C4 plants and wetland plants than cows, which relied more heavily on forbs, but no differences in diet between ages. Our analysis shows that bison primarily grazed on C4 grasses throughout the late spring and summer. However, bison foraged more on wetland species and forbs in the late summer and fall. This change in diet could have implications for wetland species and habitats, through dung inputs and trampling. The relatively high reliance on forbs for nearly one‐third of bison diet could mean intended impacts of reintroduced bison such as increased plant diversity through preferential grazing on grasses could be dampened. Managers reintroducing bison to restored prairie ecosystems should ensure adequate wetland and forb species, in addition to a mix of grasses. [ABSTRACT FROM AUTHOR]

Aim: Multiple hypotheses predict how gradients of nutrient availability, plant biomass, and temperature shape trophic pyramids. We aim to disentangle the simultaneous influence of those factors and their indirect effects on trophic structure and individual trophic levels. Location: United States. Time period: 2017. Major taxa studied: Invertebrates. Methods: To examine differences in trophic pyramid shape and abundance within trophic levels and across ecological gradients, we conducted 54 standardized surveys of invertebrate communities in North American grasslands. We tested for the direct and indirect effects of plant biomass, temperature, sodium (Na), other essential elements (e.g. N, P, and K), and toxic heavy metals, (e.g. Ar and Pb) in plant tissue on both individual trophic levels, and trophic pyramid shape, estimated as the community trophic mean (CTM). Results: Plant sodium increased CTM, indicating that high plant sodium concentrations are associated with top‐heavy invertebrate trophic pyramids. Sites with higher plant biomass had higher proportions of herbivores compared to higher trophic levels. Finally, increasing temperature resulted in more top‐heavy trophic pyramids. Overall, plant biomass, temperature, and plant chemistry directly and indirectly affected the abundances within different trophic levels, highlighting the complexity of factors regulating trophic structure. Main conclusions: Trophic structure of grassland invertebrate communities is strongly influenced by plant sodium, plant biomass, and to a lesser extent, temperature. Grasslands occupy 30% of the Earth's terrestrial surface and are an imperiled ecosystem due to conversion to row crop agriculture. As biogeochemistry and temperature in the Anthropocene are increasingly modified, our results have considerable implications for the trophic structure of future grassland communities. [ABSTRACT FROM AUTHOR]

There are inherent challenges in scaling stomatal conductance (g s) from leaf to canopy particularly over seasonal time scales when species distribution and canopy structure evolve. We address this gap using carbonyl sulfide (OCS) and CO 2 fluxes from a predominantly C3 prairie and C4 maize field in the midwestern United States. The g s derived from OCS fluxes captured a transition in the stomatal limitation on gross primary productivity (GPP) through the growing season as well as seasonally persistent g s dynamics such as temperature optimum and a positive response of nighttime g s to vapor pressure deficit. Near the termination of the prairie growing season, we observed a decrease in the relative OCS to CO 2 flux that we hypothesize emerged from a rising contribution of C4 plants to productivity. The results show how plot‐scale OCS and CO 2 fluxes can be used as a trace gas diagnostic for transitions in the limiting factors for community GPP. Key Points: Canopy stomatal conductance was derived from carbonyl sulfide (OCS) fluxes at maize and prairie sites in the midwestern United StatesSeasonal changes in the ratio of canopy stomatal conductance to GPP elucidated phenological transitions in community photosynthesisDaytime and nighttime OCS and CO 2 fluxes can be used for diagnostic trace gas signatures associated with C3 and C4 productivity [ABSTRACT FROM AUTHOR]

Plant phenology will likely shift with climate change, but how temperature and/or moisture regimes will control phenological responses is not well understood. This is particularly true in Mediterranean climate ecosystems where the warmest temperatures and greatest moisture availability are seasonally asynchronous. We examined plant phenological responses at both the population and community levels to four climate treatments (control, warming, drought, and warming plus additional precipitation) embedded within three prairies across a 520 km latitudinal Mediterranean climate gradient within the Pacific Northwest, USA. At the population level, we monitored flowering and abundances in spring 2017 of eight range‐restricted focal species planted both within and north of their current ranges. At the community level, we used normalized difference vegetation index (NDVI) measured from fall 2016 to summer 2018 to estimate peak live biomass, senescence, seasonal patterns, and growing season length. We found that warming exerted a stronger control than our moisture manipulations on phenology at both the population and community levels. Warming advanced flowering regardless of whether a species was within or beyond its current range. Importantly, many of our focal species had low abundances, particularly in the south, suggesting that establishment, in addition to phenological shifts, may be a strong constraint on their future viability. At the community level, warming advanced the date of peak biomass regardless of site or year. The date of senescence advanced regardless of year for the southern and central sites but only in 2018 for the northern site. Growing season length contracted due to warming at the southern and central sites (~3 weeks) but was unaffected at the northern site. Our results emphasize that future temperature changes may exert strong influence on the timing of a variety of plant phenological events, especially those events that occur when temperature is most limiting, even in seasonally water‐limited Mediterranean ecosystems. [ABSTRACT FROM AUTHOR]

Abstract: Two data sources, field‐collected samples and values in the NRCS SSURGO database, were used to estimate organic carbon concentration (%) and stock (Mg C/ha) in floodplain soils along rivers of the tallgrass and shortgrass prairie within the United States. Field sampling of 6 sites in the tallgrass prairie and 6 sites in the shortgrass prairie (total sample size of 370 vertical cores) indicates that percent organic carbon within a planar cross section through floodplain sediment at a site is spatially heterogeneous and does not decline systematically with depth, but statistical analyses indicate that soil organic carbon is randomly distributed. The median values of organic carbon concentration at both field‐sampled and sites remotely sampled based on soil maps in the tallgrass prairie are significantly higher than those of the shortgrass prairie. Median values of organic carbon stock are not significantly different between those obtained from forested sites for comparison and either shortgrass or tallgrass prairie sites but are significantly higher at tallgrass than at shortgrass prairie sites. These results are surprising because upland net primary productivity in prairies is lower than in forested sites. We infer that the historical abundance of floodplain wetlands in river corridors of the tallgrass prairie results in high organic carbon stocks in tallgrass prairie river corridors. This implies that management designed to enhance carbon sequestration should focus on floodplain soils, especially in the tallgrass prairie region, as well as on upland forests. [ABSTRACT FROM AUTHOR]

Perennial grasses are promising feedstocks for bioenergy production in the Midwestern USA. Few experiments have addressed how drought influences their carbon fluxes and storage. This study provides a direct comparison of ecosystem-scale measurements of carbon fluxes associated with miscanthus ( Miscanthus × giganteus), switchgrass ( Panicum virgatum), restored native prairie and maize ( Zea mays)/soybean ( Glycine max) ecosystems. The main objective of this study was to assess the influence of a naturally occurring drought during 2012 on key components of the carbon cycle and plant development relative to non-extreme years. The perennials reached full maturity 3-5 years after establishment. Miscanthus had the highest gross primary production (GPP) and lowest net ecosystem exchange (NEE) in 2012 followed by similar values for switchgrass and prairie, and the row crops had the lowest GPP and highest NEE. A post-drought effect was observed for miscanthus. Over the duration of the experiment, perennial ecosystems were carbon sinks, as indicated by negative net ecosystem carbon balance (NECB), while maize/soybean was a net carbon source. Our observations suggest that perennial ecosystems, and in particular miscanthus, can provide a high yield and a large potential for CO2 fixation even during drought, although drought may negatively influence carbon uptake in the following year, questioning the long-term consequence of its maintained productivity. [ABSTRACT FROM AUTHOR]

Groundwater seeps are characteristic hydrological and ecological features of many landscapes, yet their hydrology remains poorly understood. Here, we provide the first detailed measurements of near-surface soil moisture dynamics in a Muhly grass ( Muhlenbergia riverchonii) seep system developed in soils over interbedded limestone and marl. These features are characteristic of, and prevalent within, the North Central Texas Grand Prairie Ecoregion. The data were collected during the most severe drought in Texas history. We quantify the spatial-temporal variability of volumetric soil moisture (θv) and matric potential (ψm) along a slope containing a seep upslope, with a view to assessing whether the seep qualifies as an isolated wetland under the Environmental Protection Agency's proposed changes to Section 404 legislation for wetland determination. We found the Muhly seep to consistently be the wettest portion of the hillslope, with a statistically distinguishable drying trend downslope into a barrens environment with the thinnest soils. ψm within the seep remained at or above field capacity (θfc) 37% of the time during pre-drought conditions and was at all times wetter than lower sections of the slope between the seep and barrens. The seep responded rapidly to rainfall and remained at or close to saturation for 5 to 7 days following storm events. Saturation is controlled by fractured limestone sitting on top of a subsurface marl layer, resulting in water easily percolating through the limestone, ponding, and then moving laterally as interflow above the marl. Although the wetland characteristics of Muhly seeps could not be conclusively assessed because of extreme drought conditions, our data suggest that under normal rainfall conditions, these systems might likely qualify as isolated wetlands. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Southern Great Plains are characterized by a fine-scale mixture of different land-cover types, predominantly winter-wheat and grazed pasture, with relatively small areas of other crops, native prairie, and switchgrass. Recent droughts and predictions of increased drought in the Southern Great Plains, especially during the summer months, raise concern for these ecosystems. We measured ecosystem carbon and water fluxes with eddy-covariance systems over cultivated cropland for 10 years, and over lightly grazed prairie and new switchgrass fields for 2 years each. Growing-season precipitation showed the strongest control over net carbon uptake for all ecosystems, but with a variable effect: grasses (prairie and switchgrass) needed at least 350 mm of precipitation during the growing season to become net carbon sinks, while crops needed only 100 mm. In summer, high temperatures enhanced evaporation and led to higher likelihood of dry soil conditions. Therefore, summer-growing native prairie species and switchgrass experienced more seasonal droughts than spring-growing crops. For wheat, the net reduction in carbon uptake resulted mostly from a decrease in gross primary production rather than an increase in respiration . Flux measurements suggested that management practices for crops were effective in suppressing evapotranspiration and decomposition (by harvesting and removing secondary growth), and in increasing carbon uptake (by fertilizing and conserving summer soil water). In light of future projections for wetter springs and drier and warmer summers in the Southern Great Plains, our study indicates an increased vulnerability in native ecosystems and summer crops over time. [ABSTRACT FROM AUTHOR]

The article presents a study to understand how the demand for agrofuel production alters the abundance of habitats to grasslands birds in the U.S. It examines the ability of alternative agrofuel crops in providing habitat for grassland birds and determines how crop placement affects grassland birds. The study finds that native perennial plants as feedstock for agrofuel have potential in providing a habitat to a wide range of grassland birds which include rare and threatened species.

Migratory pathways in North American prairies are critical for sustaining endemic biodiversity. Fragmentation and loss of habitat by an encroaching human footprint has extirpated and severely truncated formerly large movements by prairie wildlife populations. Greater sage-grouse Centrocercus urophasianus, a Near Threatened landscape species requiring vast tracts of intact sagebrush Artemisia spp., exhibit varied migratory strategies across their range in response to the spatial composition of available habitats. We unexpectedly documented the longest migratory event ever observed in sage-grouse (> 120 km one way) in 2007–2009 while studying demography of a population at the north-east edge of their range. Movements that encompassed 6,687 km2 included individuals using distinct spring and summer ranges and then freely intermixing on the winter range in what is probably an obligate, annual event. The fate of greater sage-grouse in Canada is in part dependent on habitat conservation in the USA because this population spans an international border. Expanding agricultural tillage and development of oil and gas fields threaten to sever connectivity for this imperilled population. Science can help delineate high priority conservation areas but the fate of landscapes ultimately depends on international partnerships implementing conservation at scales relevant to prairie wildlife. [ABSTRACT FROM PUBLISHER]

Landscape-scale conversion of deeply rooted perennial native vegetation to annual crops has altered the ecohydrological balance in the Midwestern U.S. One of the major ways this may occur is through plant species’ abilities to access and take up water from different depths in the soil profile. In this study, we use stable isotope techniques to assess plant water uptake patterns for plants growing in four contrasting annual and perennial ecosystems in central Iowa: row-cropped cornfield, prairie, oak savanna, and woodland. To address limitations of conventional approaches to analyzing isotopic data, especially when isotopic profiles in the soil are complex, we employ an alternative ‘multiple source mass-balance isotopic’ approach suitable for determining probable contributions of multiple potential sources to total plant water uptake. Observed differences in isotopic profiles among the plant communities were attributed to differences in infiltration rates, plant water uptake rates, the degree of evaporative isotopic fractionation under the different vegetative covers, and processes of hydraulic redistribution. Savanna (Quercus macrocarpa Mixch) and woodland (Q. Macrocarpa, Umus americana L. ) trees had the lowest stem water δ18O values (−6. 12‰, −7. 77‰, and −7. 61‰, respectively), whereas corn (Zea mays L. ) and prairie (Andropogon gerardii) exhibited higher stem water δ18O values (−5. 49‰ and −5. 85‰, respectively), suggesting more shallow sources of water uptake for the latter. Frequency histographs produced from the multiple source mass-balance analysis confirmed that the corn and prairie species obtained up to 45% and 36% of their water from the upper 0–20cm soil horizon, respectively. In contrast, oak trees growing in the savanna and woodland obtained up to 40% and 20% of their water from the upper 20cm, and up to 60% and 80% of their water from depths >60cm, respectively. Lack of strong isotopic gradients in the soil profiles combined with irregularities in the slope of the isotopic gradient by depth complicated interpretation of the data. However, an important advantage of the alternative multiple source mass-balance isotopic approach over conventional approaches was its capability of producing more quantitative and objective estimates for the probable contributions of multiple sources to total plant water uptake. This study highlights how changes in land use and vegetative cover in the Midwest affects plant water uptake patterns, and suggests how these changes may influence larger landscape scale alterations in the hydrologic balance. [Copyright &y& Elsevier]

The article examines practices that can be used in the selection and use of high-quality legume inoculants and identifies ongoing concerns with the inoculation and persistence of rhizobia in restoration areas. When crop or pasture plants are inoculated, the norm is to apply the appropriate rhizobia at seeding. In some countries only a single inoculant strain is used, while in the United States it is more common to inoculate with a mixture of several strains. During inoculation, seed, inoculant and a sticker that binds microorganisms to the seed are mixed until the seeds are uniformly covered. Traditionally, seed is set in the shade to dry and is usually sown the same day. Germination for agricultural species in a moist seedbed is relatively quick and uniform, with nodules usually evident within a week of seed germination and nitrogen fixation starting soon thereafter. Requirements for a good inoculant carrier include high water-holding capacity, ease of processing, non-toxicity to rhizobia, low cost and good buffering capacity.

1. The use of off-season burns to control exotic vegetation shows promise for land managers. In California, wildfires tend to occur in the summer and autumn, when most grassland vegetation is dormant. The effects of spring fires on native bunchgrasses have been examined but their impacts on native forbs have received less attention. 2. We introduced Erodium macrophyllum, a rare native annual forb, by seeding plots in 10 different areas in a California grassland. We tested the hypotheses that E. macrophyllum would perform better (increased fecundity and germination) when competing with native grasses than with a mixture of exotic and native grasses, and fire would alter subsequent demography of E. macrophyllum and other species’ abundances. We monitored the demography of E. macrophyllum for two seasons in plots manually weeded so that they were free from exotics, and in areas that were burned or not burned the spring after seeding. 3. Weeding increased E. macrophyllum seedling emergence, survival and fecundity during both seasons. When vegetation was burned in June 2001 (at the end of the first growing season) to kill exotic grass seeds before they dispersed, all E. macrophyllum plants had finished their life cycle and dispersed seeds, suggesting that burns at this time of year would not directly impact on fecundity. In the growing season after burning (2002), burned plots had less recruitment of E. macrophyllum but more establishment of native grass seedlings, suggesting burning may differentially affect seedling recruitment. 4. At the end of the second growing season (June 2002), burned plots had less cover of exotic and native grasses but more cover of exotic forbs. Nevertheless, E. macrophyllum plants in burned plots had greater fecundity than in non-burned plots, suggesting that exotic grasses are more competitive than exotic forbs. 5. A glasshouse study showed that exotic grasses competitively suppress E. macrophyllum to a greater extent than native grasses, indicating that the poor performance of E. macrophyllum in the non-burned plots was due to exotic grass competition. 6. Synthesis and applications. This study illustrates that fire can alter the competitive environment in grasslands with differential effects on rare forbs, and that exotic grasses strongly interfere with E. macrophyllum. For land managers, the benefits of prescribed spring burns will probably outweigh the costs of decreased E. macrophyllum establishment. Land managers can use spring burns to cause a flush of native grass recruitment and to create an environment that is, although abundant with exotic forbs, ultimately less competitive compared with non-burned areas dominated by exotic grasses. Journal of Applied Ecology (2004) 41, 643–652 [ABSTRACT FROM AUTHOR]

Discusses the species composition changes in a rooftop grass and wildflower meadow. Observation of grass and wildflower meadow growing in seven radiation zones on the roof of The Church of Jesus Christ of Latter-day Saints Conference Center in Salt Lake City in Utah. Identification of species for grass and wildflower mixture; Low-maintenance alternatives to turfgrass.

We report a 36-month echo of vole (Microtus pennsylvanicus) seed-selection in the composition of synthetic forb communities in Wisconsin. An initial study showed direct suppression of an exceptionally large-seeded (seed > 15 mg) species (Silphium integrifolium, Asteraceae) by seed-size predation by rodents during the winter, resulting in indirect release of small-seeded (seed ≤ 1.5 mg) species. Twelve months after planting, plant diversities (Simpson’s D) were 33% higher in plots exposed to winter seed selection by rodents. Thirty-six months after planting, Silphium integrifolium had almost equalized densities in rodent access (20.8 ± 4.1 m–2) and exclusion (29.0 ± 5.2 m–2) plots, but still suppressed both large-seeded (≥ 3.5 mg) and small-seeded (≤ 1.5 mg) species (F1,16=11.84 and F1,16=10.42, P ≤ 0.005, respectively). A multivariate analysis of covariance (MANCOVA) distinguished effects of Silphium integrifolium (Wilk’s lambda P=0.029) from echoes of earlier winter granivory (Wilk’s lambda P=0.014). Thirty months after rodent exclusion, diversity (D) remained 27% higher in plots once opened to winter granivory (adjusted mean 4.70 ± 0.37 SE) as compared with closed plots (3.70 ± 0.26; F1,16=5.12, P < 0.05). Echoes of earlier granivory remained after rodent-induced imbalances in the abundances of the competitive driver of this system, Silphium integrifolium, all but disappeared. [ABSTRACT FROM AUTHOR]

Abstract In order to quantify the historical changes in carbon storage that result from agricultural conversion, this study compared the carbon dynamics of two sites in the loess region of Iowa: a native prairie and a cropland. Field data were obtained to determine present-day carbon storage and its variability within a landscape (a stable ridgetop vs. eroding upper-midslope vs. depositional lower slope). Models were used to recreate the historical carbon budget of these sites and determine the cropland's potential to be a net CO2 source or sink, relative to the atmosphere. Regardless of slope position, the cropland site contains approximately half the amount of carbon as prairie. Variability in soil carbon storage within a site as a consequence of slope position is as large or larger (variations of 200–300%) than temporal variation (∼200% at all slope positions). The most extreme difference in soil carbon storage between the cropland and prairie sites is found in the soil at the upper-midslope, which is the area of greatest erosion. The models estimate that 93–172% of the carbon in the original topsoil has been lost from the cropland's eroding midslope. Much of this carbon is derived from deeper soil horizons. Either a small sink or strong source of carbon to the atmosphere is created, depending on the fate of the eroded sediment and its associated carbon. [ABSTRACT FROM AUTHOR]

Plant macrofossils from sediments exposed in cutbanks of small streams on the Great Plains yield details of the history of the vegetation and climate, and potentially of the hydrologic behaviour of the streams during the past 9000 radiocarbon years. Five zones are recognized by visual inspection. Macrofossils in zone 1 (c. 9000 to c. 8500 BP) indicate that upland deciduous forest was sparsely present, but that prairie, weedy and wetland habitats were also well established. Zone 2 (c. 8500 to c. 5800 BP) is sparsely represented, but upland trees disappeared, riparian trees and wetland plants were sparse, and weeds and prairie taxa fluctuated from low to high values. This interval was probably the warmest, driest part of the Holocene. Zone 3 (c. 5800 to c. 3100 BP) had a rich riparian forest, along with well-developed prairies, disturbed habitats and wetlands. This period was more moist but had intermittent droughts. Zone 4 (c. 3100 to c. 2700 BP) has peaks in many prairie and weedy elements, whereas riparian forest elements nearly disappeared, suggesting another warm, dry interval. Zone 5 represents a return to somewhat less arid conditions and records a strong signature of introduced weeds in post-settlement time. [ABSTRACT FROM AUTHOR]

AbstractRandom amplified polymorphic DNA (RAPD) analysis was used to characterize genetic diversity and genetic distinctiveness of Andropogon gerardii from remnant Arkansas prairies. Six oligonucleotide primers, which generated 37 RAPD bands, were used to analyse 30–32 plants from six Grand Prairie populations, Baker Prairie (Arkansas Ozarks), two Illinois prairies and two cultivars. Genetic diversity of the Arkansas remnants ranged from 82.7 to 99.3%, with 89% of the total genetic variation within and 11% among populations. The partitioning of genetic variation was consistent with that reported for other outcrossing perennial grasses, using the more conservative allozyme markers. Principal component analysis indicated a northern and southern association within Arkansas’ Grand Prairie. Although there was no genetic structuring at the landscape level, the Illinois prairies and cultivars were different from all Arkansas prairies tested. There was significant within-population structuring in four of the seven Arkansas remnants, with a negative relationship between genetic similarity and geographical distance. The three nonstructured populations were from a linear railroad remnant, suggesting different population-level dynamics from nonlinear prairies. The results of this study indicated that small isolated remnant big bluestem populations were not genetically depauperate and that genetic relationships among populations could not be predicted solely on geographical proximity. [ABSTRACT FROM AUTHOR]

This research examined the influence of abiotic factors on contaminant assimilation within the water column of two wetlands (RMA3 and RMA4) located on Rocky Mountain Arsenal National Wildlife Area, north ofDenver, Colorado, USA. We define contaminant assimilation as the ability of a wetland system to reduce negative impacts of contaminants on aquatic organisms. To examine the influence of abiotic factors (i.e., alkalinity, suspended solids), chronic toxicity tests were performed from February 1992 through November 1993. Ceriodaphnia dubia were exposed to water from the wetlands, which was spiked with Zn. These tests indicated higher assimilative capacity in wetland RMA4 relative to RMA3. Dissolved organic carbon (DOC) was significantly greater in RMA4 than in RMA3, suggesting that it may have influenced differencesin bioavailability of Zn in wetland water. Suspended solids were also consistently higher in RMA4 than in RMA3. To test the influence of suspended solids on contaminant assimilation, C. dubia were exposed to filtered and unfiltered Zn-spiked water from RMA4. The greater toxicity of Zn to C. dubia in filtered water indicated that suspended solids were important in ameliorating impacts of Zn in RMA4. Results from this study suggest that from the suite of variables assessed, DOC and suspended solids were the most important physiochemical influenceson Zn toxicity within the water column of these two wetlands. Differences in habitat characteristics of RMA3 and RMA4 demonstrated the importance of site-selection toward functional design of wetlands. [ABSTRACT FROM AUTHOR]