Wisconsin Plant Research Articles

Impacts of Herbivory on Photosynthesis of Four Common Wisconsin Plant Species

Overcompensation to herbivory is prevalent among plant species. However, we do not yet fully understand why plant species vary in their compensatory abilities. It is highly likely that overcompensation is determined by the ability of plants to elevate photosynthesis in response to herbivory, which is dictated by evolutionary exposure to grazing. Here, we tested the hypothesis that photosynthetic overcompensation should be predictable based on plant life form by simulating herbivore damage on four plant species: two common range grasses with long evolutionary exposure to grazing (Andropogon gerardii, Bouteloua curtipendula) and two common understory forbs that are resistant to, and therefore experience little, grazing (Alliaria petiolata, Symplocarpus foetidus). We measured leaf-level gas exchange in a high-resolution time series that extended throughout the growing season. We found no evidence of photosynthetic compensation for three of the four plant species. Interestingly, only A. petiolata, a highly invasive species, demonstrated increased photosynthesis and stomatal conductance following clipping. Further, the effects were short-lived, as both photosynthesis and stomatal conductance returned to baseline levels within 24 h. Our results suggest that elevated photosynthesis to herbivory might not be a general mechanism by which plants either resist or tolerate herbivory.

Functional trait data for vascular plant species from northeastern North America.

Wisconsin's plant communities are responding to shifting disturbance regimes, habitat fragmentation, aerial nitrogen deposition, exotic species invasions, ungulate herbivory, and successional processes. To better understand how plant functional traits mediate species' responses to changing environmental conditions, we collected a large set of functional trait data for vascular plant species occupying Wisconsin forests and grasslands. We used standard protocols to make 76,213 measurements of 34 quantitative traits. These data provide rich information on genome size, physical leaf traits (length, width, circularity, thickness, dry matter content, specific leaf area, etc.), chemical leaf traits (carbon, nitrogen, phosphorus, potassium, calcium, magnesium, ash), life history traits (vegetative and flower heights, seed mass), and traits affecting plant palatability (leaf fiber, fat, and lignin). These trait values derive from replicate measurements on 12+ individuals of each species from multiple sites and 45+ individuals for a selected subset of species. Measurements typically reflect values for individuals although some chemical traits involved composite samples from several individuals at the same site. We also qualitatively characterized each species by plant family, woodiness, functional group, and Raunkiaer lifeform. These data allow us to characterize trait dimensionality, differentiation, and covariation among temperate plant species (e.g., leaf and stem economic syndromes). We can also characterize species' responses to environmental gradients and drivers of ecological change. With survey and resurvey data available from >400 sites in Wisconsin, we can analyze variation in community trait distributions and diversity over time and space. These data therefore allow us to assess how trait divergence vs. convergence affects community assembly and how traits may be related to half-century shifts in the distribution and abundance of these species. The data set can be used for non-commercial purposes. The data set is licensed as follows: CC-By Attribution 4.0 International. We request users cite both the OSF data set and this Ecology data paper publication.

Using the nuclear LEAFY gene to reconstruct phylogenetic relationships among invasive knotweed (Reynoutria, Polygonaceae) populations

AbstractKnotweed species in the genus Reynoutria are native to eastern Asia but have become noxious weeds in Europe and North America. In the United States, invasive populations of Japanese knotweed (Reynoutria japonica Houtt.), giant knotweed [Reynoutria sachalinensis (F. Schmidt) Nakai], and their interspecific hybrid known as Bohemian knotweed (R. × bohemica Chrtek & Chrtková) continue to expand their ranges. Although these plants are among the most invasive terrestrial species, there are relatively few molecular tools for identifying the parental species, the F1 hybrid, or subsequent hybrids or introgressed individuals. We studied Reynoutria populations in Wisconsin, a state where all three taxa grow, to determine whether molecular data would be useful for distinguishing species and identifying hybrids. We obtained DNA sequence data from the plastid matK gene and the nuclear LEAFY gene and compared these to previously published sequences. Data from the uniparentally inherited matK region included haplotypes attributable to R. japonica and R. sachalinensis. Nuclear data indicated that R. sachalinensis plants are most similar to native plants in Japan, with two Wisconsin accessions exhibiting a monomorphic genotype for the LEAFY gene. Three Wisconsin accessions of R. japonica were each characterized by having three distinct kinds of LEAFY sequence. Most plants in our study were found to possess two or three phylogenetically distinct copies of the LEAFY gene, with the copies being most closely related to R. japonica and R. sachalinensis, respectively, and these were inferred to be interspecific hybrids. Altogether, five kinds of interspecific hybrids were identified, reflecting various combinations of LEAFY sequence types from the parental species. The widespread existence of hybrid plants in Wisconsin, many of which are morphologically identifiable as R. japonica, indicates a cryptic genetic diversity that should be examined more broadly in North America using molecular tools.

Respiratory diseases, racial disparities, and residential proximity to coal power plants in Wisconsin, USA: a cross-sectional study

BackgroundThe burning of fossil fuels, including coal, is the primary source of greenhouse gas emissions driving anthropogenic climate change and its associated health harms: heat-related illnesses, arboviral diseases, trauma from extreme weather events, allergies, and chronic disease exacerbations. Coal-fired power plants (CFPP) supply 23% of electricity in the USA and 42% for the state of Wisconsin. Air pollution from CFPP has been associated with respiratory diseases, cancers, cardiovascular and neurological disorders, especially for vulnerable populations. In this cross-sectional study, we aim to measure associations between respiratory diseases and residential proximity to CFPP. MethodsWe obtained cross-sectional, population-based health data for non-institutionalised, non-active-duty adults from the Survey of the Health of Wisconsin database from 2008 to 2013. Pulmonary function was measured by spirometry as a ratio of forced expiratory volume in one second (FEV1) to forced vital capacity (FVC). An average of three or more FEV1/FVC readings <80% was considered abnormal and indicative of an obstructive disorder. We used multivariate regression analyses to evaluate pulmonary function and distance from CFPP, controlling for sex, education, race/ethnicity, age, asthma, and total years smoking history. FindingsWe included data from 2327 adults aged 21–74 years in analysis. Adults living in close proximity to one of 11 CFPP had worse pulmonary function than did adults living more than 35 km away from CFPP with an odds ratio of 1·24 (95% CI 0·90–1·70). Although not statistically significant, trends suggest higher odds of obstructive pulmonary diseases in those living within 35 km of CFPP. Protective factors, in addition to distance, were higher education and younger age. Risk factors identified were older age and having a history of smoking. Although Black residents made up 4·8% of the total sample population, they accounted for 13·3% of people living within 35 km of CFPP. Similarly, Hispanic residents accounted for 4·8% of those living within 35 km of CFPP but only made up 2·8% of the sample population. InterpretationWisconsin CFPP might be associated with worse pulmonary function in people living at or within 35km of their locations, with possible consequences related to costly inhaler medications, health-care visits, and hospitalisations. When linked with socioeconomic factors, and race and ethnicity, closing down CFPP should be considered when addressing health disparities and environmental injustices. Affordable, clean energy solutions are readily available and just transitions have recently been demonstrated in North America. As nations recover from COVID-19, there is a profound opportunity for leaders across sectors to build healthier communities and prioritise climate action for health. FundingDr Elaine Kohler Summer Academy of Global Health Research and Wisconsin Partnership Program.

Spatial phylogenetics reveals evolutionary constraints on the assembly of a large regional flora.

We used spatial phylogenetics to analyze the assembly of the Wisconsin flora, linking processes of dispersal and niche evolution to spatial patterns of floristic and phylogenetic diversity and testing whether phylogenetic niche conservatism can account for these patterns. We used digitized records and a new molecular phylogeny for 93% of vascular plants in Wisconsin to estimate spatial variation in species richness and phylogenetic α and β diversity in a native flora shaped mainly by postglacial dispersal and response to environmental gradients. We developed distribution models for all species and used these to infer fine-scale variation in potential diversity, phylogenetic distance, and interspecific range overlaps. We identified 11 bioregions based on floristic composition, mapped areas of neo- and paleo-endemism to establish new conservation priorities and predict how community-assembly patterns should shift with climatic change. Spatial phylogenetic turnover most strongly reflects differences in temperature and spatial distance. For all vascular plants, assemblages shift from phylogenetically clustered to overdispersed northward, contrary to most other studies. This pattern is lost for angiosperms alone, illustrating the importance of phylogenetic scale. Species ranges and assemblage composition appear driven primarily by phylogenetic niche conservatism. Closely related species are ecologically similar and occupy similar territories. The average level and geographic structure of plant phylogenetic diversity within Wisconsin are expected to greatly decline over the next half century, while potential species richness will increase throughout the state. Our methods can be applied to allochthonous communities throughout the world.

Recovery of Cranberry Plants Infected With Tobacco streak virus and Incidence and Distribution of TSV in the Field.

Tobacco streak virus (TSV) has been detected in cranberry plants in Wisconsin, New Jersey, and Massachusetts, and is associated with berry scarring symptoms. In the current study, cv. Mullica Queen plants that produced scarred, symptomatic, TSV-positive fruit in one year produced nonscarred, asymptomatic, TSV-positive fruit in subsequent years, consistent with the "recovery" phenomenon previously documented in other ilarvirus-woody plant interactions. In field trials, fruit set and berry weight were significantly reduced (P < 0.05) in symptomatic, TSV-positive cranberry shoots but not in recovered, TSV-positive shoots compared with healthy, TSV-negative shoots. Likewise, return bloom in the first year following berry scarring was not negatively impacted in recovered shoots. Detection of TSV in various plant parts throughout the growing season was more variable in symptomatic shoots than in recovered shoots. Of all plant parts tested, TSV detection was lowest in berries at the time of harvest in both symptomatic and recovered shoots. Minimal increases in incidence of TSV-infected shoots in cranberry beds from one year to the next, and spatial autocorrelation of TSV-infected shoots, suggest that most new infections result from TSV spreading within a bed, rather than frequent introductions of the virus from external sources.

Getting to Yes or Bailing on No: The Site Selection Process of Ethanol Plants in Wisconsin

AbstractPrior studies of ethanol location rest on the assumption that ethanol producers are economic free agents—evaluating sites as if all counties are contenders for their business, weighing the availability of feedstocks along with their infrastructure needs, operating without ties to localities, and being subject to enticement from policy incentives. We analyze the political‐economic process through which ethanol plants come into communities by examining plant location decisions, plant financing, community receptivity toward the plant, local government incentives, and the dynamics of the approval process. We use case studies of ethanol plants in Wisconsin to explore the economic, social, and political dynamics of ethanol plant location. Our case studies provide evidence in support of some findings in the ethanol location literature—such as the importance of access to corn; however, they also suggest site selection criteria not adequately addressed by the literature. Furthermore, our data suggest that capital may not be as mobile as location theory assumes it to be and that location decisions are not primarily determined by consideration of profit maximization. Instead, the location of ethanol plants is greatly influenced by the extent to which the original initiators of the plant are locally embedded in its host community. Our research answers Barkley and McNamara's (:45) call for a return to a case studies approach in order to develop “reliable insights into the location process.”

Wisconsin Vegetation Database – plant community survey and resurvey data from the Wisconsin Plant Ecology Laboratory

Legacy data provide valuable baselines for assessing ecological changes. Excellent baseline data for Wisconsin's plant communities exist because of the surveys conducted by J.T. Curtis and colleagues (the Wisconsin Plant Ecology Laboratory or PEL) in the 1940s and 1950s. They surveyed > 2,000 sites to test how plant community composition varies along environmental gradients. These sites include upland and lowland forests, prairies, savannas, meadows, sand barrens, dunes, fens, and bogs. They devised new techniques to sample and compare plant communities. Their data include species lists and often quantitative data on occurrences and tree sizes. At intensively sampled prairies and savannas, data include cover and/or the composition of quadrats. At forested sites, researchers characterized the overstory by recording tree identity and measuring size and spacing using plotless methods. For the understory, they tallied all vascular species present in 20 (occasionally 40) spaced 1-m quadrats. Subsequent PEL researchers have resurveyed > 500 of these sites. The original quadrats and sites were not marked, requiring that resurveys approximate the original locations. Sampling uses either the original or more intensive protocols. We have characterized environmental conditions at many sites (soil chemistry, exotic earthworms, deer browse, and landscape conditions). We also now measure functional traits on many species. Our goals are to test theories of community assembly and assess how plant traits interact with patch size and landscape conditions to affect species and community dynamics. We have also redesigned sampling methods. The many sites and species provide great statistical power to characterize ecological changes and evaluate the factors driving these changes. These results serve to inform the public about ecological change and improve our ability to manage these communities wisely. Both the new and the legacy data are stored in the database Wisconsin Vegetation Database (GIVD ID NA-US-008).

Life Cycle Impact Assessment and Allocation Methods Development for Cheese and Whey Processing

In this study, life cycle assessment (LCA) methods are used to develop life cycle inventory (LCI) and life cycle impact assessment (LCIA) data to estimate the global warming potential (GWP) and energy intensity (EI) of cheese and dry whey manufacturing in Wisconsin using a farm gate to plant gate approach. All of the environmental burdens and benefits are assigned to the product (cheese) and none are assigned to the land-spread waste stream (whey) for a single-output system typical of small cheese plants in Wisconsin. For a multifunction system, in which both cheese and food-grade whey are produced, the following methods are applied to handle co-product multifunctionality: subdivision, allocation ratios, and a method that combines both subdivision and allocation ratios. Total solids, nutritional content, and economic value are considered as the allocation ratios. Each of these fixed allocation ratios is applied to the entire process and to individual processes unique to each product. The differences in the GWP and EI for cheese and dry whey are highly influenced by the choice of method. The EI of cheese ranges from 7.1 to 19 MJ kg-1 cheese, and the GWP of cheese ranges from 0.46 to 1.3 kg CO2-eq kg-1 cheese. The main source of these differences is the shift of environmental burdens from cheese to the dry whey co-product resulting from different allocation strategies. The method that combines subdivision and allocation is presented as the preferred and most accurate method to deal with the multifunctionality of cheese and whey manufacturing. Sensitivity analysis shows that GWP and EI are most affected by variations in milk pasteurization, whey evaporation, whey drying, and whey pasteurization. This study demonstrates the importance of the allocation method on LCA analysis and suggests methods to more accurately assess the environmental burdens when more than one product is produced at a dairy plant.

Resilient Characteristics of Bottom Ash and Bottom Ash-Soil Mixtures

Abstract Bottom ash, a byproduct of the coal combustion process to generate electricity by power plants, is generally underutilized and ends up in landfills or ponds. This paper aims at evaluating the characteristics of the coal combustion bottom ash for potential utilization in pavement construction materials. To achieve this objective, a comprehensive laboratory testing program was undertaken to evaluate the physical properties, compaction characteristics, and resilient modulus of bottom ash, subgrade soils, and bottom ash-soil mixtures. The investigated bottom ash was obtained from power plants in Wisconsin and Michigan. Test results showed that there is a wide spectrum of bottom ash properties pertaining to specific gravity and unit weight, while the investigated bottom ash samples were classified as granular material. Repeated load triaxial testing was performed to determine the resilient modulus of the bottom ash, subgrade soil, and bottom ash-soil mixtures. Specimens were tested at the maximum dry unit weight and optimum moisture content. Test results demonstrated that the resilient modulus values of bottom ash vary depending on the physical properties and unit weight of the bottom ash. For four bottom ash-soil mixtures, the resilient modulus values were low compared with the resilient modulus of subgrade soils, while for one type the resilient modulus was comparable/higher than that of subgrade soil. Therefore, mixing the bottom ash with subgrade soil showed increased resilient modulus values of the mixture for the bottom ash sample from Oak Creek Power Plan (OCPP). Mixing 50% of the bottom ash with subgrade soil, by dry weight, was considered an optimum amount to improve the resilient modulus of the bottom ash soil mixture for OCPP bottom ash.

Intercropping Tropical Vine Legumes and Maize for Silage in Temperate Climates

ABSTRACT Maize silage is used extensively in American dairy rations. Increasing protein content would enhance maize silage quality. This study examined nine forage legume species (Austrian winter pea, common bean, cowpea, lablab, scarlet runner bean, sesbania, sunn hemp, tropical kudzu, and velvet bean) grown in mixture with maize plants in Wisconsin, in the U.S. Plants were evaluated for growth throughout the growing season, harvest forage dry matter content, total dry matter yield, and forage mixture components. Of the forage legumes tested, common bean, lablab, scarlet runner bean, sunn hemp, and velvet bean were most successfully intercropped with maize. The common bean entry was the most aggressive forage legume, comprising 23% on a dry-matter basis of the final harvested forage mixture. The lablab entry, despite a slow start, became more productive during the late growing season and comprised 7.4% on a dry-matter basis of the final harvested forage mixture. Harvested forage moisture ranged from 299 g kg−1 to 364 g kg−1 of dry matter. Except for the common bean mixture, which had a lower forage dry-matter yield, the mixtures did not differ from one another or the pure maize control for dry-matter accumulation per unit area. Similar to forage dry-matter yields, stover forage mixture fractions were not significantly different among entries, except for the common bean-maize mixture. Grain yields were inversely proportional to the amount of legume present.

Survey of Salty and Sweet Whey Composition from Various Cheese Plants in Wisconsin

Salty whey is currently underutilized in the dairy industry because of its high salt content and increased processing and disposal costs. Salty whey accounts for 2 to 5% of the total whey generated during Cheddar and other dry-salted cheese manufacture. Because relatively little information is available on salty whey, this study was conducted to determine the range of compositional components in salty whey from commercial cheese plants. Gross compositional differences in percent protein, salt, solids, and fat between sweet whey and salty whey from various dry-salted cheeses from 8 commercial plants were determined. Differences between individual whey protein compositions were determined using sodium dodecyl sulfate-PAGE. Average total solids, fat, and salt content were significantly greater in the salty whey compared with the corresponding sweet whey. True protein was reduced in salty whey although great variability existed among samples. Individual whey proteins identified included lactoferrin (Lf), BSA, immunoglobulin G, β-lactoglobulin, and α-lactalbumin. Salty whey showed an increase in Lf content and a decrease in α-lactalbumin and β-lactoglobulin content when compared with sweet whey. Salty whey may be a source of Lf, potentially increasing its value to whey processors. However, the compositional assessments showed that commercial salty whey is a highly variable waste stream.

First Report of Soybean dwarf virus on Soybean in Wisconsin.

Soybean dwarf virus (SbDV) causes widespread economic losses on soybean (Glycine max (L.) Merr.) in Japan (4), and has been reported on soybean in Virginia (2), in various legumes in the southeastern United States (1), and in peas in California (3). During late July and early August of 2003, soybean plants in Wisconsin were surveyed for SbDV. In 286 soybean fields at the R2-R4 growth stage, the uppermost fully unfurled leaf was collected from 10 plants at each of five sites. Samples were collected at random without regard to symptoms. SbDV symptom information was not recorded. Samples were stored on ice until frozen at -80°C. Five fields in four Wisconsin counties (Columbia, Lafayette, Sauk, and Waushara) tested positive for SbDV using double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). DAS-ELISA testing was conducted with reagents from Agdia, Inc (Elkhart, IN) following the manufacturer's protocol. Absorbance was read at 405 nm with a Stat Fax 2100 microplate reader (Awareness Technology, Inc., Palm City, FL) or visually evaluated. DAS-ELISA did not discriminate between strains of SbDV. The presence of SbDV was confirmed, and strain identity was inferred as dwarfing strain using reverse transcription-polymerase chain reaction (RT-PCR). Total RNA was extracted from homogenized leaf tissue, reverse transcribed, and amplified with the SuperScript One Step RT-PCR System (Invitrogen, Carlsbad, CA) and SbDV-specific primers (5'-CTGCTTCTGGTGATTACACTGCCG-3' and 5'-CGCTTTCATTTAACGYCATCAAAGGG-3'). Size of the RT-PCR products (110 bp) was consistent with the dwarfing strain, SbDV-D. All locations that tested positive for SbDV showed soybean aphids, Aphis glycines Matsumura (Homoptera: Aphididae), on 100% of soybean plants. Several aphid species have been reported to vector SbDV, but at this time, vector relations in the Wisconsin infections are unknown. To our knowledge, this is the first report of SbDV infecting soybean in Wisconsin.

Washington to provide EPC for Wisconsin plant

A combined cycle consists of combining two power cycles in series to obtain a high overall thermal efficiency, significantly higher than the individual efficiencies of the two cycles making up the combined cycle. In the combined cycle discussed in this chapter, a Brayton cycle or gas turbine is utilized for the topping cycle and a steam Rankine cycle for the bottoming cycle. Combined cycles come in a variety of sizes, depending on the size and number of gas turbines utilized, and may range from less than 10 MW to in excess of 500 MW while using a single gas turbine. In addition to having high thermal efficiencies, outstanding environmental performance, easy start-up and shut-down and low cooling water requirements, combined cycles have significantly lower staffing, capital cost and construction time requirements when compared to boiler based power plants. On the other hand, the clean fuels required by a combined cycle are significantly more expensive when compared to fuels such as coal and biomass that can be directly combusted in a boiler. Included in this chapter are a discussion of types of gas turbines for combined-cycle applications, types of steam cycles in combined-cycle plant, plant design and technology, fuel specifications, control technologies for criteria pollutants as well as for CO2 emissions, and limitations of gas-fired combined-cycle plants. Future trends for improvements in performance and emissions are also discussed.

Washington to provide EPC for Wisconsin plant

A combined cycle consists of combining two power cycles in series to obtain a high overall thermal efficiency, significantly higher than the individual efficiencies of the two cycles making up the combined cycle. In the combined cycle discussed in this chapter, a Brayton cycle or gas turbine is utilized for the topping cycle and a steam Rankine cycle for the bottoming cycle. Combined cycles come in a variety of sizes, depending on the size and number of gas turbines utilized, and may range from less than 10 MW to in excess of 500 MW while using a single gas turbine. In addition to having high thermal efficiencies, outstanding environmental performance, easy start-up and shut-down and low cooling water requirements, combined cycles have significantly lower staffing, capital cost and construction time requirements when compared to boiler based power plants. On the other hand, the clean fuels required by a combined cycle are significantly more expensive when compared to fuels such as coal and biomass that can be directly combusted in a boiler. Included in this chapter are a discussion of types of gas turbines for combined-cycle applications, types of steam cycles in combined-cycle plant, plant design and technology, fuel specifications, control technologies for criteria pollutants as well as for CO2 emissions, and limitations of gas-fired combined-cycle plants. Future trends for improvements in performance and emissions are also discussed.

John T. Curtis, Fifty Years of Wisconsin Plant Ecology.

John T. Curtis, Fifty Years of Wisconsin Plant Ecology.

Virulence, Legume Host Specificity, and Genetic Relatedness of Isolates ofFusarium oxysporumfrom Red Clover

Fusarium oxysporum is the most prevalent fungal pathogen recovered from symptomatic red clover (Trifolium pratense) plants in Wisconsin and contributes to stand loss and reduced productivity. Three field isolated and 44 single-conidium isolates of F. oxysporum were recovered from red clover plants with vascular wilt symptoms and assessed for virulence, host specificity, and source of variation in host reaction. In addition, genetic relatedness of selected isolated was determined by vegetative compatibility groups (VCG). Twenty-one populations of red clover, two populations of alfalfa (Medicago sativa), and one population each of alsike clover (Trifolium hybridum), ladino clover (Trifolium repens), and birdsfoot trefoil (Lotus corniculatus) were tested for their reaction to isolates or single-conidium isolates. Isolates differed significantly in their ability to elicit reactions both among and within host species. VCGs were not useful in predicting host reaction because isolates from distinct groupings elicited similar host reactions. The reaction of red clover to F. oxysporum is attributable to genetic diversity in isolate virulence as well as to variation within the host population for resistance

Nursery Integrated Pest Management in Wisconsin

A Nursery Integrated Pest Management program was initiated in Wisconsin in 1991. From 1991 to 1993, the educational and monitoring program enhanced grower familiarity with the IPM concept, as well as provided detailed information on the pest problems common to woody landscape plants in Wisconsin. Educational features of the program include twilight seminars and winter workshops, a pest control guide that described the management strategies available for pests of woody landscape plants, and also statewide pest reporting and pest predictions.

Reanalysis of the Wisconsin Prairie Continuum

-Numerous prairie gradient studies have documented a significant correlation between soil moisture and compositional variation. The Wisconsin prairie gradient studies of J. T. Curtis and the Wisconsin Plant Ecology Laboratory (PEL) are among these and are widely cited. Data for 247 of the original Wisconsin PEL prairies were reordinated with Detrended Correspondence Analysis (DECORANA) ordination. The first axis of the ordination was highly correlated with the original Wisconsin prairie continuum. Sand prairies and wet-mesic prairies from extreme southeastern Wisconsin separated on the second axis. Measures of soil moisture were the highest correlate of the first axis. Latitude and longitude, pH, calcium, phosphorus, potassium, nitrate and ammonium nitrogen were also significant correlates of first or second axes. Discussions of pattern in prairie vegetation should look beyond simple correlations with soil moisture, and careful experimental and descriptive studies of prairie vegetation are still needed.

Shear Tests of Extruded Hollow-Core Slabs

T hrough the years, hollow-core slabs have undergone extensive tests to verify their compliance with the provisions of the ACI Building Code. The advent of the 1971 ACI Code brought with it a number of provisions which were markedly different from prior codes to the extent that an updated, comprehensive testing program for hollow-core slabs seemed in order. The specific code area containing the most ambiguous requirement was the section dealing with minimum web reinforcement. Also, since several hollow —core extruded slab systems are made with zero slump concrete, there is an additional reason to examine their characteristics experimentally since the shear strength provisions of the ACI Code were developed from tests of wet cast concrete. While this investigation was originally developed to provide proprietary information, certain observations were deemed appropriate for publication. First, dry cast, extruded hollow-core slabs depend on compaction of a zero slump concrete to achieve a monolithic cross section. Too little data on full scale tests of such slabs is available to the profession. Secondly, shear tests also provide information on the bond strength of the prestressing strands. The Commentary to the ACI Code' specifically cautions the user on the applicability of development length equations for noslump concrete. Considerable discussion'7 has also been generated on development length in general, including some recommendations for increased development length requirements. The tests described herein provide data relative to development length. Because of the differences in production techniques of various extruded hollow-core slabs, it is necessary to state that the test specimens were Spancrete, produced in the Waukesha, Wisconsin plant owned by Spancrete Industries. Shear and bond strength are dependent