bluuebunny/crossref_metadata_2025 huggingface dataset:
Environmental Limits on Net Primary Production and Light‐Use Efficiency Across the Oregon Transect
Authors: Runyon J. , Waring R. H. , Goward S. N. , Welles J. M.
Published: April 2006

Due to climate differences, an extreme range in productivity occurs along a 250—km, west—east transect at °44° north latitude in western Oregon, USA, where coniferous evergreen forests dominate. As part of the Oregon Transect Ecosystem Research (OTTER) project, our objective was to evaluate how climate constrains net primary production (NPP) by limiting the utilization of intercepted photosynthetically active radiation (IPAR). The forests measured along the transect intercepted from 22% to 99.5% of the incident PAR. With data collected from recording meteorological stations installed near each site, we defined the hourly conditions when photosynthesis was partly or completely limited by drought, extreme humidity deficits, or frost. From this analysis we calculated that the fraction of incident PAR that could be utilized throughout the year ranged from 92% in the coastal rainforests to <25% in the juniper woodland. NPP varied from 3 to 26 Mg°ha—1°yr—1 with the fraction of belowground NPP, estimated from litterfall, increasing from 20% to 60% of the total as the environment becomes harsher. Light—use efficiency (°u) calculated under conditions when the environment did not constrain photosynthesis, averaged 0.8 g/MJ for aboveground NPP and 1.3 g/MJ for total NPP.
The Effects of Habitat Fragmentation on Midwestern Grassland Bird Communities
Authors: Herkert James R.
Published: April 2006

The influence of area and vegetation structure on breeding bird communities associated with 24 Illinois grassland fragments (0.5—600 ha) was studied between 1987 and 1989 to document the effects of habitat fragmentation in a severely fragmented midwestern landscape. Fragment area strongly influenced bird communities within grasslands and accounted for a high percentage of the variation in mean breeding bird species richness among fragments (R2 = 0.84). Breeding bird species richness patterns within 4.5—ha subsections of these grasslands also significantly increased with fragment size. Eight of the 15 (53%) most common bird species had distributions among fragments that were significantly influenced by habitat area, whereas six species (40%) had distributions within fragments that were significantly influenced by vegetation structure only. The Dickcissel (Spiza americana) was the only species with a distribution within fragments that was not significantly associated with either habitat area or vegetation structure. Four groups of birds were identified by an analysis of habitat area and vegetation structure preferences of individual species: area—sensitive species (5 species), edge species (3), vegetation—restricted species (6), and the Dickcissel. Estimates of minimal area requirements for the five area—sensitive species ranged from 5 to 55 ha. Discriminant analyses of habitat suitability within fragments suggests that the absence of area—sensitive grassland bird species form some small fragments may result, in part, from limited habitat availability. All five area—sensitive species, however, also regularly avoided structurally suitable habitat on small grassland fragments. As a result of the considerable extent to which native and, more recently, agricultural grasslands have declined in the Midwest, habitat fragmentation is likely to have caused midwestern grassland bird declines, especially for area—sensitive species.
Dynamics and Pattern of a Managed Coniferous Forest Landscape in Oregon
Authors: Spies Thomas A. , Ripple William J. , Bradshaw G. A.
Published: April 2006

We examined the process of fragmentation in a managed forest landscape by comparing rates and patterns of disturbance (primarily clear—cutting) and regrowth between 1972 and 1988 using Landsat imagery. A 2589—km2 managed forest landscape in western Oregon was classified into two forest types, closed—canopy conifer forest (CF) (typically, > 60% conifer cover) and other forest and nonforest types (OT) (typically, < 40 yr old or deciduous forest) The percentage of CF declined from 71 to 58% between 1972 and 1988. Declines were greatest on private land, least in wilderness, and intermediate in public nonwilderness. High elevations (> 914 m) maintained a greater percentage of CF than lower elevations (< 914 m). The percentage of the area at the edge of the two cover types increased on all ownerships and in both elevational zones, whereas the amount of interior habitat (defined as CF at least 100 m from OT) decreased on all ownerships and elevational zones. By 1988 public lands contained °45% interior habitat while private lands had 12% interior habitat. Mean interior patch area declined from 160 to 62 ha. The annual rate of disturbance (primarily clear—cutting) for the entire area including the wilderness was 1.19%, which corresponds to a cutting rotation of 84 yr. The forest landscape was not in a steady state or regulated condition which is not projected to occur for at least 40 yr under current forest plans. Variability in cutting rates within ownerships was higher on private land than on nonreserve public land. However, despite the use of dispersed cutting patterns on public land, spatial patterns of cutting and remnant forest patches were nonuniform across the entire public ownership. Large remaining patches (< 5000 ha) of contiguous interior forest were restricted to public lands designated for uses other than timber production such as wilderness areas and research natural areas.
Early Selection of Black Spruce Seedlings and Global Change: Which Genotypes Should We Favor?
Authors: Wang Zhang Ming , Lechowicz Martin J. , Potvin Catherine
Published: April 2006

We investigated the effects of both soil fertility and predicted changes in climate on the performance of different families of black spruce, Picea mariana (Mill.) B.S.P., during the first growing season. The results were used to examine whether reforestation programs should consider changing their preferred family lines in anticipation of altered performance given global climate change. We grew seedlings of 16 open—pollinated maternal families of black spruce under phytotron conditions simulating present and mid—21st century climatic conditions during the growing season. The realistic, simulated future climate included both elevated CO2 levels and seasonally appropriate increases in mean daily temperature. To explore the dependence of climatic responses on site quality, seedlings were irrigated with solutions having either 5 or 100 mg/L of nitrogen. The lower nitrogen level represents a poor site for black spruce growth and survival, but the higher level provides ample nitrogen. We also recorded seed size for each seedling to evaluate the degree to which maternal investments might buffer responses to future climate and fertility during the first year on the seedbed. Seedling survival and growth increased both under the future climate regime and with nitrogen fertilization. The two factors interacted synergistically, with nitrogen enrichment significantly enhancing the positive effects of the future climate regime. Nitrogen—poor conditions, however, did not preclude a positive seedling response to the future climate. Our results indicate that seedling survival and height growth are highly dependent upon initial seed mass: larger seeds produced more vigorous 1st—yr seedlings. The families differed in seed mass, seed germination, and seedling survival and growth, but their relative performances did not vary significantly among the treatments. These results suggest that black spruce families selected for rapid growth under present conditions will also do well in the future, at least in terms of early establishment and performance on sites regenerated by seeding.
Associational Susceptibility: Effects of Cropping Pattern and Fertilizer on Malawian Bean Fly Levels
Authors: Letourneau Deborah K.
Published: April 2006

Subsistence farmers with little access to costly pesticides must rely on cultural practices to enhance biological control, reduce crop apparency or suitability to pests, or increase crop tolerance to pests. Farmers in Central Malawi traditionally plant beans (Phaseolus vulgaris L.) with the first rains and apply fertilizer to bean only when it is grown in dicultures with maize (Zea mays L.). I used a factorial experiment with a key pest of beans to assess the relative effects of fertilizer (predicted to increase pest levels) and intercropping (predicted to decrease pest densities). Stem‐boring bean fly (Diptera: Agromyzidae) densities and their parasitism rates were compared with respect to cropping pattern, fertilizer application, sowing date, and Vaccinium diversity of beans. Together these factors address the effects of current practices (intercropping, mixed varieties) on bean fly infestation rates and those now encouraged for increased production (relay cropping, fertilized monoculture). In addition, associational resistance in this system is tested in the context of actual farming practices. In contrast to many other studies of specialist herbivores, neither the densities of bean flies [Ophiomyia phaseoli (Tryon) and O. spencerella (Greathead)] nor their rates of parasitism were changed significantly by diversifying the field with non‐host plants (bean‐maize dicultures). However, the two fly species were differentially susceptible to plant quality and parasitism, with fertilized bean plants harboring more bean fly puparia than did unfertilized plants regardless of cropping pattern. Thus, the indirect effect of fertilizing intercrops resulted in elevated pest densities. Differential plant quality has not been included in most studies of intercropping and pest incidence, yet reflects actual farming practices. Bean fly densities tended to increase in plants sown later in the wet season, suggesting that relay cropping of beans will exacerbate bean fly damage. In this study, greater yields were achieved in mixed variety bean treatments, but standard fertilizer applications did not contribute to increased bean production.
Symptoms of Nitrogen Saturation in a Riparian Wetland
Authors: Hanson Gay C. , Groffman Peter M. , Gold Arthur J.
Published: April 2006

Riparian forests are in a unique position in the landscape since they form a transition between uplands and aquatic systems. These ecosystems may be highly susceptible to nitrogen (N) saturation since they may be subject to high inputs of N from upland areas. We measured potential net N mineralization and nitrification, soil inorganic N levels, microbial biomass carbon (C) and N content, and the N content of litter as indicators of N saturation in two riparian zones on the eastern and western sides of a stream. The sites had similar soils, vegetation, and hydrology, but differing upland land use. The eastern or "enriched" site was downgradient of a dense residential housing development (built in the 1950s) that produced high groundwater nitrate (NO3—) concentrations. The western or "control"site had an undeveloped upland. Our objectives were (1) to evaluate if groundwater NO3— loading had induced changes in surface soil N—cycle processes that are symptoms of N saturation in the enriched site and (2) to evaluate these changes in relation to inputs and outputs of N to the site. Soil inorganic—N levels, litter N content, and potential net N mineralization and nitrification were significantly higher on the enriched site relative to the control site, suggesting that the enriched site and N saturated. However, input—output analysis indicated that the enriched site was still a sink for upland derived NO3—. High rates of denitrification and storage of N in soil organic matter appear to moderate N saturation on the enriched site.
Lessons from Lysimeters: Soil N Release from Disturbance Compromises Controlled Environment Study
Authors: Johnson Dale W. , Walker Roger F. , Ball J. Timothy
Published: April 2006

A controlled environment study of the effects of carbon dioxide (CO2) and nitrogen (N) on growth of ponderosa pine seedlings produced results contradictory to those obtained in the field with the same species, soil, and treatments. In the controlled environment study, there was a significant negative growth response to N fertilization, whereas in the field there was a significant positive response to N. The difference was due to high rates of native N mineralization after soil disturbance during potting. This was evident from soil solution NO3‐ concentrations that peaked at 5000 μmol/L in the unfertilized pots and 20 000 μmol/L in the fertilized pots. These concentrations are orders of magnitude greater than those typically observed in the field. The effects of soil disturbance on N mineralization and nitrification need to be carefully considered before initiating controlled environment studies. The results of this study show that excessive N mineralization caused by soil disturbance can seriously compromise the results of controlled environment studies
Scalable Decision Rules for Environmental Impact Studies: Effect Size, Type I, and Type II Errors
Authors: Mapstone Bruce D.
Published: April 2006

Assessments of environmental impacts are being subject to greater scientific and legal scrutiny than ever before. The application of traditional statistical decision‐making criteria to questions of environmental impacts has become increasingly inadequate as society demands greater environmental accountability from economic development. In particular, impact assessment has inherited a preoccupation with Type I error rates that has pervaded ecological research, even though Type II errors are often equally severe in impact assessment. Estimation of Type II error rates and specification of critical effect sizes–or the magnitudes of impacts considered important–are mutually dependent. Consideration of Type II errors, therefore, requires the exact specification of an hypothesized impact, which is often difficult. Insistence on low rates of Type I error (e.g., α = 0.05) typically means that equivalent rates of Type II error can be realized only when effect sizes (ES) are very large or when very many samples are taken. Rather than adhering to a fixed, arbitrary, critical, Type I error rate, I propose a procedure by which the critical ES is given primacy. Statistical decision criteria are then selected according to the relative weighting of the perceived consequences of Type I or Type II errors. The critical Type I error rate is set by iteration to some multiple (k) of the estimated potential for Type II error, and the null hypothesis is rejected if that (variable) Type I probability is not exceeded. The value of k would be determined by the ratio of the consequences (e.g., costs) of Type II and Type I errors. The procedure focuses attention on the magnitudes of impacts considered important, and provides for statistical decisions based on the a priori consideration of the development and environmental costs of Type I and Type II errors. It also provides incentive for development proponents to support rigorous environmental monitoring.
Patterns and Causes of Resistance to Tree Invasion in Rights‐of‐Way
Authors: Hill James D. , Canham Charles D. , Wood David M.
Published: April 2006

This study was designed to identify the critical life‐history stages and ecological processes responsible for variation in rates of tree invasion in utility rights‐of‐way in the Hudson Valley of New York. We used repeated censuses to estimate natural rates of tree seedling establishment, growth, and survival in the 12 major plant communities found along rights‐of‐way in the region. An individual‐based model was used to integrate our field data and calculate measures of the rate of tree invasion in each plant community. The most common tree invaders were species with large, wind‐dispersed seeds (i.e., Acer rubrum and Fraxinus americana) although these were rarely the most common tree species in the forests bordering the corridors. In narrow (°30‐50 m wide) rights‐of‐way there was little relationship between seedling density and distance to the nearest seed sources; however, in wide corridors, seed dispersal clearly limited tree invasion. Annual variation in seed production in adjacent forests was also a major factor in the high spatial and temporal variability in tree seedling establishment. Growth rates of newly established seedlings did not vary significantly among the different communities; however seedling growth rates increased dramatically once the seedlings emerged above shrub or herb‐dominated canopy. Thus, the duration of competition (i.e., the number of years required by a seedling to emerge above the shrub or herbaceous canopy) appears to have been more important than the initial intensity of competition in determining variation among communities in resistance to tree invasion. As a result, shrub communities generally had high resistance to invasion. Among herbaceous communities, the highest resistance to invasion occurred in communities dominated by the grass Schizachyrium scoparium (little bluestem) on poor soils.
The Catastrophic Loss of Torreya Taxifolia: Assessing Environmental Induction of Disease Hypotheses
Authors: Schwartz Mark W. , Hermann Sharon M. , Vogel Christoph S.
Published: April 2006

The Florida torreya (Torreya taxifolia Arn.) has decreased to near extinction during the past 30 yr, allegedly as the result of a fungal disease induced by environmental stress. Increasing regional temperatures, micro‐climatic warming, drought, and soil nutrient stress are among the environmental changes proposed as triggers for the decline of T. taxifolia. These putative disease inciting mechanisms were evaluated through historical observations of the magnitude of environmental change, as well as physiological and growth experiments used to assess the relative sensitivity of T. taxifolia to environmental change. Historical evidence of climatic warming, regionally or locally, is lacking. Likewise, physiological experiments failed to support the temperature change hypothesis. A drought, concurrent with the timing of the decline, was not notably severe and T. taxifolia was observed to be relatively drought tolerant. Greenhouse growth experiments demonstrated that low soil nutrition is not likely to limit growth in T. taxifolia. Another hypothesis states that fire suppression in the surrounding uplands triggered a disease epidemic. This hypothesis states that smoke deposition in ravines may limit foliar pathogen populations and that a chronic increase of foliar pathogens, associated with fire suppression, triggered the decline of T. taxifolia. Our experiments suggest that foliar pathogens may impose health risks to T. taxifolia and that one very common foliar fungal associate is susceptible to smoke. Decreased light levels, as a result of increased woody biomass in the absence of fire, may also increase plant stress, leading to increased disease incidence. While the low light levels characteristic of field situations limited T. taxifolia growth in the greenhouse, light level was not correlated with growth, or vigor, in the field. These results suggest that the fire suppression hypothesis is, at least, plausible and requires further examination.
Predator‐Prey Theory and Management of Multispecies Fisheries
Authors: Yodzis Peter
Published: April 2006

In population modelling the functional forms of models are at least as important as are parameter values in expressing the underlying biology and in determining the outcome. Here the influence of differing biological assumptions as to predator interference on the forms of predator—prey models is discussed, and it is shown how this aspect of the underlying biology can influence the conclusions to be drawn from multispecies population models as to how "competition from natural predators" affects human harvesting of natural populations. The importance of these issues for the current controversy over the effects of marine mammals on fisheries is stressed.
Principles for the Conservation of Wild Living Resources
Authors: Mangel Marc , Talbot Lee M. , Meffe Gary K. , Agardy M. Tundi , Alverson Dayton L. , Barlow Jay , Botkin Daniel B. , Budowski Gerardo , Clark Tim , Cooke Justin , Crozier Ross H. , Dayton Paul K. , Elder Danny L. , Fowler Charles W. , Funtowicz Silvio , Giske Jarl , Hofman Rober J. , Holt Sidney J. , Kellert Stephen R. , Kimball Lee A. , Ludgwig Donald , Magnusson Kjartan , Malayang Ben S. , Mann Charles , Norse Elliott A. , Northridge Simon P. , Perrin William F. , Perrings Charles , Norse Elliott A. , Northridge Simon P. , Perrin William F. , Perrings Charles , Peterman Randall M. , Rabb George B. , Regier Henry A. , Reynolds John E. , Sherman Kenneth , Sissenwine Michael P. , Smith Time D. , Starfield Anthony , Taylor Robert J. , Tillman Michael F. , Toft Catherine , Twiss John R. , Wilen James , Young Truman P.
Published: April 2006

We describe broadly applicable principles for the conservation of wild living resources and mechanisms for their implementation. These principles were engendered from three starting points. First, a set of principles for the conservation of wild living resources (Holt and Talbot 1978) required reexamination and updating. Second, those principles lacked mechanisms for implementation and consequently were not as effective as they might have been. Third, all conservation problems have scientific, economic, and social aspects, and although the mix may vary from problem to problem, all three aspects must be included in problem solving. We illustrate the derivation of, and amplify the meaning of, the principles, and discuss mechanisms for their implementation. The principles are: Principle I. Maintenance of healthy populations of wild living resources in perpetuity is inconsistent with unlimited growth of human consumption of and demand for those resources. Principle II. The goal of conservation should be to secure present and future options by maintaining biological diversity at genetic, species, population, and ecosystem levels; as a general rule neither the resource nor other components of the ecosystem should be perturbed beyond natural boundaries of variation. Principle III. Assessment of the possible ecological and sociological effects of resource use should precede both proposed use and proposed restriction or expansion of ongoing use of a resource. Principle IV. Regulation of the use of living resources must be based on understanding the structure and dynamics of the ecosystem of which the resource is a part and must take into account the ecological and sociological influences that directly and indirectly affect resource use. Principle V. The full range of knowledge and skills from the natural and social sciences must be brought to bear on conservation problems. Principle VI. Effective conservation requires understanding and taking account of the motives, interests, and values of all users and stakeholders, but not by simply averaging their positions. Principle VII. Effective conservation requires communication that is interactive, reciprocal, and continuous. Mechanisms for implementation of the principles are discussed.
Chlorine Dynamics and Ambient Toxicity in Receiving Streams
Authors: Stewart A. J. , Hill W. R. , Ham K. D. , Christensen S. W. , Beauchamp J. J.
Published: April 2006

This study was conducted to better understand total residual chlorine (TRC) dynamics and ambient toxicity in two chlorine‐contaminated streams in eastern Tennessee. The study used stepwise logistic analysis of Ceriodaphnia survival and water quality factors measured in 169 7‐d chronic toxicity tests of water from four sites in one stream to determine the factors significantly affecting the survival. The 7‐d mean concentrations of TRC and a measure of day‐to‐day variation in TRC concentration in each test were included as dominant factors in explaining Ceriodaphnia mortality. The logistic regression model correctly predicted the mortality or survival in individual Ceriodaphnia in 89.9% of the cases and had a low rate of false positives and false negatives. A simpler pass‐or‐fail model, which used a Ceriodaphnia survival criterion of 60%, yielded slightly better results (correctly predicted outcomes, 91.7%). We also measured TRC concentrations in situ by monitoring at two sites in one of the streams and at one site in the other stream. This monitoring showed that TRC concentrations in both streams varied approximately three‐fold in daily cycles, with TRC concentrations at night greater than those during the day. Laboratory and field experiments indicated that the diel cycles in TRC were probably driven by sunlight and stream periphyton. Two key points emerged from this study. First, the analysis show that logistic regression can be used effectively to relate temporally varying chemical conditions to the outcomes of static‐renewal ambient toxicity tests. In some situations, this method of analysis is more appropriate than other methods, such as ANOVA, that there are used to evaluate dose‐response patterns. Second, diel changes in TRC in streams, apparently caused by sunlight and periphyton, can be large and have important implications for predicting the fate and ecological effects of this widespread contaminant.
Responses of Bald Eagles to Human Activity During the Summer in Interior Alaska
Authors: Steidl Robert J. , Anthony Robert G.
Published: April 2006

Along narrow rivers, spatial restriction of human use based on wildlife responses can effectively eliminate the entire river corridor from human use. Therefore, if river use by both wildlife and humans is a goal, an alternative management strategy is necessary. We measured flush response rate and flush distance of breeding and nonbreeding Bald Eagles (Haliaeetus leucocephalus) to recreational boating along the Gulkana River in interior Alaska from 1989 to 1992. Eagle responses to our nonmotorized boat were governed by the context within which human‐eagle encounters occurred. Flush response rate of nonbreeding eagles decreased as perch height and its distance from the river's edge increased, increased as the season progressed and as eagle group size increased, was lower for juveniles (20%) than other age classes (49‐65%), and varied with the existing level of human activity in a geographic location (P < 0.01 for all parameters). Flush distance of nonbreeding eagles increased as the distance a disturbance was first visible to a perched eagle increased, as perch height and its distance from the river's edge increased, and as the season progressed. In contrast to flush response, flush distance was strongly associated with age and was greatest for adults, least for juveniles, and intermediate for subadults. Breeding adults were much less likely to flush than nonbreeding adults, and flushed at lesser distances. We recommended that along narrow wilderness rivers, the impacts of human activity on Bald Eagle populations be regulated with temporal, rather than spatial, restrictions.
Does Repeated Human Intrusion Cause Cumulative Declines in Avian Richness and Abundance?
Authors: Riffell Samuel K. , Gutzwiller Kevin J. , Anderson Stanley H.
Published: April 2006

Human intrusion, the mere presence of people in the environment, has become a dominant form of disturbance in many landscapes. Some forms of intrusion from recreationists and other groups occur repeatedly and can seriously alter avian reproduction, survival, and habitat use. Accordingly, repeated intrusion has the potential to cause impacts that accumulate through time and that are manifested as progressive declines in avian richness and abundance. From 1989 to 1993, we experimentally assessed whether or not temporally cumulative impacts occurred in Wyoming bird communities as a result of repeated intrusion by solitary hikers; the intrusions lasted 1‐2 h each week during 10 consecutive weeks of each year's breeding season. We tested a priori hypotheses about declines in overall richness and abundance, relative richness and abundance for sets of common and uncommon species, richness and abundance for six guilds, and separate abundances of four common species. Relative richness and abundance for the set of common species were the only metrices to exhibit significant declines between years during the 5‐yr period. The declines in these variables, however, were not cumulative. At a statistical power level of 0,85, minimum detectable differences for many variables were small enough to have allowed easy detection of substantive declines, had any occurred. The yearly effects we detected for some richness and abundance variables may not have led to cumulative declines because individuals displaced one year may have been replaced in subsequent years, and some individuals each year may have habituated to or learned to tolerate the intrusions. For the avian communities and intrusion levels we studied, managers should focus on trying to preclude or ameliorate short‐term impacts. Attempts to identify the types and intensities of intrusion that actually cause cumulative declines in richness and abundance should continue. Data about intrusions that do not generate cumulative declines, such as those presented here, are just as important as data about intrusions that do cause cumulative declines; managers need both to define the scope of intrusion disturbances that can lead to cumulative impacts in avian communities. Information about the cumulative effects of intrusion should be used by conservation biologists, wildlife managers, and land‐use planners to decide whether or how to control intrusion.
Spatial and Temporal Variation in Soil and Vegetation Impacts on Campsites
Authors: Marion Jeffrey L. , Cole David N.
Published: April 2006

We studied the impacts of camping on soil and vegetation at Delaware Water Gap national Recreation Area. We assessed the magnitude of impact on campsites that varied in amount of use and in topographic position. We also evaluated change over a 5‐yr period on long‐established, recently opened, and recently closed campsites, as well as on plots subjected to experimental trampling. Campsite impacts were intense and spatially variable. Amount of use and topographic position explained some of this variation. Soil and vegetation conditions changed rapidly when campsites were initially opened to use and when they were closed to use. Changes were less pronounced on the long‐established campsites that remained open to use. In the trampling experiments, impact varied greatly with trampling intensity and between vegetation types. An open‐canopy grassland vegetation type was much more resistant to trampling than a forb‐dominated forest vegetation type. Campsite impacts increased rapidly with initial disturbance, stabilized with ongoing disturbance, and–in contrast to what has been found in most other studies–decreased rapidly once disturbance was terminated. Implications of these results for campsite management strategies, such as use concentration or dispersal, and rotation or closure of campsites, are discussed.
Fire Severity and Tree Seedling Establishment in Abies Magnifica Forests, Southern Cascades, Oregon
Authors: Chappell Christopher B. , Agee James K.
Published: April 2006

To determine the relationship between fire severity and tree seedling establishment, we investigated landscape pattern and composition, fire history, and tree seedling establishment on recent natural burns in Shasta red fire (Abies magnifica var. shastensis) forests of Crater Lake National Park in the southern Oregon Cascade Range. Fire severity classes, defined by basal area mortality, were mapped on three burned sites (29‐197 ha). Variation in fire severity contributed to a landscape mosaic of patches with varying size, shape, forest stand structure, and tree species' composition. Post‐fire tree regeneration was numerically dominated by red fir in all fire severity classes, but seedling establishment and growth varied among severity classes. Density of red fir seedlings was highest in low‐ and moderate‐severity patches, and lower in high‐severity patches and unburned areas. Height growth of red fir seedling increases with fire severity. Variations in fire severity in red fir forests appear to be a major influence on post‐fire stand structure and species composition, successional pathways, and resulting landscape patterns. Our results suggest that drought may be an important mortality agent controlling red fir regeneration on these burned sites. Red fir seedling establishment occurs in pulses, usually 3‐4 yr after fire.
The Role of Reference Wetlands in Functional Assessment and Mitigation
Authors: Brinson Mark M. , Rheinhardt Richard
Published: April 2006

Compensatory mitigation for damages to wetlands in the United States occurs largely without explicit analysis and replacement of wetland functions. We offer an approach to standardize such analyses and strengthen the connection between ecological principles and policies for wetland resources. By establishing standards from reference wetlands chosen for their high level of sustainable functioning, gains and losses of functions can be quantified for wetlands used in compensatory mitigation. Advantages of a reference wetland approach include (1) making explicit the goals of compensatory mitigation through identification of reference standards from data that typify sustainable conditions in a region, (2) providing templates to which restored and created wetlands can be designed, and (3) establishing a framework whereby a decline in functions resulting from adverse impacts or a recovery of functions following restoration can be estimated both for a single project and over a larger area accumulated over time. To establish reference standards, conditions inherent to highly functioning sites must be identified for classes of wetlands that share similar geomorphic settings. Ecological functions are then identified, and variables used to model the functions are employed in developing reference standards. Variables range from the highest levels of sustainable functioning to the complete absence of functions when a wetland ecosystem is displaced. An example given for wet pine flats in the North Carolina coastal plain illustrates how to determine the loss of a given function for an impacted wetland, how to calculate recovery (gains) in function through compensatory mitigation, and how to use the relationships between the two (loss vs. gain in function) to set minimum replacement ratios of restored to impacted area. In all cases, data from reference wetlands provide the benchmarks for making these estimates and for directing restoration or creation of wetlands toward the standards established for the wetland class. Programs to implement the use of reference wetlands require regional efforts that build upon the knowledge base of existing wetlands and their functioning.
Threats to Wilderness Ecosystems: Impacts and Research Needs
Authors: Cole David N. , Landres Peter B.
Published: April 2006

One of the primary purposes of designated wilderness areas is protection of natural ecosystems. However, the ecological integrity of these most protected of public lands is threatened by direct and indirect effects of human activities both internal and external to wilderness. Accelerated research programs on threats to wilderness are needed to realize the purposes for which wilderness was established and to improve our understanding of natural ecosystems. This paper reviews current knowledge and critical research needs for some of the most significant threats to wilderness ecosystems: (1) recreational use and its management; (2) livestock grazing and its management; (3) fire management; (4) introduction of alien species; (5) diversion and impoundment of water; (6) emission of atmospheric pollutants; and (7) management of adjacent lands. Some of these threats cause highly disruptive localized impacts, whereas some have a more widespread effect. Other threats are highly significant because they threaten rare or irreplaceable ecological attributes. Ecological science needs to be applied to improve evaluations of wilderness conditions, improve efforts to protect wilderness ecosystems from further degradation, and improve efforts to restore the integrity of disturbed systems.
Grazing Frequency and Ecosystem Processes in a Northern Mixed Prairie, USA
Authors: Biondini Mario E. , Manske Llewellyn
Published: April 2006

The objective of this study was to evaluate for a 6‐yr period the effects of a twice‐over rotation grazing system (ROT) and a season‐long grazing system (SL), and compare these effects with long‐term grazing exclosures (NG) in terms of (1) species composition and basal cover, (2) aboveground net primary production (ANPP) and aboveground N uptake (ANPP‐N), (3) rates of litter and root decomposition and N release, (4) soil N mineralization and immobilization, (5) aboveground C and N flow, and (6) grazing intensity (GI) and animal performance. The study period included the drought of 1988. No major differences were found in ANPP and ANPP‐N among treatments, but there were important seasonal variations. An average of 72% of ANPP and >82% of ANPP‐N occurred by mid‐June. There were no differences among treatments in terms of decomposition and N release rates from litter and root biomass, or in soil N mineralization. Grazing, however, reduced the amount of C and N immobilized in standing dead and litter and the flow of C and N from standing dead to litter to soil organic matter. The NG and ROT treatment were more similar in this regard when compared to the SL treatment, and their similarities increased after the drought of 1988. There were no consistent differences in GI between the ROT and SL treatments. Before 1988 GI averaged 21% but in 1988 and 1989 GI increased to an average of 49% as a result of the drought and its aftereffects. Cumulative animal performance was similar under both grazing treatments but there were significant seasonal variations. Species composition was more responsive to grazing than were C and N flows. The differences in this case were found between the grazed and NG treatments but not between the two grazing treatments studied. There were no broad patterns of change in total plant basal cover as a result of grazing patterns or drought. Changes in species composition were highly dependent on range site. The most consistent pattern involved Bouteloua gracilis, which had higher relative cover in the grazed treatments than in the NG treatment. Results from this study indicate that in the grasslands of western North Dakota (1) the recommended stocking rate may be too conservative, (2) rotation grazing may allow for higher stocking rates than season‐long grazing without a major impact on animal performance, (3) rainfall is more important than grazing or grazing systems in the control of the ecosystem‐level variables measured, (4) species composition is affected by drought and grazing (but not by grazing systems) but the responses are highly dependent on range site, and (5) drought and grazing tend to increase the relative composition of warm‐season grasses and forbs.
A Novel Bayesian Approach to Assessing Impacts of Rain Forest Logging
Authors: Crome F. H. J. , Thomas M. R. , Moore L. A.
Published: April 2006

We present a novel application of Bayesian procedures to assess the impacts of logging rain forest on birds and small mammals in tropical Queensland, Australia, using data from a 1983‐1986 BACIP (measures made before and after on control and impact sites) study. The procedure was compared with the usual approach to the analysis of BACIP designs following the methods of Stewart‐Oaten et al., which are based on classical Neymann‐Pearson significance testing. Significance tests were performed at the 0.05 and 0.1 levels, power being calculated for a 25% reduction in species capture rates. For the Bayesian analysis, we elicited one noninformative and three informative prior distributions representing polarized beliefs about the effect size of logging: a strong negative effect, little or no effect, and an effect related to the amount of canopy loss. Effect size was estimated by determining the extent to which there was agreement between the posteriors for eight propositions concerning effect size. These propositions ranged from a negative effect of >25% reduction being very likely to a large positive effect of >25% increase being very likely. Of 76 bird species recorded and nine species of mammals captured, there were sufficient data for analysis of 21 bird species, five ecological groups of birds, and five mammal species. The bulk of the classical tests were of low power; of the 99 species/microhabitat combinations tested, only 10 were significant at the 0.05 level (12 at the 0.1 level). The standard classical analysis allowed few conclusions other than the data were uninformative. The Bayesian procedure was more informative. For 68 species/microhabitat combinations, there was consensus among the posterior distributions for one or more of the propositions about effect size. The Bayesian analysis indicated that, over the entire study area, negative effects were not likely to be greater than the degree of canopy opening. However, in the microhabitats that received most of the damage, negative effects were likely for far more species.
Direct and Indirect Effects of Insecticide Applications on Growth and Survival of Nestling Passerines
Authors: Howe Frank P. , Knight Richard L. , McEwen Lowell C. , George T. Luke
Published: April 2006

We conducted an experiment in 1989 and 1990 to determine the effects of malathion ultra‐low volume (ULV) aerial spray on reproduction of passerine birds in shrub‐steppe habitat of southern Idaho. The experiment consisted of reducing the insect food base with malathion, a broad‐spectrum insecticide, while monitoring nestling growth variables and daily nest survivorship. Relative arthropod abundance and biomass were reduced on the treatment plot in 1989 and 1990 (F. P. Howe et al., unpublished manuscript). Wing and tarsus lengths of nestling Sage Thrashers (Oreoscoptes montanus) were shorter on the treatment than on the control plot after malathion application in 1989 but not in 1990. Nestling Brewer's Sparrow (Spizella breweri) wing length and mass were lower on the treatment plot in 1990 but not in 1989. Primary length and foot length were unaffected for either species in either year. Multivariate ANOVA indicated that nestling Brewer's Sparrow size (a combination of five growth variables) was smaller on the treatment than on the control site after the 1990 treatment, but similar between sites after the 1989 malathion application. Sage Thrasher nestling size was smaller on the posttreatment malathion plot in 1989, but similar between plots in 1990. The percentage of eggs hatched and percentage of nestlings fledged were unaffected for either species. No differences were detected in Mayfield estimates of nest survivorship for either species in either year. The mean number of Sage Thrashers fledged per nest attempt was lower on the treatment than on the control plot in 1989, but not in 1990. The mean number of Brewer's Sparrows fledged per nest attempt was not affected on the treatment plot. No adult mortality for either species was observed, and nestling mortalities could not be attributed to malathion. Thus, few differences were detected in nestling growth variables and nest survivorship between the control and treatment plots, and these differences were not consistent across years. Under the conditions of this study, malathion had no observable direct effects, and only marginal indirect effects, through food‐base reduction, on Brewer's Sparrow and Sage Thrasher nestling growth and survival.
Minority Representation in Multimember Districts
Authors: Gerber Elisabeth R. , Morton Rebecca B. , Rietz Thomas A.
Published: April 2006

Given the recent court rulings against racial gerrymandering, the effect of multimember district elections on minority representation is an important issue. We present a model of voting in double-member district elections with two majority candidates and one minority candidate and consider the voting equilibria under straight and cumulative voting. In straight voting, while an equilibrium always exists in which the two majority candidates are expected to win the two seats, minority candidates may be elected. In cumulative voting, minority candidate wins are also possible in equilibrium but are less likely when minority voters prefer one majority candidate over another. We then present experimental evidence showing that minority candidates win significantly more seats in cumulative than in straight voting elections. When minority voters perceive a substantial difference between the majority candidates, however, they are more likely to split their votes between the minority and majority candidates, winning fewer seats.
Codable sets and orbits of computably enumerable sets
Authors: Harrington Leo , Soare Robert I.
Published: April 2006

A set X of nonnegative integers is computably enumerable (c.e.), also called recursively enumerable (r.e.), if there is a computable method to list its elements. Let ε denote the structure of the computably enumerable sets under inclusion, ε = ({We}eϵω,⊆). We previously exhibited a first order ε-definable property Q(X) such that Q(X) guarantees that X is not Turing complete (i.e., does not code complete information about c.e. sets).

Here we show first that Q(X) implies that X has a certain “slowness” property whereby the elements must enter X slowly (under a certain precise complexity measure of speed of computation) even though X may have high information content. Second we prove that every X with this slowness property is computable in some member of any nontrivial orbit, namely for any noncomputable A ϵ ε there exists B in the orbit of A such that X ≤TB under relative Turing computability (≤T). We produce B using the -automorphism method we introduced earlier.
Propositional quantification in the monadic fragment of intuitionistic logic
Authors: Połacik Tomasz
Published: April 2006

We study the monadic fragment of second order intuitionistic propositional logic in the language containing the standard propositional connectives and propositional quantifiers. It is proved that under the topological interpretation over any dense-in-itself metric space, the considered fragment collapses to Heyting calculus. Moreover, we prove that the topological interpretation over any dense-in-itself metric space of fragment in question coincides with the so-called Pitts' interpretation. We also prove that all the nonstandard propositional operators of the form q ↦ ∃p (q ↔ F(p)), where F is an arbitrary monadic formula of the variable p, are definable in the language of Heyting calculus under the topological interpretation of intuitionistic logic over sufficiently regular spaces.
Presenting Structural Innovation in an Institutional Environment: Hospitals' Use of Impression Management
Authors: Arndt Margarete , Bigelow Barbara
Published: April 2006

This research examines how the first organizations to abandon an institutionalized, taken-for-granted structure and adopt a radically different form presented the innovation to important stakeholders. A content analysis of hospitals' annual reports reveals that organizations that differed on other dimensions uniformly made preventive use of defensive impression management in announcing the change to a diversified corporate structure. The organizations invoked coercive and mimetic pressures to account for and justify the new structure, and they associated the innovation with legitimated organizational activities. The findings make two contributions that link the “old” institutionalism and neoinstitutionalism: they point to organizational agency in the preventive use of the very institutional forces that create isomorphism and suggest the presence of institutional forces even during the early stages of innovation.