bluuebunny/crossref_metadata_2025 huggingface dataset:
Ecological Remote Sensing at OTTER: Satellite Macroscale Observations
Authors: Goward Samuel N. , Waring Richard H. , Dye Dennis G. , Yang Jingli
Published: April 2006

Coarse, global—scale, satellite remotely sensed observations are compared with ground measurements collected during the OTTER study. The objective was derivation of ecological and environmental variables from the satellite data needed to define primary production in western Oregon. Observations from the TOMS sensor and the AVHRR sensor provide estimates of incident PAR radiation, intercepted PAR, atmospheric humidity, air temperature, vapor pressure deficit, and drought. The satellite observations compared favorably with the coincident ground measurements, but the strength of the relation was modest in some cases. Atmospheric attenuation of the remotely sensed measurements and ground measurement quality both limit stronger relations. This study demonstrates that satellite remote sensing is capable of providing information needed for macroscale ecological monitoring. Currently, it appears possible, from AVHRR and TOMS observations, to derive periodic approximations of ecological conditions sufficient to drive a simple—production—efficiency—type model. More refined remote—sensing methods will be needed to provide the type of measurement precision required by more refined ecosystem models.
Controls of Plant and Soil Carbon in a Semihumid Temperate Grassland
Authors: Seastedt T. R. , Coxwell C. C. , Ojima D. S. , Parton W. J.
Published: April 2006

A modeling study evaluated the importance of photosynthetic pathways (C3, C4, or both) and management strategies to the foliage productivity and soil carbon characteristics of a semihumid temperate grassland subjected to various combinations of climate change. Model values for plant and soil characteristics were obtained at sites near Manhattan, Kansas, and the Manhattan climate record provided the nominal climatic drivers. Model runs used both actual monthly temperature and precipitation data for a 100—yr interval and average weather conditions generated from this record. Monthly temperatures were increased 2°C, left unchanged, or decreased 2°C; annual precipitation was increased 6 cm, left unchanged, or decreased 6 cm. All possible combinations of temperature and precipitation were then used in 100—yr simulations. Regardless of the specific climate scenario, plant production was lowest for C3 grasses and highest for the mixed C3—C4 community. The nominal seasonal pattern of precipitation favored an active C3 plant community in early to late spring, prior to the emergence of the C4 vegetation. However, the higher growth and water use efficiencies of C4 vegetation during summer contributed to the maximization response of the grasslands containing both C3 and C4 grasses. An analysis of variance of annual average values observed from 100—yr simulations was used to evaluate the relative importance of climate, photosynthetic pathways, and management activities (annually burned, burned every 4 yr, unburned, or lightly grazed) to plant production and soil carbon values. Photosynthetic pathway and precipitation were identified as the most significant single variables affecting foliage production; the interaction between photosynthetic and temperature was the most significant interaction term. Management treatments were by far the most important variables affecting soil carbon values, but 2°C warming did produce substantial soil carbon losses from C3 grasslands. Enhanced carbon fixation by the C4 and C3—C4 plant communities negated the losses of soil carbon caused by enhanced soil respiration at warmer temperatures.
Root Gap Dynamics in Lodgepole Pine Forest: Nitrogen Transformations in Gaps of Different Size
Authors: Parsons William F. J. , Knight Dennis H. , Miller Steven L.
Published: April 2006

Belowground responses to aboveground disturbance were studied in experimental gaps created in a 95—yr—old stand of Pinus contorta in southeastern Wyoming. One—, 5—, 15—, and 30—tree clusters were felled to create a series of gaps in the root mat, and solution—phase N was monitored over two consecutive snow—melt periods via tension—tube water collectors. We hypothesized that dissolved and extractable nitrogen concentrations would not exceed predisturbance levels until a threshold canopy gap size had been achieved. As predicted, NOx—N attained significantly higher solution N concentrations (2—5 mg/L) only with the death of 15 trees or more. However, dissolved organic nitrogen decreased gradually with increasing gap size. Net mineralization and nitrification were studied using 30—d in situ incubation assays in each gap. Extractable nitrate routinely was negligible until the 30—tree gaps had been attained. Predicting the effects of disturbance on nutrient cycling, including timber—harvesting practices, requires information on belowground responses to gap formation. Our experiments suggest that gap size is important; removal of 15—30 tree clusters represented a threshold above which significant losses of available N to the groundwater may be incurred, at least in Rocky Mountain coniferous forests.
The Effects of Management Systems on Ground‐Foraging Ant Diversity in Costa Rica
Authors: Roth Dana S. , Perfecto Ivette , Rathcke Beverly
Published: April 2006

The impacts of four different management systems on diversity of ground—foraging ants were examined to assess potential for conservation of biological diversity in human—influenced agricultural or agroforestry systems. Using a variety of indices, diversity was measured along a gradient of anthropogenically disturbed habitats. The gradient, in terms of increasing levels of disturbance, ranged from primary rain forest, abandoned cacao plantations, productive cacao plantations, to banana plantations. The primary forest and abandoned cacao plantations were situated in a reserve and the productive cacao plantations, and banana plantations were located on privately owned land within 35 km of the reserve in the Sarapiqui Valley of Costa Rica. To sample ground—foraging ants, we placed tuna baits along the ground in each habitat. Although tuna baits attract a generalist assemblage of ants that may be better able to adapt to more disturbed sites, diversity of this community was significantly reduced with increased disturbance. Ant diversity was not different for forest and abandoned cacao sites except in terms of evenness, with the forest having a more even distribution of species. Forest and abandoned cacao sites were significantly more diverse than both productive cacao and banana plantations. The latter two did not differ significantly from each other in terms of diversity, but there was considerable variability within each of these habitat types. The results of this study suggest that conservation of diversity may be possible in a "mosaic" of different land uses, but further studies, such as those addressing the importance of scale and nearby source populations, are necessary before management practices can be implemented.
Modeling Population Viability for the Desert Tortoise in the Western Mojave Desert
Authors: Doak Daniel , Kareiva Peter , Klepetka Brad
Published: April 2006

The desert tortoise is a threatened species living in the deserts of the American Southwest. Using size—structured demographic models, we analyzed the status of the tortoise in the Western Mojave desert and evaluated the effectiveness of possible management measures. Our demographic analyses agree with the trends reported by field censuses in showing rapid population decline. Importantly, simulations that include variation and correlation in vital rates yield highly variable forecasts of population growth, indicating the uncertainties inherent in even short—term projections of tortoise population sizes. To determine where conservation efforts and data collection should be focused, we performed a series of sensitivity analyses in which the effects of changing different vital rates were quantified. We found that the rate of population growth is most sensitive to the survival of large adult females and that improving survival of this size class to reputably "pristine" rates could reverse population declines; in contrast, large improvements in other vital rates will not, alone, reverse population decline. Thus, shooting, off—road vehicles, upper respiratory tract disease (URTD), and other major sources of adult mortality should be the primary focus of management strategies. Finally, we discuss the impact of the proposed expansion of the U.S. Army's Fort Irwin, which would reduce the Western Mojave tortoise population by ≤13%. We argue that the expansion could have a grave impact on the long—term population viability of the tortoise, but that this impact will be a function of the management of remaining tortoise habitat. We conclude that, although many anthropogenic impacts threaten the tortoise, the species' future could be bright, provided that research and land—use planning focus on biologically important aspects of its life history.
Simulating Winter Interactions Among Ungulates, Vegetation, and Fire in Northern Yellowstone Park
Authors: Turner Monica G. , Wu Yegang , Wallace Linda L. , Romme William H. , Brenkert Antoinette
Published: April 2006

The interaction of large—scale fire, vegetation, and ungulates is an important management issue in Yellowstone National Park. A spatially explicit individual—based simulation model was developed to explore the effects of fire scale and pattern on the winter foraging dynamics and survival of free—ranging elk (Cervus elaphus) and bison (Bison bison) in northern Yellowstone National Park. The Northern Yellowstone Park (NOYELP) model simulates the search, movement, and foraging activities of individuals or small groups of elk and bison. The 77 020—ha landscape is represented as a gridded irregular polygon with a spatial resolution of 1 ha. Forage intake is a function of an animal's initial body mass, the absolute amount of forage available on a site, and the depth and density of snow. When the energy expenditures of an animal exceed the energy gained during a day, the animal's endogenous reserves are reduced to offset the deficits. Simulations are conducted with a 1—d time step for a duration of 180 d, °1 November through the end of April. Simulated elk survival for three winters (1987—1988; 1988—1989; 1990—1991) agreed with observed data. A factorial simulation experiment was conducted to explore the effects on ungulate survival of fire size, fire pattern, and winter severity during an initial postfire winter (when no forage is available in burned areas) and a later postfire winter (when forage is enhanced in burned areas). Initial ungulate population sizes were held constant at 18 000 elk and 600 bison. Winter severity played a dominant role in ungulate survival. When winter conditions were extremely mild, even fires that affected 60% of the landscape had no effect on ungulate survival during the initial postfire winter. The effects of fire on ungulate survival become important when winter conditions were average to severe, and effects were apparent in both the initial and later postfire winters. The spatial patterning of fire influenced ungulate survival if fires covered small to moderate proportions of the landscape (e.g., 15% or 30%) and if winter snow conditions were moderate to severe. Ungulate survival was higher with a clumped than with a fragmented fire pattern,suggesting that a single, large fire is not equivalent to a group of smaller disconnected fires. The interaction between fire scale and spatial pattern suggests that knowledge of fire size alone is not always sufficient to predict ungulate survival.
The Influence of Plant Population Spatial Arrangement on Individual Plant Yield
Authors: Lindquist J. L. , Rhode D. , Puettmann K. J. , Maxwell B. D.
Published: April 2006

Two greenhouse experiments were conducted to evaluate the performance of individual oat (Avena sativa) target plants as influenced by neighbor oat plants with different spatial arrangements. Crop spatial arrangement was separated into three components: (1) population density, (2) distance between plants (distance dispersion, DD), and (3) angular arrangement of plants about one another (angular dispersion, AD). Distance dispersion was quantified using a weighted mean distance from a target individual to its neighbors. Angular dispersion of neighbors around the target was quantified using a measure of circular variance. DD and AD were combined to create a dispersion index (DI). At constant density, distance dispersion treatments were combined with angular dispersion treatments in a randomized—block factorial design. Target plant biomass production was predicted using a rectangular hyperbola equation including population density, DD, AD, and DI as independent variables. Fifty—five and 44% of the residual variation (the variation not accounted for by density alone) in individual plant yield was accounted for when spatial arrangement (DI) was added to the regression. The approach can be used to compare the intensity of competition among different crop planting patterns.
Assessing the Impacts of an Increase in Water Level on Wetland Vegetation
Authors: van der Valk A. G. , Squires L. , Welling C. H.
Published: April 2006

Three different approaches for assessing the impact of a permanent increase in water level on wetland vegetation were studied using a long—term, controlled, and replicated experiment. These three approaches were: (1) digitized vegetation maps derived from aerial photographs; (2) vegetation data (species abundance, species diversity) from 10 permanent quadrats in each cell; and (3) Bray—Curtis similarity indices comparing the composition of the vegetation in permanent quadrats within a cell and among cells. This study was conducted in a 10—celled wetland complex in the Delta Marsh, Manitoba, Canada. There were three water level treatments: (1) the normal or mean regulated water level in the surrounding Delta Marsh, (2) the medium (30 cm above normal), and (3) the high (60 cm above normal). There were four, three, and three cells (ranging in total area from 6 to 8 ha), respectively, in each treatment. The vegetation in all cells had been reestablished with a drawdown just prior to this study. To reduce cell—to—cell variation, we adjusted the indicators derived from vegetation maps from 1985 through 1989 by subtracting the mean values of the same indicators in 1979 and 1980, after 15—16 yr of normal water level conditions. The adjusted percentage of a cell covered with open water increased significantly and two other adjusted indicators, the number of vegetation types and the number of multispecies vegetation types, decreased significantly in the flooded treatments. The percentage of a cell covered with sparse emergent vegetation and percentage covered with standing litter did not differ significantly among treatments. In permanent quadrats, species richness, total shoot density of the emergent species, and the Shannon diversity index showed significant treatment effects: all three declined in the flooded treatments. The Simpson's index, however, did not show a treatment effect. When Bray—Curtis similarity indices comparing the vegetation either among permanent quadrats within a cell or for the same permanent quadrat in a cell among years were used, either within—cell vegetation heterogeneity or ongoing successional changes in the vegetation made it impossible to detect treatment effects.
The Response of Temperate Tree Seedlings Grown in Elevated CO"2 to Extreme Temperature Events
Authors: Bassow S. L. , McConnaughay K. D. M. , Bazzaz F. A.
Published: April 2006

Mean global temperatures have been predicted to increase in the next century; if so the frequency of extreme temperature events may also increase. Extreme temperatures may damage plant tissue and consequently limit the survival of certain plant species in a region. Elevated concentrations of CO2 in the atmosphere alter plant allocation, physiology, and growth, and may accentuate or ameliorate the damage from extreme temperatures. In this paper we explore the interactive effects of atmospheric CO2 concentration, nutrient levels, and exposure to extreme temperatures on seedlings of three species of temperate deciduous trees. A 1—d exposure to extreme heat (45°C) significantly decreased conductance the following day and decreased biomass as measured at both 35 and 105 d following the extreme temperature event, regardless of atmospheric CO2 concentration. The most shade—tolerant species, striped maple, was most severely impacted by the extreme heat event in both CO2 environments. Furthermore, striped maple seedlings grown in elevated CO2 concentrations had a significantly greater decrease in biomass due to the extreme heat event as compared with striped maple plants grown in ambient CO2 concentrations at 35 d after the heat event; however, at the end of the growing season at 105 d post treatment, this difference was not significant. A one—night exposure to low temperatures (4°C) did not affect biomass for any of these species. With an increase in global mean temperatures, the frequency of extreme temperature events, particularly hot weather events, may increase and may extend to shaded understory sites. If the frequency of extremely high temperatures increases, the role that temperature extremes may play in changing competitive interactions and thus affecting community composition may increase in importance, as these temperatures appear to severely alter plant survival and growth in some species.
Domestic Geese: Biological Weed Control in an Agricultural Setting
Authors: Wurtz Tricia L.
Published: April 2006

Vertebrate herbivores can be effective agents of biological weed control in certain applications. I compared the use of domestic geese for weed control in an agricultural field with the herbicide hexazinone and with hand control. Newly planted spruce seedlings acted as a prototype crop that would be unpalatable to the geese. Trampling by geese led to as much as 47% tree seedling mortality during the 1st yr; this was reduced significantly by either limiting the amount of time the geese spent in the plots or surrounding seedlings with small wire fences. When compared with plots with no weed control, weed control by geese improved the diameter growth of the surviving seedlings by over 100% during the 1st yr of the study, but had no effect in the 2nd yr. The geese controlled a variety of weed species, but were most effective against quackgrass (Agropyron repens). However, grazing effectively selected for unpalatable weed species (including pineapple weed, Matricaria matricarioides, prostrate knotweed, Polygonum aviculare, and wild chamomile, Tripleurospermum phaeocephalum) so that by the end of the 2nd yr plots weeded only by geese had 25 times as much cover of unpalatable species as plots with no weed control. In contrast, the herbicide was ineffective against grass and effective against the unpalatable weed species. A successful integrated weed management strategy would thus require combining geese with another method of weed control, and would include measures to prevent crop trampling.
Sciurids in Pacific Northwest Managed and Old‐Growth Forests
Authors: Carey Andrew B.
Published: April 2006

An understanding of the factors governing sciurid abundance in the Pacific Northwest is essential for prescribing forest management practices for second‐growth forests where recovery of Spotted Owl (Strix occidentalis) populations and enhancement of biodiversity are objectives. We compared results of companion studies of sciurids in western Washington and Oregon and examined patterns of abundance in relation to habitat elements on the Olympic Peninsula to elucidate governing factors and make recommendations for forest management. Regional contrasts show that Glaucomys sabrinus and Tamias townsendii in Douglas‐fir forests in Oregon are 4 times more abundant than in western hemlock forests in Washington, and dietaries of Glaucomys, and the fungal communities that provide its food, are more diverse in Oregon than in Washington. Glaucomys sabrinus in old forests are 2 times more abundant than in young, managed forests without old‐forest legacies (large live trees, large snags and large, decaying fallen trees); populations in young forests with old‐forest legacies and with understory development may equal those in old growth. On the Olympic Peninsula, Glaucomys sabrinus abundance can be predicted by density of large snags and abundance of ericaceous shrubs. At least seven large snags/ha and well‐distributed patches of dense shrubs (cover within patches >24% and patches covering 40% of the total area) are necessary for high densities of Glaucomys sabrinus. Abundance of Tamias townsendii reflects size of dominant tree and well‐developed understories. Abundance of Tamiasciurus douglasii seems to reflect territoriality in concordance with food supply and was greatest where Glaucomys and Tamias were low in abundance. Patterns of abundance of the sciurids in old‐ and managed forests suggests that silvicultural manipulation of vegetation and creative snag or den‐tree management could be used in a management strategy to accelerate the development of Spotted Owl habitat in areas where old growth is lacking.
Chesapeake Bay Watershed Historical Land Use: Impact on Water Quality and Diatom Communities
Authors: Cooper Sherri Rumer
Published: April 2006

Stratigraphic records preserved in the sediments of the mesohaline Chesapeake Bay were used to reconstruct a 2000‐yr history of sedimentation, eutrophication, anoxia, and diatom community structure over time. Diatoms, pollen, total and organic carbon (TOC), total and organic nitrogen, total sulfur, acid‐soluble iron, an estimate of the degree of pyritization of iron (DOP), and biogenic silica (BSi) were used as paleoecological indicators in four cores collected from a transect across the Chesapeake Bay from the Choptank River to Plum Point, Maryland. This paper covers results for diatoms, pollen, and BSi. Sediments were dated using radiocarbon and pollen techniques, and sedimentation rates were determined (0.2‐5.8 mm/yr) using pollen methods. Geochemical indicators were measured and diatom species identified at subsampled intervals within each core. More than 400 diatom species, primarily marine and estuarine taxa, were identified in the sediments, some for the first time. Analysis of the data indicates that sedimentation rates, eutrophication, turbidity, and anoxia have increased in the Chesapeake Bay since the time of European settlement of the watershed. There is also evidence that freshwater input to the mesohaline Chesapeake Bay has increased. Changes in diatom community structure and geochemical indicators reflect major changes in land use patterns of the watershed and increasing population. Diatom community diversity exhibits a continuing decline, while centric/pennate ratios rise dramatically in most recent sediments.
Winter Habitat Use by Large Ungulates Following Fire in Northern Yellowstone National Park
Authors: Pearson Scott M. , Turner Monica G. , Wallace Linda L. , Romme William H.
Published: April 2006

The effect of fire and habitat heterogeneity on winter foraging by ungulates was studied in northern Yellowstone National Park (YNP). Grazing was monitored at 15 study sites for 14 wk during the winters of 1991 and 1992. The location and intensity of grazing activity within each site were recorded on topographic maps and digitized into a geographic information system. Maps of grazing intensity were compared to map layers of grassland habitat type, elevation, slope, aspect, annual precipitation, and the spatial pattern of fires that occurred in 1988. Burned areas were used by ungulates more often than expected based on their availability, especially during mid‐ to late winter, but the spatial pattern of burned areas (i.e., fragmented or clumped) was not related to grazing intensity. Ungulate grazing, as measured by minimum cumulative grazing intensity (MCGI), was greatest at low‐elevation drier sites across the northern range and on steep southerly slopes. The influence of environmental characteristics on MCGI was evaluated at four spatial scales (1, 9, 81, and 255 ha). Grazing intensity was best predicted by environmental heterogeneity, especially the presence of burned areas, and topography (slope and aspect), at broader scales (81 and 255 ha) rather than on a per‐hectare basis. The explanatory power of broad‐scale features suggests that wintering ungulates in YNP respond strongly to coarse‐grained variation in these landscapes. Interpreting or predicting ungulate grazing at a specific location requires understanding of environmental heterogeneity in the surrounding landscape.
Atmospheric Deposition of Nutrients and Pollutants in North America: An Ecological Perspective
Authors: Lovett Gary M.
Published: April 2006

Research on air pollution and acidic deposition during the last 15 yr has greatly increased our knowledge of the rates and the processes of atmospheric deposition. The invigoration of the field has been a direct result of interchange and cooperation among ecosystem ecologists, micrometeorologists, and plant physiological ecologists who each approach the study of atmospheric deposition from different perspectives. This has led to the widespread realization among ecologists of the importance of dry and cloud deposition and the introduction of new methods to estimate these fluxes. In this paper I summarize the current understanding of atmospheric deposition processes, measurement methods, and patterns of deposition in North America. Dry deposition measurements are still highly uncertain in most cases, and methodology is still an active area of research and debate, but it seems clear that ecologists will require a suite of different methods to evaluate dry deposition fluxes of the various elements important to ecosystems. Standard model formulations have been developed for estimating dry and cloud deposition, and these models are finding wide use in flux estimation at sites where direct measurements are unavailable. National monitoring networks for wet and dry deposition have been established and are providing information on continental— and regional—scale patterns. Research has demonstrated that deposition rates are increased substantially at high—elevation sites by enhancement of wet, dry, and especially, cloud deposition. Patterns of O3 exposure are also different at high—elevation sites. The deposition of O3, while mechanistically similar to that of other gases, has been treated differently in the ecological and botanical literature because of its direct phytotoxicity at ambient concentrations in industrialized areas. Current efforts in ozone exposure research involve determining appropriate exposure indices for interpreting biological responses and coupling models of atmospheric transport with models of ozone disposition within the plant.
Mechanistic Analysis of Plant Responses To Air Pollution
Authors: Winner William E.
Published: April 2006

Human activity is altering the chemistry of the atmosphere, which, in turn is affecting the physiology and growth of plants. The purpose of this article is to develop four ideas that are currently emerging from the work of a diverse group of plant scientists. (1) Air pollution definitions: The definition of air pollution has been broadened, and research activities are expanding to include analysis of plant responses to a wide range of atmospheric chemicals emitted from anthropogenic sources but not previously considered as air pollutants. Thus experiments with CO2 and other trace gases are being pursued with approaches developed in air pollution research. (2) Air pollution uptake: Efforts are increasing to better quantify air pollution absorption rates through stomata in order to calculate actual dose vs. plant responses. The flux rates of gaseous pollutants into leaves, especially O3, are largely dependent upon stomatal conductance. Approaches are being developed to calculate stomatal absorption of gaseous pollutants, based on stomatal conductance values for water vapor and ambient air—pollution concentrations. Calculation of air pollution absorption rates will allow responses of plants to pollutants to be assessed in toxicological frameworks and will help characterize the strength of vegetation as sinks for some gaseous pollutants. (3) Compensatory responses: Plant responses to air pollutants can be interpreted as compensatory, i.e., a physiological adjustment to an environmental stress that maximizes productivity above that which would have occurred in the absence of compensation. Examples of compensatory responses to air pollutants are shifts in root—to—shoot ratio and accelerated rates of leaf maturation. Recognition of compensatory responses to air pollutants allows these responses to be placed in a framework that relates to whole—plant processes and ecosystem functions. (4) Air pollution and multiple stresses: Air pollution stress seldom occurs in isolation, and research approaches are being developed around the concept of multiple interacting stresses. Multiple—stress experiments are important because factors such as plant water status, light, and nutrient availability are known to alter plant responses to air pollutants. Multiple—stress studies will involve experiments with model plant species and high degrees of environmental control and monitoring.
Clearing the Air at Great Smoky Mountains National Park
Authors: Shaver Christine L. , Tonnessen Kathy A. , Maniero Tonnie G.
Published: April 2006

Great Smoky Mountains National Park, located in the southern Appalachians on the border of Tennessee and North Carolina, was designated by Congress in 1977 as a Class I area, where resources are to be protected from damage due to air pollution. The National Park Service, Air Quality Division, collected and then used data on levels of pollutants and response of sensitive resources in the park and found that forests, soils, surface waters, and visibility in the park were experiencing adverse impacts from air pollution. We reviewed the data and process that supported this finding as well as the legal tools available to federal land managers confronted with evidence that sources of air pollution outside the boundaries of Class I areas are affecting resources. We prepared this case study to describe how the National Park Service has used scientific information in regulatory arenas to address air pollution problems at Great Smoky Mountains National Park. Based on this case we show that the requirement for Federal Land Manager review of permits for new stationary sources of air pollution is not sufficient to protect the parks from what has become a regional air quality problem.
Combining Remote Sensing and Climatic Data to Estimate Net Primary Production Across Oregon
Authors: Law Beverly E. , Waring Richard H.
Published: April 2006

A range in productivity and climate exists along an east—west transect in Oregon. Remote sensing and climatic data for several of the Oregon Transect Ecosystem Research Project (OTTER) forested sites and neighboring shrub sites were combined to determined whether percentage intercepted photosynthetically active radiation (%IPAR) can be estimated from remotely sensed observations and to evaluate climatic constraints on the ability of vegetation to utilize intercepted of radition for production. The Thematic Mappers Simulator (TMS) normalized difference vegetation index (NDVI) provided a good linear estimate of %IPAR (R2 = 0.97). Vegetation intercepted from 24.8% to 99.9% of incident photosynthetically active radiation (PAR), and aboveground net primary production (ANPP) ranged from 53 to 1310 g·m—2·yr—1. The ANPP was linearly related to annual IPAR across sites (R2 = 0.70). Constraints on the ability of each species to utilize intercepted light, as defined by differential responses to freezing temperatures, drought, and vapor pressure deficit, were quantified from hourly meteorological station measurements near the sites and field physiological measurements. Vegetation could utilize from 30% of intercepted radiation at the eastside semiarid juniper woodland and shrub sites to 97% at the maritime coastal sites. Energy—size efficiency (ϵu), calculated from aboveground production and IPAR modified by the environmental limits, averaged 0.5 g/MJ for the shrub sites and 0.9 g/MJ for the forested sites.
Acceptance Criteria for Using Individual‐Based Models to Make Management Decisions
Authors: Bart Jonathan
Published: April 2006

Individual‐based population models are beginning to have substantial influence in conservation biology. One of the dangers of such models is that their reliability may be poorly understood, and generally over‐estimated. To help avoid this problem a set of guidelines is suggested here for evaluating individual‐based models. Major components of the evaluation include a description of the model and estimates of the reliability of its predictions. The description should include detailed explanations of the model's purpose(s), its structure, and the assumptions it makes. Analyses of reliability at four levels may be useful: structural assumptions, parameter values, secondary predictions of the model, and primary predictions of the model. The guidelines also recommend that "best‐" and "worst‐case" scenarios, intended to span the range of plausible outcomes, be prepared using the model, rather than presenting single predictions or conclusions. I argue that results from such an evaluation should be prepared and peer reviewed before the model is used to make or defend management decisions.
A Carbon Budget for Forests of the Conterminous United States
Authors: Turner David P. , Koerper Greg J. , Harmon Mark E. , Lee Jeffrey J.
Published: April 2006

The potential need for national‐level comparisons of greenhouse gas emissions, and the desirability of understanding terrestrial sources and sinks of carbon, has prompted interest in quantifying national forest carbon budgets. In this study, we link a forest inventory database, a set of stand‐level carbon budgets, and information on harvest levels in order to estimate the current pools and flux of carbon in forests of the conterminous United States. The forest inventory specifies the region, forest type, age class, productivity class, management intensity, and ownership of all timberland. The stand‐level carbon budgets are based on growth and yield tables, in combination with additional information on carbon in soils, the forest floor, woody debris, and the understory. Total carbon in forests of the conterminous U.S. is estimated at 36.7 Pg, with half of that in the soil compartment. Tree carbon represents 33% of the total, followed by woody debris (10%), the forest floor (6%), and the understory (1%). The carbon uptake associated with net annual growth is 331 Tg, however, much of that is balanced by harvest‐related mortality (266 Tg) and decomposition of woody debris. The forest land base at the national level is accumulating 79 Tg/yr, with the largest carbon gain in the Northeast region. The similarity in the magnitude of the biologically driven flux and the harvest‐related flux indicates the importance of employing an age‐class‐based inventory, and of including effects associated with forest harvest and harvest residue, when modeling national carbon budgets in the temperate zone.
Usefulness of Spatially Explicit Population Models in Land Management
Authors: Turner Monica G. , Arthaud Greg J. , Engstrom R. Todd , Hejl Sallie J. , Liu Jianguo , Loeb Susan , McKelvey Kevin
Published: April 2006

Land managers need new tools, such as spatial models, to aid them in their decision‐making processes because managing for biodiversity, water quality, or natural disturbance is challenging, and landscapes are complex and dynamic. Spatially explicit population models are helpful to managers because these models consider both species‐habitat relationships and the arrangement of habitats in space and time. The visualizations that typically accompany spatially explicit models also permit managers to "see" the effects of alternative management strategies on populations of interest. However, the expense entailed in developing the data bases required for spatially explicit models may limit widespread implementation. In addition, many of the models are developed for one or a few species, and dealing with multiple species in a landscape remains a significant challenge. To be most useful to land managers, spatially explicit population models should be user friendly, easily portable, operate on spatial and temporal scales appropriate to management decisions, and use input and output variables that can be measured affordably.
Sustainability of Sewage Sludge Land Application to Northern Hardwood Forests
Authors: Crohn David M.
Published: April 2006

A model representing the nitrogen dynamics of a northern hardwood forest is amended to include a mass balance and to predict percolating nitrate‐nitrogen concentrations. A component for including land application of municipal sewage sludge is added and Monte Carlo simulation used to predict the long‐term impact of land application on stand development, soil humus dynamics, nitrogen saturation, and nitrate losses at Hubbard Brook Experimental Forest in New Hampshire. Simulations suggest that applying 4 Mg/ha (dry mass) of anaerobically digested sludge to a 30‐yr‐old forest at 3‐yr intervals for 50 yr may increase production of harvestable boles and branches by an average of 24.6% over controls. An application rate of 8 Mg/ha results in little additional biomass increase but significantly threatens groundwater and surface water quality. Repeated applications significantly increase the nitrogen in soil humus. Species representation is not affected significantly unless sludge is applied after harvest during forest reorganization. Sustainable loading rates are on the order of 3‐4 Mg/ha if sludge is applied at 3‐yr intervals.
Influence of Macroclimate, Landscape Position, and Management on Soil Organic Matter in Agroecosystems
Authors: Burke Ingrid C. , Elliott Edward T. , Cole C. Vernon
Published: April 2006

We investigated patterns of soil organic matter, microbial biomass, and potential C and N mineralization in soils across landscape, regional, and management treatments in eastern Colorado. Total soil C, N, and P, microbial biomass, and C and N mineralization were highest at a northern site and on toeslope landscape positions. No‐tillage and perennial grass treatments had significantly higher microbial biomass and C mineralization rates than conventional tillage treatments after only 5 yr of treatment, but only at the sites and landscape positions with high production and organic matter contents. Potential N mineralization was not different among management treatments. We suggest that a simple relationship between total soil organic matter and nutrient supply rates holds for relatively static systems represented by spatial gradients, but that transient systems undergoing losses or gains in soil organic matter may have a lag in nutrient supply responses due to immobilization dynamics.
Effects of Selective Seed Predation by Rodents on Shortgrass Establishment
Authors: Hoffmann Lyn A. , Redente Edward F. , McEwen Lowell C.
Published: April 2006

Our experiment tested whether selective seed predation by rodents affects the establishment of blue grama (Bouteloua gracilis) and buffalo grass (Buchloe dactyloides) at a disturbed site in the Colorado shortgrass steppe. We hypothesized that foraging rodent granivores respond positively to large seed sizes and to high seed densities, and we predicted that intensive foraging would constrain grass establishment. Capture‐recapture studies confirmed that heteromyid granivores, kangaroo rats (Dipodomys ordii) and hispid pocket mice (Perognathus hispidus), comprised 48% of the local rodent community. Seeds of blue grama and buffalo grass were shallowly planted at three densities in replicated plots within and outside rodent exclosures. The frequency of digging in seeded rows (seed predation) and the frequency of herbivory on seedling were calculated. We assessed grass establishment using seedling frequency and harvested aboveground biomass. Seed foraging was related positively to seed size, but foraging responses to seed densities were not confirmed. Herbivory on seedlings was not intensive and was similar between the two grasses. Seedling frequency and harvested biomass numbers for the species with the larger seeds, buffalo grass, were reduced more in rodent‐accessible plots than were values for blue grama. Rodent seed predation can constrain the establishment of large‐seeded species, but results should be interpreted to reflect site‐specific conditions and the characteristics of seeded species.
Identifying Conservation Priorities in Mexico Through Geographic Information Systems and Modeling
Authors: Bojorquez-Tapia Luis A. , Azuara Ivan , Ezcurra Exequiel , Flores-Villela Oscar
Published: April 2006

Environmental assessments of regional development projects have been used in Mexico to determine where conflicts between conservation of biodiversity and resource extraction are likely to occur. Species‐rich areas have been acknowledged as a priority for conservation. However, biological information is incomplete and biased toward accessible sites, so species‐rich areas cannot be depicted directly from current biological knowledge. An alternative approach to predicting species‐rich areas is presented in this article. It is based on the gap analysis technique and involves the use of ordination analysis and generalized linear models integrated with a geographic information system. This approach was used for locating species‐rich areas in the Mexican states of Guerrero and Oaxaca, where a regional forestry development project was proposed. Baseline information consisted of geo‐referenced collection sites of terrestrial vertebrates. Thirty‐two species assemblages were identified by the ordination analysis, as well as by 25 generalized linear models. Validation of six of these models showed no significant differences between observed and predicted species frequencies. Results demonstrated that species‐rich areas could be depicted even under the constraints of environmental assessment in Mexico. A large number of species could be used in this analysis due to the minimal information required for each species record. This predictive approach optimized available biological information for the integration of conservation into regional development planning.
Isohaline Position as a Habitat Indicator for Estuarine Populations
Authors: Jassby Alan D. , Kimmerer William J. , Monismith Stephen G. , Armor Charles , Cloern James E. , Powell Thomas M. , Schubel Jerry R. , Vendlinski Timothy J.
Published: April 2006

Populations of native and introduced aquatic organisms in the San Francisco Bay/Sacramento‐San Joaquin Delta Estuary ("Bay/Delta") have undergone significant declines over the past two decades. Decreased river inflow due to drought and increased freshwater diversion have contributed to the decline of at least some populations. Effective management of the estuary's biological resources requires a sensitive indicator of the response to freshwater inflow that has ecological significance, can be measured accurately and easily, and could be used as a "policy" variable to set standards for managing freshwater inflow. Positioning of the 2% (grams of salt per kilogram of seawater) bottom salinity value along the axis of the estuary was examined for this purpose. The 2% bottom salinity position (denoted by X2) has simple and significant statistical relationships with annual measures of many estuarine resources, including the supply of phytoplankton and phytoplankton‐derived detritus from local production and river loading; benthic macroinvertebrates (molluscs); mysids and shrimp; larval fish survival; and the abundance of planktivorous, piscivorous, and bottom‐foraging fish. The actual mechanisms are understood for only a few of these populations. X2 also satisfies other recognized requirements for a habitat indicator and probably can be measured with greater accuracy and precision than alternative habitat indicators such as net freshwater inflow into the estuary. The 2% value may not have special ecological significance for other estuaries (in the Bay/Delta, it marks the locations of an estuarine turbidity maximum and peaks in the abundance of several estuarine organisms), but the concept of using near‐bottom isohaline position as a habitat indicator should be widely applicable. Although X2 is a sensitive index of the estuarine community's response to net freshwater inflow, other hydraulic features of the estuary also determine population abundances and resource levels. In particular, diversion of water for export from or consumption within the estuary can have a direct effect on population abundance independent of its effect on X2. The need to consider diversion, in addition to X2, for managing certain estuarine resources is illustrated using striped bass survival as an example. The striped bass survival data were also used to illustrate a related important point: incorporating additional explanatory variables may decrease the prediction error for a population or process, but it can increase the uncertainty in parameter estimates and management strategies based on these estimates. Even in cases where the uncertainty is currently too large to guide management decisions, an uncertainty analysis can identify the most practical direction for future data acquisition.
Detection of Environmental Impacts: Natural Variability, Effect Size, and Power Analysis
Authors: Osenberg Craig W. , Schmitt Russell J. , Holbrook Sally J. , Abu-Saba Khalil E. , Flegal A. Russell
Published: April 2006

The power of any test of an environmental impact is simultaneously constrained by (1) the variability of the data, (2) the magnitude of the putative impact, and (3) the number of independent sampling events. In the context of the Before–After—Control–Impact design with Paired sampling (BACIP), the variability of interest is the temporal variation in the estimated differences in a parameter (e.g., population density) between two unperturbed sites. The challenges in designing a BACIP study are to choose appropriate parameters to measure and to determine the adequate number and timing of sampling events. Two types of studies that are commonly conducted can provide useful information in designing a BACIP study. These are (1) long—term studies that provide estimates of the natural temporal and spatial variability of environmental parameters and (2) spatial surveys around already—perturbed areas ("After—only" studies) that can suggest the magnitude of impacts. Here we use data from a long—term study and an After—only study to illustrate their potential contributions to the design of BACIP studies. The long—term study of parameters sampled at two undisturbed sites yielded estimates of natural temporal variability. Between site differences in chemical—physical parameters (e.g., elemental concentration) and in individual—based biological parameters (e.g., body size) were quite consistent through time, while differences in population—based parameters (e.g., density) were more variable. Serial correlation in the time series of differences was relatively small and did not appear to vary among the parameter groups. The After—only study yielded estimates of the magnitude of impacts through comparison of sites near and distant from a point—source discharge. The estimated magnitude of effects was greatest for population—based parameters and least for chemical—physical parameters, which tended to balance the statistical power associated with these two parameter groups. Individual—based parameters were intermediate in estimates of effect size. Thus, the ration of effect size to variability was greatest for individual—based parameters and least for population and chemical—physical parameters. The results suggest that relatively few of the population and chemical—physical parameters could provide adequate power given the time constraints of most studies. This indicates that greater emphasis on individual—based parameters is needed in field assessments of environmental impacts. It will be critical to develop and test predictive models that link these impacts with effects on populations.