David A. Weinstein

Effect of grid size on runoff and soil moisture for a variable‐source‐area hydrology model

Soil chemical and biological dynamics in mixed use landscapes are dependent on the distribution and pattern of soil moisture and water transport. In this paper we examine the effect of different grid sizes on soil water content for a spatially explicit, variable-source-area hydrology model applied to a watershed in central New York. Data on topography, soil type, and land use were input at grid sizes from 10 to 600 m. Output data consisted of runoff and spatial pattern of soil moisture. To characterize the spatial variability at different grid sizes, information theory was used to calculate the information content of the input and output variables. Simulation results showed higher average soil water contents and higher evaporation rates for large grid sizes. During a wet year, runoff was not affected by grid size, whereas during a dry year runoff was greatest for the smallest grid size. While the information content (i.e., spatial variability) of soil type and land use maps was not affected by the different grid sizes, increasing grid sizes caused the information content of the slope gradient to decrease slightly and the Laplacian (or curvature of the landscape) to decrease greatly. In other words, increasing grid cell size misrepresented the curvature of the landscape. During wet periods the decrease in information content of the soil moisture data was the same as for the Laplacian as grid size increased. During dry periods, when local fluxes such as evaporation and runoff determine the moisture content, this relation did not exist. The Laplacian can be used to provide a priori estimates of the moisture content deviations by aggregation. These deviations will be much smaller for the slowly undulating landscapes than the landscape with steep valleys simulated in this study.

Comparison of the response of red oak (Quercus rubra) seedlings and mature trees to ozone exposure using simulation modeling

Field studies have determined that the photosynthetic rates of mature northern red oak (Quercus rubra L.) trees are sensitive to ozone exposure whereas those of seedlings are not. We used a model of tree physiology to determine the consequences of these differences in photosynthetic response to carbon allocation and tissue growth in seedlings and mature trees over a 2-year period. In the seedling simulations at twice ambient ozone, only the total non-structural carbohydrate (TNC) storage pool was affected. The effects in the simulated mature tree were much greater, with large decreases predicted for TNC, fine root, leaf, stem, branch, and coarse root tissues. The model produced many ozone-induced responses in the mature tree that were similar or consistent with observations made in a field study, but the simulations overestimated the effect of twice ambient ozone on root TNC and growth. The discrepancy between field and simulated results suggests that the field study trees exposed to elevated ozone levels may use carbon at a reduced rate, particularly through reduced respiration.

Assessing potential climate change effects on loblolly pine growth: A probabilistic regional modeling approach

Abstract Most models of the potential effects of climate change on forest growth have produced deterministic predictions. However, there are large uncertainties in data on regional forest condition, estimates of future climate, and quantitative relationships between environmental conditions and forest growth rate. We constructed a new model to analyze these uncertainties along with available experimental results to make probabilistic estimates of climate change effects on the growth of loblolly pine ( Pinus taeda L.) throughout its range in the USA. Complete regional data sets were created by means of spatial interpolation, and uncertainties in these data were estimated. A geographic information system (GIS) was created to integrate current and predicted climate data with regional data including forest distribution, growth rate, and stand characteristics derived from USDA Forest Service data. A probabilistic climate change scenario was derived from the results of four different general circulation models (GCM). Probabilistic estimates of forest growth were produced by linking the GIS to a Latin Hypercube carbon (C) budget model of forest growth. The model estimated a greater than 50% chance of a decrease in loblolly pine growth throughout most of its range. The model also estimated a 10% chance that the total regional basal area growth will decrease by more than 24×10 6 m 2 yr −1 (a 92% decrease), and a 10% chance that basal area growth will increase by more than 62×10 6 m 2 yr −1 (a 142% increase above current rates). The most influential factor at all locations was the relative change in C assimilation. Of climatic factors, CO 2 concentration was found to be the most influential factor at all locations. Substantial regional variation in estimated growth was observed, and probably was due primarily to variation in historical growth rates and to the importance of historical growth in the model structure.

Using the ECLPSS software environment to build a spatially explicit component-based model of ozone effects on forest ecosystems

Abstract We have developed a modeling framework to support grid-based simulation of ecosystems at multiple spatial scales, the Ecological Component Library for Parallel Spatial Simulation (ECLPSS) . ECLPSS helps ecologists to build robust spatially explicit simulations of ecological processes by providing a growing library of reusable interchangeable components and automating many modeling tasks. To build a model, a user selects components from the library, and then writes new components as needed. Some of these components represent specific ecological processes, such as how environmental factors influence the growth of individual trees. Other components provide simulation support such as reading and writing files in various formats to allow inter-operability with other software. The framework manages components and variables, the order of operations, and spatial interactions. The framework provides only simulation support; it does not include ecological functions or assumptions. This separation allows biologists to build models without becoming computer scientists, while computer scientists can improve the framework without becoming ecologists. The framework is designed to operate on multiple platforms and be used across networks via a World Wide Web-based user interface. ECLPSS is designed for use with both single processor computers for small models, and multiple processors in order to simulate large regions with complex interactions among many individuals or ecological compartments. To test Version 1.0 of ECLPSS , we created a model to evaluate the effect of tropospheric ozone on forest ecosystem dynamics. This model is a reduced-form version of two existing models: tregro , which represents an individual tree, and zelig , which represents forest stand growth and succession. This model demonstrates key features of ECLPSS , such as the ability to examine the effects of cell size and model structure on model predictions.

Response of sugar maple to multiple year exposures to ozone and simulated acidic precipitation

Potted sugar maple seedlings were exposed to ozone and acidic precipitation in open-top chambers for three consecutive growing seasons. Periodic measurements of photosynthesis, dark respiration, through-fall and soil solution chemistry, and annual measurements of the weight of plant parts were made. Experimental treatments caused few and minor effects on above- or below-ground growth of the seedlings, even after three growing seasons. There were trends for reduced photosynthesis in trees exposed to elevated concentrations of ozone and increased photosynthesis in those exposed to the lowest pH simulated rain treatment. The chemistries of soil-solutions and through-fall were not altered significantly by treatment. Although major effects were not observed, sugar maple may respond to exposures that take place over a significant part of its life cycle.

The Effects of Chemicals on the Structure of Terrestrial Ecosystems: Mechanisms and Patterns of Change

Chemicals introduced into natural terrestrial ecosystems can be considered disturbances, similar in mode of action to natural disturbances such as fires, windstorms, and species invasions. The effects of releases of chemicals on the structure of terrestrial ecosystems have not been studied extensively. However, responses of ecosystems to natural disturbances have received substantial scientific scrutiny. Exploration of the parallels between disruptions brought about by chemicals and by natural forces is useful because, in the absence of a large body of experimental evidence or case studies that have followed the effects of chemical releases, we are forced to extrapolate from the numerous studies of the effects of natural disturbances. It is critical, therefore, to evaluate the ways in which ecosystems are likely to respond differently to chemicals than they respond to natural disturbance. We must identify the patterns and mechanisms of change in terrestrial ecosystems exposed to chemical inputs that are unique to this type of anthropogenic disturbance.

Benefits, motivations, and barriers related to environmental volunteerism for older adults: developing a research agenda.

Interest in civic engagement focused on the natural environment has grown dramatically, as has the population of older adults. Our article explores the potential for increased environmental volunteerism among older adults to enrich the lives of volunteers while benefitting the community and environmental quality. Curiously, this convergence has been relatively neglected by researchers and program developers. We review existing literatures on trends in volunteerism, motivations, benefits, and barriers to participation, with a special focus on elements most relevant to older adults. Based on this review, we identify a number of critical areas of research, and pose key research questions.

Local-Scale Carbon Budgets and Mitigation Opportunities for the Northeastern United States

Economic and political realities present challenges for implementing an aggressive climate change abatement program in the United States. A high-efficiency approach will be essential. In this synthesis, we compare carbon budgets and evaluate the carbon-mitigation potential for nine counties in the northeastern United States that represent a range of biophysical, demographic, and socioeconomic conditions. Most counties are net sources of carbon dioxide (CO2) to the atmosphere, with the exception of rural forested counties, in which sequestration in vegetation and soils exceed emissions. Protecting forests will ensure that the regions largest CO2 sink does not become a source of emissions. For rural counties, afforestation, sustainable fuelwood harvest for bioenergy, and utility-scale wind power could provide the largest and most cost-effective mitigation opportunities among those evaluated. For urban and suburban counties, energy-efficiency measures and energy-saving technologies would be most cost effective. Through the implementation of locally tailored management and technology options, large reductions in CO2 emissions could be achieved at relatively low costs.

Simulating spatial nitrogen dynamics in a forested reference watershed, Hubbard Brook Watershed 6, New Hampshire, USA

We demonstrate that available information on spatial heterogeneity in biotic, topographic, and climatic variables within a forested watershed, Hubbard Brook Experimental Forest (HBEF) Watershed 6, New Hampshire, USA, was sufficient to reproduce the observed elevational pattern in stream NO3 concentration during the 1982–1992 period. Five gridded maps (N mineralization factor, N uptake factor, precipitation, elevation, and soil depth factor) were created from spatial datasets and successively added to the spatially explicit model SINIC-S as spatially varying input parameters. Adding more spatial information generally improved model predictions, with the exception of the soil depth factor. Ninety percent of the variation in the observed stream NO3 concentration was explained by the combination of the spatial variation of the N mineralization and N uptake factors. Simulated streamflow NO3 flux at the outlet point was improved slightly by introducing spatial variability in the model parameters. The model exhibited substantial cell-to-cell variation in soil N dynamics and NO3 loss within the watershed during the simulation period. The simulation results suggest that the spatial distributions of forest floor organic matter and standing biomass are most responsible for creating the elevational pattern in stream NO3 concentration within this watershed.

Energy flow and the persistence of a human population: a simulation analysis.

A human ecosystem model, NUÑOA, simulates the yearly energy balance of individuals, families, and extended families in a hypothetical farming and herding community of Quechua Indians in the high Andes. The yearly energy demand of each family, based on the caloric requirements of its members, is computed by simulation of agricultural and herding activities in response to stochastic environmental conditions. The family energy balance is used in determining births, deaths, marriages, and resource sharing. The model user has the opportunity to investigate the effect of changes in marriage patterns, resource sharing patterns, or subsistence activities on the ability of the human population to survive in the harsh Andean environment. Results from the model suggest that the substructuring of a population into extended families provides a mechanism for sheltering the population from control by exogenous influences. A population without substructures for resource sharing is shown to be unstable in such an unpredictable environment.