Wilfried M. Post

Multiple nutrient limitations in ecological models

Abstract Ecological processes are often limited by more than one nutrient, for example, nitrogen and phosphorus. Therefore, mathematical representation of simultaneous limitations becomes important in many modeling and data analysis problems. This article reviews eight functional forms that have been proposed in the literature and presents a general theoretical framework that illustrates the commonalities and differences among the functions. Based on the general framework, three additional functional forms are derived. We then evaluate the functions based on their ability to fit experimental data. A total of eleven functions are fitted to eleven data sets by nonlinear least-squares. A new functional form, the Additive model, is selected as the most general function based on available data.

An integrative modeling framework to evaluate the productivity and sustainability of biofuel crop production systems

The potential expansion of biofuel production raises food, energy, and environmental challenges that require careful assessment of the impact of biofuel production on greenhouse gas (GHG) emissions, soil erosion, nutrient loading, and water quality. In this study, we describe a spatially explicit integrative modeling framework (SEIMF) to understand and quantify the environmental impacts of different biomass cropping systems. This SEIMF consists of three major components: (1) a geographic information system (GIS)‐based data analysis system to define spatial modeling units with resolution of 56 m to address spatial variability, (2) the biophysical and biogeochemical model Environmental Policy Integrated Climate (EPIC) applied in a spatially‐explicit way to predict biomass yield, GHG emissions, and other environmental impacts of different biofuel crops production systems, and (3) an evolutionary multiobjective optimization algorithm for exploring the trade‐offs between biofuel energy production and unintended ecosystem‐service responses. Simple examples illustrate the major functions of the SEIMF when applied to a nine‐county Regional Intensive Modeling Area (RIMA) in SW Michigan to (1) simulate biofuel crop production, (2) compare impacts of management practices and local ecosystem settings, and (3) optimize the spatial configuration of different biofuel production systems by balancing energy production and other ecosystem‐service variables. Potential applications of the SEIMF to support life cycle analysis and provide information on biodiversity evaluation and marginal‐land identification are also discussed. The SEIMF developed in this study is expected to provide a useful tool for scientists and decision makers to understand sustainability issues associated with the production of biofuels at local, regional, and national scales.

Soil Organic Matter Models and Global Estimates of Soil Organic Carbon

The large size and potentially long residence time of the soil organic matter pool make it an important component of the global carbon cycle (Schlesinger, 1977; Post et al., 1982, 1985, 1990). The input rates and decomposition rates for different terrestrial ecosystems vary over several orders of magnitude resulting in widely different amounts and turnover rates of soil organic matter. The amounts of carbon stored in soils and the rates of exchange of soil carbon with the atmosphere depend on many factors related to the chemistry, biology, and physics of soil and soil organic matter.

Aspects of the Interaction Between Vegetation and Soil Under Global Change

Responses of terrestrial ecosystems to a world undergoing a change in atmospheric CO2 concentration presents a formidable challenge to terrestrial ecosystem scientists. Strong relationships among climate, atmosphere, soils and biota at many different temporal and spatial scales make the understanding and prediction of changes in net ecosystem production (NEP) at a global scale difficult. Global C cycle models have implicitly attempted to account for some of this complexity by adapting lower pool sizes and smaller flux rates representing large regions and long temporal averages than values appropriate for a small area. However, it is becoming increasingly evident that terrestrial ecosystems may be experiencing a strong transient forcing as a result of increasing levels of atmospheric CO2 that will require a finer temporal and spatial representation of terrestrial systems than the parameters for current global C cycle models allow. To adequately represent terrestrial systems in the global C cycle it is necessary to explicitly model the response of terrestrial systems to primary environmental factors. While considerable progress has been made experimentally and conceptually in aspects of photosynthetic responses, and gross and net primary production, the application of this understanding to NEP at individual sites is not well developed. This is an essential step in determining effects of plant physiological responses on the global C cycle. We use a forest stand succession model to explore the effects of several possible plant responses to elevated atmospheric CO2 concentration. These simulations show that ecosystem C storage can be increased by increases in individual tree growth rate, reduced transpiration, or increases in fine root production commensurate with experimental observations.

Ecological modelling and disturbance evaluation

Abstract The idea of ‘disturbance’ has played contradictory roles in ecological theory. In some cases, disturbances have been viewed as disruptive to ecological systems, whereas in others they have been seen as necessary to maintain ecological systems. In this paper we show that the role of disturbance is dependent on the temporal and spatial characteristics of the systems. Our approach is to examine a variety of ecological models. We divide models into three spatial categories (closed, multicell, and open systems) and three categories of stability (equilibrium, loose equilibrium, and nonequilibrium). In the ‘classical’ closed equilibrium models of ecology, disturbances act primarily in a destructive way, reducing the ecological structure that can be maintained, whereas in other categories disturbances promote species diversity and richness of spatial pattern. We attempt to make clearer the role of scale in affecting the system properties ‘equilibrium vs. nonequilibrium’, ‘closed vs. open’, and the disturbance property ‘endogenous vs. exogenous’.

Soil Carbon Change and Net Energy Associated with Biofuel Production on Marginal Lands: A Regional Modeling Perspective

The use of marginal lands for biofuel production has been proposed as a promising solution for meeting biofuel demands while avoiding food-feed-fuel conflicts. However, uncertainty surrounds whether marginal lands can be reliably located, as well as their inherent biofuel potential and the possible environmental impacts. We developed a quantitative approach that integrates high-resolution land cover and land productivity to classify productive croplands and nonarable marginal lands in a nine-county region in southern Michigan. The classified lands were then examined with the spatially explicit modeling framework using the Environmental Policy Integrated Climate (EPIC) model to estimate net energy (NE) and soil organic carbon (SOC) changes associated with the cultivation of different annual and perennial production systems. Simulation results suggest that biofuel production systems underperform on marginal lands when compared to productive croplands. However, we found perennial grasses could perform better than annual crops. Hence, when growing perennial bioenergy crops on marginal lands instead of productive croplands, less additional land (about 0.09 ha per each hectare planted) would be needed to achieve the same NE than if growing annual bioenergy crops (additional 0.17 ha per hectare planted). Miscanthus ( × ) and switchgrass ( L.) can produce 112.43 and 74.61 GJ ha yr NE, respectively, and have the potential to sequester, on average, 0.59 and 0.23 Mg C ha yr SOC, respectively. Notably, simulation results indicate substantial variability of the NE and SOC storage potential across the study region. Thus, although perennial energy crops are promising options for biofuel production on marginal lands, given the large spatial variability, regional- and site-specific management strategies are required for sustainable biofuel production.

CSiTE Studies on Carbon Sequestration in Soils

Publisher Summary The Consortium for Research on Enhancing Carbon Sequestration in Terrestrial Ecosystems was created in 1999 to perform fundamental research that will lead to methods to enhance Carbon (C) sequestration as one component of a C management strategy. Research at one member of this consortium, Oak Ridge National Laboratory, has focused on C sequestration in soils. Studies of C and N dynamics are leading to an understanding of the factors that affect the inputs to and outputs from soils and how these might bemanipulated to enhance C sequestration. Both the quantity and the quality of soil C inputs influence C storage and the potential for C sequestration. Changes in tillage intensity and crop rotations can affect C sequestration by changing the soil physical and biological conditions and by changing the amounts and types of organic inputs to the soil. Analyses of changes in soil C are supplemented with studies of the changes in the associated management practices and their implications for fossil-fuel use, emission of other greenhouse gases such as N2O and CH4, and impacts on agricultural productivity. Improved understanding of the factors and mechanisms that control the spatial and temporal variations in soil C can lead to land management strategies that incorporate C management and increase the C stocks of terrestrial ecosystems.