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Loehle C.,National Council for Air and Stream Improvement Inc. | Irwin L.,PO Box 68
Forest Ecology and Management | Year: 2015

Bell et al. (2015) and Dunk et al. (2015) comment on our appraisal (Loehle et al., 2015) of biological insights from the US Fish and Wildlife Service models for northern spotted owl critical habitat. We here respond to those comments. We argue that while the low predictability of vegetation plot data by the gradient nearest neighbor (GNN) models may average out at very large scales and thus be useful in that context, errors at the site-specific scale may confound the modeling used to develop critical habitat designations. We further found that GNN errors violate statistical assumptions and are not propagated through the modeling exercise. We found multiple lines of evidence for habitat model instability, which may result from GNN uncertainty. We believe our evidence for lack of demographic predictability from the MaxEnt RHS values remains relevant to judicious use of these models for conservation. We similarly respond to other particular concerns with our analysis and conclude with suggestions. © 2015 Elsevier B.V..

Dandres T.,Ecole Polytechnique de Montréal | Gaudreault C.,National Council for Air and Stream Improvement Inc. | Tirado-Seco P.,Ecole Polytechnique de Montréal | Samson R.,Ecole Polytechnique de Montréal
Renewable and Sustainable Energy Reviews | Year: 2012

This paper describes a new tool to assess the medium- and long-term economic and environmental impacts of large-scale policies. The approach - macro life cycle assessment (M-LCA) - is based on life cycle assessment methodology and includes additional elements to model economic externalities and the temporal evolution of background parameters. The general equilibrium model GTAP was therefore used to simulate the economic consequences of policies in a dynamic framework representing the temporal evolution of macroeconomic and technological parameters. Environmental impacts, expressed via four indicators (human health, ecosystems, global warming and natural resources), are computed according to policy life cycle and its indirect economic consequences. In order to illustrate the approach, two 2005-2025 European Union (EU) energy policies were compared using M-LCA. The first policy, the bioenergy policy, aims to significantly increase energy generation from biomass and reduce EU energy demand for coal. The second policy, the baseline policy, is a business as usual policy where year 2000 energy policies are extended to 2025. Results show that, compared to the baseline policy, the bioenergy policy generates fewer impacts on three of the four environmental indicators (human health, global warming and natural resources) at the world and EU scales, though the results may differ significantly at a regional level. The results also highlight the key contribution of economic growth to the total environmental impacts computed for the 2005-2025 period. A comparison of the results with a more conventional consequential LCA approach illustrates the benefits of M-LCA when modeling the indirect environmental impacts of large-scale policies. The sensitivity and uncertainty analysis indicates that the method is quite robust. However, its robustness must still be evaluated based on the sensitivity and uncertainty of additional parameters, including the evolution of economic growth. © 2011 Elsevier Ltd. All rights reserved.

Loehle C.,National Council for Air and Stream Improvement Inc.
Journal of Wildlife Management | Year: 2013

Territoriality leads to non-random sorting of individuals into habitats of differing quality. This can affect empirical estimates of population growth rate (λ), a measure of habitat quality, such that habitat-specific λ varies with population size. I present a simple model of territorial behavior in which territory acquisition depends on age and individual vigor. Under this model, with a low initial population, the λ associated with the best habitat stays constant until all territories are full. At that point, as less competitive individuals move to secondary habitat, the λ value in the better habitat increases. Similarly, as secondary habitat becomes occupied by individuals of successively greater vigor, λ can switch from a sink (λ < 1) to a source (λ > 1). This means that habitat quality is not a fixed quantity but results from an interaction of the characteristics of the habitat with competitive sorting of individuals. If all individuals are in a good habitat, its conservation value will be underestimated and likewise the value of secondary habitat may not be properly assessed. © 2013 The Wildlife Society.

McLaughlin D.B.,National Council for Air and Stream Improvement Inc.
Integrated environmental assessment and management | Year: 2014

High levels of the nutrients nitrogen and phosphorus can cause unhealthy biological or ecological conditions in surface waters and prevent the attainment of their designated uses. Regulatory agencies are developing numeric criteria for these nutrients in an effort to ensure that the surface waters in their jurisdictions remain healthy and productive, and that water quality standards are met. These criteria are often derived using field measurements that relate nutrient concentrations and other water quality conditions to expected biological responses such as undesirable growth or changes in aquatic plant and animal communities. Ideally, these numeric criteria can be used to accurately "diagnose" ecosystem health and guide management decisions. However, the degree to which numeric nutrient criteria are useful for decision making depends on how accurately they reflect the status or risk of nutrient-related biological impairments. Numeric criteria that have little predictive value are not likely to be useful for managing nutrient concerns. This paper presents information on the role of numeric nutrient criteria as biological health indicators, and the potential benefits of sufficiently accurate criteria for nutrient management. In addition, it describes approaches being proposed or adopted in states such as Florida and Maine to improve the accuracy of numeric criteria and criteria-based decisions. This includes a preference for developing site-specific criteria in cases where sufficient data are available, and the use of nutrient concentration and biological response criteria together in a framework to support designated use attainment decisions. Together with systematic planning during criteria development, the accuracy of field-derived numeric nutrient criteria can be assessed and maximized as a part of an overall effort to manage nutrient water quality concerns. © 2013 SETAC.

Loehle C.,National Council for Air and Stream Improvement Inc.
Atmospheric Environment | Year: 2010

A paper by Hofmann et al. (2009, this journal) is critiqued. It is shown that their exponential model for characterizing CO2 trajectories for historical data is not estimated properly. An exponential model is properly estimated and is shown to fit over the entire 51 year period of available data. Further, the entire problem of estimating models for the CO2 historical data is shown to be ill-posed because alternate model forms fit the data equally well. To illustrate this point the past 51 years of CO2 data were analyzed using three different time-dependent models that capture the historical pattern of CO2 increase. All three fit with R2>0.98, are visually indistinguishable when overlaid, and match each other during the calibration period with R2>0.999. Projecting the models forward to 2100, the exponential model comes quite close to the Intergovernmental Panel on Climate Change (IPCC) best estimate of 836ppmv. The other two models project values far below the IPCC low estimates. The problem of characterizing historical CO2 levels is thus indeterminate, because multiple models fit the data equally well but forecast very different future trajectories. © 2010 Elsevier Ltd.

Loehle C.,National Council for Air and Stream Improvement Inc.
Ecography | Year: 2012

A new approach to habitat distribution modeling is presented and tested with data on North American plants. The relative frequency function (RFF) algorithm compares the relative frequencies of a species' sample points to that of random points or absence points on the landscape to compute a frequency ratio. The relative frequency ratio r is smoothed across the range of values using moving, overlapping windows. The ratio of frequencies at a sample point for each variable is used to compute the geometric mean score for all data with non-missing values. Variables are added using a forward stepwise method. Confidence intervals are computed with bootstrap resampling. The method was tested with artificial and species habitat and geographic range data. The RFF method in all cases gave results comparable to other methods tested. For the species with good geographic range maps, the results were consistent with known biogeography. The RFF method is particularly well-suited to irregularly shaped distributions and can classify sample points even when the data contain missing values. The method is extremely simple to use and comes with a free software tool, does not require a large sample size, does not require absence data, and is more interpretable and portable than certain other methods. © 2012 The Authors. Ecography © 2012 Nordic Society Oikos.

Loehle C.,National Council for Air and Stream Improvement Inc.
Ecological Modelling | Year: 2012

The ideal free distribution posits that at equilibrium habitats of all degrees of quality should have similar population growth rate (λ) values (≈1), but in fact sink habitats are often observed with λ< 1 when source habitats have λ> 1. This is the source-sink paradox. Animals appear to be choosing habitat that will lower their fitness. It is argued that the paradox can be resolved by considering individual decisions in a conditional choice model with non-identical individuals that differ in competitive ability and current expected reproductive output. Individuals that are more mature, healthier, and/or arrive earlier to the source will acquire territory at lower cost and will defend it more vigorously and effectively. For other individuals, costs (including running out of time for breeding) of acquiring territory in the source become so high that moving to the sink increases their fitness. The model is implemented in an individual-based modeling framework. The cost-benefit decision model unites previously disparate topics into a single framework, including protandry, territoriality, philopatry, and juvenile dispersal. Simulation results and a literature survey support predictions. Results indicate that individuals with lower competitive ability (e.g., juveniles) obtain a fitness advantage from moving to a sink. Random sorting of individuals (simple pre-emption) results in lower population λ than competitive sorting. The effective population λ in the source is increased and in the sink is decreased by competitive sorting such that individual and population λ are not simple functions of habitat quality. The theory and models developed link individual behaviours to population processes and resolve the source-sink paradox. It is suggested that metapopulation modeling theory needs to be revisited based on the results presented. © 2012 Elsevier B.V.

Loehle C.,National Council for Air and Stream Improvement Inc. | Eschenbach W.,16869 Lauri Lane
Diversity and Distributions | Year: 2012

Aim Conservation of species is an ongoing concern. Location Worldwide. Methods We examined historical extinction rates for birds and mammals and contrasted island and continental extinctions. Australia was included as an island because of its isolation. Results Only six continental birds and three continental mammals were recorded in standard databases as going extinct since 1500 compared to 123 bird species and 58 mammal species on islands. Of the extinctions, 95% were on islands. On a per unit area basis, the extinction rate on islands was 177 times higher for mammals and 187 times higher for birds than on continents. The continental mammal extinction rate was between 0.89 and 7.4 times the background rate, whereas the island mammal extinction rate was between 82 and 702 times background. The continental bird extinction rate was between 0.69 and 5.9 times the background rate, whereas for islands it was between 98 and 844 times the background rate. Undocumented prehistoric extinctions, particularly on islands, amplify these trends. Island extinction rates are much higher than continental rates largely because of introductions of alien predators (including man) and diseases. Main conclusions Our analysis suggests that conservation strategies for birds and mammals on continents should not be based on island extinction rates and that on islands the key factor to enhance conservation is to alleviate pressures from uncontrolled hunting and predation. © 2011 Blackwell Publishing Ltd.

Loehle C.,National Council for Air and Stream Improvement Inc.
Ecological Modelling | Year: 2014

Climate sensitivity summarizes the net effect of a change in forcing on Earth's surface temperature. Estimates based on energy balance calculations give generally lower values for sensitivity (<2°C per doubling of forcing) than those based on general circulation models, but utilize uncertain historical data and make various assumptions about forcings. A minimal model was used that has the fewest possible assumptions and the least data uncertainty. Using only the historical surface temperature record, the periodic temperature oscillations often associated with the Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation were estimated and subtracted from the surface temperature data, leaving a linear warming trend identified as an anthropogenic signal. This estimated rate of warming was related to the fraction of a log CO2 doubling from 1959 to 2013 to give an estimated transient sensitivity of 1.093°C (0.96-1.23°C 95% confidence limits) and equilibrium climate sensitivity of 1.99°C (1.75-2.23°C). It is argued that higher estimates derived from climate models are incorrect because they disagree with empirical estimates. © 2014 Elsevier B.V.

Loehle C.,National Council for Air and Stream Improvement Inc.
Trees - Structure and Function | Year: 2016

Key message: Mechanical properties of wood constrain most conifers to an excurrent form and limit the width of tree crowns. Development of support tissue alters allometric relations during ontogeny.Abstract: Biomechanical constraints on tree architecture are explored. Torque on a tree branch is a multiplicative function of mass and moment arm. As such, the need for support rises faster than branch length, which leads to increased taper as branch size increases. This violates assumptions of models, such as the pipe-model theory, for large trees and causes changing allometry with tree size or exposure. Thus, assumptions about optimal design for light capture, self-similarity, or optimal hydraulic architecture need to be modified to account for mechanical constraints and costs. In particular, it is argued that mechanical limitations of compression wood in conifers prevent members of this taxon from developing large branches. With decurrent form ruled out (for larger species), only a conical or excurrent form can develop. Wind is shown to be a major mortality risk for trees. Adaptations for wind include dynamic responses of wood properties and height. It is argued that an adaptation to wind could be the development of an open crown in larger trees to let the wind penetrate, thereby reducing wind-throw risk. It is thus argued that crown shape and branching may result not just from optimal light capture considerations but also from adaptation to and response to wind as well as from mechanical constraints. Results have implications for allometric theory, life history theory, and simulations of tree architecture. © 2016 Springer-Verlag Berlin Heidelberg

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