Craig Loehle

Craig Loehle
NCASI | NCASI · Department of Forestry

About

177
Publications
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6,787
Citations
Citations since 2017
17 Research Items
1664 Citations
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2017201820192020202120222023050100150200250
2017201820192020202120222023050100150200250
2017201820192020202120222023050100150200250
Introduction
Skills and Expertise

Publications

Publications (177)
Article
The Marbled Murrelet (Brachyramphus marmoratus) is a small seabird found on the western coast of North America, listed as federally threatened in the US. It has been in decline for a prolonged period over most of its range. To better understand this population trend, we analyzed relative abundance from at-sea survey transects of Marbled Murrelets t...
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When working forest stands are harvested, vegetated strips along streams are often retained as part of forestry best management practices (BMPs) to protect water quality. These riparian buffers, known as streamside management zones, when following forestry BMP recommendations, also likely provide benefits to various terrestrial wildlife species. To...
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The southeastern U.S. is widely known as a bastion of privately-owned, managed pine (Pinus spp.) forests, comprised primarily of native pine species. The region supports high levels of biodiversity, but also a multi-billion-dollar forest products economy critical to socioeconomic stability of rural areas. We conducted a systematic review of studies...
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Tree retention after forest harvest is often used to enhance biodiversity in forests that are otherwise managed using even-aged systems. It remains unclear to what extent scattered trees and residual patches (i.e., retained structures) actually facilitate recolonization of species in logged areas. For assessing recolonization benefits, it is necess...
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Because a change in the frequency (number/year) of hurricanes could be a result of climate change, we analyzed the historical record of Atlantic basin and US landfalling hurricanes, as well as US continental accumulated cyclone energy to evaluate issues related to trend detection. Hurricane and major hurricane landfall counts exhibited no significa...
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Changes over the past century in factors such as temperature, precipitation, fire regimes, ozone, atmospheric CO 2 , and nitrogen deposition naturally lead to questions about forest growth over this same time period. Determining changes in forest growth over long intervals is complicated by constantly changing growth conditions due to tree maturati...
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Purpose We tested the effectiveness of the global and ecoregion-based average characterization factors (CFs) for “Potential Species Loss” recommended by the UNEP-SETAC Life Cycle Initiative to identify hotspots and improvement opportunities compared to using a land competition indicator for a product for which the predominant life cycle use of land...
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Changes in factors such as temperature, precipitation, fire regimes, ozone, atmospheric CO ² , and nitrogen deposition may have altered forest growth over the past century. Determining changes in forest growth over long intervals is complicated by constantly changing growing conditions due to tree maturation, stand self-thinning, disturbance, and o...
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Geographic range is an important metric used to evaluate species’ environmental relationships. Additionally, a very small or rapidly shrinking range may indicate elevated extinction risk. However, a species does not fully occupy its range in the way a lake fills a basin and is instead best thought of as a cloud of points rather than an area per se....
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Reports have identified changes in abiotic factors that potentially affect forest growth. A synthesis of studies of thesechanges in Canada over the past century was undertaken to evaluate how these factors may be influencing forest growth.Reviewed papers used multiple sources of data including long-term inventory plots, tree-ring reconstructions, h...
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Climate change is widely expected to pose a threat to many of Earth's plant and animal species. Based on climate models, a multitude of studies project that certain species will not be able to migrate fast enough to keep up with changing environmental conditions, presenting a greater risk of their possible extinction. However, many of these studies...
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Forecasts of both likely anthropogenic effects on climate and consequent effects on nature and society are based on large, complex software tools called general circulation models (GCMs). Forecasts generated by GCMs have been used extensively in policy decisions related to climate change. However, the relation between underlying physical theories a...
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Estimates of plant biomass derived from field measurements can be used to quantify wildlife habitat, fuel loads, net primary production, and nutrient cycling. The difficulty involved with developing species-specific allometric equations for plant biomass results in many studies utilizing estimates of shrub cover instead. We assess whether reasonabl...
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In retrospective studies, discrete population units such as ponds may be resurveyed at a later time using only the set of initially occupied sites. There are possible confoundings that affect estimates of occupancy change under these conditions. For most possible parameter values for a metapopulation, simulations and analytical results show that tu...
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Management of wildlife and protection of endangered species depend on determination of population trends. Because population changes are stochastic and autoregressive, there is reason to believe that population trends might not be properly determined by simple regression over short time periods. A bounded random walk (BRW) model is introduced as a...
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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 su...
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The health of United States forests is of concern for biodiversity conservation, ecosystem services, forest commercial values, and other reasons. Climate change, rising concentrations of CO2 and some pollutants could plausibly have affected forest health and growth rates over the past 150years and may affect forests in the future. Multiple factors...
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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 ma...
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Multidecadal climate variability has proven difficult to deal with when estimating temperature trends. This possible unforced internal oscillation of the climate system provides an opportunity to correct temperature trends. The Atlantic Multidecadal Oscillation (AMO) is proposed as a potential index for this unforced variability. The AMO pattern do...
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Conservation planning for spotted owls (Strix occidentalis) hinges upon retaining late-successional and old-growth forests. This strategy is to be supplemented over time by creating structural conditions found in such forests using innovative silviculture in less well-developed forests. Recent research indicates that spotted owls often hunt for pre...
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When a species potentially at risk of extinction is considered for legally protected status, changes in geographic range over time are often evaluated and utilized in listing decisions. Range changes are also used to guide conservation management decisions. Although changes in geographic range may provide information relevant to conservation decisi...
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Recently the US Fish and Wildlife Service, as part of a critical habitat analysis for the northern spotted owl (Strix occidentalis caurina), developed habitat suitability models based on thousands of owl nest sites distributed across 11 regions using the MaxEnt tool. Because these models formed the basis for critical habitat designations on million...
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Short rotation woody crops (SRWC), fast growing tree species that are harvested on short, repeated intervals, can augment traditional fiber sources. These crops have economic and environmental benefits stemming from their capability of supplying fiber on a reduced land base in close proximity to users and when sensitive sites cannot be accessed. Eu...
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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 forci...
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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 in...
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Detectability issues create uncertainty in field surveys of animal and plant populations. Detectability correction is one method employed to deal with this problem when there is reasonable certainty that detectability is roughly constant with time or in different areas. Two new reduced-variance estimators of detectability are introduced and evaluat...
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The climate change attribution problem is addressed using empirical decomposition. Cycles in solar motion and activity of 60 and 20 years were used to develop an empirical model of Earth temperature variations. The model was fit to the Hadley global temperature data up to 1950 (time period before anthropogenic emissions became the dominant forcing...
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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 arg...
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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...
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In the southern United States, owners of potential forest habitat for the federally threatened gopher tortoise (Gopherus polyphemus) often conduct surveys prior to implementing management practices that could affect tortoise burrows. Results from such surveys can enhance understanding of the status and habitat associations of this species. During 1...
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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 datab...
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There is concern about the potential impacts of climate change on species and ecosystems. To address this concern, a large body of literature has developed in which these impacts are assessed. In this study, criteria for conducting reliable and useful assessments of impacts of future climate are suggested. The major decisions involve: clearly defin...
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This journal concerns itself with ecological complexity and theoretical ecology. In order to study complex systems it is often necessary to make categorizations, simplifying assumptions and analogies, and to use particular model structures and statistical tools. Such operations on the raw sensory data of nature may or may not be valid, and can make...
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The northern spotted owl (Strix occidentalis caurina (Merriam, 1898)) is listed as threatened in both Canada and the United States. As part of a 1998–2004 study of habitat usage, we attached radio tags to 197 northern spotted owls. Owls that died or emigrated from the study areas could be identified with high certainty. The long-term data we obtain...
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Analysis of energy partitioning between defensive investments and growth in woody plants indicates that increasing a tree's life-span should require increased energy investment in protective measures such as thick bark and defensive chemicals. Increased investment in such defenses, however, logically must slow down the growth rate, thereby raising...
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Wildlife population models are potentially valuable for conservation planning. Validation is necessary to ensure that models are sufficiently robust for predicting management outcomes consistent with conservation objectives. Sorensen et al. (2008) produced a model of woodland caribou (Rangifer tarandus) population growth rate that was recently modi...
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Past studies have detected an *1500-year climate cycle in various types of Pleistocene geologic or ice deposits. It has been proposed that a 1470-year cycle fits the Pleistocene Dansgaard–Oeschger (DO) oscillations and can be ex-plained by a threshold model with forcing. We used nine temperature reconstructions to see if this cycle exists during th...
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Detectability issues create uncertainty in field surveys of populations. Methods to overcome this problem include mark-recapture methods and double sampling. Partial double sampling involves estimating detectability, , and using this to correct the estimate in areas sampled only once. Results of this study indicate that, if population density is no...
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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...
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Global satellite data is analyzed for temperature trends for the period January 1979 through June 2009. Beginning and ending segments show a cooling trend, while the middle segment evinces a warming trend. The past 12 to 13 years show cooling using both satellite data sets, with lower confidence limits that do not exclude a negative trend until 16...
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Managed forests are a primary land use within the Coastal Plain of the southern United States. These forests are generally managed under standards, guidelines, or regulations to conserve ecosystem functions and services. Economic value of commercial forests provides incentives for landowners to maintain forests rather than convert them to other use...
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Ocean heat content data from 2003 to 2008 (4.5 years) were evaluated for trend. A trend plus periodic (annual cycle) model fit with R(2) = 0.85. The linear component of the model showed a trend of -0.35 (+/- 0.2) x 10(22) Joules per year. The result is consistent with other data showing a lack of warming over the past few years.
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Scientific research requires both innovation and attention to detail, clever breakthroughs and routine procedures. This indispensable guide gives students and researchers across all scientific disciplines practical advice on how to succeed. All types of scientific careers are discussed, from those in industry and academia to consulting, with emphas...
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Numerous studies have explored the influence of forest management on avian communities empirically, but uncertainty about causal relationships between landscape patterns and temporal dynamics of bird communities calls into question how observed historical patterns can be projected into the future, particularly to assess consequences of differing ma...
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Large-scale divestiture of commercial forestlands is occurring in the United States. Furthermore, increasing demand for cellulose for bioenergy may modify forest management practices widely enough to impact the spatial characteristics of forested landscapes. We used the HARVEST timber harvest simulator to investigate the potential consequences of d...
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Tree rings provide a primary data source for reconstructing past climates, particularly over the past 1,000years. However, divergence has been observed in twentieth century reconstructions. Divergence occurs when trees show a positive response to warming in the calibration period but a lesser or even negative response in recent decades. The mathema...
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A climatic reconstruction published in E&E (Loehle, 2007) is here corrected for various errors and data issues, with little change in the results. Standard errors and 95% confidence intervals are added. The Medieval Warming Period (MWP) was significantly warmer than the bimillennial average during most of the period 820 -1040 AD. The Little Ice Age...
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While the cumulative effects of the actions of multiple owners have long been recognized as critically relevant to efforts to maintain sustainable forests at the landscape scale, few studies have addressed these effects. We used the HARVEST timber harvest simulator to predict the cumulative effects of four owner groups (two paper companies, a state...
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Historical data provide a baseline for judging how anomalous recent temperature changes are and for assessing the degree to which organisms are likely to be adversely affected by current or future warming. Climate histories are commonly reconstructed from a variety of sources, including ice cores, tree rings, and sediment. Tree-ring data, being the...
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In both percolation models and metapopulation (habitat patch) models, habitat pattern is assumed to be fixed and binary (matrix is unsuitable). In percolation models movement (dispersal) is strictly to neighbors whereas in metapopulation models movement is not explicitly considered but is factored into the colonization coefficients. Models with exp...
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The demand for accurate forecasting of the effects of global warming on biodiversity is growing, but current methods for forecasting have limitations. In this article, we compare and discuss the different uses of four forecasting methods: (1) models that consider species individually, (2) niche-theory models that group species by habitat (more spec...
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Climates at the Last Glacial Maximum have been inferred from fossil pollen assemblages, but these inferred climates are colder for eastern North America than those produced by climate simulations. It has been suggested that low CO<sub>2</sub> levels could account for this discrepancy. In this study biogeographic evidence is used to test the CO<sub>...
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Ownership parcelization of forest land and divestiture of industrial forest land is increasing throughout the U.S. This may affect (positively or negatively) the ability of forested landscapes to produce benefits that society values, such as fiber, biodiversity and recreation. We used a timber harvest simulator and neutral model landscapes to syste...
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The conservation of rare plants is an important goal. Many rare plants are, in fact, endemics rather than remnants of once abundant populations. Plant endemics pose both challenges and opportunities for conservation. For eastern North America, there is a North-South gradient in endemic richness, with the highest concentrations in two parts of Flori...
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We reply to Franklin et al.’s critique of our recent work in which we computed survival for northern spotted owls (Strix occidentalis caurina (Merriam, 1898)) from sites in western Oregon and northern California based on 197 radio-collared owls. Several methods gave similar results and we noted that our estimated survival rates might be closer to t...
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Climates at the Last Glacial Maximum have been inferred from fossil pollen assemblages, but these inferred climates are colder than those produced by climate simulations. Biogeographic evidence also argues against these inferred cold climates. The recolonization of glaciated zones in eastern North America following the last ice age produced distinc...
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Abundance distributions are a central characteristic of ecosystems. Certain distributions have been derived from theoretical models of community organization, and therefore the fit of data to these distributions has been proposed as a test of these theories. However, it is shown here that the geometric sequence distribution can be derived directly...
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Wildlife-habitat relationship models have sometimes been linked with forest simulators to aid in evaluating outcomes of forest management alternatives. However, linking wildlife-habitat models with harvest scheduling software would provide a more direct method for assessing economic and ecological implications of alternative harvest schedules in co...
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Summary • Control theory is a well-developed branch of mathematics and engineering that identifies optimal control policies for dynamic systems. While it should be useful for managing ecosystems, it is currently used only in certain fields of ecology and resource management, and only certain aspects of the theory are applied. Where optimal control...
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Little is known about factors that structure biodiversity on landscape scales, yet current land management protocols, such as forest certification programs, place an increasing emphasis on managing for sustainable biodiversity at landscape scales. We used a replicated landscape study to evaluate relationships between forest structure and avian dive...
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Mathematica provides a suite of built-in and 3rd party tools for nonlinear optimization. These tools are tested on a set of hard problems. The built-in Mathematica functions are tested as well as the tools in the MathOptimizer and Global Optimization packages. The problems tested represent classes of problems that cause difficulties for global solv...
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The distribution of biodiversity across the Pacific and Inland Northwest (PINW) is currently not well known. This knowledge is important for setting management priorities within agency and industrial forest holdings. Previous attempts to map biodiversity across regions largely relied on scaling up from our understanding of stand-scale habitat relat...
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Forest structural features at the stand scale (e.g., snags, stem density, species composition) and habitat attributes at larger spatial scales (e.g., landscape pattern, road density) can influence biological diversity and have been proposed as indicators in sustainable forestry programs. This study investigated relationships between such factors an...
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Species accumulation curves were used to study relationships between herpetofaunal richness and habitat characteristics on four watersheds in Arkansas that differed markedly with respect to management intensity. Selected habitat characteristics were estimated for stands containing the sample points and within buffers with radii of 250, 500 m, and 1...
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The problem of scaling is considered for community abundance distributions. Whereas species number scales predictably with spatial extent according to the species–area relation, it is shown that scaling of abundance distributions is not simple. To develop a scaling model, the structure of the bird community for the US Pacific and Inland Northwest w...
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Timeseries of estimated temperature have been combined to create global or hemispheric climate series over periods exceeding 1000 yr. The data used in these studies, however, may be subject to dating errors. It is shown that when timeseries with dating error are combined, the noise in the data smoothes periodic signals but leaves linear trends inta...
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Fire spreads in a specifically spatial manner, which suggests the applicability of percolation models to the risk reduction problem. It is shown that under fairly general conditions a threshold exists below which a landscape becomes essentially fireproof. Arranging treated acres into a grid, analogous to bulkheads on a ship, drastically reduces the...
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Complexity poses enormous challenges in ecology. In order to study complexity or factor it into our theories or mod-els, a better understanding of complexity is needed. Complexity has at least six dimensions in ecology: spatial, temporal, structural, process, behavioral, and geometric. These six sources of complexity are discussed. Issues and appro...
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Two questions about climate change remain open: detection and attribution. Detection of change for a complex phenomenon like climate is far from simple, because of the necessary averaging and correcting of the various data sources. Given that change over some period is detected, how do we attribute that change to natural versus anthropogenic causes...
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A strong case for global warming has been made based on reconstructed global climate histories. However, certain unique features of paleoclimate data make statistical inference problematic. Historical climate data have dating error of such a magnitude that combined series will really represent very long-term averages, which will flatten peaks in th...
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Various global change factors such as natural and anthropogenic climate change, tropospheric ozone, CO2, SO2, and nitrogen deposition affect forest growth, but in species-specific ways. Since even small differences in growth rates between competing species can lead to eventual competitive exclusion, it is important to know the rate at which displac...
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radius. C will indeed be dubious if data are recorded so fre- quently that the animal is still standing and chewing at both t and t + At. For C to be useful, At must be sufficiently large so that successivecirclesdonot overlap when the animal is foraging, though clearly no such condition is relevant if the predator uses a perch. The objection of Ga...
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Forest products companies undertake landscape planning to demonstrate the compatibility of forest management with ecological functions, to develop management systems that are more compatible with nonfinancial objectives, and to explore viable alternatives to restrictive regulations. Because of scientific and economic uncertainties, however, the ove...
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Increasing requirements for maintenance and enhancement of ecological values have recently led forest products companies to approach forest management in a more comprehensive way. Many companies have developed landscape-level management plans and programs for the conservation of wildlife, fish, and other values. This report documents approaches tak...
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Most current methods for describing animal home range assume that it may be represented as a Euclidean type shape such as a bell shaped curve or a closed polygon. Landscape ecology has increasingly shown that ecological objects are more often highly fragmented and irregular. A fractal approach to description of animal home range was thus developed....
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Past simulation studies using a variety of models have generally agreed that climatic warming could have adverse effects on forests, including large-scale diebacks in some regions and drastic range shrinkages of many species. These effects should be most evident at biome transition zones. Other studies have pointed out, however, that past models ha...
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The disturbance spectrum consists of disturbance patterns differing in type, size, intensity, and frequency. It is proposed that tree life-history traits are adaptations to particular disturbance regimes. Four independent axes are proposed to define the dominant dimensions of tree strategy space: shade tolerance, tree height, capacity for vegetativ...
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Increasingly, forest management practices are being evaluated from a watershed or landscape perspective. Currently, few tools are available for incorporating the impact of spatial patterns of management on spatially distributed dynamic processes. A new algorithm is presented for scheduling that can maximize timber harvest while meeting spatial cons...
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Landscape functions, including sediment and nutrient trapping, pollutant degradation, and flood control, are often adversely affected by human activities. Tools are needed for assessing the effects of human activities at the landscape scale. An approach is presented that addresses this goal. Spatially-explicit ecosystem units and their connections...
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The disturbance spectrum consists of disturbance patterns differing in type, size, intensity, and frequency. It is proposed that tree life‐history traits are adaptations to particular disturbance regimes. Four independent axes are proposed to define the dominant dimensions of tree strategy space: shade tolerance, tree height, capacity for vegetativ...
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Wildlife tradeoffs based on landscape models of habitat preference were presented. Multiscale logistic regression models were used and based on these models a spatial optimization technique was utilized to generate optimal maps. The tradeoffs were analyzed by gradually increasing the weighting on a single species in the objective function over a se...
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Habitat fragmentation is being increasingly recognized as a serious problem for a variety of wildlife species. While it is possible to approximately determine by eye where on a map a habitat alteration could be used to decrease fragmentation, this is a slow and imprecise method that is impractical for large maps. An algorithm is presented that auto...
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Identifying the biological determinants of range limits of trees is an unsolved problem of critical importance for predicting the effects of climate change on forests. Data showing that many boreal trees can grow in temperate climates indicate that southern range limits do not necessarily result from excessive temperature per se. A growth tradeoff...
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The current theory that sexual selection results from female preference for males with good genes suffers from several problems. An alternative explanation, the pathogen transmission avoidance hypothesis, argues that the primary function of showy traits is to provide a reliable signal of current disease status, so that sick individuals can be avoid...
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A recent study explored the adaptive significance of trunk inclination for trees growing on steep slopes. The authors used an optimality argument to predict how much a tree should respond to sidelight. Their calculations of the costs of leaning are flawed, because: (i) leaf mass has an allometric relationship with total volume, rather than being a...
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Model evaluation is argued to necessitate the use of a hypothesis testing framework instead of the use of goodness-of-fit (GOD) against time series data. A test statistic T is developed, based on model deviation from expected system behaviors. If a model does not exceed the error bounds on expected behavior, then we cannot say that it differs from...

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