Author
Christopher B. Edgar
Other affiliations: United States Forest Service
Bio: Christopher B. Edgar is an academic researcher from University of Minnesota. The author has contributed to research in topics: Forest inventory & Drought tolerance. The author has an hindex of 5, co-authored 11 publications receiving 143 citations. Previous affiliations of Christopher B. Edgar include United States Forest Service.
Topics: Forest inventory, Drought tolerance, Population, Estimation, Canopy
Papers
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TL;DR: A widespread tree mortality event that resulted from the worst 1-year drought on record for the state of Texas, USA is investigated, highlighting that drought-driven mortality alters forest structure differently across climatic regions and genera.
Abstract: Significant areas of the southern USA periodically experience intense drought that can lead to episodic tree mortality events. Because drought tolerance varies among species and size of trees, such events can alter the structure and function of terrestrial ecosystem in ways that are difficult to detect with local data sets or solely with remote-sensing platforms. We investigated a widespread tree mortality event that resulted from the worst 1-year drought on record for the state of Texas, USA. The drought affected ecoregions spanning mesic to semiarid climate zones and provided a unique opportunity to test hypotheses related to how trees of varying genus and size were affected. The study was based on an extensive set of 599 distributed plots, each 0.16 ha, surveyed in the summer following the drought. In each plot, dead trees larger than 12.7 cm in diameter were counted, sized, and identified to the genus level. Estimates of total mortality were obtained for each of 10 regions using a combination of design-based estimators and calibrated remote sensing using MODIS 1-yr change in normalized difference vegetation index products developed by the U.S. Forest Service. As compared with most of the publicized extreme die-off events, this study documents relatively low rates of mortality occurring over a very large area. However, statewide, regional tree mortality was massive, with an estimated 6.2% of the live trees perishing, nearly nine times greater than normal annual mortality. Dead tree diameters averaged larger than the live trees for most ecoregions, and this trend was most pronounced in the wetter climate zones, suggesting a potential re-ordering of species dominance and downward trend in tree size that was specific to climatic regions. The net effect on carbon storage was estimated to be a redistribution of 24-30 Tg C from the live tree to dead tree carbon pool. The dead tree survey documented drought mortality in more than 29 genera across all regions, and surprisingly, drought resistant and sensitive species fared similarly in some regions. Both angiosperms and gymnosperms were affected. These results highlight that drought-driven mortality alters forest structure differently across climatic regions and genera.
68 citations
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TL;DR: The reasoning for moving to an annual timber products monitoring program is presented and a comparison of sample designs is presented to facilitate an annual program without increased effort, finding that both probability proportional to size and stratified simple random sampling designs were viable options, but the stratifiedsimple random sampling design provided more flexibility.
Abstract: Understanding roundwood production in the United States at fine spatial and temporal scales is needed to support a range of analyses for decision making. Currently, estimates of county-level roundwood production are available at various time intervals for different regions of the country and for different products. Here we present our reasoning for moving to an annual timber products monitoring program and further present a comparison of sample designs to facilitate an annual program without increased effort. We found that both probability proportional to size and stratified simple random sampling designs were viable options, but the stratified simple random sampling design provided more flexibility. This flexibility was deemed important to target emerging markets and to enable sampling with certainty of specific firms. Our results lay the foundations for moving to an annual timber products output monitoring design in support of market, sustainability, and policy analyses as well as projections.
46 citations
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TL;DR: Investigation of relationships among stand composition, stemwood productivity, and canopy structure in northeastern Minnesota found aspen, primarily quaking and to a lesser degree bigtooth, was a significant component of every study area.
Abstract: Relationships among stand composition, stemwood productivity, and canopy structure were investigated for 55 study areas in northeastern Minnesota. Tree species composition among study areas was del...
45 citations
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20 citations
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TL;DR: In this article, the authors compare how temporal aggregation approaches with NFI data affects estimates of standing dead trees as these respond to extreme disturbance events, and they find that interpretations of disturbance event impacts varied depending on which sets of estimates were considered.
11 citations
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TL;DR: In his seminal book, Shewhart (1931) makes no demand on the distribution of the characteristic to be plotted on a control chart, so how can the idea that normality is, if not required, at least highly desirable be explained?
Abstract: In his seminal book, Shewhart (1931) makes no demand on the distribution of the characteristic to be plotted on a control chart. How then can we explain the idea that normality is, if not required, at least highly desirable? I believe that it has come about through the many statistical studies of control-chart behavior. If one is to study how a control chart behaves, it is necessary to relate it to some distribution. The obvious choice is the normal distribution because of its ubiquity as a satisfactory model. This is bolstered by the existence of the Central Limit Theorem.
896 citations
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TL;DR: This work focuses on the current understanding of tree hydraulic performance under drought, the identification of physiological thresholds that precipitate mortality and the mechanisms of recovery after drought, and the potential application of hydraulic thresholds to process-based models that predict mortality.
Abstract: Severe droughts have caused widespread tree mortality across many forest biomes with profound effects on the function of ecosystems and carbon balance. Climate change is expected to intensify regional-scale droughts, focusing attention on the physiological basis of drought-induced tree mortality. Recent work has shown that catastrophic failure of the plant hydraulic system is a principal mechanism involved in extensive crown death and tree mortality during drought, but the multi-dimensional response of trees to desiccation is complex. Here we focus on the current understanding of tree hydraulic performance under drought, the identification of physiological thresholds that precipitate mortality and the mechanisms of recovery after drought. Building on this, we discuss the potential application of hydraulic thresholds to process-based models that predict mortality.
811 citations
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TL;DR: This analysis is the first to demonstrate the critical role of species evenness, richness and the importance of contrasting traits in defining net diversity effects in forest polycultures and should motivate future studies to link richness,Evenness, contrasting traits and life-history stage to the mechanisms that are expected to produce positive net biodiversity effects.
Abstract: Summary 1. Although there is ample support for positive species richness–productivity relationships in planted grassland experiments, a recent 48-site study found no diversity–productivity relationship (DPR) in herbaceous communities. Thus, debate persists about diversity effects in natural versus planted systems. Additionally, current knowledge is weak regarding the influence of evenness on the DPRs, how DPRs are affected by the variation in life-history traits among constituent species in polycultures and how DPRs differ among biomes. The impacts of these factors on DPRs in forest ecosystems are even more poorly understood. 2. We performed a meta-analysis of 54 studies to reconcile DPRs in forest ecosystems. We quantified the net diversity effect as log effect size [ln(ES)], the log ratio of the productivity in polycultures to the average of those in monocultures within the same type of mixture, site condition and stand age of each study. The first use of a boosted regression tree model in meta-analysis, a useful method to partition the effects of multiple predictors rather than relying on vote-counting of individual studies, unveiled the relative influences of individual predictors. 3. Global average ln(ES) was 0.2128, indicating 23.7% higher productivity in polycultures than monocultures. The final model explained 21% of the variation in ln(ES). The predictors that substantially accounted for the explained variation included evenness (34%), heterogeneity of shade tolerance (29%), richness (13%) and stand age (15%). In contrast, heterogeneity of nitrogen fixation and growth habits, biome and stand origin (naturally established versus planted) contributed negligibly (each £ 4%). Log effect size strongly increased with evenness from 0.6 to 1 and with richness from 2 to 6. Furthermore, it was higher with heterogeneity of shade tolerance and generally increased with stand age. 4. Synthesis. Our analysis is, to our knowledge, the first to demonstrate the critical role of species evenness, richness and the importance of contrasting traits in defining net diversity effects in forest polycultures. While testing the specific mechanisms is beyond the scope of our analysis, our results should motivate future studies to link richness, evenness, contrasting traits and life-history stage to the mechanisms that are expected to produce positive net biodiversity effects such as niche differentiation, facilitation and reduced Janzen–Connell effects.
613 citations
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Oregon State University1, University of Natural Resources and Life Sciences, Vienna2, University of Trás-os-Montes and Alto Douro3, École Polytechnique Fédérale de Lausanne4, University of Franche-Comté5, Lund University6, Czech University of Life Sciences Prague7, Agro ParisTech8, Potsdam Institute for Climate Impact Research9, Institut national de la recherche agronomique10, Technical University of Lisbon11, Wageningen University and Research Centre12
TL;DR: A review of the wide variety of approaches to modelling natural disturbances in forest ecosystems, addressing the full spectrum of disturbance modelling from single events to integrated disturbance regimes, is presented in this paper.
338 citations
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Max Planck Society1, University of Lisbon2, University of Coimbra3, University of Utah4, Karlsruhe Institute of Technology5, University of Edinburgh6, University of Helsinki7, United States Geological Survey8, University of Melbourne9, University of Arizona10, Institut national de la recherche agronomique11, University of Leeds12, Botanic Gardens and Parks Authority13, Murdoch University14, Swiss Federal Institute for Forest, Snow and Landscape Research15, University of Auckland16, Oklahoma State University–Stillwater17, University of Innsbruck18, University of Antwerp19, ETH Zurich20, California Polytechnic State University21, Technische Universität München22, University of Ulm23, Spanish National Research Council24
TL;DR: A global tree mortality map is updated and a roadmap to a more holistic understanding of forest mortality across scales is presented to achieve scientific understanding for realistic predictions of drought-induced tree mortality.
Abstract: Accumulating evidence highlights increased mortality risks for trees during severe drought, particularly under warmer temperatures and increasing vapour pressure deficit (VPD). Resulting forest die-off events have severe consequences for ecosystem services, biophysical and biogeochemical land–atmosphere processes. Despite advances in monitoring, modelling and experimental studies of the causes and consequences of tree death from individual tree to ecosystem and global scale, a general mechanistic understanding and realistic predictions of drought mortality under future climate conditions are still lacking. We update a global tree mortality map and present a roadmap to a more holistic understanding of forest mortality across scales. We highlight priority research frontiers that promote: (1) new avenues for research on key tree ecophysiological responses to drought; (2) scaling from the tree/plot level to the ecosystem and region; (3) improvements of mortality risk predictions based on both empirical and mechanistic insights; and (4) a global monitoring network of forest mortality. In light of recent and anticipated large forest die-off events such a research agenda is timely and needed to achieve scientific understanding for realistic predictions of drought-induced tree mortality. The implementation of a sustainable network will require support by stakeholders and political authorities at the international level.
293 citations