143 research outputs found
Fire risk assessment of the western portion of the central hardwoods forest region
Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 25, 2010).Ph. D. University of Missouri--Columbia 2008.Vita.Dissertation advisor: Dr. Richard P. Guyette.The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file.This study examined how fire risk, a combination of fuels conditions and fire probabilities, varied across a large portion of Missouri, Illinois, and Indiana. Case studies were conducted to evaluate the fuel loading variability in Missouri Ozark forests, determine the temporal variability in fuel accumulation rates, and quantify the role of topographic roughness in fire regimes. Using knowledge gained from these case studies two regional scale studies were conducted describing 1) variability in fuel loading and hazard and, 2) fire probabilities. Overall, litter hazard appeared to be relatively homogeneous throughout the study area with greatest levels attained in southeastern Missouri. Month of year and drought condition are likely the most important parameters concerning fuel hazard. For the fire probability study a large set of fire occurrence records (> 12,000) for the period 1986 to 2008 were used to develop a predictive model of fire probability. The fire probability model showed fire probabilities to be substantially greater in the southern Ozark Highlands compared to the northern Ozarks and most of Illinois and Indiana. Areas of highest fire risk were identified as being primarily located on Mark Twain National Forest lands. The model appears to have captured much of the variability observed in the modern fire locations, however likely did not characterize the variability associated with known cultural patterns related to fires.Includes bibliographical reference
The Age and Density of Ancient and Modern Oak Wood in Streams and Sediments
Large wood of oak trees (Quercus spp.) has resided in the streams and sediments of north Missouri, USA for many thousands of years. This
wood affords the opportunity to compare a chronosequence of differences in wood density over a very long period. We analyzed the relationship between the age (residence time) and density of heartwood from oak boles using tree-ring and 14C dating methods and discuss their implications. The residence time of large oak wood (> 25 cm diameter) sampled
in the streams and sediments ranged from less than 14 years to more than 12,320 years. The oak wood ranged in density from 0.82 g cm-3 for a tree that had recently fallen into the stream to 0.14 g cm-3 for ancient oak wood. Two regression equations relate age (residence time) and density of oak wood and explain 88 percent of the variance in the dependent variables. Equation 1, heartwood density = age, can be used for studies in carbon cycling, wood as invertebrate habitat, or other questions related to the density and ecology of wood in streams such as wood
retention and export. Equation 2, age = heartwood density, can be used for estimating when oak wood was formed on a very coarse scale over many thousands of years
Risk Analysis Associated with Loss of Toxic Gases During Orion Landing and Recovery Operations
Mission, landing and recovery operations for the Orion crew module involve reentry into the Earth's atmosphere and the deployment of three Nomex parachutes to slow the descent before landing along the west coast of the United States. Orion may have residual fuel (hydrazine, N2H4) or coolant (ammonia, NH3) on board which are both highly toxic to crew in the event of exposure. These risks were evaluated using a first principles analysis approach through fluid dynamics modeling. Plume calculations were first performed with the ANSYS Fluent computational fluid dynamics code. Data were then extracted at locations relevant to crew safety such as the snorkel fan inlet and the egress hatch. Mixing calculations were performed to quantify exposure concentrations within the crew bay before and during egress and departure. Finally, results included herein were used to inform the Orion post-landing Concept of Operations (ConOps) so that strategies could be formulated to maintain crew safety in the event of the loss of fuel or coolant
Climate forcing of regional fire years in the upper Great Lakes Region, USA
Background. Drivers of fire regimes vary among spatial scales, and fire history reconstructions are often limited to stand scales, making it difficult to partition effects of regional climate forcing versus individual site histories. Aims. To evaluate regional-scale historical fire regimes over 350 years, we analysed an extensive fire-scar network, spanning 240 km across the upper Great Lakes Region in North America. Methods. We estimated fire frequency, identified regionally widespread fire years (based on the fraction of fire-scarred tree samples, fire extent index (FEI), and synchronicity of fire years), and evaluated fire seasonality and climate-fire relationships. Key results. Historically, fire frequency and seasonality were variable within and among Great Lakes' ecoregions. Climate forcing at regional scales resulted in synchronised fires, primarily during the late growing season, which were ubiquitous across the upper Great Lakes Region. Regionally significant fire years included 1689, 1752, 1754, 1791, and 1891. Conclusions. We found significant climate forcing of region-wide fire regimes in the upper Great Lakes Region. Implications. Historically, reoccurring fires in the upper Great Lakes Region were instrumental for shaping and maintaining forest resilience. The climate conditions that helped promote widespread fire years historically may be consistent with anticipated climate-fire interactions due to climate change
Robust Projections of Future Fire Probability for the Conterminous United States
Globally increasing wildfires have been attributed to anthropogenic climate change. However, providing decision makers with a clear understanding of how future planetary warming could affect fire regimes is complicated by confounding land use factors that influence wildfire and by uncertainty associated with model simulations of climate change. We use an ensemble of statistically downscaled Global Climate Models in combination with the Physical Chemistry Fire Frequency Model (PC2FM) to project changing potential fire probabilities in the conterminous United States for two scenarios representing lower (RCP 4.5) and higher (RCP 8.5) greenhouse gas emission futures. PC2FM is a physically-based and scale-independent model that predicts mean fire return intervals from both fire reactant and reaction variables, which are largely dependent on a locale\u27s climate. Our results overwhelmingly depict increasing potential fire probabilities across the conterminous US for both climate scenarios. The primary mechanism for the projected increases is rising temperatures, reflecting changes in the chemical reaction environment commensurate with enhanced photosynthetic rates and available thermal molecular energy. Existing high risk areas, such as the Cascade Range and the Coastal California Mountains, are projected to experience greater annual fire occurrence probabilities, with relative increases of 122% and 67%, respectively, under RCP 8.5 compared to increases of 63% and 38% under RCP 4.5. Regions not currently associated with frequently occurring wildfires, such as New England and the Great Lakes, are projected to experience a doubling of occurrence probabilities by 2100 under RCP 8.5. This high resolution, continental-scale modeling study of climate change impacts on potential fire probability accounts for shifting background environmental conditions across regions that will interact with topographic drivers to significantly alter future fire probabilities. The ensemble modeling approach presents a useful planning tool for mitigation and adaptation strategies in regions of increasing wildfire risk
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Spring temperature responses of oaks are synchronous with North Atlantic conditions during the last deglaciation
Paleoclimate proxies based on the measurement of xylem cell anatomy have rarely been developed across the temperature range of a species or applied to wood predating the most recent millennium. Here we describe wood anatomy-based proxies for spring temperatures in central North America from modern bur oaks (Quercus macrocarpa Michx.). The strong coherence of temperature signals across the species range supports the use of these proxies across thousands of years of climatic change. We also used 79 subfossil oak log cross sections from northern Missouri, ¹⁴C-dated to 9.9-13.63 ka (ka is 1000 cal yr BP), to assess the frequency of oak deposition into alluvial sediments and a subset of these oaks for a wood anatomy-based reconstruction of spring paleotemperatures. Temperatures during the Younger Dryas cold period (YD) were up to 3.5 degrees C lower than modern temperatures for that region, equivalent to or lower than those experienced at the northern edge of the modern species range. Compared to extant oaks growing at much higher [CO₂], subfossil oaks had greater vessel frequencies. Besides very low theoretical (or estimated) xylem conductivity near the beginning of the oak record near 13.6 ka, vessel frequencies greater than modern trees compensated for reduced vessel dimensions so that theoretical xylem conductivity was consistently above that of modern trees at the cold northern sites. Significant correlations were found between the frequency of ¹⁴C-dated oaks and either delta δ¹⁸O from the NGRIP (North Greenland Ice Core Project) ice core or from the Cariaco grayscale marine-sediment record from the southern Caribbean sea. Oak deposition into alluvial sediments during the YD was significantly lower than expected given the average sample depth of oaks from 9.9 to 13.6 ka. Reduced oak deposition during the YD suggests that an abrupt shift in climate reduced oak populations across the region and/or changed the rates of channel movement across drainages.Keywords: Pleistocene, Quercus macrocarpa, Holocene, Pre-Boreal, Younger Dryas, Radiocarbon, Wood anatomy, Great Plains\, USA, Phenology, Bolling-Allerod, Xylem, Bur oa
Advancing dendrochronological studies of fire in the United States
© 2018 by the authors. Licensee MDPI, Basel, Switzerland. Dendroecology is the science that dates tree rings to their exact calendar year of formation to study processes that influence forest ecology (e.g., Speer 2010 [1], Amoroso et al., 2017 [2]). Reconstruction of past fire regimes is a core application of dendroecology, linking fire history to population dynamics and climate effects on tree growth and survivorship. Since the early 20th century when dendrochronologists recognized that tree rings retained fire scars (e.g., Figure 1), and hence a record of past fires, they have conducted studies worldwide to reconstruct [2] the historical range and variability of fire regimes (e.g., frequency, severity, seasonality, spatial extent), [3] the influence of fire regimes on forest structure and ecosystem dynamics, and [4] the top-down (e.g., climate) and bottom-up (e.g., fuels, topography) drivers of fire that operate at a range of temporal and spatial scales. As in other scientific fields, continued application of dendrochronological techniques to study fires has shaped new trajectories for the science. Here we highlight some important current directions in the United States (US) and call on our international colleagues to continue the conversation with perspectives from other countries
A dynamic leaf gas-exchange strategy is conserved in woody plants under changing ambient CO2: evidence from carbon isotope discrimination in paleo and CO2 enrichment studies
Rising atmospheric [CO2 ], ca , is expected to affect stomatal regulation of leaf gas-exchange of woody plants, thus influencing energy fluxes as well as carbon (C), water and nutrient cycling of forests. Researchers have proposed various strategies for stomatal regulation of leaf gas-exchange that include maintaining a constant leaf internal [CO2 ], ci , a constant drawdown in CO2 (ca - ci ), and a constant ci /ca . These strategies can result in drastically different consequences for leaf gas-exchange. The accuracy of Earth systems models depends in part on assumptions about generalizable patterns in leaf gas-exchange responses to varying ca . The concept of optimal stomatal behavior, exemplified by woody plants shifting along a continuum of these strategies, provides a unifying framework for understanding leaf gas-exchange responses to ca . To assess leaf gas-exchange regulation strategies, we analyzed patterns in ci inferred from studies reporting C stable isotope ratios (δ(13) C) or photosynthetic discrimination (∆) in woody angiosperms and gymnosperms that grew across a range of ca spanning at least 100 ppm. Our results suggest that much of the ca -induced changes in ci /ca occurred across ca spanning 200 to 400 ppm. These patterns imply that ca - ci will eventually approach a constant level at high ca because assimilation rates will reach a maximum and stomatal conductance of each species should be constrained to some minimum level. These analyses are not consistent with canalization towards any single strategy, particularly maintaining a constant ci . Rather, the results are consistent with the existence of a broadly conserved pattern of stomatal optimization in woody angiosperms and gymnosperms. This results in trees being profligate water users at low ca , when additional water loss is small for each unit of C gain, and increasingly water-conservative at high ca , when photosystems are saturated and water loss is large for each unit C gain. This article is protected by copyright. All rights reserved.Rising atmospheric [CO2], c(a), is expected to affect stomatal regulation of leaf gas-exchange of woody plants, thus influencing energy fluxes as well as carbon (C), water, and nutrient cycling of forests. Researchers have proposed various strategies for stomatal regulation of leaf gas-exchange that include maintaining a constant leaf internal [CO2], c(i), a constant drawdown in CO2 (c(a)-c(i)), and a constant c(i)/c(a). These strategies can result in drastically different consequences for leaf gas-exchange. The accuracy of Earth systems models depends in part on assumptions about generalizable patterns in leaf gas-exchange responses to varying c(a). The concept of optimal stomatal behavior, exemplified by woody plants shifting along a continuum of these strategies, provides a unifying framework for understanding leaf gas-exchange responses to c(a). To assess leaf gas-exchange regulation strategies, we analyzed patterns in c(i) inferred from studies reporting C stable isotope ratios (C-13) or photosynthetic discrimination () in woody angiosperms and gymnosperms that grew across a range of c(a) spanning at least 100ppm. Our results suggest that much of the c(a)-induced changes in c(i)/c(a) occurred across c(a) spanning 200 to 400ppm. These patterns imply that c(a)-c(i) will eventually approach a constant level at high c(a) because assimilation rates will reach a maximum and stomatal conductance of each species should be constrained to some minimum level. These analyses are not consistent with canalization toward any single strategy, particularly maintaining a constant c(i). Rather, the results are consistent with the existence of a broadly conserved pattern of stomatal optimization in woody angiosperms and gymnosperms. This results in trees being profligate water users at low c(a), when additional water loss is small for each unit of C gain, and increasingly water-conservative at high c(a), when photosystems are saturated and water loss is large for each unit C gain
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