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Medieval warming initiated exceptionally large wildfire outbreaks in the Rocky Mountains
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Many of the largest wildfires in US history burned in recent decades, and climate change explains much of the increase in area burned. The frequency of extreme wildfire weather will increase with continued warming, but many uncertainties still exist about future fire regimes, including how the risk of large fires will persist as vegetation changes. Past fire-climate relationships provide an opportunity to constrain the related uncertainties, and reveal widespread burn- ing across large regions of western North America during past warm intervals. Whether such episodes also burned large portions of individual landscapes has been difficult to determine, however, because uncertainties with the ages of past fires and limited spatial resolution often prohibit specific estimates of past area burned. Accounting for these challenges in a subalpine landscape in Colorado, we estimated century-scale fire synchroneity across 12 lake- sediment charcoal records spanning the past 2,000 y. The percent- age of sites burned only deviated from the historic range of vari- ability during the Medieval Climate Anomaly (MCA) between 1,200 and 850 y B.P., when temperatures were similar to recent decades. Between 1,130 and 1,030 y B.P., 83% (median estimate) of our sites burned when temperatures increased ∼0.5 °C relative to the preceding centuries. Lake-based fire rotation during the MCA decreased to an estimated 120 y, representing a 260% higher rate of burning than during the period of dendroecological sampling (360 to −60 y B.P.). Increased burning, however, did not persist throughout the MCA. Burning declined abruptly before temperatures cooled, indicating possible fuel limitations to continued burning.
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Reform forest fire management: Agency incentives undermine policy effectiveness
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Globally, wildfire size, severity, and frequency have been increasing, as have related fatalities and taxpayer- funded firefighting costs (1). In most accessible forests, wildfire response prioritizes suppression because fires are easier and cheaper to contain when small (2). In the United States, for example, 98% of wildfires are suppressed before reaching 120 ha in size (3). But the 2% of wildfires that escape containment often burn under extreme weather conditions in fuel-loaded forests and account for 97% of fire-fighting costs and total area burned (3). Changing climate and decades of fuel accumulation make efforts to suppress every fire dangerous, expensive, and ill advised (4).
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Palaeodata-informed modelling of large carbon losses from recent burning of boreal forests
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Wildfires play a key role in the boreal forest carbon cycle(1,2), and models suggest that accelerated burning will increase boreal C emissions in the coming century (3). However, these predictions may be compromised because brief observational records provide limited constraints to model initial conditions (4). We confronted this limitation by using palaeoenvironmental data to drive simulations of long-term C dynamics in the Alaskan bo- real forest. Results show that fire was the dominant control on C cycling over the past millennium, with changes in fire frequency accounting for 84% of C stock variability. A recent rise in fire frequency inferred from the palaeorecord5 led to simulated C losses of 1.4 kg C m?2(12% of ecosystem C stocks) from 1950 to 2006. In stark contrast, a small net C sink of 0.3 kg C m?2 occurred if the past fire regime was assumed to be similar to the modern regime, as is common in models of C dynamics. Although boreal fire regimes are heterogeneous, recent trends6 and future projections (7) point to increasing fire activity in response to climate warming throughout the biome. Thus, predictions (8) that terrestrial C sinks of northern high latitudes will mitigate rising atmospheric CO2 may be over-optimistic.
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Pedoecological Modeling to Guide Forest Restoration using Ecological Site Descriptions
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the u.s. department of agriculture (usda)-natural resources conservation service (nrcs) uses an ecological site description (esd) framework to help incorporate interactions between local soil, climate, flora, fauna, and humans into schema for land management decision-making. we demonstrate esd and digital soil mapping tools to (i) estimate potential o horizon carbon (c) stock accumulation from restoring alternative ecological states in high-elevation forests of the central appalachian Mountains in west Virginia (wV), usa, and (ii) map areas in alternative ecological states that can be targeted for restoration. this region was extensively disturbed by clear-cut harvests and related fires during the 1880s through 1930s. we combined spodic soil property maps, recently linked to historic red spruce–eastern hemlock (Picea rubens–Tsuga canadensis) forest communities, with current forest inventories to provide guidance for restoration to a historic reference state. this allowed mapping of alternative hardwood states within areas of the spodic shale uplands conifer forest (scF) ecological site, which is mapped along the regional conifer-hardwood transition of the central appalachian Mountains. Plots examined in these areas suggest that many of the spruce-hemlock dominated stands in wV converted to a hardwood state by historic disturbance have lost at least 10 cm of o horizon thickness, and possibly much more. Based on this 10 cm estimate, we calculate that at least 3.74 to 6.62 tg of c were lost from areas above 880 m elevation in wV due to historic disturbance of o horizons, and that much of these stocks and related ecosystem functions could potentially be restored within 100 yr under focused management, but more practical scenarios would likely require closer to 200 yr.
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How the South Fights Fire with Fire, and What the West Can Learn
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Most years Georgia intentionally burns around a million acres of forest. That’s about 30 times the size of California’s prescribed burns. Florida performs prescribed burns over twice that much land. That’s according to data from the national interagency fire center and compiled by the non-profit Climate Central.
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