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Conifer regeneration following stand-replacing wildfire varies along an elevation gradient in a ponderosa pine forest, Oregon, USA
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Climate change is expected to increase disturbances such as stand-replacing wildfire in many ecosystems, which have the potential to drive rapid turnover in ecological communities. Ecosystem recovery, and therefore maintenance of critical structures and functions (resilience), is likely to vary across environmental gradients such as moisture availability, but has received little study. We examined conifer regeneration a decade following complete stand-replacing wildfire in dry coniferous forests spanning a 700 m elevation gradient where low elevation sites had relatively high moisture stress due to the combination of high temperature and low precipitation. Conifer regeneration varied strongly across the elevation gradient, with little tree regeneration at warm and dry low elevation sites. Logistic regression models predicted rapid increases in regeneration across the elevation gradient for both seedlings of all conifer species and ponderosa pine seedlings individually. This pattern was especially pronounced for well-established seedlings (P38 cm in height). Graminoids dominated lower elevation sites following wildfire, which may have added to moisture stress for seedlings due to competition for water. These results suggest moisture stress can be a critical factor limiting conifer regeneration following stand- replacing wildfire in dry coniferous forests, with predicted increases in temperature and drought in the coming century likely to increase the importance of moisture stress. Strongly moisture limited forested sites may fail to regenerate for extended periods after stand-replacing disturbance, suggesting these sites are high priorities for management intervention where maintaining forests is a priority.
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Cumulative Effects of Fire and Fuels Management on Stream Water Quality and Ecosystem Dynamics
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Prescribed fires and wildland fire-use are increasingly important management tools used to reduce fuel loads and restore the ecological integrity of western forests. Although a basic understanding of the effects of fire on aquatic ecosystems exists, the cumulative and possibly synergistic effects of wildfire following prescribed fire are unknown. Wildfires following prescribed fire may produce different burn severities and effects on riparian and stream ecosystems than wildfires in fire suppressed forests (e.g., fires absent >70 yrs) or prescribed fires alone. The goal of this study was to quantify and compare the effects of wildfire on stream and riparian ecosystems under three fire management practices: (1) wildfire following prescribed fire, (2) wildfire in fire suppressed forests, and (3) wildfire occurring at historic fire return intervals. We compared 6-7 years (2001-2006/07) of stream and riparian data collected prior to two large wildfire events to 3 years (2008-2010) of similar data collected after wildfire in catchments along the South Fork Salmon River and Big Creek in central Idaho. Here we report our preliminary findings on riparian- and catchment-level burn severity patterns, riparian forest structure, hydrology, amphibians, aquatic macroinvertebrates, periphyton, and instream habitat, including temperature, chemistry, substrate, sedimentation, and large woody debris. We found that the management practice of prescribed fire treatment prior to wildfire significantly reduced wildfire burn severity patterns in treated catchments relative to untreated catchments. This reduction in burn severity appeared to reduce wildfire effects on stream and riparian ecosystems rather than cause cumulative effects of prescribed fire plus wildfire. Instead, we found that the effects of natural inter-annual variability in stream flow and stochastic disturbances, such as debris flows and channel scouring events, are the dominant drivers of change in stream and riparian habitats in this region, with fire management practices playing a much smaller role.
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Climate change and disruptions to global fire activity
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Future disruptions to fire activity will threaten ecosystems and human well-being throughout the world, yet there are few fire projections at global scales and almost none from a broad range of global climate models (GCMs). Here we integrate global fire datasets and environmental covariates to build spatial statistical models of fire probability at a 0.58 resolution and examine environmental controls on fire activity. Fire models are driven by climate norms from 16 GCMs (A2 emissions scenario) to assess the magnitude and direction of change over two time periods, 2010–2039 and 2070–2099. From the ensemble results, we identify areas of consensus for increases or decreases in fire activity, as well as areas where GCMs disagree. Although certain biomes are sensitive to constraints on biomass productivity and others to atmospheric conditions promoting combustion, substantial and rapid shifts are projected for future fire activity across vast portions of the globe. In the near term, the most consistent increases in fire activity occur in biomes with already somewhat warm climates; decreases are less pronounced and concentrated primarily in a few tropical and subtropical biomes. However, models do not agree on the direction of near- term changes across more than 50% of terrestrial lands, highlighting major uncertainties in the next few decades. By the end of the century, the magnitude and the agreement in direction of change are projected to increase substantially. Most far-term model agreement on increasing fire probabilities (;62%) occurs at mid- to high-latitudes, while agreement on decreasing probabilities (;20%) is mainly in the tropics. Although our global models demonstrate that long-term environmental norms are very successful at capturing chronic fire probability patterns, future work is necessary to assess how much more explanatory power would be added through interannual variation in climate variables. This study provides a first examination of global disruptions to fire activity using an empirically based statistical framework and a multi-model ensemble of GCM projections, an important step toward assessing fire-related vulnerabilities to humans and the ecosystems upon which they depend.
Key words: climatic constraints; ensemble model uncertainty; flammability; global climate models (GCM); GCM agreement; global fire probabilities; resources to burn; spatial statistical models; species distribution models.
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Characterizing Fire-on-Fire interactions in three Large Wilderness areas
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The interaction of fires, where one fire burns into another recently burned area, is receiving increased attention from scientists and land managers wishing to describe the role of fire scars in affecting landscape pattern and future fire spread. Here, we quantify fire-on- fire interactions in terms of frequency, size, and time-since-previous fire (TSPF) in three large wilderness areas in Montana and Idaho, USA, from 1984 to present, using spatially consistent large fire perimeter data from the Monitoring Trends in Burn Severity (MTBS) dataset. The analysis is supplemented with less consistent fire perimeter data from a re- gional fire atlas in order to examine the potential role played by smaller fires in fire-on-fire interactions. We compare current rates of burning to existing estimates using the natural fire rotation (NFR) to determine whether recent fire activity falls within established historical ranges. We also compare actual fires to randomly located fires to establish whether the frequency and size of re-burns differ by chance. Finally, we systematically classify shared fire edges as fire-stopping or breached to quantify the effect of previous fires on subsequent fire spread. In total, more than half of the Frank Church, one-quarter of the Bob Marshall, and fifteen percent of the Selway-Bitterroot wilderness areas have burned since 1984. Area burned within each of the study areas yielded NFRs that are consistent with results derived from fire atlas and tree-ring research studies. The data show that re- burning occurs less frequently than chance in the Frank Church Wilderness Area, perhaps less frequently in the Bob Marshall Wilderness Area, and the same as chance in the Selway-Bitterroot Wilderness Area. In each of the study areas, the total amount of edge at which a fire met another fire was less than three percent of the total available perimeter. However, ~80% of the total edge encountered was breached, resulting in fire spreading onto previously burned landscapes and re-burning at least 40 ha. Year-to-year variability in re-burn occurrence was high, and the size of re-burns was typically small, implying a general resistance to re-burning, but the preponderance of small patches resulting from fire interactions has perhaps significant ecological implications. There was a systematic decrease in the frequency of small to medium sized re-burns (40 ha to 405 ha) as time be- tween fires increased in all three wilderness areas. The frequency of large re-burns in- creased with time in the Frank Church wilderness area, but this trend was not apparent in the other two wilderness areas. Overall, fire-on-fire interactions show a high degree of complexity, making direct comparisons between the three wilderness areas difficult, but the evidence suggests that large wildfires generally inhibit the spread of subsequent fires, while small fires appear to have little impact on the spread of other fires.
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Contingent Pacific-Atlantic Ocean influence on multicentury wildfire synchrony over western North America
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Widespread synchronous wildfires driven by climatic variation, such as those that swept western North America during 1996, 2000, and 2002, can result in major environmental and societal impacts. Understanding relationships between continental-scale patterns of drought and modes of sea surface temperatures (SSTs) such as El Nin ̃o-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) may explain how interannual to multidecadal variability in SSTs drives fire at continental scales. We used local wildfire chronologies recon- structed from fire scars on tree rings across western North America and independent reconstructions of SST developed from tree-ring widths at other sites to examine the relationships of multicentury patterns of climate and fire synchrony. From 33,039 annually resolved fire-scar dates at 238 sites (the largest paleofire record yet assembled), we examined forest fires at regional and subconti- nental scales. Since 1550 CE, drought and forest fires covaried across the West, but in a manner contingent on SST modes. During certain phases of ENSO and PDO, fire was synchronous within broad subregions and sometimes asynchronous among those re- gions. In contrast, fires were most commonly synchronous across the West during warm phases of the AMO. ENSO and PDO were the main drivers of high-frequency variation in fire (interannual to decadal), whereas the AMO conditionally changed the strength and spatial influence of ENSO and PDO on wildfire occurrence at multidecadal scales. A current warming trend in AMO suggests that we may expect an increase in widespread, synchronous fires across the western U.S. in coming decades.
Atlantic Multidecadal Oscillation El Nino Southern Oscillation fire history network ocean warming Pacific Decadal Oscillation
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CLIMATE’S SMOKY SPECTRE
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With their focus on greenhouse gases, atmospheric scientists have largely overlooked lowly soot particles. But black carbon is now a hot topic among researchers and politicians.
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Carbon loss from an unprecedented Arctic tundra wildfire
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Arctic tundra soils store large amounts of carbon (C) in organic soil layers hundreds to thousands of years old that insulate, and in some cases maintain, permafrost soils1,2. Fire has been largely absent from most of this biome since the early Holocene epoch3, but its frequency and extent are increasing, probably in response to climate warming4. The effect of fires on the C balance of tundra landscapes, however, remains largely unknown. The Anaktuvuk River fire in 2007 burned 1,039 square kilometres of Alaska’s Arctic slope, making it the largest fire on record for the tundra biome and doubling the cumulative area burned since 1950 (ref. 5). Here we report that tundra ecosystems lost 2,016 6 435 g C m22 in the fire, an amount two orders of magnitude larger than annual net C exchange in undisturbed tundra6. Sixty per cent of this C loss was from soil organic matter, and radiocarbon dating of residual soil layers revealed that the maximum age of soil C lost was 50 years. Scaled to the entire burned area, the fire released approximately 2.1 teragrams of C to the atmosphere, an amount similar in magnitude to the annual net C sink for the entire Arctic tundra biome averaged over the last quarter of the twentieth century7. The mag- nitude of ecosystem C lost by fire, relative to both ecosystem and biome-scale fluxes, demonstrates that a climate-driven increase in tundra fire disturbance may represent a positive feedback, potentially offsetting Arctic greening 8 and influencing the net C balance of the tundra biome.
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Coupling of Vegetation Growing Season Anomalies and Fire Activity with Hemispheric and Regional-Scale Climate Patterns in Central and East Siberia
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An 18-yr time series of the fraction of absorbed photosynthetically active radiation (fAPAR) taken in by
the green parts of vegetation data from the NOAA Advanced Very High Resolution Radiometer
(AVHRR) instrument series was analyzed for interannual variations in the start, peak, end, and length of
the season of vegetation photosynthetic activity in central and east Siberia. Variations in these indicators of
seasonality can give important information on interactions between the biosphere and atmosphere. A
second-order local moving window regression model called the “camelback method” was developed to
determine the dates of phenological events at subcontinental scale. The algorithm was validated by comparing
the estimated dates to phenological field observations. Using spatial correlations with temperature
and precipitation data and climatic oscillation indices, two geographically distinct mechanisms in the system
of climatic controls of the biosphere in Siberia are postulated: central Siberia is controlled by an “Arctic
Oscillation–temperature mechanism,” while east Siberia is controlled by an “El Niño–precipitation mechanism.”
While the analysis of data from 1982 to 1991 indicates a slight increase in the length of the growing
season for some land-cover types due to an earlier beginning of the growing season, the overall trend from
1982 to 1999 is toward a slightly shorter season for some land-cover types caused by an earlier end of season.
The Arctic Oscillation tended toward a more positive phase in the 1980s leading to enhanced high pressure
system prevalence but toward a less positive phase in the 1990s. The results suggest that the two mechanisms
also control the fire regimes in central and east Siberia. Several extreme fire years in central Siberia were
associated with a highly positive Arctic Oscillation phase, while several years with high fire damage in east
Siberia occurred in El Niño years. An analysis of remote sensing data of forest fire partially supports this
hypothesis
VOLUME 20
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A new, global, multi-annual (2000–2007) burnt area product at 1 km resolution Vol. 35
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This paper reports on the development and validation
of a new, global, burnt area product. Burnt areas are
reported at a resolution of 1 km for seven fire years (2000 to
2007). A modified version of a Global Burnt Area (GBA)
2000 algorithm is used to compute global burnt area. The
total area burnt each year (2000– 2007) is estimated to be
between 3.5 million km2 and 4.5 million km2
. The total
amount of vegetation burnt by cover type according to the
Global Land Cover (GLC) 2000 product is reported.
Validation was undertaken using 72 Landsat TM scenes
was undertaken. Correlation statistics between estimated
burnt areas are reported for major vegetation types. The
accuracy of this new global data set depends on vegetation
type.
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Don't Blame the Beetles
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Bark beetles have devastated western forests, but that may not mean more severe fires.
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