B43E-01 13:40h
Hierarchical Controls of Fire Weather and Fire Climate in the Western United States
The incidence of wildfire in the western United States is governed by climatological, meteorological, and ecological controls that operate across a range of spatial and temporal scales, from hemispheric to landscape, and from decadal (and longer) to diurnal. These controls are responsible for fire weather (i.e., the conditions responsible for the ignition, spread, and suppression of individual fires) and fire climate (i.e., the conditions responsible for the severity of a particular fire season). Interannual, seasonal, and monthly anomalies of Pacific Ocean SSTs and North American land-surface conditions produce anomalous components of atmospheric circulation, and variations in airmass distributions, moisture flux, large-scale vertical motions and precipitation fields on monthly-to-daily time scales. The synoptic situations that result from these circulation configurations determine the meteorological conditions that are directly responsible for the outbreak of fires on daily-to-diurnal time scales, such as the surface water- and energy-balances, atmospheric stability, lightning and wind. Fire outbreaks over the West often form a coherent pattern associated with the temporal and spatial dynamics of circulation. The severity of a particular fire season is largely determined by the integration across time spans of seasons to months of the water-balance related variables described above, which determine soil-moisture status, as well as by the condition of the vegetation, which determines fuel load and flammability. We are investigating these hierarchal controls of wildfires using a combination of observations (including monthly-to-decadal averages of atmospheric circulation indices and surface temperature, precipitation and soil moisture-related variables), reanalysis data sets, and simulations using a GCM/regional climate model/dynamic global vegetation model combination.
http://geography.uoregon.edu/envchange/
B43E-02 INVITED 13:55h
Fire and Climate Change in Boreal Forests
Fire is the major stand-renewing agent for much of the circumboreal forest, and greatly influences the structure and function of boreal ecosystems from regeneration through mortality. Current estimates are that an average of 5-15 million hectares burn annually in boreal forests, almost exclusively in Siberia, Canada and Alaska. There is a growing global awareness of the importance and vulnerability of the boreal region to projected future climate change. Fire activity is strongly influenced by four factors - weather/climate, vegetation \(fuels\), natural ignition agents and humans. Climate and weather are strongly linked to fire activity which suggests that the fire regime will respond rapidly to changes in climate. Recent results suggest that area burned by fire is related to temperature and fuel moisture. The climate of the northern hemisphere has been warming due to an influx of radiatively active gases \(carbon dioxide, methane etc.\) as a result of human activities. This altered climate, modelled by General Circulation Models \(GCMs\), indicates a profound impact on fire activity in the circumboreal forest. Recent results using GCMs suggest that in many regions fire weather/fire danger conditions will be more severe, area burned will increase, people-caused and lightning-caused ignitions will increase, fire seasons will be longer and the intensity and severity of fires will increase. This increase in fire activity may lead to a positive feedback cycle with the increased release of greenhouse gases. Although a run away scenario is unlikely as changes in vegetation would limit the positive feedback cycle. Changes in fire activity as a result of climate change could have a greater and more immediate impact on vegetation distribution and abundance as compared to the direct impact of climate change.
B43E-03 14:10h
Fire and Climate: Past, Present (and Future?)
Absolutely dated fire histories based on fire scars recorded in tree rings provide evidence of the relationships between fire and climate over the past several centuries. Fire/climate relationships demonstrated in paleo-records offer some predictive capability for not only seasonal to annual wildfire forecasts but also some indication where fire regimes and ecosystems might be heading under scenarios for current and future climate change. Broad-scale networks of fire-scar chronologies have been developed from forests across most of western North America. These chronologies, when compared to independently derived tree-ring and other proxy based reconstructions of hydroclimate and circulation indices, exhibit strong scaling with regionally synchronous fire years driven by broad-scale droughts and synoptic features such as the El Niño- Southern Oscillation (ENSO). This talk will discuss methods for reconstructing fire histories and fire climatologies from tree-ring data, how climate forcing affected fire occurrences in the past and what this may tell us about the future, and what effects that several decades of fire exclusion and changes in forest structure may have on future fire regimes and ecosystem responses.
B43E-04 14:25h
A Long Term Perspective on Decadal Variability in Climate and Wildfire in the Western United States
Despite progress in reconstructing the western United States' paleo- fire and climate regimes, placing recent fire seasons into the context of past variability is difficult. Management practices have altered ecosystems, and modern records and paleo reconstructions of wildfire seldom overlap. Recent work helped to bridge that gap, using statistical models trained on 20th century fire and drought histories (1916 to 1978) to successfully reproduce a reconstruction of annual wildfire extent derived from a fire scar network for the U.S. Southwest for 1701 to 1900. We found that managed wildfire regimes still contained strong climate signals similar to paleofire reconstructions. Moreover, El Nino-Southern Oscillation and Pacific Decadal Oscillation patterns appeared to modulate western U.S. fire activity. Using Cook et al.'s newly available drought reconstructions for North America, this analysis now extends to a minimum of 1000 years the period covered by our statistical reconstruction of western U.S. wildfire. We analyze the decadal variability in reconstructed fire regimes over this longer period, and compare the results to available ENSO and PDO reconstructions. The validation of statistical reconstructions of wildfire area burned against fire scar networks is expanded to include sites in California, the Pacific Northwest, and Rocky Mountains. We extend our statistical reconstruction through 2003 and compare the recent increase in observed annual area burned to the increases in both modeled area burned and the land area protected against wildfires in the western United States since the 1970s. Based on this analysis, we place the recent very active fire seasons experienced in the West into the perspective of the past 1000 years of climate variability, and demonstrate an application of long-term climate-fire relationships to budgeting for fire suppression in the USDA Forest Service.
B43E-05 14:40h
Scaling Fire Regimes in Space and Time.
Spatial and temporal variability are important properties of the forest fire regimes of coniferous forests of southwestern North America. We use a variety of analytical techniques to examine scaling in a surface fire regime in the Jemez Mountains of northern New Mexico, USA, based on an original data set collected from Monument Canyon Research Natural Area (MCN). Spatio-temporal scale dependence in the fire regime can be analyzed quantitatively using statistical descriptors of the fire regime, such as fire frequency and mean fire interval. We describe a theory of the event-area (EA) relationship, an extension of the species-area relationship for events distributed in space and time; the interval-area (IA) relationship, is a related form for fire intervals. We use the EA and IA to demonstrate scale dependence in the MCN fire regime. The slope and intercept of these functions are influenced by fire size, frequency, and spatial distribution, and thus are potentially useful metrics of spatio-temporal synchrony of events in the paleofire record. Second, we outline a theory of fire interval probability, working from first principles in fire ecology and statistics. Fires are conditional events resulting from the interaction of multiple contingent factors that must be satisfied for an event to occur. Outcomes of this kind represent a multiplicative process for which a lognormal model is the limiting distribution. We examine the application of this framework to two probability models, the Weibull and lognormal distributions, which can be used to characterize the distribution of fire intervals over time. Lastly, we present a general model for the collector's curve, with application to the theory and effects of sample size in fire history. Sources of uncertainty in fire history can be partitioned into an error typology; analytical methods used in fire history (particularly the formation of composite fire records) are designed to minimize certain types of error in inference. We describe a theory of the collector's curve based on accumulation of sets of discrete events and the serial probability of recording a fire as a function of sample size. Using the Monument Canyon data set, we develop a nonlinear regression method to correct for differences in sample size among composite fire records. All measures of the fire regime in the MCN fire record reflected sensitivity to sample size, but these differences can be corrected at least in part by applying the regression correction, which can increase confidence in quantitative estimates of the fire regime.
B43E-06 14:55h
Spatiotemporal Dynamics of Fire in Whitebark Pine Stands on two Mountains in the Lolo National Forest, Montana, USA.
Whitebark pine (Pinus albicaulis) is a long-lived tree species that exists throughout high elevation and treeline forest communities of western North America. It is the foundation of a diminishing ecosystem that supports Clark's nutcrackers (Nucifraga columbiana), red squirrels (Tamiasciurus hudsonicus), grizzly bears (Ursus arctos), and black bears (U. americana). Several factors are directly linked to the decline of the whitebark pine ecosystem: mortality from recent and widespread mountain pine beetle (Dendroctonus ponderosae) outbreaks, infestation by the invasive white pine blister rust (Cronartium ribicola, an exotic fungal canker that weakens and eventually kills white pines), and fire suppression that may have altered the historic fire regime and enabled fire-intolerant tree species to encroach upon whitebark pine stands. The synergistic effects of these factors have led to a dramatic decline in whitebark pine communities throughout its native range, and in response land managers and conservationists have called for research to better understand the ecological dynamics of this little studied ecosystem. My research uses dendrochronology to investigate the fire history of whitebark pine stands on three mountains in the Lolo National Forest, Montana, via fire-scar and age structure analyses. I present here the results from the fire-scar analyses from Morrell Mountain where I obtained 40 cross sections from dead and down whitebark pines. Individual tree mean fire return intervals (MFRI) range from 33 to 119 years, with a stand MFRI of 49 years that includes fire scars dating to the 16th century. Fire events scarred multiple trees in AD 1754, 1796, and 1843, indicating a mixed-severity fire regime. The majority of the samples recorded a frost event in AD 1601, perhaps evidence of the AD 1600 eruption of Mt. Huaynapatina in the Peruvian Andes. My research not only provides an historical framework for land managers, but also provides an opportunity to examine long-term spatiotemporal dynamics of fire activity over the northern Rocky Mountains in terms of climate change and atmospheric teleconnections.
B43E-07 INVITED 15:10h
Fire Cycles on the Northern Great Plains and Their Relation to Prairie Drought
Drought is a naturally occurring, recurrent phenomenon that has historically gripped large regions of the United States, often with catastrophic consequences. Human insight into the duration, frequency, and dynamics of drought is largely limited to short-term observation. For example, the "Dust Bowl" of the 1930's in the central plains is one of the most vivid cases of prolonged drought in the USA and yet it persisted for less than a decade. To circumnavigate this limited perspective, we employed a paleoenvironmental approach to better characterize landscape response to prairie droughts and specifically document fire response to droughts. Two long sediment cores were collected from Kettle and Brush lakes in the Northern Great Plains (NGP) and age-depth models were developed for the cores by fitting locally weighted loess curves to AMS radiocarbon dates. The cores were continuously sub-sampled at high resolution (1 cm) for particulate charcoal, pollen, sediment mineralogy, and loss-on-ignition. In contrast to recent human observation, spectral and wavelet analyses reveal that multi-decadal to centennial drought cycles have persisted on the northern plains for much of the last ca. 10,000 years, though there were intervals where the cycles were muted, further compounding the dynamics of climate on the plains. In the latest Holocene interval, 160-year fire and drought cycles are clearly denoted. Fires are more common during the wet phases of the drought cycles because moist conditions foster increased grass productivity, resulting in greater fuel loads. In contrast, forbs expanded during the drier periods, limiting fuel loads which resulted in less fire. The charcoal data reveal three general Holocene fire intervals on the NGP associated with millennial-scale changes in climate. In general, the incidence of fire was greater in the early- and late-Holocene with less fire during the warm dry mid-Holocene.
B43E-08 15:25h
Holocene changes in fire frequency in north-western boreal forest of Quebec, Canada
Changes in fire frequency were reconstructed for the last 8,000 yrs in the boreal forest of north-western Quebec using dendrochronology and charcoal records in lake sediments and organic soils. During the middle Holocene, fire frequency was characterized by a long period of low frequency between ca. 7500 and 2000 yrs BP. The high fire frequency during the last 2000 years was interrupted by periods of lower fire frequency notably since the end of the Little Ice Age ca 1850 AD. Climate appears to be the main process triggering fire. Simulations using GCMs (2xCO2 scenarios), buttressed by palaeoecological and dendrochronological evidence, suggest that future warming is unlikely to significantly increase fire frequency in the boreal forest of north-eastern Quebec since higher temperature appears to be associated with less frequent drought in this area. Palaeoecological and dendrochronological data clearly demonstrate the changing nature of forest ecosystem dynamics. We discuss the implications of these dynamics on disturbance-based forest management strategies