Cathy Whitlock

Montana State University, Bozeman, Montana, United States

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Publications (94)254.34 Total impact

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    ABSTRACT: Natural factors and human activity influence fire variability including changes in temperature and precipitation, increasing greenhouse gas concentrations, altering ignitions, vegetation cover and fuel availability. Ice cores archive chemical signatures of both past climate and fire activity, and understanding this interaction is increasingly important in a warming climate. The specific molecular marker levoglucosan (1,6-anhydro-ß-D-glucopyranose) can only be produced by burning woody tissue at temperatures greater than 300°C. Levoglucosan is present in the fine fraction of smoke plumes, is transported distances of thousands of kilometers, is deposited on glacier surfaces, and is detectable in both polar and mountain ice cores providing an unambiguous fire history. Here, we present a high-resolution 10,000-year levoglucosan record in the EPICA Dome C (75°06'S, 123°21'E, 3233 masl) ice core and implications for determining natural and human-caused fire variability. A recent provocative hypothesis by Ruddiman suggests that humans may have had a significant impact on the Earth's climate thousands of years ago through carbon and methane emissions originating from biomass burning associated with early agriculture. This hypothesis is centered on the observation that atmospheric carbon dioxide and methane levels recorded in ice cores increased irrespective of insolation changes beginning 7,000 to 5,000 years before present. The EDC levoglucosan record does not demonstrate augmented fire activity at 5000 and/or 7000 years ago in the Southern Hemisphere. We are currently determining Holocene levoglucosan concentrations in the NEEM, Greenland (77°27' N; 51°3'W, 2454 masl) ice core to provide a Northern Hemisphere comparison at 5000 and/or 7000 years ago. The highest EDC Holocene fire activity occurs during the past 500 years. Mean levoglucosan concentrations between 500 to 10,000 BP are approximately 50 ppt, but rise to 300 ppt at present. This substantial increase is not present in NEEM. Unlike methane and its isotopic signatures, levoglucosan is not a globally mixed marker, and these hemispheric differences are consistent with the atmospheric lifetime, sources, and transport of levoglucosan. This considerable increase in fire activity over the past 500 years is also present in Southern Hemisphere compilations of charcoal records. The EDC levoglucosan profile is most similar to regional charcoal compilations from New Zealand and southeastern Australia. Transport models demonstrate the possibility of New Zealand and Australia as major levoglucosan sources to EDC. This contemporary biomass burning increase is likely due to human activity as opposed to the Holocene background levels between 500 to 10,000 BP.
    04/2013;
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    ABSTRACT: Aim The increased incidence of large fires around much of the world in recent decades raises questions about human and non-human drivers of fire and the likelihood of increased fire activity in the future. The purpose of this paper is to outline a conceptual framework for examining where human-set fires and feedbacks are likely to be most pronounced in temperate forests world-wide and to establish and test a methodology for evaluating this framework using palaeoecological records. Location Tasmania, north-western USA, southern South America and New Zealand. Methods We outline a conceptual framework for predicting the sensitivity of ecosystems to human impacts on fire regimes and then use a circum-Pacific comparison of existing historical reconstructions of fire, climate, human settlement and vegetation to evaluate this approach. Results Previous research investigating important controls on fire activity shows that the sensitivity of temperate ecosystems to human-set fires is modulated by the frequency of natural fire occurrence, fuel moisture and fuel type and availability. Palaeoecological data from four temperate regions suggest that the effects of anthropogenic burning are greatest where fire is naturally rare, vegetation is poorly adapted to fire and fuel biomass is abundant and contiguous. Alternatively, where fire activity is naturally high and vegetation is well adapted to fire, evidence of human influence on fire and vegetation is less obvious. Main conclusions Palaeofire records suggest that the most dynamic and persistent ecosystem transitions occur where human activities increase landscape flammability through fire–vegetation feedbacks. Rapid forest transitions in biomass-rich ecosystems such as New Zealand and areas of Tasmania and southern South America illustrate how landscapes experiencing few fires can shift past tipping points to become fire-prone landscapes with new alternative stable state communities. Comparisons of palaeoecological data from different regions with similar biophysical gradients but different human settlement histories can provide new opportunities for understanding ecosystem vulnerability to fire–climate–human interactions.
    Global Ecology and Biogeography. 01/2013;
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    Global Ecology and Biogeography 01/2013; · 7.22 Impact Factor
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    ABSTRACT: Patagonian vegetation has dramatically changed in composition and distribution over the last 16,000 yr. Although patterns of vegetation change are relatively clear, our understanding of the processes that produce them is limited. High-resolution pollen and charcoal records from two lakes located at lat 41°S provide new information on the postglacial history of vegetation and fire activity at the forest–steppe ecotone, and help clarify the relative importance of local and regional drivers of late-Holocene ecological change. Our results suggest that late-glacial parkland was colonized by shrubs at ca. 11,200 cal yr BP and this vegetation persisted until 4900 cal yr BP, when increased humidity allowed for the establishment of Nothofagus forest. The late Holocene is characterized by oscillations in forest dominance largely driven by changes in humidity, possibly associated with the onset or strengthening of ENSO. In the last 4900 yr, humid periods (4900–3800 and 2850–1350 cal yr BP) have promoted Nothofagus forest, whereas drier times (3800–2850 and 1350–450 cal yr BP) have favored Austrocedrus expansion. At intermediate moisture levels, however, the lower forest supported both taxa, and fire became an important control of community composition, with severe, infrequent fires facilitating Nothofagus regeneration and high fire frequency and intensity supporting Austrocedrus.
    Quaternary Research 11/2012; 78(3):502–512. · 2.20 Impact Factor
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    ABSTRACT: Along the eastern Andes, a sharp ecotone separates steppe from North Patagonian forest dominated by Nothofagus spp. and Austrocedrus chilensis. The longitudinal position of the ecotone is largely determined by effective moisture, which in turn is partly governed by the strength and latitudinal position of the Southern Westerlies. As a result, changes in the ecotone provide an opportunity to examine past climate variations. Holocene environmental history at two sites in close proximity is inferred from pollen and high-resolution charcoal data. Prior to 9000 cal. yr BP, vegetation resembled a steppe, in accordance with widespread aridity. Fires were infrequent, likely as a consequence of fuel discontinuity associated with low vegetation cover. At 9000 cal. yr BP, forest taxa expanded into steppe and fires became frequent, indicating that summers were arid enough to support fires but winter moisture was sufficient for Nothofagus spp. to expand. A two-step increase in effective moisture is inferred for the middle Holocene. The first step occurred at 8500 cal. yr BP, as interpreted from the increase in A. chilensis in the region, probably as a consequence of an eastward migration from glacial refugia. The second step at 5500 cal. yr BP is based on a Nothofagus spp. expansion into the steppe. Steppe readvances into the forest between 5250 and 3000 cal. yr BP indicate decreased temperatures and/or effective moisture. The last 3000 years are characterized by expansions of A. chilensis and an eastward shift of the ecotone, suggesting more humid conditions. European settlement is reflected in the establishment of non-native species and disturbance-adapted taxa.
    The Holocene 11/2012; 22(11):1297-1307. · 3.22 Impact Factor
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    Proceedings of the National Academy of Sciences 07/2012; 109(34):E2243; author reply E2245-7. · 9.74 Impact Factor
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    ABSTRACT: Deciphering the evolution of global climate from the end of the Last Glacial Maximum approximately 19 ka to the early Holocene 11 ka presents an outstanding opportunity for understanding the transient response of Earth's climate system to external and internal forcings. During this interval of global warming, the decay of ice sheets caused global mean sea level to rise by approximately 80 m; terrestrial and marine ecosystems experienced large disturbances and range shifts; perturbations to the carbon cycle resulted in a net release of the greenhouse gases CO(2) and CH(4) to the atmosphere; and changes in atmosphere and ocean circulation affected the global distribution and fluxes of water and heat. Here we summarize a major effort by the paleoclimate research community to characterize these changes through the development of well-dated, high-resolution records of the deep and intermediate ocean as well as surface climate. Our synthesis indicates that the superposition of two modes explains much of the variability in regional and global climate during the last deglaciation, with a strong association between the first mode and variations in greenhouse gases, and between the second mode and variations in the Atlantic meridional overturning circulation.
    Proceedings of the National Academy of Sciences 02/2012; 109(19):E1134-42. · 9.74 Impact Factor
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    ABSTRACT: We present arguments and evidence against the hypothesis that a large impact or airburst caused a significant abrupt climate change, extinction event, and termination of the Clovis culture at 12.9 ka. It should be noted that there is not one single Younger Dryas (YD) impact hypothesis but several that conflict with one another regarding many significant details. Fragmentation and explosion mechanisms proposed for some of the versions do not conserve energy or momentum, no physics-based model has been presented to support the various concepts, and existing physical models contradict them. In addition, the a priori odds of the impact of a >4 km comet in the prescribed configuration on the Laurentide Ice Sheet during the specified time period are infinitesimal, about one in 1015. There are three broad classes of counterarguments. First, evidence for an impact is lacking. No impact craters of the appropriate size and age are known, and no unambiguously shocked material or other features diagnostic of impact have been found in YD sediments. Second, the climatological, paleontological, and archeological events that the YD impact proponents are attempting to explain are not unique, are arguably misinterpreted by the proponents, have large chronological uncertainties, are not necessarily coupled, and do not require an impact. Third, we believe that proponents have misinterpreted some of the evidence used to argue for an impact, and several independent researchers have been unable to reproduce reported results. This is compounded by the observation of contamination in a purported YD sample with modern carbon.
    01/2012: pages 13-26;
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    ABSTRACT: The last glacial-interglacial transition (LGIT; 19–9ka) was characterized by rapid climate changes and significant ecosystem reorganizations worldwide. In western Colorado, one of the coldest locations in the continental US today, mountain environments during the late-glacial period are poorly known. Yet, archaeological evidence from the Mountaineer site (2625m elev.) indicates that Folsom-age Paleoindians were over-wintering in the Gunnison Basin during the Younger Dryas Chronozone (YDC; 12.9–11.7ka). To determine the vegetation and fire history during the LGIT, and possible explanations for occupation during a period thought to be harsher than today, a 17-ka-old sediment core from Lily Pond (3208m elev.) was analyzed for pollen and charcoal and compared with other high-resolution records from the southern Rocky Mountains. Widespread tundra and Picea parkland and low fire activity in the cold wet late-glacial period transitioned to open subalpine forest and increased fire activity in the Bølling–Allerød period as conditions became warmer and drier. During the YDC, greater winter snowpack than today and prolonged wet springs likely expanded subalpine forest to lower elevations than today, providing construction material and fuel for the early inhabitants. In the early to middle Holocene, arid conditions resulted in xerophytic vegetation and frequent fire.
    Quaternary Research 01/2012; · 2.20 Impact Factor
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    ABSTRACT: The influence of substrate on long-term vegetation dynamics has received little attention, and yet nutrient-limited ecosystems have some of the highest levels of endemism in the world. The diverse geology of the Klamath Mountains of northern California (USA) allows examination of the long-term influence of edaphic constraints in subalpine forests through a comparison of vegetation histories between nutrient-limited ultramafic substrates and terrain that is more fertile. Pollen and charcoal records spanning up to 15000 years from ultramafic settings reveal a distinctly different vegetation history compared to other soil types. In non-ultramafic settings, the dominant trees and shrubs shifted in elevation in response to Holocene climate variations resulting in compositional and structural changes, whereas on ultramafic substrates changes were primarily structural, not compositional. Fire activity was similar through most of the Holocene with the exception of declines over the last 4000 years on ultramafic substrates, likely due to the reduction of understory fuels and cooler wetter conditions than in the middle Holocene. These results suggest that the tree and shrub distributions were more responsive to past climate changes on non-ultramafic substrates compared to those on ultramafic substrates. The combination of these dynamics may help explain high levels of plant diversity in the Klamath Mountains and provide insights for managing these complex ecosystems.
    Ecology 03/2011; 92(3):590-601. · 5.18 Impact Factor
  • M. J. Power, C. Whitlock, P. J. Bartlein
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    ABSTRACT: A 13,100-year-long high-resolution pollen and charcoal record from Foy Lake in western Montana is compared with a network of vegetation and fire-history records from the Northern Rocky Mountains. New and previously published results were stratified by elevation into upper and lower and tree line to explore the role of Holocene climate variability on vegetation dynamics and fire regimes. During the cooler and drier Lateglacial period, ca 13,000 cal yr BP, sparsely vegetated Picea parkland occupied Foy Lake as well as other low- and high-elevations with a low incidence of fire. During the warmer early Holocene, from ca 11,000–7500 cal yr BP, low-elevation records, including Foy, indicate significant restructuring of regional vegetation as Lateglacial Picea parkland gave way to a mixed forest of Pinus-Pseudotsuga-Larix. In contrast, upper tree line sites (ca >2000 m) supported Pinus albicaulis and/or P. monticola-Abies-Picea forests in the Lateglacial and early Holocene. Regionally, biomass burning gradually increased from the Lateglacial times through the middle Holocene. However, upper tree line fire-history records suggest several climate-driven decreases in biomass burning centered at 11,500, 8500, 4000, 1600 and 500 cal yr BP. In contrast, lower tree line records generally experienced a gradual increase in biomass burning from the Lateglacial to ca 8000 cal yr BP, then reduced fire activity until a late Holocene maximum at 1800 cal yr BP, as structurally complex mesophytic forests at Foy Lake and other sites supported mixed-severity fire regimes. During the last two millennia, fire activity decreased at low elevations as modern forests developed and the climate became cooler and wetter than before. Embedded within these long-term trends are high amplitude variations in both vegetation dynamics and biomass burning. High-elevation paleoecological reconstructions tend to be more responsive to long-term changes in climate forcing related to growing-season temperature. Low-elevation records in the NRM have responded more abruptly to changes in effective precipitation during the late Holocene. Prolonged droughts, including those between 1200 and 800 cal yr BP, and climatic cooling during the last few centuries continues to influence vegetation and fire regimes at low elevation while increasing temperature has increased biomass burning in high elevations.
    Quaternary Science Reviews 01/2011; 30(19):2520-2533. · 4.08 Impact Factor
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    Philip E Higuera, Cathy Whitlock, Josh A Gage
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    ABSTRACT: Reconstructing specific fire-history metrics with charcoal records has been difficult, in part because calibration data sets are rare. We calibrated charcoal accumulation in sediments from three medium (14–19 ha) and one large (4250 ha) lake with a 300 yr tree-ring-based fire-history reconstruction from central Yellowstone National Park (YNP) to reconstruct local fire occurrence and area burned within a 128 840 ha study area. Charcoal peaks most accurately reflected fires within 1.2–3.0 km of coring sites, whereas total charcoal accumulation correlated best with area burned within 6.0–51 km (r 2 =0.22–0.62, p<0.05). To reconstruct area burned for the entire study area, we developed a statistical model based on a composite charcoal record. The model explained 64–79% of the variability in area burned from ad 1675 to 1960 and was robust to cross-validation. Reconstructed area burned from ad 1240–1975 was significantly higher during periods including extreme annual drought (p=0.05), and area burned varied significantly at ≈ 60 yr timescales (p<0.05), similar to the variability in an independent precipitation reconstruction covering the same period. Widespread burning (>10 000 ha) occurred at 150–300 yr intervals, and at the site level, fire probability increased with stand age (composite Weibull c parameter = 1.61 [95% CI 1.36–2.54]), both suggesting that post-fire stand development played an important intermediary role between climate and fire by increasing fuel abundance and probability of fire spread. Our study illustrates the possibility of reconstructing area burned with multiple charcoal records, and results imply that future fire regimes in YNP will be governed by direct impacts of altered moisture regimes and by vegetation dynamics affecting the abundance and continuity of fuels.
    The Holocene 01/2011; 21(2). · 3.22 Impact Factor
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    ABSTRACT: The paucity of low- and middle-elevation paleoecologic records in the Northern Rocky Mountains limits our ability to assess current environmental change in light of past conditions. A 10,500-yr-long vegetation, fire and climate history from Lower Decker Lake in the Sawtooth Range provides information from a new region. Initial forests dominated by pine and Douglas-fir were replaced by open Douglas-fir forest at 8420 cal yr BP, marking the onset of warmer conditions than present. Presence of closed Douglas-fir forest between 6000 and 2650 cal yr BP suggests heightened summer drought in the middle Holocene. Closed lodgepole pine forest developed at 2650 cal yr BP and fires became more frequent after 1450 cal yr BP. This shift from Douglas-fir to lodgepole pine forest was probably facilitated by a combination of cooler summers, cold winters, and more severe fires than before. Five drought episodes, including those at 8200 cal yr BP and during the Medieval Climate Anomaly, were registered by brief intervals of lodgepole pine decline, an increase in fire activity, and mistletoe infestation. The importance of a Holocene perspective when assessing the historical range of variability is illustrated by the striking difference between the modern forest and that which existed 3000 yr ago.
    Quaternary Research 01/2011; · 2.20 Impact Factor
  • Meeting of the International Quaternary Association, Bern, Switzerland; 01/2011
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    ABSTRACT: The 1988 Yellowstone fires were among the first in what has proven to be an upsurge in large severe fires in the western USA during the past 20 years. At the time of the fires, little was known about the impacts of such a large severe disturbance because scientists had had few previous opportunities to study such an event. Ecologists predicted short-and long-term effects of the 1988 fires on vegetation, biogeochemistry, primary productivity, wildlife, and aquatic ecosystems based on scientific understanding of the time. Twenty-plus years of subsequent study allow these early predictions to be evaluated. Most of the original predictions were at least partially supported, but some predictions were refuted, others nuanced, and a few postfire phenomena were entirely unexpected. Post-1988 Yellowstone studies catalyzed advances in ecology focused on the importance of spatial and temporal heterogeneity, contingent influences, and multiple interacting drivers. Post-1988 research in Yellow-stone also has changed public perceptions of fire as an ecological process and attitudes towards fire management. Looking ahead to projected climate change and more frequent large fires, the well-documented ecological responses to the 1988 Yel-lowstone fires provide a foundation for detecting and evaluating potential changes in fire regimes of temperate mountainous regions.
    Ecosystems 01/2011; · 3.17 Impact Factor
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    ABSTRACT: Humans have altered natural patterns of fire for millennia, but the impact of human-set fires is thought to have been slight in wet closed-canopy forests. In the South Island of New Zealand, Polynesians (Māori), who arrived 700-800 calibrated years (cal y) ago, and then Europeans, who settled ∼150 cal y ago, used fire as a tool for forest clearance, but the structure and environmental consequences of these fires are poorly understood. High-resolution charcoal and pollen records from 16 lakes were analyzed to reconstruct the fire and vegetation history of the last 1,000 y. Diatom, chironomid, and element concentration data were examined to identify disturbance-related limnobiotic and biogeochemical changes within burned watersheds. At most sites, several high-severity fire events occurred within the first two centuries of Māori arrival and were often accompanied by a transformation in vegetation, slope stability, and lake chemistry. Proxies of past climate suggest that human activity alone, rather than unusually dry or warm conditions, was responsible for this increased fire activity. The transformation of scrub to grassland by Europeans in the mid-19th century triggered further, sometimes severe, watershed change, through additional fires, erosion, and the introduction of nonnative plant species. Alteration of natural disturbance regimes had lasting impacts, primarily because native forests had little or no previous history of fire and little resilience to the severity of burning. Anthropogenic burning in New Zealand highlights the vulnerability of closed-canopy forests to novel disturbance regimes and suggests that similar settings may be less resilient to climate-induced changes in the future.
    Proceedings of the National Academy of Sciences 12/2010; 107(50):21343-8. · 9.74 Impact Factor
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    ABSTRACT: High-resolution pollen records from North America show that terrestrial environments were affected by Dansgaard-Oeschger (D-O) and Heinrich climate variability during the last glacial. In the western, more mountainous regions, these climate changes are generally observed in the pollen records as altitudinal movements of climate-sensitive plant species, whereas in the southeast, they are recorded as latitudinal shifts in vegetation. Heinrich (HS) and Greenland (GS) stadials are generally correlated with cold and dry climate and Greenland interstadials (GI) with warm-wet phases. The pollen records from North America confirm that vegetation responds rapidly to millennial-scale climate variability, although the difficulties in establishing independent age models for the pollen records make determination of the absolute phasing of the records to surface temperatures in Greenland somewhat uncertain.
    Quaternary Science Reviews 10/2010; 29(21-22):2865-2881. · 4.08 Impact Factor
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    01/2010; National Park Service, Fort Collins, Colorado.
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    ABSTRACT: Fire is well recognized as a key Earth system process, but its causes and influences vary greatly across spatial and temporal scales. The controls of fire are often portrayed as a set of superimposed triangles, with processes ranging from oxygen to weather to climate, combustion to fuel to vegetation, and local to landscape to regional drivers over broadening spatial and lengthening temporal scale. Most ecological studies and fire management plans consider the effects of fire-weather and fuels on local to sub-regional scales and time frames of years to decades. Fire reconstructions developed from high-resolution tree-ring records and lake-sediment data that span centuries to millennia offer unique insights about fire's role that cannot otherwise be obtained. Such records help disclose the historical range of variability in fire activity over the duration of a vegetation type; the role of large-scale changes of climate, such as seasonal changes in summer insolation; the consequences of major reorganizations in vegetation; and the influence of prehistoric human activity in different ecological settings. This paleoecological perspective suggests that fire-regime definitions, which focus on the characteristic frequency, size and intensity of fire and particular fuel types, should be reconceptualized to better include the controls of fire regimes over the duration of a particular biome. We suggest that approaches currently used to analyze fire regimes across multiple spatial scales should be employed to examine fire occurrence across multiple temporal scales. Such cross-scale patterns would better reveal the full variability of particular fire regimes and their controls, and provide relevant information for the types of fire regimes likely to occur in the future with projected climate and land-use change.
    The Open Ecology Journal. 01/2010; 3(2):6-23.
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    ABSTRACT: High-resolution macroscopic charcoal and pollen analyses were used to reconstruct the fire and vegetation history of the Willamette Valley for the last 1200 years. Presented in this paper are three new paleoecological reconstructions from Lake Oswego, Porter Lake, and Warner Lake, Oregon, and portions of previous reconstructions from Battle Ground Lake, Washington, and Beaver Lake, Oregon. The reconstructions show that prior to Euro-American settlement vegetation and fire regimes were influenced by a combination of natural and anthropogenic factors. Battle Ground Lake shows a stronger influence from climate, while Lake Oswego, Beaver Lake, Porter Lake, and Warner Lake were more controlled by human activity. However, human-set fires were also modulated by regional climate variability during the Medieval Climate Anomaly and the Little Ice Age. Fire reconstructions from Battle Ground Lake, Lake Oswego, Beaver Lake, and Porter Lake imply that fires were infrequent in the Willamette Valley 200–300 years prior to Euro-American settlement. The decline of Native American populations due to introduced disease may have led to this reduction in fire activity. The prehistoric record from Warner Lake, however, indicates that fires in the foothills of the Cascade Range were more frequent than on the valley floor, at least until ca. AD 1800. The historic portions of the reconstructions indicate that Euro-American land clearance for agriculture and logging produced the most dramatic shifts in vegetation and fire regimes. All five records indicate that few fires in the Willamette Valley have occurred since ca. AD 1930, and fires today are predominantly grass fires.
    Palaeogeography Palaeoclimatology Palaeoecology 01/2010; 297(2):273-289. · 2.75 Impact Factor

Publication Stats

2k Citations
254.34 Total Impact Points

Institutions

  • 2006–2013
    • Montana State University
      • Department of Earth Sciences
      Bozeman, Montana, United States
  • 2012
    • University of Wisconsin, Madison
      • Department of Geography
      Madison, MS, United States
  • 2011
    • Columbia University
      New York City, New York, United States
  • 1993–2009
    • University of Oregon
      • Department of Geography
      Eugene, OR, United States
  • 2008
    • University of Wisconsin - Oshkosh
      • Department of Geography and Urban Planning
      Oshkosh, WI, United States
  • 2007
    • University of Wyoming
      • Department of Botany
      Laramie, WY, United States
  • 2005
    • Northern Arizona University
      • School of Earth Sciences and Environmental Sustainability
      Flagstaff, Arizona, United States