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Browsing by Author "Kreye, Jesse K."

Now showing 1 - 4 of 4
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    Fires without tanoak: the effects of a non-native disease on future community flammability
    Varner, J. Morgan; Kuljian, Howard G.; Kreye, Jesse K. (2017-08)
    Non-native pathogens affect forests throughout North America, resulting in changes in species composition, structure, and ecosystem processes. We studied the effects of the emergent disease sudden oak death (SOD) and the resulting functional extinction of tanoak, a highly susceptible native tree with flammable litter, on future community flammability. We quantified four flammability metrics (flame height; flaming duration; smoldering duration; and fuel consumed) for litter from each of five species that co-occur with tanoak and for species mixtures with and without tanoak (n = 14). We combined these flammability metrics in a Principal Components Analysis to evaluate potential shifts in litter flammability from pre-SOD (with tanoak litter) to post-SOD (where tanoak was replaced equally with remaining species). Litter flammability changed following the loss of tanoak, but the differences were species- and community-specific. Mixed-evergreen fuels where coast Douglas-fir litter replaced tanoak experienced consistent declines in flammability. Few substantive changes occurred in communities where coast redwood or other hardwoods co-occurred. We found consistent synergistic flammability effects when multiple species' litters were mixed; in cases where two or more species were mixed, most (75%) combinations burned with higher intensity (+8.1%) and fuelbeds flamed for a longer duration (+17.1%). Our work demonstrates that potential surface fire behavior in northwestern California may be dampened where Douglas-fir replaces tanoak, while those communities with other hardwoods or coast redwood may have redundant fuels and tanoak's absence in future fires may be inconspicuous. These results underscore the potential for cascading effects of non-native pathogens on ecosystem function in fire-prone ecosystems.
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    The impact of aging on laboratory fire behaviour in masticated shrub fuelbeds of California and Oregon, USA
    Kreye, Jesse K.; Varner, J. Morgan; Kane, Jeffrey M.; Knapp, Eric E.; Reed, Warren P. (2016)
    Mastication of shrubs and small trees to reduce fire hazard has become a widespread management practice, yet many aspects of the fire behaviour of these unique woody fuelbeds remain poorly understood. To examine the effects of fuelbed aging on fire behaviour, we conducted laboratory burns with masticated Arctostaphylos spp. and Ceanothus spp. woody debris that ranged from 2 to 16 years since treatment. Masticated fuels that were 10 years or older burned with 18 to 29% shorter flame heights and 19% lower fireline intensities compared with the younger fuelbeds across three different fuel loads (25, 50 and 75 Mg ha(-1)). Older fuelbeds smouldered for almost 50% longer than the younger masticated fuelbeds. Fuel consumption was 96% in the two higher fuel load categories regardless of fuelbed age, whereas consumption was 77% in the lighter fuel load. Fire intensity in masticated fuels may decrease over time owing to particle degradation, but in dry environments where decomposition is slow, combustion of the remaining fuels may still pose risks for tree mortality and smoke production associated with protracted smouldering.
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    Long-term changes in masticated woody fuelbeds in northern California and southern Oregon, USA
    Reed, Warren P.; Varner, J. Morgan; Knapp, Eric E.; Kreye, Jesse K. (2020-06-05)
    Mechanical mastication is a fuels treatment that shreds midstorey trees and shrubs into a compacted woody fuel layer to abate fire hazards in fire-prone ecosystems. Increased surface fuel loading from mastication may, however, lead to undesirable fire intensity, long-duration flaming or smouldering, and undesirable residual tree mortality. Two major questions facing fuels managers are: how long do masticated fuels persist, and how does the composition of masticated fuelbeds change over time? To evaluate these changes, we measured 25 masticated sites with a range of vegetation, species masticated and time since treatment (1-16 years) in the western US. Seven of the 25 sites were sampled nearly a decade earlier, providing a unique opportunity to document fuelbed changes. Woody fuel loading ranged from 12.1 to 91.9 Mg ha(-1) across sites and was negatively related to time since treatment. At remeasured sites, woody fuel loads declined by 20%, with the greatest losses in 1- and 10-h woody fuels (69 and 33% reductions in mass respectively). Reductions were due to declines in number of particles and reduced specific gravity. Mastication treatments that generate greater proportions of smaller-diameter fuels may result in faster decomposition and potentially be more effective at mitigating fire hazard.
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    Suites of Fire-Adapted Traits of Oaks in the Southeastern USA: Multiple Strategies for Persistence
    Varner, J. Morgan; Kane, Jeffrey M.; Hiers, J. Kevin; Kreye, Jesse K.; Veldman, Joseph W. (2016-08-01)
    Fire is integral to the functioning of terrestrial ecosystems of the southeastern USA and is a strong selective force on plant species. Among woody plants, oak species (Quercus spp. L) have diverse life history traits that appear to reflect their evolution in this fire-prone region. Oaks also occur across wide gradients of fire frequency and intensity, from annually burned savannas to fire-protected forests. As such, oak functional traits are presumed to reflect adaptations to acquire limited resources (i.e., "physiological traits") or survive environmental stress (i.e., "protective traits"). Oak functional traits may also influence fire regimes (i.e., via "flammability traits") by altering fire behavior through effects on fuels and their combustion. We synthesized evidence from ecophysiological measurements, laboratory burning and drying experiments, and field experiments to determine the suites of functional traits that reflect fire adaptive strategies in eight Southeastern oaks for which abundant data were available. We found strong correlations among Principal Components Analysis axes for flammability (litter burning and drying), protective (bark and wound responses), and physiological (growth) traits. The eight oaks clustered into three strategies: 1) pyrophytic species that produce highly flammable leaf litter, accrue thick bark rapidly, close wounds rapidly, and grow slowly; 2) mesophytic species that produce low flammability litter, have thin bark, and are fast growing; and 3) fire-avoider species with a mixture of traits from the two extremes. This synthesis clarifies the relative pyrophily of Southeastern oaks and suggests how suites of fire-related traits influence fire regimes and species habitat preferences.