We developed a risk score integrating several environmental variables associated with drought and heat stress to predict the likelihood and intensity of mortality at the stand scale. At the landscape scale, Douglas-fir mortality increased as average annual precipitation declined and average climatic water deficit increased. Our results provide strong evidence for a decline spiral in which Douglas-fir growing on hot, dry sites (predisposing factor) are further stressed by drought (inciting factor) and are then exploited by the flatheaded fir borer (Phaenops drummondi) and other secondary biotic agents (contributing factors), resulting in decline and mortality. We used data from the USDA Forest Service Aerial Detection Survey and ninety-six field plots to explore the relationships between physiographic and climate variables and Douglas-fir mortality. menziesii) mortality in the Klamath Mountains ecoregion raise concerns about the long-term resilience of Douglas-fir in the ecoregion and increased potential for uncharacteristic wildfire. Recent increases in Douglas-fir (Psuedotsuga menziesii var. The low-severity model is rejected and mixed-severity model is supported by the corrected body of scientific evidence. Our rebuttal shows that evidence omitted in the review left a falsification of the scientific record, with significant land management implications. These included numerous direct observations by early scientists, early forest atlases, early newspaper accounts, early oblique and aerial photographs, seven paleo-charcoal reconstructions, ≥18 tree-ring reconstructions, 15 land survey reconstructions, and analysis of forest inventory data. A large body of published evidence supporting the mixed-severity model was omitted. A central finding of high-severity fire recently exceeding its historical rates was not supported by evidence in the review itself. Here, we simply rebut evidence in the low-severity model’s latest review, including its 37 critiques of the mixed-severity model. The “low-severity” model is that dry forests were relatively uniform, low in tree density, and dominated by low- to moderate-severity fires the “mixed-severity” model is that dry forests were heterogeneous, with both low and high tree densities and a mixture of fire severities.
Two models of HRV, with different implications, have been debated since the 1990s in a complex series of papers, replies, and rebuttals. Management is guided by current conditions relative to the historical range of variability (HRV). The structure and fire regime of pre-industrial (historical) dry forests over ~26 million ha of the western USA is of growing importance because wildfires are increasing and spilling over into communities.
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