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• 1. [Article] Dead fuels and understory vegetation six years after a large mixed-severity wildfire in southwest Oregon

  Though the mixed-evergreen forests of the Klamath Siskiyous have a long history of large, mixed-severity fires, most research in this region has concentrated on the impacts of high-severity fire. Knowledge ...

  Citation × Citation Citation Abstract Copy Title: Dead fuels and understory vegetation six years after a large mixed-severity wildfire in southwest Oregon Author: Nathanson, Amy Though the mixed-evergreen forests of the Klamath Siskiyous have a long history of large, mixed-severity fires, most research in this region has concentrated on the impacts of high-severity fire. Knowledge of the ecological effects of low- and moderate-severity areas within mixed-severity fires is important because such areas may account for over half the landscape affected by a fire. The purpose of this study was to understand the relationship of fire severity with dead fuels and understory vegetation across a full range of fire severities. Study sites were located within and just outside the boundary of the 2002 Biscuit Fire, which burned 200,000 hectares in a mosaic of burn severities. Six years after the Biscuit Fire, the biomass and depth of litter and duff was lower on burned sites than unburned sites, and lowest on high-severity sites. This relationship was reversed for woody fuels >7.62 cm in diameter, where quantities were highest in high- and extreme-severity areas, though there was no evidence that quantities differed between low-severity and unburned sites. There was no evidence of a relationship between woody fuels 0.64-7.62 cm in diameter and fire severity, 6 years post-fire. There was no evidence that fuel quantities differed between sites that burned only in the Biscuit Fire with sites that also burned 15 years earlier in the 1987 Silver Fire. Fuel quantities and composition differed between burned and unburned sites, but these differences disappeared if litter and duff were not considered. Fuel classes were correlated with each other within three general size classes: small (litter, duff, and fuels <2.54 cm), medium (fuels 2.54-30 cm), and large (fuels >30 cm). There was little correlation between these size classes. Vegetation response also varied by fire severity, species, and height. Generally, density for tree seedlings <0.5 m was highest on low-severity sites and lowest on high-severity sites. For seedlings 0.5-1.37 m the relationship was reversed, with the highest seedling densities in high-severity areas. Specific seedling relationships to burn severity and other explanatory factors (e.g. shrub cover, elevation, precipitation, maxiumun August temperatures) varied by species and seedling height. Average seedling densities were above the minimum acceptable stocking levels of 333 trees per hectare (135 seedlings/acre) as identified in federal plans for the fire area. Shrub species richness and diversity did not vary with burn severity; however, shrub species and ground cover composition did differ with burn severity six years after the Biscuit Fire. The relationship of understory cover composition with burn severity aligned with species life history traits; fire-adapted, nitrogen-fixing species were more prevalent on high- and extreme-severity sites while species associated with low-severity fire or old-growth forests were more prevalent on low-severity or unburned sites. I found no evidence of difference in total graminoid or forb cover based on fire severity, but shrub quantities were lower on low-severity sites than on unburned, high-, and extreme-severity sites. This study reveals how fuel and vegetation vary across the full range of fire severities. It demonstrates that mixed-severity fires create a mix of ecological responses. It also provides a baseline for future studies, as the relationships between fire severity and fuels or vegetation may disappear or change in subsequent decades. Title: Dead fuels and understory vegetation six years after a large mixed-severity wildfire in southwest Oregon Author: Nathanson, Amy Though the mixed-evergreen forests of the Klamath Siskiyous have a long history of large, mixed-severity fires, most research in this region has concentrated on the impacts of high-severity fire. Knowledge of the ecological effects of low- and moderate-severity areas within mixed-severity fires is important because such areas may account for over half the landscape affected by a fire. The purpose of this study was to understand the relationship of fire severity with dead fuels and understory vegetation across a full range of fire severities. Study sites were located within and just outside the boundary of the 2002 Biscuit Fire, which burned 200,000 hectares in a mosaic of burn severities. Six years after the Biscuit Fire, the biomass and depth of litter and duff was lower on burned sites than unburned sites, and lowest on high-severity sites. This relationship was reversed for woody fuels >7.62 cm in diameter, where quantities were highest in high- and extreme-severity areas, though there was no evidence that quantities differed between low-severity and unburned sites. There was no evidence of a relationship between woody fuels 0.64-7.62 cm in diameter and fire severity, 6 years post-fire. There was no evidence that fuel quantities differed between sites that burned only in the Biscuit Fire with sites that also burned 15 years earlier in the 1987 Silver Fire. Fuel quantities and composition differed between burned and unburned sites, but these differences disappeared if litter and duff were not considered. Fuel classes were correlated with each other within three general size classes: small (litter, duff, and fuels <2.54 cm), medium (fuels 2.54-30 cm), and large (fuels >30 cm). There was little correlation between these size classes. Vegetation response also varied by fire severity, species, and height. Generally, density for tree seedlings <0.5 m was highest on low-severity sites and lowest on high-severity sites. For seedlings 0.5-1.37 m the relationship was reversed, with the highest seedling densities in high-severity areas. Specific seedling relationships to burn severity and other explanatory factors (e.g. shrub cover, elevation, precipitation, maxiumun August temperatures) varied by species and seedling height. Average seedling densities were above the minimum acceptable stocking levels of 333 trees per hectare (135 seedlings/acre) as identified in federal plans for the fire area. Shrub species richness and diversity did not vary with burn severity; however, shrub species and ground cover composition did differ with burn severity six years after the Biscuit Fire. The relationship of understory cover composition with burn severity aligned with species life history traits; fire-adapted, nitrogen-fixing species were more prevalent on high- and extreme-severity sites while species associated with low-severity fire or old-growth forests were more prevalent on low-severity or unburned sites. I found no evidence of difference in total graminoid or forb cover based on fire severity, but shrub quantities were lower on low-severity sites than on unburned, high-, and extreme-severity sites. This study reveals how fuel and vegetation vary across the full range of fire severities. It demonstrates that mixed-severity fires create a mix of ecological responses. It also provides a baseline for future studies, as the relationships between fire severity and fuels or vegetation may disappear or change in subsequent decades. Close

• 2. [Article] The use of burned forest by breeding birds following the Biscuit Fire in southwest Oregon

  Fire severity is hypothesized as an important driver of bird responses to wildfire. For those species that typically respond negatively to increasing severity, Accessibility of high-severity burned forest ...

  Citation × Citation Citation Abstract Copy Title: The use of burned forest by breeding birds following the Biscuit Fire in southwest Oregon Author: Donaghy Cannon, Michelle M. Fire severity is hypothesized as an important driver of bird responses to wildfire. For those species that typically respond negatively to increasing severity, Accessibility of high-severity burned forest may be dependent on the proximity of unburned or low-severity burned forest to meet all of the needs of breeding bird species that typically respond negatively to increasing fire severity. We used dynamic occupancy modeling and intensive surveys to test the hypothesis that the presence of live trees explained distribution of birds in high-severity burned forest in the first three years following the Biscuit Complex Fire in southwest Oregon. Proximity of low-moderate severity burned forest appeared to be important for some foliage- and bark-gleaning species. However, probability of occurrence in high-severity patches for several canopy-associates was not associated with distance from low-moderate severity burned forest. We found strong evidence that large snags (>52-cm) and large live conifers provided important nest substrates for several of these open-cup nesting species. Sprouts from top-killed hardwood species provided primary nesting substrates for early-seral associates and some species that nest in live trees or mature shrubs in unburned forest. Large areas of high-severity burned forest appeared to provide important breeding habitat for edge-sensitive cavity-nesting species. Most cavity nests were in large fire-killed or legacy snags with significant decay. In all, bird species that were likely to nest in high-severity forest also were likely to persist in the early post-fire period. Identifying the structures used for nesting by these species provides a mechanistic understanding of the distributions of many species of breeding birds following wildfire, and underscores the importance of local ecological context in interpretation of the effects of disturbance. We used intensive surveys to evaluate the efficacy of point count surveys to detect breeding birds. Most species had significantly higher detection probabilities at sites with evidence of breeding activity than at sites without such evidence. Among species, however, detection probability did not predict prevalence of breeding. Most species for which detection probabilities during point counts were low or moderate were those predicted to decline following high-severity fire. This finding highlights the importance of evaluating detection probabilities to identify effective sampling methods for species expected to respond negatively to habitat alteration. Title: The use of burned forest by breeding birds following the Biscuit Fire in southwest Oregon Author: Donaghy Cannon, Michelle M. Fire severity is hypothesized as an important driver of bird responses to wildfire. For those species that typically respond negatively to increasing severity, Accessibility of high-severity burned forest may be dependent on the proximity of unburned or low-severity burned forest to meet all of the needs of breeding bird species that typically respond negatively to increasing fire severity. We used dynamic occupancy modeling and intensive surveys to test the hypothesis that the presence of live trees explained distribution of birds in high-severity burned forest in the first three years following the Biscuit Complex Fire in southwest Oregon. Proximity of low-moderate severity burned forest appeared to be important for some foliage- and bark-gleaning species. However, probability of occurrence in high-severity patches for several canopy-associates was not associated with distance from low-moderate severity burned forest. We found strong evidence that large snags (>52-cm) and large live conifers provided important nest substrates for several of these open-cup nesting species. Sprouts from top-killed hardwood species provided primary nesting substrates for early-seral associates and some species that nest in live trees or mature shrubs in unburned forest. Large areas of high-severity burned forest appeared to provide important breeding habitat for edge-sensitive cavity-nesting species. Most cavity nests were in large fire-killed or legacy snags with significant decay. In all, bird species that were likely to nest in high-severity forest also were likely to persist in the early post-fire period. Identifying the structures used for nesting by these species provides a mechanistic understanding of the distributions of many species of breeding birds following wildfire, and underscores the importance of local ecological context in interpretation of the effects of disturbance. We used intensive surveys to evaluate the efficacy of point count surveys to detect breeding birds. Most species had significantly higher detection probabilities at sites with evidence of breeding activity than at sites without such evidence. Among species, however, detection probability did not predict prevalence of breeding. Most species for which detection probabilities during point counts were low or moderate were those predicted to decline following high-severity fire. This finding highlights the importance of evaluating detection probabilities to identify effective sampling methods for species expected to respond negatively to habitat alteration. Close