Mixed-Severity Fire Effects on Biological Legacies and Vegetation Response in Pseudotsuga Forests of Western Oregon's Central Cascades, USA

Mixed-Severity Fire Effects on Biological Legacies and Vegetation Response in Pseudotsuga Forests of Western Oregon's Central Cascades, USA
Author: Christopher J. Dunn
Publisher:
Total Pages: 126
Release: 2015
Genre: Conifers
ISBN:
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Mixed-severity fire occurrence is increasingly recognized in Pseudotsuga forests of the Pacific Northwest, but questions remain about how tree mortality varies, and forest structure is altered, across the disturbance gradient observed in these fires. Therefore, we sampled live and dead biological legacies at 45 one ha plots, with four 0.10 ha nested plots, stratified across an unburned, low, moderate and high-severity fire gradient. We used severity estimates based on differenced Normalized Burn Ratio (dNBR), and captured a disturbance gradient, but plots in our low-severity class underestimated fire effects because of misclassification or delayed mortality. We estimated probability of mortality for shade-intolerant (Douglas-fir, incense-cedar, sugar pine) and shade-tolerant (western hemlock, western redcedar, true fir) trees from 5,079 sampled trees and snags. The probability of mortality was higher for shade-tolerant species across all fire-severity classes, and decreased with increasing DBH except for western hemlock. Only large, shade-intolerant trees survived high-severity fire. Post-fire snag fall and fragmentation were estimated from 2,746 sampled snags and logs. The probability of snag fall decreased with increasing DBH for all species, and was positively correlated with fire severity, except for Douglas-fir that had a higher probability following low-severity fire. Snag fragmentation was positively correlated with DBH and fire severity for all species. We also estimated the coefficient of variation within- and among-plots by fire severity class, as well as across all sampled conditions. Structural attributes varied more within- than among-plots, likely a result of increasing sub-hectare patchy mortality as fire intensity increased. Although vertical and horizontal structural diversity increased at sub-hectare scales, the coefficient of variation was highest for all structural attributes when compared across all fire severity classes. Therefore, the range of fire effects observed in mixed-severity fires may be functionally important in creating structural complexity across landscapes, which is an important attribute of old-growth forests in the Pacific Northwest. Understory vegetation response to mixed-severity fires has not been characterized for these forests even though the majority of vegetation diversity is found in these vegetation layers. Therefore, we sampled forest structure (1000 m2 circular plots) and understory vegetation (100 m2 plots) at 168 collocated plots stratified across unburned, low, moderate and high-severity conditions 10 years (Tiller Complex) and 22 years (Warner Fire) post-fire. We focused on shrub species, but sampled forbs, graminoids, ferns and moss as functional groups. Offsite colonization and fire stimulated soil seedbanks increased the total species richness from 23 to 46. The life-history strategies of residual and colonizing species resulted in three dominant species response-curves to the magnitude of disturbance: 1) 'disturbance-sensitive', when relative abundance was highest in unburned plots and continued to decline with increasing fire severity, 2) 'disturbance-stimulated', when relative abundance was highest following low or moderate-severity fire and 3) 'disturbance-amplified', when relative abundance increased with increasing fire severity. Residual and colonizing species assemblages promoted five or six distinct understory communities, dominantly driven by legacy tree basal area rather than the proportion of basal area killed. Understory communities were rarely associated with one disturbance severity class as fire refugia, variation in overstory and understory fire severity, and compensatory conditions offset fire effects. Early-seral habitats were the most different from unburned forests, but were not the only post-fire conditions important across these burned landscapes. Interactions among live and dead forest structures following low or moderate-severity fire, and the vegetation response to these conditions, are also unique to the post-fire landscape and likely important for various wildlife species. Therefore, if ecological forestry paradigms focus dominantly on creating old-growth structure or early-seral habitats, they might exclude important conditions that contribute to the landscape structural complexity created by mixed-severity fires. Additionally, tree regeneration response to mixed-severity fires has not been characterized for these forests even though they offer insight into one aspect of the resilience of these ecosystems to disturbance. Therefore, we sampled forest structure (1000 m2 circular plots) and regeneration dynamics (100 m2 plots) at 168 collocated plots stratified across unburned, low, moderate and high-severity conditions 10 years (Tiller Complex) and 22 years (Warner Fire) post-fire. The largest marginal increase in tree mortality (stems ha−1) occurred between unburned and low-severity fires, given preferential mortality of small trees and shade-tolerant species, but basal area mortality had the largest marginal increase moving from moderate to high-severity. Pairwise comparisons of legacy tree basal area between low and moderate-severity weren't as significant as other comparisons, but did capture a gradient of increasing fire effects. Quadratic mean diameter and canopy base height were positively correlated with fire severity as incrementally larger trees were killed and canopy ascension followed. Regeneration density increased regardless of severity, relative to unburned forests (median density of 1,384 trees ha−1), but the highest median density (16,220 trees ha−1) followed low-severity fire at the Tiller Complex and moderate-severity fire (14,472 trees ha−1) at Warner Fire. Plot-level average species richness was highest following these same fire severity classes, supporting the Intermediate Disturbance Hypothesis. Statistically distinct regeneration communities occurred across the fire severity gradient at both fire sites. The relative abundance of shade-tolerant tree species decreased as fire severity increased, except for a divergent response following stand-initiation at the Warner Fire. While divergent successional pathways were evident within a couple decades following stand-initiation, low or moderate-severity fires also modified successional trajectories and may be the most functionally important disturbance magnitude because it has the greatest potential to increase compositional and structural diversity. Incorporating mixed-severity fire effects into landscape management of Pseudotsuga forests could increase structural complexity at stand and landscape-scales.

Dead Fuels and Understory Vegetation Six Years After a Large Mixed-severity Wildfire in Southwest Oregon

Dead Fuels and Understory Vegetation Six Years After a Large Mixed-severity Wildfire in Southwest Oregon
Author: Amy Nathanson
Publisher:
Total Pages: 145
Release: 2011
Genre: Biscuit Fire, 2002
ISBN:
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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 (fuels30 cm). There was little correlation between these size classes. Vegetation response also varied by fire severity, species, and height. Generally, density for tree seedlings

Fire Severity and Vegetation Response to Fire in Riparian Areas of the Biscuit and B & B Complex Fires, Oregon

Fire Severity and Vegetation Response to Fire in Riparian Areas of the Biscuit and B & B Complex Fires, Oregon
Author: Jessica E. Halofsky
Publisher:
Total Pages: 312
Release: 2007
Genre: Biscuit Fire, 2002
ISBN:
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Fire is the dominant disturbance process in western U.S. forests, and although effects of fire in upland forests are relatively well-studied, there is little information about fire effects on riparian forests, critical areas of the landscape for both habitat and water quality. This dissertation examines different aspects of fire effects in riparian areas of two recent fires in Oregon, the Biscuit Fire in southwestern Oregon and the B & B Complex Fire in the Cascade Mountain Range. In the first of three studies, I compared riparian fire severity to that in uplands and investigated factors influencing riparian fire severity in both fire areas. In a second study, the relationships among ground-based indices of fire severity in riparian areas, and the relationships between ground-based and remotely-sensed indices of fire severity, were examined. In a third study, I investigated patterns in post-fire riparian plant community regeneration in the same areas. I found that understory fire severity was significantly lower in riparian areas compared to adjacent uplands, suggesting a decoupling of understory fire effects in riparian areas versus uplands. However, there were no differences in overstory fire severity between riparian areas and uplands in either fire. Understory and overstory fire severity indices were found to be weakly related, suggesting that there are limitations in the use of both types of fire severity indices. However, both overstory and understory fire severity in riparian areas were most strongly predicted by upland fire severity. Riparian fuel properties were also strong predictors of riparian fire severity. Patterns in post-fire riparian regeneration were influenced, at a coarse spatial scale, by factors associated with position in a watershed (headwater versus main stem channels) in the Biscuit Fire and by elevation/plant association in the B & B Complex Fire. At a finer spatial scale, differences in species composition and microsite conditions between deciduous hardwood- and conifer-dominated communities, and understory fire severity, influenced patterns of post-fire regeneration. Results of these studies suggest that management practices that reduce upland fire severity may also reduce riparian fire severity. Results also suggest that post-fire riparian regeneration efforts be tailored to site-specific vegetation conditions of complex riparian environments.

Long-term Effects of Fire Hazard Reduction Treatments in the Southern Cascades and Northern Sierra Nevada, California

Long-term Effects of Fire Hazard Reduction Treatments in the Southern Cascades and Northern Sierra Nevada, California
Author: Lindsay Aney Chiono
Publisher:
Total Pages: 162
Release: 2012
Genre:
ISBN:
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Historic fire regimes in the dry conifer forests of the southern Cascade and northern Sierra Nevada regions of California were characterized by relatively frequent fires of low and mixed severity. Human management practices since the mid-19th century have altered the disturbance role of fire in these dry yellow pine and mixed conifer forest ecosystems. Fire suppression, high-grade timber harvesting, and livestock grazing have reduced the frequency of burning and caused a shift in the structure and species composition of forest vegetation. These changes, including high levels of accumulated fuel and increased structural homogeneity and dominance of shade-tolerant tree species, combined with a warming climate, have rendered many stands susceptible to high-severity fire. In many forests of the western United States, wildfires are increasingly difficult and costly to control, and human communities are regularly threatened during the fire season. Treating wildland fuels to reduce wildfire hazards has become a primary focus of contemporary forest management, particularly in the wildland-urban interface. The specific objectives of treatment are diverse, but in general, treatments address accumulated surface fuels, the fuel ladders that carry fire into the forest canopy, and surface and canopy fuel continuity. These modifications to forest fuels can alleviate the severity of a future wildfire and support suppression activities through improved access and reduced fire intensity. While fuel reduction treatments are increasingly common in western forests, the long-term structural and ecological effects of treatment remain poorly understood. This dissertation uses a chronosequence of treated stands to examine the temporal influence of treatment on forest structure, the understory plant community, and wildfire hazard. The first chapter examines the effects of fuels reduction treatment on stand structure, overstory species composition, and ground and surface fuels. The stand structures and reduced surface fuel loads created by fuels modification are temporary, yet few studies have assessed the lifespan of treatment effects. The structural legacies of treatment were still present in the oldest treatment sites. Treatments reduced site occupancy (stand density and basal area) and increased quadratic mean diameter by approximately 50%. The contribution of shade-tolerant true firs to stand density was also reduced by treatment. Other stand characteristics, particularly timelag fuel loads, seedling density, and shrub cover, exhibited substantial variability, and differences between treatment age classes and between treatment and control groups were not statistically significant. The second chapter evaluates fuel treatment longevity based on potential wildfire behavior and effects on vegetation. Forest managers must divide scarce resources between fuel treatment maintenance, which is necessary to retain low hazard conditions in treated stands, and the construction of new treatments. Yet the most basic questions concerning the lifespan of treatment effectiveness have rarely been engaged in the literature. In this study, field-gathered fuels and vegetation data were used to aid fuel model selection and to parameterize a fire behavior and effects model, Fuels Management Analyst Plus. In addition, a semi-qualitative, semi-quantitative protocol was applied to assess ladder fuel hazard in field sampling plots. Untreated sites exhibited fire behavior that would challenge wildfire suppression efforts, and projected overstory mortality was considerable. In contrast, estimated fire behavior and severity were low to moderate in even the oldest fuel treatments, those sampled 8-26 years after treatment implementation. Findings indicate that in the forest types characteristic of the northern Sierra Nevada and southern Cascades, treatments for wildfire hazard reduction retain their effectiveness for more than 10-15 years and possibly beyond a quarter century. Fuel treatment activities disturb the forest floor, increase resource availability, and may introduce non-native plant propagules to forest stands. Non-native plant invasions can have profound consequences for ecosystem structure and function. For these reasons, there is concern that treatment for fire hazard reduction may promote invasion by exotic species. Several short-term studies have shown small increases in non-native abundance as a result of treatment, but the long-term effects have rarely been addressed in the literature. The final chapter examines treatment effects on the understory plant community and on cover of the forest floor, as mineral soil exposure has been linked to invasion. Regression tree analysis provided insights into the influence of treatment and site characteristics on these variables. Treatments increased forb and graminoid cover, but temporal trends in abundance were opposite. An initial increase in forb cover in the most recently treated sites was followed by a gradual decline, while mean graminoid cover was highest in the oldest treatments. Shrubs dominated live plant abundance. Shrub cover showed few temporal trends, but was negatively associated with canopy cover. Mineral soil exposure was increased by treatment and declined slowly over time, remaining elevated in the oldest treatments. Non-native plant species were very rare in the treatment sites sampled in this study. Despite the availability of bare mineral soil and the proximity of transportation corridors, a source of non-native propagules, non-natives were recorded in only 2% of sampling plots. This study suggests that forest disturbance associated with treatment for hazardous fuels reduction may not produce significant invasions in these forest types.

Age Structure, Developmental Pathways, and Fire Regime Characterization of Douglas-fir/western Hemlock Forests in the Central Western Cascades of Oregon

Age Structure, Developmental Pathways, and Fire Regime Characterization of Douglas-fir/western Hemlock Forests in the Central Western Cascades of Oregon
Author: Alan J. Tepley
Publisher:
Total Pages: 556
Release: 2011
Genre: Fire ecology
ISBN:
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Descriptions of the fire regime in the Douglas-fir/western hemlock region of the Pacific Northwest traditionally have emphasized infrequent, predominantly stand-replacement fires and an associated linear pathway of stand development, where all stands proceed along a common pathway until reset by the next fire. Although such a description may apply in wetter parts of the region, recent fire-history research suggests drier parts of the region support a mixed-severity regime, where most fires have substantial representation of all severity classes and most stands experience at least one non-stand-replacing fire between stand-replacement events. This study combines field and modeling approaches to better understand the complex fire regime in the central western Cascades of Oregon. Stand-structure data and ages of more than 3,000 trees were collected at 124 stands throughout two study areas with physiography representative of western and eastern portions of the western Cascade Range. Major objectives were to (1) develop a conceptual model of fire-mediated pathways of stand development, (2) determine the strengths of influences of topography on spatial variation in the fire regime, (3) provide a stronger understanding of modeling approaches commonly used to gain insight into historical landscape structure, and (4) develop methods to predict trajectories of change in landscape age structure under a non-stationary fire regime. In the study area, non-stand-replacing fire interspersed with infrequent, stand-replacement events led to a variety of even-aged and multi-cohort stands. The majority of stands (75%) had two or more age cohorts, where post-fire cohorts were dominated either by shade-intolerant species or shade-tolerant species, depending largely on fire severity. Age structure, used as a proxy for the cumulative effects of fire on stand development, showed a moderately strong relationship to topography overall, but relationships were strongest at both extremes of a continuum of the influences of fire frequency and severity on stand development and relatively weak in the middle. High topographic relief in the eastern part of the western Cascades may amplify variation in microclimate and fuel moisture, leading to a finer-scale spatial variation in fire spread and behavior, and thus a broader range of stand age structures and stronger fidelity of age structure to slope position and terrain shape in the deeply dissected terrain of the eastern part of the western Cascades than in the gentler terrain of the western part. In the modeling component of my research, I was able to use analytical procedures to reproduce much of the output provided by a stochastic, spatial simulation model previously applied to evaluate historical landscape structure of the Oregon Coast Range. The analytical approximation provides an explicit representation of the effects of input parameters and interactions among them. The increased transparency of model function given by such an analysis may facilitate communication of model output and uncertainty among ecologists and forest managers. Analytical modeling approaches were expanded to characterize trajectories of change in forest age structure in response to changes in the fire regime. Following a change in fire frequency, the proportion of the landscape covered by stands of a given age class is expected to change along a non-monotonic trajectory rather than transition directly to its equilibrium abundance under the new regime. Under some scenarios of change in fire frequency, the time for the expected age distribution of a landscape to converge to the equilibrium distribution of the new regime can be determined based only on the magnitude of change in fire frequency, regardless of the initial value or the direction of change. The theoretical modeling exercises provide insight into historical trends in the study area. Compiled across all sample sites, the age distribution of Douglas-fir trees was strongly bimodal. Peaks of establishment dates in the 16th and 19th centuries were synchronous between the two study areas, and each peak of Douglas-fir establishment coincides with one of the two periods of region-wide extensive fire identified in a previous synthesis of fire-history studies. The modeling exercises support the development of such a bimodal age distribution in response to centennial-scale changes in fire frequency, and they illustrate how the relative abundance of different stand-structure types may have varied over the last several centuries.

The Effect of Fire Regime on Coarse Woody Debris in the West Central Cascades, Oregon

The Effect of Fire Regime on Coarse Woody Debris in the West Central Cascades, Oregon
Author: Pamela J. Wright
Publisher:
Total Pages: 218
Release: 1998
Genre: Fire ecology
ISBN:
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This study examined the effect of fire regime on coarse woody debris (CWD) mass using a combination of field data and modeling. The objectives were to use field sampling to determine how CWD differs between two areas that have had different fire regimes, and investigate how fire frequency and severity, stand growth and development, decomposition, and mortality rates affect the amount of CWD for sites experiencing two different fire regimes. One regime had infrequent, high severity fires, with a mean fire return interval over 300 years. The second regime exhibited more frequent (120 years), mixed-severity fires which created a mosaic of patches with multiple disturbance cohorts of shade tolerant tree species within stands. A conceptual model of how CWD might be affected by different fire regimes was developed. Then field data were gathered on CWD mass, tree biomass, and site productivity in Douglas-fir forests within stands that have had two different fire regimes for the past 500 years. Finally, a mass-budget model was developed to compare field data and model results, and was used to better understand the dynamics of CWD with regard to fire regime. While fire frequency and severity established the pattern of CWD succession, it is the interaction of fire regime with the other controlling factors that is responsible for the differences in CWD mass. The study yielded the following findings: 1) Field data indicated that CWD mass was almost twice as high in stands having an infrequent, stand-replacing fire regime (173 Mg/ha) compared with stands having a moderately frequent, mixed-severity fire regime (95 Mg/ha). 2) Factors that appear to have the greatest influence in the study area are decomposition rates, fire severity, fire frequency, and fuel consumption, suggesting that environment and stand structure control CWD mass more than fire regime per Se. 3) Site productivity and mortality rates are similar among sites in the study area, and do not exert a detectable influence for the range of environments examined. 4) CWD distribution was skewed toward the fresher decay classes in the stand-replacing fire regime, but was normally distributed in the mixed-severity regime. 5) CWD levels have greater temporal variability in the infrequent, stand-replacing fire regime than the mixed-severity regime. 6) In the stand-replacing regime, mortality over time contributes to CWD mass since there is a long span of time between events; whereas, in the mixed-severity regime mortality is more associated with events than with stand mortality over time.

Coarse Woody Detritus Dynamics, Variable Decay Rates and Their Contribution to Wildland Fuel Succession Following High-severity Fire Disturbance in Dry-mixed Conifer Forests of Oregon's Eastern Cascades

Coarse Woody Detritus Dynamics, Variable Decay Rates and Their Contribution to Wildland Fuel Succession Following High-severity Fire Disturbance in Dry-mixed Conifer Forests of Oregon's Eastern Cascades
Author: Christopher J. Dunn
Publisher:
Total Pages: 140
Release: 2011
Genre:
ISBN:
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Reducing future fire severity is a proposed ecological benefit of salvage logging following wildfire disturbance. Considerable debate continues over the ability of such management practices to achieve this objective given limited understanding of coarse woody detritus (CWD) dynamics, fuel bed alterations, and post-fire vegetative growth. The objective of this study was to estimate the dynamics of snags and logs in conjunction with surface fuel accumulation following high-severity fire disturbance in dry-mixed conifer forests of Oregon's eastern Cascades. Snag dynamics (fall and breakage rates) were estimated for Abies sp., Pinus ponderosa and Pinus contorta in three DBH classes of 23 cm (small), 23-41 cm (medium) and41 cm (large). A total of 5,103 snags in thirty 0.25-ha plots were sampled at seven different fire sites, covering a 24 year chronosequence following high-severity fire disturbance. Pinus ponderosa and Pinus contorta snags had the quickest fall rates with estimated half-lives of 7-8 and 12-13 years for small and medium sized snags, respectively. Large Pinus ponderosa snags had an estimated half-life of 17-18 years. Abies sp. snags fall rates were slower, with half-life estimates of 8-9, 14-15 and 20-21 years for small, medium and large snags respectively. Breakage rates were variable but correlated with wood strength, crown and stem weight and crown position (exposure to wind). Decomposition loss rate-constants were obtained from the same fire sites, up to seven years post-fire, by removing three cross-sections from each of sixty fire-killed Abies sp. snags, sixty Pinus ponderosa snags, and forty Pinus ponderosa logs. Abies sp. snags exhibited significant decay with an estimated decomposition loss rate-constant of k = 0.0149 yr−1. Pinus ponderosa snags did not exhibit significant decay, but logs did. Sapwood and heartwood decomposition loss rate-constants equaled k = 0.0362 yr−1 and k = 0.0164 yr−1, respectively. These values confirm hypothesized differences in decay rates among species and between snags and logs in dry forest environments. An empirical model was developed to link snag fall and breakage with snag and log decomposition during succession in order to estimate the contribution of fire killed biological legacies to fine and coarse woody detritus accumulation. Legacy CWD is responsible for the largest total accumulation of surface fuel as snags break and fall, but primarily in 100- and 1000-hr fuel classes. Decomposition rates increase as CWD moves from standing to downed material, reducing total CWD biomass by 30-50% in 24 years. Fine fuels are primarily derived from post-fire vegetation and steadily increase over the 24-year period. Herbaceous fuel loads peak within 2-4 years but decrease rapidly as Ceanothus velutinus and Arctostaphylos patula shrubs establish quickly and steadily increase in total biomass over 24 years. Spread rates and flame lengths in post-fire environments are primarily driven by fuels generated from new growth. The dynamic process of snag fall and breakage, and decomposition of snags and logs, limits CWD's effect on fire spread and intensity if reburning occurs, although soil heating and total heat release can be exacerbated by the combustion of decayed logs. Salvage logging significantly reduces CWD fuels but has limited impacts on other fuel bed components. Results of this study suggest post-fire management decisions consider vegetation dynamics as well as dead wood dynamics if reducing fire hazard is a primary objective.

The Ecological Importance of Mixed-Severity Fires

The Ecological Importance of Mixed-Severity Fires
Author: Dominick A. DellaSala
Publisher: Elsevier
Total Pages: 450
Release: 2015-06-08
Genre: Nature
ISBN: 0128027606
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The Ecological Importance of High-Severity Fires, presents information on the current paradigm shift in the way people think about wildfire and ecosystems. While much of the current forest management in fire-adapted ecosystems, especially forests, is focused on fire prevention and suppression, little has been reported on the ecological role of fire, and nothing has been presented on the importance of high-severity fire with regards to the maintenance of native biodiversity and fire-dependent ecosystems and species. This text fills that void, providing a comprehensive reference for documenting and synthesizing fire's ecological role. Offers the first reference written on mixed- and high-severity fires and their relevance for biodiversity Contains a broad synthesis of the ecology of mixed- and high-severity fires covering such topics as vegetation, birds, mammals, insects, aquatics, and management actions Explores the conservation vs. public controversy issues around megafires in a rapidly warming world

Variability in Historical Fire Patterns of a Moist Mixed-Conifer Forest in the Northern Blue Mountains of Oregon

Variability in Historical Fire Patterns of a Moist Mixed-Conifer Forest in the Northern Blue Mountains of Oregon
Author:
Publisher:
Total Pages: 64
Release: 2020
Genre: Conifers
ISBN:
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High variability in historical fire patterns characteristic to mixed-severity fire regimes is expected to have contributed to a structurally heterogeneous landscape throughout much of the forested ecosystems of the western United States. After more than a hundred years of fire exclusion in the region, many forests have shifted to a more homogeneous structure, which raises concern regarding these forests' ability to sustain expected increases in fire activity with a warming climate. The shift is not uniform across the west, however, and differences in historical disturbance patterns and changes due to land management are not well characterized in forests across a wide range of environmental settings. While there is broad agreement on the high (low) impact of fire exclusion on the structure and composition of low (high) elevation, dry (wet) forests in the west, much less is known about its effect in mid elevation, moist mixed-conifer forests. In order to provide reference conditions of wildfire patterns, this study reconstructs the variability in historical fire occurrence and severity and tree establishment in a moist mixed-conifer forest in northeastern Oregon's Blue Mountains. We used a novel multi-proxy approach, combining remote sensing, dendroecology, and mathematical models to comprehensively sample and reconstruct multi-century fire frequency and severity, and forest structural patterns. Based on over 550 tree-core and 100 fire-scar samples collected at 38 plots, we quantified historical fire severity and assessed the spatial heterogeneity of disturbance and establishment patterns across 9,300 ha in two subwatersheds. We identified high variability in historical fire patterns over fine scales between forest stands. Despite speculation that moist mixed-conifer forests experienced primarily infrequent and severe fires, relatively frequent fire (median intervals ranging from 14-42 years) of all severities (low, medium and high) at fine scales was common throughout the study area, with an abrupt decrease in fire activity after 1900. Concurrent post-fire establishment pulses of both shade-intolerant and shade-tolerant species were common, suggesting an initial floristics vegetation succession model. The results of this study highlight the complexity of the mixed-severity fire regime, long-term challenges and untested assumptions of post-fire responses of shade-tolerant species, as well as assumed infrequent fire activity in moist mixed-conifer forests, and thus can help inform discussions around appropriate restoration of fire-excluded, moist mixed-conifer forests of the northern Blue Mountains Ecoregion.