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• 1. [Article] Disturbance and dynamics of riparian forests in southwestern Oregon

  Fire exclusion has been associated with structural and compositional changes in many upland forests of the western United States, but little is known about the impacts on riparian forests, portions of ...

  Citation × Citation Citation Abstract Copy Title: Disturbance and dynamics of riparian forests in southwestern Oregon Author: Messier, Michael S. Fire exclusion has been associated with structural and compositional changes in many upland forests of the western United States, but little is known about the impacts on riparian forests, portions of the landscape protected for habitat and water quality. For this study, I characterized the historic disturbance and tree recruitment processes of riparian forests in southwestern Oregon. I identified the ways in which riparian forest structure and composition have changed over the past 100 to 150 years, with a particular focus on the effects of fire exclusion. I used dendro-ecological methods to analyze tree ring data collected in riparian forest stands of two vegetation types in the Rogue River basin of southwestern Oregon: the mesic 'Mixed Conifer' zone (Pinus-Pseudotsuga-Calocedrus-Abies) and the more xeric 'Interior Valley' zone (Pinus-Quercus-Pseudotsuga). My results suggest riparian forests in both vegetation zones developed with frequent disturbance by fire and that, since fire has been excluded, these forests have entered a new successional trajectory. In the Mixed Conifer zone, tree recruitment in the pre-settlement period appears to have been driven by the interaction between climatic fluctuations and mixed-severity fires, which historically maintained multi-aged stands of shade-intolerant species. Patches of highseverity fire within the mixed-severity matrix created large canopy gaps (>30 m in diameter) in which new cohorts of Douglas-fir (Pseudotsuga menziesii) could establish within existing stands and perpetuate Douglas-fir overstory dominance. Tree recruitment appears to have been closely linked Since fire exclusion became effective, there has been an increase in tree density and a shift toward the establishment of white fir (Abies concolor), a fire-sensitive, shade-tolerant species. In the Interior Valley zone, riparian forests were most likely shaped by a low-severity fire regime. Frequent fires likely killed most tree seedlings and maintained open savannas or woodlands with shade-intolerant hardwoods and scattered, open-grown conifers. Fire exclusion in the Interior Valley zone has resulted in exceptionally high survival rates in Douglas-fir recruited during the late 19th and early 20th centuries. This led to the establishment of a closed-canopy conifer forest with fewer shade-intolerant hardwoods, which are an important source of food and habitat for wildlife. My findings suggest future management guidelines for riparian forests in fire-prone forests of the Pacific Northwest should consider the substantial and potentially undesirable ecological effects of the current hands-off management policy in riparian forests. Future proposals to attempt restoration of pre-settlement forest structure and composition in upland forests should also consider including restoration treatments within adjoining riparian forests. Title: Disturbance and dynamics of riparian forests in southwestern Oregon Author: Messier, Michael S. Fire exclusion has been associated with structural and compositional changes in many upland forests of the western United States, but little is known about the impacts on riparian forests, portions of the landscape protected for habitat and water quality. For this study, I characterized the historic disturbance and tree recruitment processes of riparian forests in southwestern Oregon. I identified the ways in which riparian forest structure and composition have changed over the past 100 to 150 years, with a particular focus on the effects of fire exclusion. I used dendro-ecological methods to analyze tree ring data collected in riparian forest stands of two vegetation types in the Rogue River basin of southwestern Oregon: the mesic 'Mixed Conifer' zone (Pinus-Pseudotsuga-Calocedrus-Abies) and the more xeric 'Interior Valley' zone (Pinus-Quercus-Pseudotsuga). My results suggest riparian forests in both vegetation zones developed with frequent disturbance by fire and that, since fire has been excluded, these forests have entered a new successional trajectory. In the Mixed Conifer zone, tree recruitment in the pre-settlement period appears to have been driven by the interaction between climatic fluctuations and mixed-severity fires, which historically maintained multi-aged stands of shade-intolerant species. Patches of highseverity fire within the mixed-severity matrix created large canopy gaps (>30 m in diameter) in which new cohorts of Douglas-fir (Pseudotsuga menziesii) could establish within existing stands and perpetuate Douglas-fir overstory dominance. Tree recruitment appears to have been closely linked Since fire exclusion became effective, there has been an increase in tree density and a shift toward the establishment of white fir (Abies concolor), a fire-sensitive, shade-tolerant species. In the Interior Valley zone, riparian forests were most likely shaped by a low-severity fire regime. Frequent fires likely killed most tree seedlings and maintained open savannas or woodlands with shade-intolerant hardwoods and scattered, open-grown conifers. Fire exclusion in the Interior Valley zone has resulted in exceptionally high survival rates in Douglas-fir recruited during the late 19th and early 20th centuries. This led to the establishment of a closed-canopy conifer forest with fewer shade-intolerant hardwoods, which are an important source of food and habitat for wildlife. My findings suggest future management guidelines for riparian forests in fire-prone forests of the Pacific Northwest should consider the substantial and potentially undesirable ecological effects of the current hands-off management policy in riparian forests. Future proposals to attempt restoration of pre-settlement forest structure and composition in upland forests should also consider including restoration treatments within adjoining riparian forests. Close

• 2. [Article] CEO 1 ; An Illustrated Guide to Fire in Central Oregon Forests

  This pictorial guide is primarily intended to serve as a backdrop for field tours of central Oregon that involve topics surrounding wildland fire. It also is designed to provide an overview of the role ...

  Citation × Citation Citation Abstract Copy Title: CEO 1 ; An Illustrated Guide to Fire in Central Oregon Forests Author: Tappeiner, J. C. (John C.), Eckert, Bradley E., Walstad, John D., Oregon State University. Forest Research Laboratory This pictorial guide is primarily intended to serve as a backdrop for field tours of central Oregon that involve topics surrounding wildland fire. It also is designed to provide an overview of the role of fire in the major ecosystems characteristic of this region. Topics covered include fire history, fire regimes, current fire conditions, fire behavior, fire threats to natural resources, fuel treatments, interactions with the public, and future challenges and management options. A list of key references and glossary are also included. Title: CEO 1 ; An Illustrated Guide to Fire in Central Oregon Forests Author: Tappeiner, J. C. (John C.), Eckert, Bradley E., Walstad, John D., Oregon State University. Forest Research Laboratory This pictorial guide is primarily intended to serve as a backdrop for field tours of central Oregon that involve topics surrounding wildland fire. It also is designed to provide an overview of the role of fire in the major ecosystems characteristic of this region. Topics covered include fire history, fire regimes, current fire conditions, fire behavior, fire threats to natural resources, fuel treatments, interactions with the public, and future challenges and management options. A list of key references and glossary are also included. Close

• 3. [Article] Fire exclusion effects on riparian forest dynamics in southwestern Oregon

  This is the authors' peer-reviewed final manuscript. The published version is copyrighted by Elsevier and can be found here: http://www.journals.elsevier.com/forest-ecology-and-management/#description

  Citation × Citation Citation Abstract Copy Title: Fire exclusion effects on riparian forest dynamics in southwestern Oregon Author: Shatford, Jeff P.A., Messier, Michael S., Hibbs, David E. This is the authors' peer-reviewed final manuscript. The published version is copyrighted by Elsevier and can be found here: http://www.journals.elsevier.com/forest-ecology-and-management/#description Title: Fire exclusion effects on riparian forest dynamics in southwestern Oregon Author: Shatford, Jeff P.A., Messier, Michael S., Hibbs, David E. This is the authors' peer-reviewed final manuscript. The published version is copyrighted by Elsevier and can be found here: http://www.journals.elsevier.com/forest-ecology-and-management/#description Close

• 4. [Article] Mixed-Severity Fire Effects on Biological Legacies and Vegetation Response in Pseudotsuga Forests of Western Oregon's Central Cascades, USA

  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 ...

  Citation × Citation Citation Abstract Copy Title: Mixed-Severity Fire Effects on Biological Legacies and Vegetation Response in Pseudotsuga Forests of Western Oregon's Central Cascades, USA Author: Dunn, Christopher J. 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. Title: Mixed-Severity Fire Effects on Biological Legacies and Vegetation Response in Pseudotsuga Forests of Western Oregon's Central Cascades, USA Author: Dunn, Christopher J. 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. Close

• 5. [Article] Post-fire tree establishment and early cohort development in conifer forests of the western Cascades of Oregon, USA

  To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the author(s) ...

  Citation × Citation Citation Abstract Copy Title: Post-fire tree establishment and early cohort development in conifer forests of the western Cascades of Oregon, USA Author: Tepley, Alan J., Swanson, Frederick J., Spies, Thomas A. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by the Ecological Society of America. The published article can be found at: http://www.esajournals.org/loi/ecsp. Title: Post-fire tree establishment and early cohort development in conifer forests of the western Cascades of Oregon, USA Author: Tepley, Alan J., Swanson, Frederick J., Spies, Thomas A. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by the Ecological Society of America. The published article can be found at: http://www.esajournals.org/loi/ecsp. Close

• 6. [Article] Forest Successional and Disturbance Dynamics in the Southern Blue Mountains of Eastern Oregon

  The application of modern land management practices beginning at the turn of the 20th century is widely believed to have dramatically transformed forest landscapes of the inland Pacific Northwest. Restoring ...

  Citation × Citation Citation Abstract Copy Title: Forest Successional and Disturbance Dynamics in the Southern Blue Mountains of Eastern Oregon Author: Johnston, James D. (James Daniel) The application of modern land management practices beginning at the turn of the 20th century is widely believed to have dramatically transformed forest landscapes of the inland Pacific Northwest. Restoring historical conditions to make forests resilient to future climate and disturbance regimes is a major goal of federal forest managers. However, information about historical relationships between forest structure, forest composition, topography, climate, and disturbance sufficient to parameterize managers' decision-making is often lacking. This study uses dendroecological methods to reconstruct historical (1650-1900 CE) forest structure, composition, and fire disturbance, and to describe change over time across a wide range of forest types in the southern Blue Mountains of eastern Oregon. Results indicate that both fire frequency and climate controls on fire occurrence were similar across a broad range of forest types. Southern Blue Mountains forests are markedly different with respect to inherent site productivity and species composition, but frequent fire tended to equalize stand densities across the landscape prior to the exclusion of fire in the late 1800s. In the absence of fire, more productive mixed conifer sites have generally experienced the same or greater successional change as drier pine dominated sites. If restoring historical conditions is a goal, treatments appropriate to restore dry ponderosa pine forests are also appropriate for moister mixed conifer forest types. Title: Forest Successional and Disturbance Dynamics in the Southern Blue Mountains of Eastern Oregon Author: Johnston, James D. (James Daniel) The application of modern land management practices beginning at the turn of the 20th century is widely believed to have dramatically transformed forest landscapes of the inland Pacific Northwest. Restoring historical conditions to make forests resilient to future climate and disturbance regimes is a major goal of federal forest managers. However, information about historical relationships between forest structure, forest composition, topography, climate, and disturbance sufficient to parameterize managers' decision-making is often lacking. This study uses dendroecological methods to reconstruct historical (1650-1900 CE) forest structure, composition, and fire disturbance, and to describe change over time across a wide range of forest types in the southern Blue Mountains of eastern Oregon. Results indicate that both fire frequency and climate controls on fire occurrence were similar across a broad range of forest types. Southern Blue Mountains forests are markedly different with respect to inherent site productivity and species composition, but frequent fire tended to equalize stand densities across the landscape prior to the exclusion of fire in the late 1800s. In the absence of fire, more productive mixed conifer sites have generally experienced the same or greater successional change as drier pine dominated sites. If restoring historical conditions is a goal, treatments appropriate to restore dry ponderosa pine forests are also appropriate for moister mixed conifer forest types. Close

• 7. [Article] The Role of Plant-soil Feedback in the Invasion of Brachypodium sylvaticum in Douglas-fir Forests

  Invasive plants have the capacity to transform landscapes and alter ecosystem function, causing significant economic and ecological damage. These effects include displacement and reduction of native flora ...

  Citation × Citation Citation Abstract Copy Title: The Role of Plant-soil Feedback in the Invasion of Brachypodium sylvaticum in Douglas-fir Forests Author: Esterson, Andrew Invasive plants have the capacity to transform landscapes and alter ecosystem function, causing significant economic and ecological damage. These effects include displacement and reduction of native flora and fauna, altered fire regimes, modification of biotic and abiotic soil properties, as well as local, regional, and global economic impacts. With such large impacts it is important that we better understand invasion dynamics to help with prevention, control and mitigation of invasive species. One process that has been associated with plant invasion is plant-soil feedback (PSF). A PSF occurs when plants alter biotic and abiotic soil properties through a variety of root exudates and litter decomposition such that subsequent plant growth is either positively or negatively affected. Positive conspecific and negative heterospecific responses have been theorized to be invasive species traits that promote invasion. Once an invasive species is removed from a system, there is a chance that PSFs generated by that species will persist in the soil, which is often referred to as 'plant legacies' or 'legacy effects' and may negatively influence restoration efforts. In the U.S. Pacific Northwest (PNW), Brachypodium sylvaticum (slender false brome), a perennial bunch grass native to Eurasia, is listed as a quarantined invasive species in California, Oregon, and Washington. Currently, B. sylvaticum is in the midst of rapid population growth and range expansion with populations in New York, Virginia, and Ontario, Canada. With a quickly expanding range research is critical for successful efforts to reduce the spread of B. sylvaticum. We developed two experiments to determine if PSF is a contributing factor to B. sylvaticum invasion in PNW forests. We hypothesized that 1) B. sylvaticum has positive conspecific and negative heterospecific PSF, 2) native species PSF has no effect on B. sylvaticum, and 3) PSF generated by B. sylvaticum will persist in the soil once removed, but over time, response of native species, soil nutrients and bacterial community composition will change from the invaded conditioned. To test our first two hypotheses, B. sylvaticum and five common native plants from the Oregon Coastal range, including the economically important tree, Pseudotsuga menziesii (Douglas-fir), were grown in a greenhouse on wild forest soils that had either been sterilized or kept live to condition the soil biotic community to the invader and the native species. Brachypodium sylvaticum was then grown on soil conditioned by itself and soil conditioned by natives; each of the five native species was grown on soil conditioned by B. sylvaticum and on their own conditioned soils. Plant biomass along with species specific measurements (number of leaves, stems, tillers, stem diameter and height) were recorded and a relative response (RR) index was used to determine the direction of PSF for the invader and native species. To test our third hypothesis, in March, 2015, ten plots were established in the McDonald-Dunn Research Forest located in Corvallis, OR where B. sylvaticum had at least 75% cover. Herbicide was applied to half of each plot to make two soil treatments: soil with B. sylvaticum and soil without B. sylvaticum. Over a nine-month period three soil collections took place where soil was collected from all plots and treatments. Plant response was evaluated by growing four native species and B. sylvaticum on both soil treatments and evaluating total biomass with a RR index; plant response (via growth), soil nutrients and bacterial communities were measured for each collection period. Bacterial communities were measured with phospholipid fatty acid (PLFA) analysis and high throughput 16s rRNA amplicon sequencing. Contrary to our hypotheses, the RR to PSF generated by B. sylvaticum was negative for the invader and P. menziesii and neutral for all other natives. Soils conditioned by Bromus vulgaris inhibited B. sylvaticum growth whereas soils conditioned by Prunella vulgaris and P. menziesii promoted B. sylvaticum growth. When testing for legacy effects, the RR of P. menziesii was negative when grown on soils where B. sylvaticum had been removed for six-months (six-month soils) but when grown on soils where B. sylvaticum had been removed for nine-months (nine-month soil) the RR of P. menziesii was neutral. The RR of P. vulgaris to six-month soils was positive while its RR to nine-month soils was negative. Nutrient and bacterial communities did not change in response to B. sylvaticum removal suggesting that the biotic and abiotic legacy requires longer than nine-months to be observed or B. sylvaticum does not affect the response variables measured. Overall, our data suggest that PSF generated by B. sylvaticum does not facilitate the invasion process but does differentially affect native species growth over time. PSF generated by native grasses may be a useful restoration tool to help prevent B. sylvaticum invasion and we suggest planting native species at least nine-months after B. sylvaticum removal. Title: The Role of Plant-soil Feedback in the Invasion of Brachypodium sylvaticum in Douglas-fir Forests Author: Esterson, Andrew Invasive plants have the capacity to transform landscapes and alter ecosystem function, causing significant economic and ecological damage. These effects include displacement and reduction of native flora and fauna, altered fire regimes, modification of biotic and abiotic soil properties, as well as local, regional, and global economic impacts. With such large impacts it is important that we better understand invasion dynamics to help with prevention, control and mitigation of invasive species. One process that has been associated with plant invasion is plant-soil feedback (PSF). A PSF occurs when plants alter biotic and abiotic soil properties through a variety of root exudates and litter decomposition such that subsequent plant growth is either positively or negatively affected. Positive conspecific and negative heterospecific responses have been theorized to be invasive species traits that promote invasion. Once an invasive species is removed from a system, there is a chance that PSFs generated by that species will persist in the soil, which is often referred to as 'plant legacies' or 'legacy effects' and may negatively influence restoration efforts. In the U.S. Pacific Northwest (PNW), Brachypodium sylvaticum (slender false brome), a perennial bunch grass native to Eurasia, is listed as a quarantined invasive species in California, Oregon, and Washington. Currently, B. sylvaticum is in the midst of rapid population growth and range expansion with populations in New York, Virginia, and Ontario, Canada. With a quickly expanding range research is critical for successful efforts to reduce the spread of B. sylvaticum. We developed two experiments to determine if PSF is a contributing factor to B. sylvaticum invasion in PNW forests. We hypothesized that 1) B. sylvaticum has positive conspecific and negative heterospecific PSF, 2) native species PSF has no effect on B. sylvaticum, and 3) PSF generated by B. sylvaticum will persist in the soil once removed, but over time, response of native species, soil nutrients and bacterial community composition will change from the invaded conditioned. To test our first two hypotheses, B. sylvaticum and five common native plants from the Oregon Coastal range, including the economically important tree, Pseudotsuga menziesii (Douglas-fir), were grown in a greenhouse on wild forest soils that had either been sterilized or kept live to condition the soil biotic community to the invader and the native species. Brachypodium sylvaticum was then grown on soil conditioned by itself and soil conditioned by natives; each of the five native species was grown on soil conditioned by B. sylvaticum and on their own conditioned soils. Plant biomass along with species specific measurements (number of leaves, stems, tillers, stem diameter and height) were recorded and a relative response (RR) index was used to determine the direction of PSF for the invader and native species. To test our third hypothesis, in March, 2015, ten plots were established in the McDonald-Dunn Research Forest located in Corvallis, OR where B. sylvaticum had at least 75% cover. Herbicide was applied to half of each plot to make two soil treatments: soil with B. sylvaticum and soil without B. sylvaticum. Over a nine-month period three soil collections took place where soil was collected from all plots and treatments. Plant response was evaluated by growing four native species and B. sylvaticum on both soil treatments and evaluating total biomass with a RR index; plant response (via growth), soil nutrients and bacterial communities were measured for each collection period. Bacterial communities were measured with phospholipid fatty acid (PLFA) analysis and high throughput 16s rRNA amplicon sequencing. Contrary to our hypotheses, the RR to PSF generated by B. sylvaticum was negative for the invader and P. menziesii and neutral for all other natives. Soils conditioned by Bromus vulgaris inhibited B. sylvaticum growth whereas soils conditioned by Prunella vulgaris and P. menziesii promoted B. sylvaticum growth. When testing for legacy effects, the RR of P. menziesii was negative when grown on soils where B. sylvaticum had been removed for six-months (six-month soils) but when grown on soils where B. sylvaticum had been removed for nine-months (nine-month soil) the RR of P. menziesii was neutral. The RR of P. vulgaris to six-month soils was positive while its RR to nine-month soils was negative. Nutrient and bacterial communities did not change in response to B. sylvaticum removal suggesting that the biotic and abiotic legacy requires longer than nine-months to be observed or B. sylvaticum does not affect the response variables measured. Overall, our data suggest that PSF generated by B. sylvaticum does not facilitate the invasion process but does differentially affect native species growth over time. PSF generated by native grasses may be a useful restoration tool to help prevent B. sylvaticum invasion and we suggest planting native species at least nine-months after B. sylvaticum removal. Close