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• 1. [Article] Does wildfire likelihood increase following insect outbreaks in conifer forests?

  This is the publisher’s final pdf. The published article is copyrighted by Ecological Society of America and can be found at: http://www.esajournals.org/loi/ecsp

  Citation × Citation Citation Abstract Copy Title: Does wildfire likelihood increase following insect outbreaks in conifer forests? Author: Shaw, David C., Campbell, John L., Bailey, John D., Kennedy, Robert E., Zald, Harold S. J., Meigs, Garrett W. This is the publisher’s final pdf. The published article is copyrighted by Ecological Society of America and can be found at: http://www.esajournals.org/loi/ecsp Title: Does wildfire likelihood increase following insect outbreaks in conifer forests? Author: Shaw, David C., Campbell, John L., Bailey, John D., Kennedy, Robert E., Zald, Harold S. J., Meigs, Garrett W. This is the publisher’s final pdf. The published article is copyrighted by Ecological Society of America and can be found at: http://www.esajournals.org/loi/ecsp Close

• 2. [Article] Does wildfire likelihood increase following insect outbreaks in conifer forests?

  This is the publisher’s final pdf. The published article is copyrighted by The Author(s) and published by the Ecological Society of America. It can be found at: http://www.esajournals.org/loi/ecsp

  Citation × Citation Citation Abstract Copy Title: Does wildfire likelihood increase following insect outbreaks in conifer forests? Author: Meigs, Garrett W., Campbell, John L., Bailey, John D., Kennedy, Robert E., Zald, Harold S. J., Shaw, David C. This is the publisher’s final pdf. The published article is copyrighted by The Author(s) and published by the Ecological Society of America. It can be found at: http://www.esajournals.org/loi/ecsp Title: Does wildfire likelihood increase following insect outbreaks in conifer forests? Author: Meigs, Garrett W., Campbell, John L., Bailey, John D., Kennedy, Robert E., Zald, Harold S. J., Shaw, David C. This is the publisher’s final pdf. The published article is copyrighted by The Author(s) and published by the Ecological Society of America. It can be found at: http://www.esajournals.org/loi/ecsp Close

• 3. [Article] Does wildfire likelihood increase following insect outbreaks in conifer forests?

  This is the publisher’s final pdf. The published article is copyrighted by The Author(s) and published by the Ecological Society of America. It can be found at: http://www.esajournals.org/loi/ecsp

  Citation × Citation Citation Abstract Copy Title: Does wildfire likelihood increase following insect outbreaks in conifer forests? Author: Shaw, David C., Campbell, John L., Bailey, John D., Kennedy, Robert E., Zald, Harold S. J., Meigs, Garrett W. This is the publisher’s final pdf. The published article is copyrighted by The Author(s) and published by the Ecological Society of America. It can be found at: http://www.esajournals.org/loi/ecsp Title: Does wildfire likelihood increase following insect outbreaks in conifer forests? Author: Shaw, David C., Campbell, John L., Bailey, John D., Kennedy, Robert E., Zald, Harold S. J., Meigs, Garrett W. This is the publisher’s final pdf. The published article is copyrighted by The Author(s) and published by the Ecological Society of America. It can be found at: http://www.esajournals.org/loi/ecsp Close

• 4. [Article] Fire effects on wetland prairie species: final report

  Project No. 14-48-0001-96749

  Citation × Citation Citation Abstract Copy Title: Fire effects on wetland prairie species: final report Author: Wilson, Mark V., Clark, Deborah Louise, 1950- Project No. 14-48-0001-96749 Title: Fire effects on wetland prairie species: final report Author: Wilson, Mark V., Clark, Deborah Louise, 1950- Project No. 14-48-0001-96749 Close

• 5. [Article] Mapping disturbance interactions from earth and space : insect effects on tree mortality, fuels, and wildfires across forests of the Pacific Northwest

  Given the vital role of forest ecosystems in landscape pattern and process, it is important to quantify the effects, feedbacks, and uncertainties associated with forest disturbance dynamics. In western ...

  Citation × Citation Citation Abstract Copy Title: Mapping disturbance interactions from earth and space : insect effects on tree mortality, fuels, and wildfires across forests of the Pacific Northwest Author: Meigs, Garrett W. Given the vital role of forest ecosystems in landscape pattern and process, it is important to quantify the effects, feedbacks, and uncertainties associated with forest disturbance dynamics. In western North America, insects and wildfires are both native disturbances that have influenced forests for millennia, and both are projected to increase with anthropogenic climate change. Although there is acute concern that insect-caused tree mortality increases the likelihood or severity of subsequent wildfire, previous research has been mixed, with results often based on individual fire or insect events. Much of the ambivalence in the literature can be attributed to differences in the particular insect of interest, forest type, and fire event, but it is also related to the spatiotemporal scale of analysis and a general lack of geospatial datasets spanning enough time and space to capture multiple forest disturbances consistently and accurately. This dissertation presents a regional-scale framework to map, quantify, and understand insect-wildfire interactions across numerous insect and fire events across the Pacific Northwest region (PNW). Through three related studies, I worked with many collaborators to develop regionally extensive but fine-grained maps to assess the spatiotemporal patterns of wildfires and the two most pervasive, damaging forest insects in the PNW – mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins [Coleoptera: Scolytidae]; a bark beetle) and western spruce budworm (WSB; Choristoneura freemani Razowksi [Lepidoptera: Tortricidae]; a defoliator). The proximate objectives of developing new maps and summarizing where and when insects have occurred before wildfires enable us to address the ultimate question: How does forest insect activity influence the likelihood of subsequent wildfire? In a pilot study focused on the forest stand scale (Chapter Two), we leveraged a Landsat time series change detection algorithm (LandTrendr), annual forest health aerial detection surveys (ADS), and field measurements to investigate MPB and WSB effects on spectral trajectories, tree mortality, and fuel profiles at 38 plots in the Cascade Range of Oregon. Insect effects were evident in the Landsat time series as combinations of both short- and long-duration changes. WSB trajectories appeared to show a consistent temporal evolution of long-duration spectral decline followed by recovery, whereas MPB trajectories exhibited both short- and long-duration spectral declines and variable recovery rates. When comparing remote sensing data with field measurements of insect impacts, we found that spectral changes were related to cover-based estimates (e.g., tree basal area mortality and down coarse woody detritus). In contrast, ADS changes were related to count-based estimates (e.g., dead tree density). Fine woody detritus and forest floor depth were not well correlated with Landsat- or aerial survey-based change metrics. This study demonstrated the utility of insect mapping methods that capture a wide range of spectral trajectories, setting the stage for regional-scale mapping and analysis. In a regional assessment of MPB and WSB effects on tree mortality (Chapter Three), we developed Landsat-based insect maps and presented comparisons across space, time, and insect agents that have not been possible to date, complementing existing ADS maps by: (1) quantifying change in terms of field-measured tree mortality; (2) providing consistent estimates of change for multiple agents, particularly long-duration changes; (3) capturing variation of insect impacts at a finer spatial scale within ADS polygons, substantially reducing estimated insect extent. Despite high variation across the study region, spatiotemporal patterns were evident in both the ADS- and Landsat-based maps of insect activity. MPB outbreaks occurred in two phases -- first during the 1970s and 1980s in eastern and central Oregon and then more synchronously during the 2000s throughout the dry interior conifer forests of the PNW. Reflecting differences in habitat susceptibility and epidemiology, WSB outbreaks exhibited early activity in northern Washington and an apparent spread from the eastern to central PNW during the 1980s, returning to northern Washington during the 1990s and 2000s. Across the region, WSB exceeded MPB in extent and tree mortality impacts in all ecoregions except for one, suggesting that ongoing studies should account for both bark beetles and defoliators, particularly given recent and projected increases in wildfire extent. By combining these insect maps with an independent wildfire database (Chapter Four), we investigated wildfire likelihood following recent MPB and WSB outbreaks at ecoregional and regional scales. We computed wildfire likelihood with two-way binary matrices between fire and insects, testing for paired differences between percent burned with and without prior insect activity. All three disturbance agents occurred primarily in the drier, interior conifer forests east of the Cascade Range, with recent wildfires extending through the southern West Cascades and Klamath Mountains. In general, insect extent exceeded wildfire extent, and each disturbance typically affected less than 2% annually of a given ecoregion. In recent decades across the PNW, wildfire likelihood is not consistently higher in forests with prior insect outbreaks, but there is evidence of linked interactions that vary across insect agent (MPB and WSB), space (ecoregions), and time (interval since insect onset). For example, fire likelihood is higher following MPB activity in the North Cascades and West Cascades, particularly within the past 10 years, whereas fire likelihood is lower at various time lags following MPB in the Northern Rockies, East Cascades, and Blue Mountains. In contrast, fire likelihood is lower following WSB outbreaks at multiple time lags across all ecoregions. In addition, there are no consistent relationships between insect-fire likelihood and interannual fire extent, suggesting that other factors (such as climate) control the disproportionately large fire years accounting for the majority of regional fire extent. Although insects and wildfires do not appear to overlap enough to facilitate consistently positive linked disturbance interactions, specific fire events and years – such as 2003 and 2006 in the North Cascades – demonstrate high insect-fire co-occurrence and potential compound disturbance effects at the landscape scale. The results from this dissertation highlight the key ecological roles that native disturbances play in PNW forests. WSB, MPB, and wildfire have been relatively rare at the regional scale, but all three have had and will continue to have profound effects on particular forest stands and landscapes. Because scale is such an important aspect of both the disturbance phenomena themselves as well as our ability to detect the ecological changes they render, our results also underscore the importance of geospatial datasets that span multiple scales in space and time. Given concerns about forest health in a rapidly changing climate, long-term monitoring will enable forest managers to quantify and anticipate the independent and interactive effects of insects, wildfires, and other disturbances. Title: Mapping disturbance interactions from earth and space : insect effects on tree mortality, fuels, and wildfires across forests of the Pacific Northwest Author: Meigs, Garrett W. Given the vital role of forest ecosystems in landscape pattern and process, it is important to quantify the effects, feedbacks, and uncertainties associated with forest disturbance dynamics. In western North America, insects and wildfires are both native disturbances that have influenced forests for millennia, and both are projected to increase with anthropogenic climate change. Although there is acute concern that insect-caused tree mortality increases the likelihood or severity of subsequent wildfire, previous research has been mixed, with results often based on individual fire or insect events. Much of the ambivalence in the literature can be attributed to differences in the particular insect of interest, forest type, and fire event, but it is also related to the spatiotemporal scale of analysis and a general lack of geospatial datasets spanning enough time and space to capture multiple forest disturbances consistently and accurately. This dissertation presents a regional-scale framework to map, quantify, and understand insect-wildfire interactions across numerous insect and fire events across the Pacific Northwest region (PNW). Through three related studies, I worked with many collaborators to develop regionally extensive but fine-grained maps to assess the spatiotemporal patterns of wildfires and the two most pervasive, damaging forest insects in the PNW – mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins [Coleoptera: Scolytidae]; a bark beetle) and western spruce budworm (WSB; Choristoneura freemani Razowksi [Lepidoptera: Tortricidae]; a defoliator). The proximate objectives of developing new maps and summarizing where and when insects have occurred before wildfires enable us to address the ultimate question: How does forest insect activity influence the likelihood of subsequent wildfire? In a pilot study focused on the forest stand scale (Chapter Two), we leveraged a Landsat time series change detection algorithm (LandTrendr), annual forest health aerial detection surveys (ADS), and field measurements to investigate MPB and WSB effects on spectral trajectories, tree mortality, and fuel profiles at 38 plots in the Cascade Range of Oregon. Insect effects were evident in the Landsat time series as combinations of both short- and long-duration changes. WSB trajectories appeared to show a consistent temporal evolution of long-duration spectral decline followed by recovery, whereas MPB trajectories exhibited both short- and long-duration spectral declines and variable recovery rates. When comparing remote sensing data with field measurements of insect impacts, we found that spectral changes were related to cover-based estimates (e.g., tree basal area mortality and down coarse woody detritus). In contrast, ADS changes were related to count-based estimates (e.g., dead tree density). Fine woody detritus and forest floor depth were not well correlated with Landsat- or aerial survey-based change metrics. This study demonstrated the utility of insect mapping methods that capture a wide range of spectral trajectories, setting the stage for regional-scale mapping and analysis. In a regional assessment of MPB and WSB effects on tree mortality (Chapter Three), we developed Landsat-based insect maps and presented comparisons across space, time, and insect agents that have not been possible to date, complementing existing ADS maps by: (1) quantifying change in terms of field-measured tree mortality; (2) providing consistent estimates of change for multiple agents, particularly long-duration changes; (3) capturing variation of insect impacts at a finer spatial scale within ADS polygons, substantially reducing estimated insect extent. Despite high variation across the study region, spatiotemporal patterns were evident in both the ADS- and Landsat-based maps of insect activity. MPB outbreaks occurred in two phases -- first during the 1970s and 1980s in eastern and central Oregon and then more synchronously during the 2000s throughout the dry interior conifer forests of the PNW. Reflecting differences in habitat susceptibility and epidemiology, WSB outbreaks exhibited early activity in northern Washington and an apparent spread from the eastern to central PNW during the 1980s, returning to northern Washington during the 1990s and 2000s. Across the region, WSB exceeded MPB in extent and tree mortality impacts in all ecoregions except for one, suggesting that ongoing studies should account for both bark beetles and defoliators, particularly given recent and projected increases in wildfire extent. By combining these insect maps with an independent wildfire database (Chapter Four), we investigated wildfire likelihood following recent MPB and WSB outbreaks at ecoregional and regional scales. We computed wildfire likelihood with two-way binary matrices between fire and insects, testing for paired differences between percent burned with and without prior insect activity. All three disturbance agents occurred primarily in the drier, interior conifer forests east of the Cascade Range, with recent wildfires extending through the southern West Cascades and Klamath Mountains. In general, insect extent exceeded wildfire extent, and each disturbance typically affected less than 2% annually of a given ecoregion. In recent decades across the PNW, wildfire likelihood is not consistently higher in forests with prior insect outbreaks, but there is evidence of linked interactions that vary across insect agent (MPB and WSB), space (ecoregions), and time (interval since insect onset). For example, fire likelihood is higher following MPB activity in the North Cascades and West Cascades, particularly within the past 10 years, whereas fire likelihood is lower at various time lags following MPB in the Northern Rockies, East Cascades, and Blue Mountains. In contrast, fire likelihood is lower following WSB outbreaks at multiple time lags across all ecoregions. In addition, there are no consistent relationships between insect-fire likelihood and interannual fire extent, suggesting that other factors (such as climate) control the disproportionately large fire years accounting for the majority of regional fire extent. Although insects and wildfires do not appear to overlap enough to facilitate consistently positive linked disturbance interactions, specific fire events and years – such as 2003 and 2006 in the North Cascades – demonstrate high insect-fire co-occurrence and potential compound disturbance effects at the landscape scale. The results from this dissertation highlight the key ecological roles that native disturbances play in PNW forests. WSB, MPB, and wildfire have been relatively rare at the regional scale, but all three have had and will continue to have profound effects on particular forest stands and landscapes. Because scale is such an important aspect of both the disturbance phenomena themselves as well as our ability to detect the ecological changes they render, our results also underscore the importance of geospatial datasets that span multiple scales in space and time. Given concerns about forest health in a rapidly changing climate, long-term monitoring will enable forest managers to quantify and anticipate the independent and interactive effects of insects, wildfires, and other disturbances. Close

• 6. [Article] Contemporary regional forest dynamics in the Pacific Northwest

  Recent climatic warming trends and increases in the frequency and extent of wildfires have prompted much concern regarding the potential for rapid change in the structure and function of forested ecosystems ...

  Citation × Citation Citation Abstract Copy Title: Contemporary regional forest dynamics in the Pacific Northwest Author: Reilly, Matthew J. (Matthew Justin), 1975- Recent climatic warming trends and increases in the frequency and extent of wildfires have prompted much concern regarding the potential for rapid change in the structure and function of forested ecosystems around the world. Episodes of mortality in wildfires and insect outbreaks associated with drought have affected large areas and altered landscapes, but little is known about the cumulative effects of these disturbances at the regional scales. I used data from two different forest inventories in the Pacific Northwest to develop a framework for tracking regional forest dynamics and examine variation in tree mortality rates among vegetation zones that differ in biophysical setting as well as recent and historical disturbance regimes. In the second chapter I developed an empirically based framework for tracking regional forest dynamics using regional inventory data collected from 2001 to 2010. I characterized the major dimensions of forest structure and developed a classification incorporating multiple attributes of forest structure including biomass, size, and density of live trees, the distribution and abundance of dead wood, and the cover of understory vegetation. A single dimension related to live tree biomass accounted for almost half of the variation in a principal components analysis of structural attributes, but dimensions related to density and size of live trees, dead wood, and understory vegetation accounted for as much additional variation. Snags and biomass of dead and downed wood were related to multiple dimensions while understory vegetation acted independent of other dimensions. Results indicated that structural development is more complex than a monotonic accumulation of live biomass and that some components act independently or emerge at multiple stages of structural development. The hierarchical classification reduced the data into three “groups” based on live tree biomass, followed by eleven "classes" that varied in density and size of live trees, and finally twenty-five structural types that differed further in the abundance of dead wood and cover of understory vegetation. Most structural types were geographically widespread but varied in age of dominant trees by vegetation zone indicating that similar structural conditions developed in environments with different biophysical setting, climate, and disturbance/successional histories. Low live biomass structural types (<25 Mg/ha) differed in live tree density and the abundance of live and dead legacies, demonstrating that the variation in early developmental stages depends on the rate of tree establishment and the nature and severity of recent disturbance. Forests in early developmental stages made up less than 20% of most vegetation zones and diverse types with live or dead legacies associated with wildfires were rare. Moderate live biomass structural types (25-99 Mg/ha) represented multiple mid, mature, and late developmental stages, some of which lack analogs in existing conceptual models of structural development such as lower density woodlands with big trees. These structural types included two that have high densities of snags indicative of recent episodes of mortality; together these made up as much as 10% of some dry vegetation zones. Several high live biomass structural types (100->300 Mg/ha) were identified and substantiated the diversity and relative dominance of mature and later developmental stages, particularly in wet vegetation zones. The relative abundance and make up of structural types varied widely by vegetation zone. Most forests in wet vegetation zones had moderate to high live biomass and were in mid and mature developmental stages, while diverse early developmental stage stages were extremely rare. Dry forests had a far greater range of variation in the relative abundance of structural types which is partially attributable to the greater range of climatic conditions they included, but also to the occurrence of recent episodes of mortality associated with wildfires and insects. In the third chapter I examined variation in tree mortality rates using a different regional inventory that occurred from the mid-1990s to the mid-2000s. I compared the distribution of rates among stands in different vegetation zones and stages of structural developmental. I developed a simple framework based on changes in live tree density and mean tree size and examined trends in structural change associated with disturbances at different levels of mortality across all stages of structural development. Most plots were within the range of "background" mortality rates reported in other studies (<1.0 %/yr) and extremely high "stand-replacing" levels of mortality (>25%/yr) were rare. Approximately 30% of plot mortality rates occurred at intermediate levels (>1%/yr and <25%/yr) as result of insects and fire, highlighting the importance of conceptualizing mortality as a continuum as opposed to just “background” or “stand-replacement” to fully represent dynamics at a regional scale. The distributions of mortality differed among many vegetation zones. Levels of mortality were primarily <2.5%/yr in western hemlock, silver fir, and mountain hemlock vegetation zones where fires were rare and insects and pathogens occurred predominantly at endemic levels. Rates were highest in subalpine forests and higher elevation grand fir and Douglas-fir forests as a result of fire and insects. Mortality rates in ponderosa pine, the hottest driest forest vegetation zone, were surprisingly low, and there was little to no mortality in plots with no evidence of disturbance. Mortality rates varied among developmental stages in all vegetation zones but few consistent patterns emerged. Levels of mortality were often lowest in early developmental stages but varied in later stages where they were lowest in wet vegetation zones and highest in subalpine and dry vegetation zones. Application of a simple framework indicated that multiple trajectories of structural change were common at levels of mortality <2.5%/yr, but structural change at higher levels was predominantly associated with a “thinning” trajectory defined by decreases in density and increases in mean tree size. Results indicated that the rate and magnitude of mortality related change during the study period varies widely across the region. Rapid change has occurred in subalpine, grand fir/white fir, Douglas-fir, and ponderosa pine vegetation zones where disturbances such as insects and fire were widespread. However, these disturbances have potentially restored some aspects of historical structure by reducing overall density and increasing the dominance of bigger trees. In western hemlock, silver fir, and mountain hemlock vegetation zones where higher levels of mortality related to disturbances were rare, wildfires have increased landscape diversity by creating diverse early successional habitats and most change was more subtle but may be manifest oevr longer periods if current trends continue. This examination of short-period mortality rates and associated structural change across a broad geographic provides context for understanding trends from localized studies and potential ecological consequences of mortality, but there is still a great deal of uncertainty as to how the effects of a changing climate and disturbance regimes will manifest themselves over longer time scales. This dissertation is one of the first field based assessments of recent forest dynamics at a regional scale. The results of both chapters, each based on a different dataset, told a similar story. The abundance of structural types in various vegetation zones estimated during the mid-2000s was consistent with the cumulative effects of tree mortality during the preceding decade. It was evident that wildfire effects and recent mortality were small relative to the regional extent of the study and have contributed to structural diversity and restoration of historic structure in stands where fire exclusion and past logging has increased total stand density and decreased the dominance of big trees. However, the rate of change and cumulative effects of recent forest dynamics varied widely by geographic location and vegetation zone and there was greater variability and uncertainty regarding the effects of mortality at smaller landscape scales where individual events like large wildfires have the potential to rapidly alter the landscape structure and composition. Assessing this variability and the scales at which trade-offs (e.g. losses of old-growth and creation of diverse early developmental stages) occur will be an important next step in understanding the cumulative ecological effects of recent wildfires and tree mortality on Pacific Northwest forests. Title: Contemporary regional forest dynamics in the Pacific Northwest Author: Reilly, Matthew J. (Matthew Justin), 1975- Recent climatic warming trends and increases in the frequency and extent of wildfires have prompted much concern regarding the potential for rapid change in the structure and function of forested ecosystems around the world. Episodes of mortality in wildfires and insect outbreaks associated with drought have affected large areas and altered landscapes, but little is known about the cumulative effects of these disturbances at the regional scales. I used data from two different forest inventories in the Pacific Northwest to develop a framework for tracking regional forest dynamics and examine variation in tree mortality rates among vegetation zones that differ in biophysical setting as well as recent and historical disturbance regimes. In the second chapter I developed an empirically based framework for tracking regional forest dynamics using regional inventory data collected from 2001 to 2010. I characterized the major dimensions of forest structure and developed a classification incorporating multiple attributes of forest structure including biomass, size, and density of live trees, the distribution and abundance of dead wood, and the cover of understory vegetation. A single dimension related to live tree biomass accounted for almost half of the variation in a principal components analysis of structural attributes, but dimensions related to density and size of live trees, dead wood, and understory vegetation accounted for as much additional variation. Snags and biomass of dead and downed wood were related to multiple dimensions while understory vegetation acted independent of other dimensions. Results indicated that structural development is more complex than a monotonic accumulation of live biomass and that some components act independently or emerge at multiple stages of structural development. The hierarchical classification reduced the data into three “groups” based on live tree biomass, followed by eleven "classes" that varied in density and size of live trees, and finally twenty-five structural types that differed further in the abundance of dead wood and cover of understory vegetation. Most structural types were geographically widespread but varied in age of dominant trees by vegetation zone indicating that similar structural conditions developed in environments with different biophysical setting, climate, and disturbance/successional histories. Low live biomass structural types (<25 Mg/ha) differed in live tree density and the abundance of live and dead legacies, demonstrating that the variation in early developmental stages depends on the rate of tree establishment and the nature and severity of recent disturbance. Forests in early developmental stages made up less than 20% of most vegetation zones and diverse types with live or dead legacies associated with wildfires were rare. Moderate live biomass structural types (25-99 Mg/ha) represented multiple mid, mature, and late developmental stages, some of which lack analogs in existing conceptual models of structural development such as lower density woodlands with big trees. These structural types included two that have high densities of snags indicative of recent episodes of mortality; together these made up as much as 10% of some dry vegetation zones. Several high live biomass structural types (100->300 Mg/ha) were identified and substantiated the diversity and relative dominance of mature and later developmental stages, particularly in wet vegetation zones. The relative abundance and make up of structural types varied widely by vegetation zone. Most forests in wet vegetation zones had moderate to high live biomass and were in mid and mature developmental stages, while diverse early developmental stage stages were extremely rare. Dry forests had a far greater range of variation in the relative abundance of structural types which is partially attributable to the greater range of climatic conditions they included, but also to the occurrence of recent episodes of mortality associated with wildfires and insects. In the third chapter I examined variation in tree mortality rates using a different regional inventory that occurred from the mid-1990s to the mid-2000s. I compared the distribution of rates among stands in different vegetation zones and stages of structural developmental. I developed a simple framework based on changes in live tree density and mean tree size and examined trends in structural change associated with disturbances at different levels of mortality across all stages of structural development. Most plots were within the range of "background" mortality rates reported in other studies (<1.0 %/yr) and extremely high "stand-replacing" levels of mortality (>25%/yr) were rare. Approximately 30% of plot mortality rates occurred at intermediate levels (>1%/yr and <25%/yr) as result of insects and fire, highlighting the importance of conceptualizing mortality as a continuum as opposed to just “background” or “stand-replacement” to fully represent dynamics at a regional scale. The distributions of mortality differed among many vegetation zones. Levels of mortality were primarily <2.5%/yr in western hemlock, silver fir, and mountain hemlock vegetation zones where fires were rare and insects and pathogens occurred predominantly at endemic levels. Rates were highest in subalpine forests and higher elevation grand fir and Douglas-fir forests as a result of fire and insects. Mortality rates in ponderosa pine, the hottest driest forest vegetation zone, were surprisingly low, and there was little to no mortality in plots with no evidence of disturbance. Mortality rates varied among developmental stages in all vegetation zones but few consistent patterns emerged. Levels of mortality were often lowest in early developmental stages but varied in later stages where they were lowest in wet vegetation zones and highest in subalpine and dry vegetation zones. Application of a simple framework indicated that multiple trajectories of structural change were common at levels of mortality <2.5%/yr, but structural change at higher levels was predominantly associated with a “thinning” trajectory defined by decreases in density and increases in mean tree size. Results indicated that the rate and magnitude of mortality related change during the study period varies widely across the region. Rapid change has occurred in subalpine, grand fir/white fir, Douglas-fir, and ponderosa pine vegetation zones where disturbances such as insects and fire were widespread. However, these disturbances have potentially restored some aspects of historical structure by reducing overall density and increasing the dominance of bigger trees. In western hemlock, silver fir, and mountain hemlock vegetation zones where higher levels of mortality related to disturbances were rare, wildfires have increased landscape diversity by creating diverse early successional habitats and most change was more subtle but may be manifest oevr longer periods if current trends continue. This examination of short-period mortality rates and associated structural change across a broad geographic provides context for understanding trends from localized studies and potential ecological consequences of mortality, but there is still a great deal of uncertainty as to how the effects of a changing climate and disturbance regimes will manifest themselves over longer time scales. This dissertation is one of the first field based assessments of recent forest dynamics at a regional scale. The results of both chapters, each based on a different dataset, told a similar story. The abundance of structural types in various vegetation zones estimated during the mid-2000s was consistent with the cumulative effects of tree mortality during the preceding decade. It was evident that wildfire effects and recent mortality were small relative to the regional extent of the study and have contributed to structural diversity and restoration of historic structure in stands where fire exclusion and past logging has increased total stand density and decreased the dominance of big trees. However, the rate of change and cumulative effects of recent forest dynamics varied widely by geographic location and vegetation zone and there was greater variability and uncertainty regarding the effects of mortality at smaller landscape scales where individual events like large wildfires have the potential to rapidly alter the landscape structure and composition. Assessing this variability and the scales at which trade-offs (e.g. losses of old-growth and creation of diverse early developmental stages) occur will be an important next step in understanding the cumulative ecological effects of recent wildfires and tree mortality on Pacific Northwest forests. Close

• 7. [Article] A Landsat time series approach to characterize bark beetle and defoliator impacts on tree mortality and surface fuels in conifer forests

  This is the publisher’s final pdf. The published article is copyrighted by Elsevier and can be found at: http://www.elsevier.com/.

  Citation × Citation Citation Abstract Copy Title: A Landsat time series approach to characterize bark beetle and defoliator impacts on tree mortality and surface fuels in conifer forests Author: Meigs, Garrett W., Cohen, Warren B., Kennedy, Robert E. This is the publisher’s final pdf. The published article is copyrighted by Elsevier and can be found at: http://www.elsevier.com/. Title: A Landsat time series approach to characterize bark beetle and defoliator impacts on tree mortality and surface fuels in conifer forests Author: Meigs, Garrett W., Cohen, Warren B., Kennedy, Robert E. This is the publisher’s final pdf. The published article is copyrighted by Elsevier and can be found at: http://www.elsevier.com/. Close