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• 1. [Article] Correction of deposit ages for inherited ages of charcoal: implications for sediment dynamics inferred from random sampling of deposits on headwater valley floors

  This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.sciencedirect.com/science/journal/0277...

  Citation × Citation Citation Abstract Copy Title: Correction of deposit ages for inherited ages of charcoal: implications for sediment dynamics inferred from random sampling of deposits on headwater valley floors Author: Frueh, W. Terry, Lancaster, Stephen T. This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.sciencedirect.com/science/journal/02773791. Title: Correction of deposit ages for inherited ages of charcoal: implications for sediment dynamics inferred from random sampling of deposits on headwater valley floors Author: Frueh, W. Terry, Lancaster, Stephen T. This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.sciencedirect.com/science/journal/02773791. Close

• 2. [Article] Role of Extreme Events on Sedimentation in Loon Lake, Oregon Coast Range, USA

  Sediment cores were retrieved from a landslide-dammed lake, recording events back to the 5th century AD in a forested, mountainous catchment. These cores provide an opportunity to compare the impacts of ...

  Citation × Citation Citation Abstract Copy Title: Role of Extreme Events on Sedimentation in Loon Lake, Oregon Coast Range, USA Author: Richardson, Kristin Noel Duckworth Sediment cores were retrieved from a landslide-dammed lake, recording events back to the 5th century AD in a forested, mountainous catchment. These cores provide an opportunity to compare the impacts of known recent perturbations, including floods and timber harvesting with those of the early period of the core, flood, fire, and earthquake. A multi-parameter approach was used to measure characteristics of sediment with high-resolution grain size, %TC, %TN, and magnetic susceptibility analysis. ¹³⁷Cs atmospheric deposition and radiocarbon dating techniques were used for age control, as well as a varved record in the last 75 years. The estimated mean mass accumulation rate from 1939 to 1978 AD, the time of peak timber harvest and a cool wet phase of the Pacific Decadal Oscillation (PDO), was 0.79 (0.74-0.92) g cm⁻² y⁻¹, significantly higher than estimated mean rates of both the more recent contemporary period, 1979-2012 AD, at 0.58 (0.48-0.70) and the entire early period, 0.44 (0.41-0.46). Several event beds are coeval with estimated ages of eight Cascadia subduction zone earthquakes in the early period, including the 1700 AD Mw 9.0 earthquake. These beds are predominantly hyperpycnites, as are the known flood deposits in the contemporary period, with the exception of one debris flow within a 23-cm thick event bed deposited at approximately 700 AD. The high mass accumulation rate and high concentration of thick event beds and layers during the early contemporary period point to the extraordinary role of timber harvesting in priming the landscape for subsequent sedimentary delivery during floods. Title: Role of Extreme Events on Sedimentation in Loon Lake, Oregon Coast Range, USA Author: Richardson, Kristin Noel Duckworth Sediment cores were retrieved from a landslide-dammed lake, recording events back to the 5th century AD in a forested, mountainous catchment. These cores provide an opportunity to compare the impacts of known recent perturbations, including floods and timber harvesting with those of the early period of the core, flood, fire, and earthquake. A multi-parameter approach was used to measure characteristics of sediment with high-resolution grain size, %TC, %TN, and magnetic susceptibility analysis. ¹³⁷Cs atmospheric deposition and radiocarbon dating techniques were used for age control, as well as a varved record in the last 75 years. The estimated mean mass accumulation rate from 1939 to 1978 AD, the time of peak timber harvest and a cool wet phase of the Pacific Decadal Oscillation (PDO), was 0.79 (0.74-0.92) g cm⁻² y⁻¹, significantly higher than estimated mean rates of both the more recent contemporary period, 1979-2012 AD, at 0.58 (0.48-0.70) and the entire early period, 0.44 (0.41-0.46). Several event beds are coeval with estimated ages of eight Cascadia subduction zone earthquakes in the early period, including the 1700 AD Mw 9.0 earthquake. These beds are predominantly hyperpycnites, as are the known flood deposits in the contemporary period, with the exception of one debris flow within a 23-cm thick event bed deposited at approximately 700 AD. The high mass accumulation rate and high concentration of thick event beds and layers during the early contemporary period point to the extraordinary role of timber harvesting in priming the landscape for subsequent sedimentary delivery during floods. Close

• 3. [Article] Distribution of juvenile salmonids and stream habitat relative to 15-year-old debris-flow deposits in the Oregon Coast Range

  Debris flows, common disturbances in many mountainous areas, initially scour or bury stream habitats; however, debris flows deliver vast amounts of wood, boulders, and gravel that may ultimately form complex ...

  Citation × Citation Citation Abstract Copy Title: Distribution of juvenile salmonids and stream habitat relative to 15-year-old debris-flow deposits in the Oregon Coast Range Author: Kirkby, Kristen-Marie S. Debris flows, common disturbances in many mountainous areas, initially scour or bury stream habitats; however, debris flows deliver vast amounts of wood, boulders, and gravel that may ultimately form complex stream habitat to potentially support a diverse salmonid assemblage. The materials deposited by debris flows would otherwise be inaccessible to streams, and thus deposits may play an important role in creating and maintaining complex salmonid habitat over time. Despite the potential of deposits for increasing habitat complexity, most fish studies have focused on the destructive effects of debris flows and short-term recovery and re-colonization in scour zones. Debris-flows that occurred during the record-setting winter storms of 1996 in western Oregon, USA, provide an opportunity to study intermediate-term effects of debris-flow deposits on abundances and habitat for juvenile salmonids. In this setting, I surveyed salmonid abundance and habitat in three Oregon Coast Range streams that contained several debris-flow deposits from the 1996 storms. I explained fish abundance using hierarchical models, accounting for heterogeneous detection probabilities with repeated counts from multiple-pass snorkeling. The "best" hierarchical model of detection probability and abundance was selected (QAIC) from pool and snorkel-pass characteristics separately for juvenile coho salmon (Oncorhynchus kisutch), age 0+ trout, and age 1+ trout (Oncorhynchus spp.) in each stream. Adding distance to the nearest 1996 debris-flow deposit (DDF) produced a significant drop-in-deviance for four of nine "best" models, including at least one in each stream and for each species/age-class. In these four models, salmonid abundance decreased with increasing distance from deposit. As a potential explanation, several pool habitat characteristics were correlated (Spearman's rank) with DDF. Results varied across streams, but generally, percent of substrate as bedrock was lower and boulder density and percent substrate as gravel were higher closer to deposits. Although repeat counts are increasingly used in hierarchical modeling of heterogeneous detection probabilities and abundance for other wildlife species, studies of fish often rely on uncalibrated, single-pass snorkel counts. When exploring the value of repeat counts, I found that juvenile salmonid abundance decreased with increasing distance from debris-flow deposits in more multiple-pass hierarchical models that accounted for heterogeneous detection probabilities than for single-pass models that did not. Thus, modeling heterogeneous detection probabilities with repeated snorkel counts may be beneficial in other situations, addressing limitations of uncalibrated indices without relying on methods such as electrofishing, which may be difficult or impossible for remote study areas, longer surveys, or sensitive species. My findings suggest that debris-flow deposits may influence salmonid abundances after 15 years, and support management of debris flow-prone hillslopes and low-order channels to deliver elements of stream habitat complexity. Title: Distribution of juvenile salmonids and stream habitat relative to 15-year-old debris-flow deposits in the Oregon Coast Range Author: Kirkby, Kristen-Marie S. Debris flows, common disturbances in many mountainous areas, initially scour or bury stream habitats; however, debris flows deliver vast amounts of wood, boulders, and gravel that may ultimately form complex stream habitat to potentially support a diverse salmonid assemblage. The materials deposited by debris flows would otherwise be inaccessible to streams, and thus deposits may play an important role in creating and maintaining complex salmonid habitat over time. Despite the potential of deposits for increasing habitat complexity, most fish studies have focused on the destructive effects of debris flows and short-term recovery and re-colonization in scour zones. Debris-flows that occurred during the record-setting winter storms of 1996 in western Oregon, USA, provide an opportunity to study intermediate-term effects of debris-flow deposits on abundances and habitat for juvenile salmonids. In this setting, I surveyed salmonid abundance and habitat in three Oregon Coast Range streams that contained several debris-flow deposits from the 1996 storms. I explained fish abundance using hierarchical models, accounting for heterogeneous detection probabilities with repeated counts from multiple-pass snorkeling. The "best" hierarchical model of detection probability and abundance was selected (QAIC) from pool and snorkel-pass characteristics separately for juvenile coho salmon (Oncorhynchus kisutch), age 0+ trout, and age 1+ trout (Oncorhynchus spp.) in each stream. Adding distance to the nearest 1996 debris-flow deposit (DDF) produced a significant drop-in-deviance for four of nine "best" models, including at least one in each stream and for each species/age-class. In these four models, salmonid abundance decreased with increasing distance from deposit. As a potential explanation, several pool habitat characteristics were correlated (Spearman's rank) with DDF. Results varied across streams, but generally, percent of substrate as bedrock was lower and boulder density and percent substrate as gravel were higher closer to deposits. Although repeat counts are increasingly used in hierarchical modeling of heterogeneous detection probabilities and abundance for other wildlife species, studies of fish often rely on uncalibrated, single-pass snorkel counts. When exploring the value of repeat counts, I found that juvenile salmonid abundance decreased with increasing distance from debris-flow deposits in more multiple-pass hierarchical models that accounted for heterogeneous detection probabilities than for single-pass models that did not. Thus, modeling heterogeneous detection probabilities with repeated snorkel counts may be beneficial in other situations, addressing limitations of uncalibrated indices without relying on methods such as electrofishing, which may be difficult or impossible for remote study areas, longer surveys, or sensitive species. My findings suggest that debris-flow deposits may influence salmonid abundances after 15 years, and support management of debris flow-prone hillslopes and low-order channels to deliver elements of stream habitat complexity. Close

• 4. [Article] Tillamook volcanic series : further evidence for tectonic rotation of the Oregon Coast Range

  copyrighted by American Geophysical Union

  Citation × Citation Citation Abstract Copy Title: Tillamook volcanic series : further evidence for tectonic rotation of the Oregon Coast Range Author: Cox, Allan, Magill, James, Duncan, Robert A. copyrighted by American Geophysical Union Title: Tillamook volcanic series : further evidence for tectonic rotation of the Oregon Coast Range Author: Cox, Allan, Magill, James, Duncan, Robert A. copyrighted by American Geophysical Union Close

• 5. [Article] Silvicultural Treatment Impacts on Understory Trees and 20-Year Understory Vegetation Dynamics in Mature Douglas-Fir Forests

  Policy regarding the management of public forests has undergone a drastic shift over the past couple of decades due to the loss old-growth forests in the Pacific Northwest (PNW) of the United States. For ...

  Citation × Citation Citation Abstract Copy Title: Silvicultural Treatment Impacts on Understory Trees and 20-Year Understory Vegetation Dynamics in Mature Douglas-Fir Forests Author: Priebe, Jim E. Policy regarding the management of public forests has undergone a drastic shift over the past couple of decades due to the loss old-growth forests in the Pacific Northwest (PNW) of the United States. For much of the 20th century, forest management on public lands emphasized timber production through the use of even-aged management practices. There has been increasing recognition, however, that traditional even-aged management approaches are unable to support species that rely on the complex, heterogeneous structures provided by old-growth forests. In response, public forest managers have redirected their focus to developing more ecologically sustainable forests capable of meeting a broad array of objectives including an increasing emphasis on the development of late-seral and old-growth characteristics. Thinning has been identified as a promising method for promoting late-seral characteristics in managed stands. Recent long-term studies have shown that thinning stands does indeed accelerate the development of at least some late-seral structure characteristics, particularly when varying levels of thinning intensity and non-uniform retention patterns are incorporated into silvicultural prescriptions. Likewise, thinning has also shown some ability to increase the abundance of late-seral associated plant species in the understory. The impacts of thinning on vegetation dynamics are complicated by external factors such as natural disturbance events and the influence of pre-treatment vegetation on post-treatment communities. Within the context of managing for late-seral attributes, thinning is used to imitate natural disturbance processes. However, this does not preclude the occurrence of natural disturbances, which may either disrupt or compound treatment effects. Initial site conditions create another potential complication for the development of late-seral attributes by limiting the potential for change in understory communities. While some studies have shown that thinning improves late-seral plant abundance, others have found that the legacy of pre-treatment vegetation has a stronger impact on post-treatment communities. This study focused on the impacts of ice storm disturbance and pre-treatment vegetation on the understory of mature Douglas-fir forests using the ongoing Mature Forest Study (MFS), a long-term silvicultural experiment evaluating the effects of thinning and understory vegetation management treatments, as a framework. The first study examined the impact of an ice storm (glaze disturbance) on planted understory trees. Specifically, I looked at the effect of understory tree species, tree size, and overstory neighborhood environment on the type (bending, crown loss), source (ice loading, falling debris), and severity of damage experienced by planted understory trees at one of the MFS sites. Tree species, size, and overstory environment all affected the amount of understory glaze damage. Frequency and severity of damage both varied among underplanted tree species. In general, smaller trees were more prone to being bent, while larger trees were more susceptible to crown loss. The Douglas-fir component of the overstory provided enough additional sheltering that the increased risk to understory trees from falling debris was balanced by a corresponding decrease in the odds of damage by ice loading. This was not the case for the hardwood component; increasing risk of damage to understory trees from falling debris with increasing hardwood basal area drove an overall increase in the risk of understory damage as hardwood basal area increased. This study suggests that species, tree size, and overstory environment all need to be considered by managers hoping to reduce glaze damage risk to younger cohorts in multi-aged stands. The second study investigated the impacts of thinning intensity and herbicide application on the long-term (20-year post-treatment) development of understory vegetation communities on both of the MFS sites. Trends were examined with a focus on the ability of herbicide application, in concert with thinning treatments, to reduce the legacy of common pre-treatment species and promote the abundance of late-seral associates. Results indicated that both thinning intensity and herbicide application affected 20-year changes in understory plant community composition. Herbicide application was associated with a decrease in the abundance of common pre-treatment species, suggesting that it did reduce the legacy effect. However, this was not associated with any change in the abundance of late-seral species. While light thinning showed some ability to mitigate decline in late-seral species relative to higher intensity thinnings, there was no evidence of treatment interaction with herbicide application. These results suggest that while managers may be able to reduce the influence of initial site conditions on post-treatment vegetation communities, the use of herbicides offers little control over the successional trajectory of the understory. Light thinning appears to be the most effective means of increasing late-seral species abundance, although the use of herbicides to meet other management objectives is not contraindicated by the results of this study. Overall, these results suggest that the best options available to managers to both reduce glaze disturbance impacts to understory trees and hasten the development of late-seral plant communities are heavy thinning with unmanaged leave patches to provide late-seral refugia, or light thinning with gaps to provide growing space for better tree regeneration. Title: Silvicultural Treatment Impacts on Understory Trees and 20-Year Understory Vegetation Dynamics in Mature Douglas-Fir Forests Author: Priebe, Jim E. Policy regarding the management of public forests has undergone a drastic shift over the past couple of decades due to the loss old-growth forests in the Pacific Northwest (PNW) of the United States. For much of the 20th century, forest management on public lands emphasized timber production through the use of even-aged management practices. There has been increasing recognition, however, that traditional even-aged management approaches are unable to support species that rely on the complex, heterogeneous structures provided by old-growth forests. In response, public forest managers have redirected their focus to developing more ecologically sustainable forests capable of meeting a broad array of objectives including an increasing emphasis on the development of late-seral and old-growth characteristics. Thinning has been identified as a promising method for promoting late-seral characteristics in managed stands. Recent long-term studies have shown that thinning stands does indeed accelerate the development of at least some late-seral structure characteristics, particularly when varying levels of thinning intensity and non-uniform retention patterns are incorporated into silvicultural prescriptions. Likewise, thinning has also shown some ability to increase the abundance of late-seral associated plant species in the understory. The impacts of thinning on vegetation dynamics are complicated by external factors such as natural disturbance events and the influence of pre-treatment vegetation on post-treatment communities. Within the context of managing for late-seral attributes, thinning is used to imitate natural disturbance processes. However, this does not preclude the occurrence of natural disturbances, which may either disrupt or compound treatment effects. Initial site conditions create another potential complication for the development of late-seral attributes by limiting the potential for change in understory communities. While some studies have shown that thinning improves late-seral plant abundance, others have found that the legacy of pre-treatment vegetation has a stronger impact on post-treatment communities. This study focused on the impacts of ice storm disturbance and pre-treatment vegetation on the understory of mature Douglas-fir forests using the ongoing Mature Forest Study (MFS), a long-term silvicultural experiment evaluating the effects of thinning and understory vegetation management treatments, as a framework. The first study examined the impact of an ice storm (glaze disturbance) on planted understory trees. Specifically, I looked at the effect of understory tree species, tree size, and overstory neighborhood environment on the type (bending, crown loss), source (ice loading, falling debris), and severity of damage experienced by planted understory trees at one of the MFS sites. Tree species, size, and overstory environment all affected the amount of understory glaze damage. Frequency and severity of damage both varied among underplanted tree species. In general, smaller trees were more prone to being bent, while larger trees were more susceptible to crown loss. The Douglas-fir component of the overstory provided enough additional sheltering that the increased risk to understory trees from falling debris was balanced by a corresponding decrease in the odds of damage by ice loading. This was not the case for the hardwood component; increasing risk of damage to understory trees from falling debris with increasing hardwood basal area drove an overall increase in the risk of understory damage as hardwood basal area increased. This study suggests that species, tree size, and overstory environment all need to be considered by managers hoping to reduce glaze damage risk to younger cohorts in multi-aged stands. The second study investigated the impacts of thinning intensity and herbicide application on the long-term (20-year post-treatment) development of understory vegetation communities on both of the MFS sites. Trends were examined with a focus on the ability of herbicide application, in concert with thinning treatments, to reduce the legacy of common pre-treatment species and promote the abundance of late-seral associates. Results indicated that both thinning intensity and herbicide application affected 20-year changes in understory plant community composition. Herbicide application was associated with a decrease in the abundance of common pre-treatment species, suggesting that it did reduce the legacy effect. However, this was not associated with any change in the abundance of late-seral species. While light thinning showed some ability to mitigate decline in late-seral species relative to higher intensity thinnings, there was no evidence of treatment interaction with herbicide application. These results suggest that while managers may be able to reduce the influence of initial site conditions on post-treatment vegetation communities, the use of herbicides offers little control over the successional trajectory of the understory. Light thinning appears to be the most effective means of increasing late-seral species abundance, although the use of herbicides to meet other management objectives is not contraindicated by the results of this study. Overall, these results suggest that the best options available to managers to both reduce glaze disturbance impacts to understory trees and hasten the development of late-seral plant communities are heavy thinning with unmanaged leave patches to provide late-seral refugia, or light thinning with gaps to provide growing space for better tree regeneration. Close

• 6. [Article] Particulate organic matter export by two contrasting small mountainous rivers from the Pacific Northwest, U.S.A.

  This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/jgr/.

  Citation × Citation Citation Abstract Copy Title: Particulate organic matter export by two contrasting small mountainous rivers from the Pacific Northwest, U.S.A. Author: Hatten, Jeff A., Goni, Miguel A., Borgeld, Jeffry C., Wheatcroft, Robert A. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/jgr/. Title: Particulate organic matter export by two contrasting small mountainous rivers from the Pacific Northwest, U.S.A. Author: Hatten, Jeff A., Goni, Miguel A., Borgeld, Jeffry C., Wheatcroft, Robert A. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/jgr/. Close

• 7. [Article] Eocene extension in Idaho generated massive sediment floods into the Franciscan trench and into the Tyee, Great Valley, and Green River basins

  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 Geological ...

  Citation × Citation Citation Abstract Copy Title: Eocene extension in Idaho generated massive sediment floods into the Franciscan trench and into the Tyee, Great Valley, and Green River basins Author: Kent, Adam J.R., Wells, Ray E., Dumitru, Trevor A., Ernst, W.G., Graham, Stephan A., Farmer, Lucia P., Wright, James E., Wooden, Joseph L. 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 Geological Society of America and can be found at: http://www.geosociety.org/. Title: Eocene extension in Idaho generated massive sediment floods into the Franciscan trench and into the Tyee, Great Valley, and Green River basins Author: Kent, Adam J.R., Wells, Ray E., Dumitru, Trevor A., Ernst, W.G., Graham, Stephan A., Farmer, Lucia P., Wright, James E., Wooden, Joseph L. 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 Geological Society of America and can be found at: http://www.geosociety.org/. Close

• 8. [Article] Early Oligocene intrusions in the central Coast Range of Oregon : petrography, geochemistry, geochronology and implications for the Tertiary magmatic evolution of the Cascadia forearc

  The Early Oligocene Oregon Coast Range Intrusions (OCRI) consist of gabbroic rocks and lesser alkalic intrusive bodies that were emplaced in marine sedimentary units and volcanic sequences within a Tertiary ...

  Citation × Citation Citation Abstract Copy Title: Early Oligocene intrusions in the central Coast Range of Oregon : petrography, geochemistry, geochronology and implications for the Tertiary magmatic evolution of the Cascadia forearc Author: Oxford, Jeremiah The Early Oligocene Oregon Coast Range Intrusions (OCRI) consist of gabbroic rocks and lesser alkalic intrusive bodies that were emplaced in marine sedimentary units and volcanic sequences within a Tertiary Cascadia forearc basin. The alkalic intrusions include nepheline syenite, camptonite, and alkaline basalt. The gabbros occur as dikes and differentiated sills. Presently, erosional remnants of the intrusions underlie much of the high topography along the axis of the central Oregon Coast Range. The intrusive suite is most likely associated with Tertiary oblique rifting of the North America continental margin. Dextral shear and extension along the continental margin may have been a consequence of northeast-directed oblique Farallon plate convergence. However, while both the gabbroic and alkaline OCRI appear to be related to tectonic extension, major and trace element geochemistry reveal separate parental magma sources between the two suites. The OCRI are part of a long-lived (42-30 Ma) magmatic forearc province that includes the Yachats Basalt and Cascade Head Basalt. The timing of Cascadia forearc magmatism correlates with a significant decrease in convergence rates between the Farallon and North American plates from 42 to 28 Ma. The OCRI are also contemporaneous with magmatism that occurred over a broad area of the Pacific Northwest (e.g. Western Cascades, John Day Formation). New radiometric age data acquired from the [superscript 40]Ar-[superscript 39]Ar incremental heating experiments indicate that OCRI magmatism occurred between ~36 to 32 Ma; a longer interval than previously thought. The alkaline OCRI are closely associated with the late Eocene OIB-like Yachats Basalt and Cascade Head Basalt forearc volcanic centers in both space and time. In addition, trace element geochemical data suggest similar parental magma sources for the alkaline OCRI and the forearc volcanic centers. The geochemistry of the OCRI camptonites and alkaline basalts is typical of continental rift zones and oceanic intraplate environments. Major element geochemical data indicate that differentiation by crystal fractionation was the primary process involved in the magmatic evolution of the alkaline OCRI. The OCRI camptonites are volatile-rich equivalents of alkaline basaltic or basanitic parental magmas. Both trace element and major element geochemical data imply that the nepheline syenites and the camptonites were derived from similar alkaline parental magma sources. However, the nepheline syenites are not simple derivatives of the camptonite magmas. Instead, they appear to be alkaline variations of trachyandesites and rhyolites found in the forearc volcanic centers. The alkaline OCRI parental magmas were generated from small degrees of partial melting of an enriched OIB-like mantle source. There are two possible mantle sources for the alkaline OCRI: 1) An enriched lithospheric Siletzia mantle source that was previously metasomatized by deep-sourced alkaline melts or 2) upwelling asthenospheric mantle from beneath the subducting slab which would require a slab window. If the alkaline OCRI were derived from the lithospheric Siletzia mantle, then the mantle wedge would have been significantly thicker and possibly hotter during the Tertiary. Presently, the crustal rocks of Siletzia rest directly on the subducting Juan de Fuca plate. The tholeiitic OCRI gabbros are a separate, more widespread, and voluminous pulse of forearc magmatism that was contemporaneous with alkaline OCRI and Cascade Head Basalt magmatism. The [superscript 40]Ar-[superscript 39]Ar geochronology and previous K-Ar age data reveal that the gabbroic OCRI magmatism was short-lived. The Marys Peak sill and nearby dikes were emplaced between approximately 32 and 33 Ma. The major element geochemistry of the gabbros indicates that their magmatic evolution was driven by crystal fractionation processes at crustal levels. In contrast with the alkaline OCRI, the gabbros are characterized by tholeiitic compositions with lower degrees of incompatible element enrichment. Their trace element chemistry also displays an arc-like signature which indicates the involvement of a subduction-modified mantle source component in their petrogenesis. The formation of the OCRI gabbroic magmas involved upwelling and decompressional melting within the mantle wedge. Oligocene forearc extension may have become more widespread for a short duration (~2 m.y.) which aided the ascension of relatively dense, iron-rich gabbroic OCRI magmas. During this period, the mantle wedge beneath the forearc experienced larger degrees of decompressional partial melting allowing for the generation of voluminous tholeiitic magmas. Since the gabbros are in close proximity to the Western Cascades arc, their petrogenesis was also linked to the Cascades subduction system, as indicated by their trace element geochemistry. Overall, the OCRI represent the final episode of widespread forearc magmatism and record significant changes in tectonic interactions between the Farallon and North America plates. Title: Early Oligocene intrusions in the central Coast Range of Oregon : petrography, geochemistry, geochronology and implications for the Tertiary magmatic evolution of the Cascadia forearc Author: Oxford, Jeremiah The Early Oligocene Oregon Coast Range Intrusions (OCRI) consist of gabbroic rocks and lesser alkalic intrusive bodies that were emplaced in marine sedimentary units and volcanic sequences within a Tertiary Cascadia forearc basin. The alkalic intrusions include nepheline syenite, camptonite, and alkaline basalt. The gabbros occur as dikes and differentiated sills. Presently, erosional remnants of the intrusions underlie much of the high topography along the axis of the central Oregon Coast Range. The intrusive suite is most likely associated with Tertiary oblique rifting of the North America continental margin. Dextral shear and extension along the continental margin may have been a consequence of northeast-directed oblique Farallon plate convergence. However, while both the gabbroic and alkaline OCRI appear to be related to tectonic extension, major and trace element geochemistry reveal separate parental magma sources between the two suites. The OCRI are part of a long-lived (42-30 Ma) magmatic forearc province that includes the Yachats Basalt and Cascade Head Basalt. The timing of Cascadia forearc magmatism correlates with a significant decrease in convergence rates between the Farallon and North American plates from 42 to 28 Ma. The OCRI are also contemporaneous with magmatism that occurred over a broad area of the Pacific Northwest (e.g. Western Cascades, John Day Formation). New radiometric age data acquired from the [superscript 40]Ar-[superscript 39]Ar incremental heating experiments indicate that OCRI magmatism occurred between ~36 to 32 Ma; a longer interval than previously thought. The alkaline OCRI are closely associated with the late Eocene OIB-like Yachats Basalt and Cascade Head Basalt forearc volcanic centers in both space and time. In addition, trace element geochemical data suggest similar parental magma sources for the alkaline OCRI and the forearc volcanic centers. The geochemistry of the OCRI camptonites and alkaline basalts is typical of continental rift zones and oceanic intraplate environments. Major element geochemical data indicate that differentiation by crystal fractionation was the primary process involved in the magmatic evolution of the alkaline OCRI. The OCRI camptonites are volatile-rich equivalents of alkaline basaltic or basanitic parental magmas. Both trace element and major element geochemical data imply that the nepheline syenites and the camptonites were derived from similar alkaline parental magma sources. However, the nepheline syenites are not simple derivatives of the camptonite magmas. Instead, they appear to be alkaline variations of trachyandesites and rhyolites found in the forearc volcanic centers. The alkaline OCRI parental magmas were generated from small degrees of partial melting of an enriched OIB-like mantle source. There are two possible mantle sources for the alkaline OCRI: 1) An enriched lithospheric Siletzia mantle source that was previously metasomatized by deep-sourced alkaline melts or 2) upwelling asthenospheric mantle from beneath the subducting slab which would require a slab window. If the alkaline OCRI were derived from the lithospheric Siletzia mantle, then the mantle wedge would have been significantly thicker and possibly hotter during the Tertiary. Presently, the crustal rocks of Siletzia rest directly on the subducting Juan de Fuca plate. The tholeiitic OCRI gabbros are a separate, more widespread, and voluminous pulse of forearc magmatism that was contemporaneous with alkaline OCRI and Cascade Head Basalt magmatism. The [superscript 40]Ar-[superscript 39]Ar geochronology and previous K-Ar age data reveal that the gabbroic OCRI magmatism was short-lived. The Marys Peak sill and nearby dikes were emplaced between approximately 32 and 33 Ma. The major element geochemistry of the gabbros indicates that their magmatic evolution was driven by crystal fractionation processes at crustal levels. In contrast with the alkaline OCRI, the gabbros are characterized by tholeiitic compositions with lower degrees of incompatible element enrichment. Their trace element chemistry also displays an arc-like signature which indicates the involvement of a subduction-modified mantle source component in their petrogenesis. The formation of the OCRI gabbroic magmas involved upwelling and decompressional melting within the mantle wedge. Oligocene forearc extension may have become more widespread for a short duration (~2 m.y.) which aided the ascension of relatively dense, iron-rich gabbroic OCRI magmas. During this period, the mantle wedge beneath the forearc experienced larger degrees of decompressional partial melting allowing for the generation of voluminous tholeiitic magmas. Since the gabbros are in close proximity to the Western Cascades arc, their petrogenesis was also linked to the Cascades subduction system, as indicated by their trace element geochemistry. Overall, the OCRI represent the final episode of widespread forearc magmatism and record significant changes in tectonic interactions between the Farallon and North America plates. Close

• 9. [Article] Interactions between ecosystem nitrogen and bedrock control long-term calcium sources in Oregon Coast Range forests

  Ecosystem nitrogen (N) supply strongly influences the availability and cycling of other essential nutrients in temperate forests, especially calcium (Ca). Short-term additions of N that exceed ecosystem ...

  Citation × Citation Citation Abstract Copy Title: Interactions between ecosystem nitrogen and bedrock control long-term calcium sources in Oregon Coast Range forests Author: Hynicka, Justin D. Ecosystem nitrogen (N) supply strongly influences the availability and cycling of other essential nutrients in temperate forests, especially calcium (Ca). Short-term additions of N that exceed ecosystem demands often increase dissolved nitrate fluxes and decrease soil pH, which can stimulate soil Ca loss. However, the long-term effects of high N supply on ecosystem Ca availability are more difficult to determine, and may depend on the Ca content of bedrock and mineral soils. To address this, we examined major and trace element concentrations and ⁸⁷Sr/⁸⁶Sr ratios that trace Ca sources in precipitation, foliage, soil pools, and bedrock at 24 forested sites in the Oregon Coast Range having a wide, natural range of soil N (0.16 - 0.97 % N, 0-10 cm) on contrasting basaltic and sedimentary bedrock. Using a suite of 17 site properties, we also evaluated whether soil N variation across sites was related to the five major state-factors of soil and ecosystem development: climate, organisms, topography, parent material, and time. We found that as soil N increased across sites, its ¹⁵N/¹⁴N ratio declined towards atmospheric values, suggesting that soil N variation reflects a biotic legacy of symbiotic N fixation inputs. In contrast, soil N variation was unrelated to 17 other metrics of soil forming factors that represented climate (mean annual precipitation, mean annual temperature, and distance from the coast), topography (slope, soil depth, and abundance of coarse rock fragments), parent material (within bedrock type bulk and 1 M HNO₃ leachable rock Ca chemistry), and proxies of soil age (Hurst's redness rating, effective cation exchange capacity, Ca in non-exchangeable soil residues, chemical index of alteration, weathering index of Parker, Ca in coarse soil fragments, and soil Ca loss relative to bedrock). These analyses highlight symbiotic N-fixing red alder as a keystone organismal state-factor that produces a wide range of soil N accumulation in coastal Oregon forests. Strontium isotopes (⁸⁷Sr/⁸⁶Sr) and other geochemical analyses indicate that long-term Ca sources in foliage and exchangeable soil pools in Oregon Coast Range forests depend on an interactive effect between N availability and bedrock. Basaltic rocks contained nearly 20-times more Ca than sedimentary rocks across our sites, and this difference was reflected in Sr-isotope partitioning of base cation sources. Atmospheric sources dominated plant and soil pools in forests overlying Ca-poor sedimentary rock, regardless of variation in soil N, indicating extremely limited capacity of weathering to support forest Ca demands. In contrast, forests overlying basaltic rock obtained as much as 80% of Ca from rock weathering in low N sites, yet relied to a greater extent on atmospheric Ca as soil N increased, with less than 10% of Ca from rock weathering at sites with the highest soil N. Surprisingly, differences in fresh rock Ca content and base cation sources between sedimentary and basaltic sites was not reflected in ecosystem Ca availability, and instead increasing soil N caused similar declines in foliar and exchangeable Ca across both rock types. This illustrates that nutrient pool sizes do not necessarily reflect long-term nutrient supply, and highlights how coupled biogeochemical cycles within ecosystems can regulate nutrient loss and supply to biota. Broadly, our results highlight how interactions between biological and geologic factors can influence base cation sources in forest ecosystems. The sustainability of base cation supplies to forests may therefore depend greatly on variation in bedrock weathering at low N sites, yet converge to depend on atmospheric inputs in sites that receive high N loading from biological fixation or anthropogenic deposition. Title: Interactions between ecosystem nitrogen and bedrock control long-term calcium sources in Oregon Coast Range forests Author: Hynicka, Justin D. Ecosystem nitrogen (N) supply strongly influences the availability and cycling of other essential nutrients in temperate forests, especially calcium (Ca). Short-term additions of N that exceed ecosystem demands often increase dissolved nitrate fluxes and decrease soil pH, which can stimulate soil Ca loss. However, the long-term effects of high N supply on ecosystem Ca availability are more difficult to determine, and may depend on the Ca content of bedrock and mineral soils. To address this, we examined major and trace element concentrations and ⁸⁷Sr/⁸⁶Sr ratios that trace Ca sources in precipitation, foliage, soil pools, and bedrock at 24 forested sites in the Oregon Coast Range having a wide, natural range of soil N (0.16 - 0.97 % N, 0-10 cm) on contrasting basaltic and sedimentary bedrock. Using a suite of 17 site properties, we also evaluated whether soil N variation across sites was related to the five major state-factors of soil and ecosystem development: climate, organisms, topography, parent material, and time. We found that as soil N increased across sites, its ¹⁵N/¹⁴N ratio declined towards atmospheric values, suggesting that soil N variation reflects a biotic legacy of symbiotic N fixation inputs. In contrast, soil N variation was unrelated to 17 other metrics of soil forming factors that represented climate (mean annual precipitation, mean annual temperature, and distance from the coast), topography (slope, soil depth, and abundance of coarse rock fragments), parent material (within bedrock type bulk and 1 M HNO₃ leachable rock Ca chemistry), and proxies of soil age (Hurst's redness rating, effective cation exchange capacity, Ca in non-exchangeable soil residues, chemical index of alteration, weathering index of Parker, Ca in coarse soil fragments, and soil Ca loss relative to bedrock). These analyses highlight symbiotic N-fixing red alder as a keystone organismal state-factor that produces a wide range of soil N accumulation in coastal Oregon forests. Strontium isotopes (⁸⁷Sr/⁸⁶Sr) and other geochemical analyses indicate that long-term Ca sources in foliage and exchangeable soil pools in Oregon Coast Range forests depend on an interactive effect between N availability and bedrock. Basaltic rocks contained nearly 20-times more Ca than sedimentary rocks across our sites, and this difference was reflected in Sr-isotope partitioning of base cation sources. Atmospheric sources dominated plant and soil pools in forests overlying Ca-poor sedimentary rock, regardless of variation in soil N, indicating extremely limited capacity of weathering to support forest Ca demands. In contrast, forests overlying basaltic rock obtained as much as 80% of Ca from rock weathering in low N sites, yet relied to a greater extent on atmospheric Ca as soil N increased, with less than 10% of Ca from rock weathering at sites with the highest soil N. Surprisingly, differences in fresh rock Ca content and base cation sources between sedimentary and basaltic sites was not reflected in ecosystem Ca availability, and instead increasing soil N caused similar declines in foliar and exchangeable Ca across both rock types. This illustrates that nutrient pool sizes do not necessarily reflect long-term nutrient supply, and highlights how coupled biogeochemical cycles within ecosystems can regulate nutrient loss and supply to biota. Broadly, our results highlight how interactions between biological and geologic factors can influence base cation sources in forest ecosystems. The sustainability of base cation supplies to forests may therefore depend greatly on variation in bedrock weathering at low N sites, yet converge to depend on atmospheric inputs in sites that receive high N loading from biological fixation or anthropogenic deposition. Close

• 10. [Article] Influences of clearcut logging on macroinvertebrates in perennial and intermittent headwaters of the Central Oregon Coast Range

  This research was designed to broaden the understanding of how timber-harvest affects aquatic macroinvertebrates in perennial and intermittent headwater streams. This study compared emergent and benthic ...

  Citation × Citation Citation Abstract Copy Title: Influences of clearcut logging on macroinvertebrates in perennial and intermittent headwaters of the Central Oregon Coast Range Author: Banks, Janel This research was designed to broaden the understanding of how timber-harvest affects aquatic macroinvertebrates in perennial and intermittent headwater streams. This study compared emergent and benthic macroinvertebrate assemblages from 20 headwater streams in the central Oregon Coast Range that varied by harvest condition and flow duration. Through comparison of the community and functional characteristics of the macroinvertebrates in similar streams under different harvest conditions, logging impacts on adult and immature aquatic macroinvertebrates in perennial and intermittent streams were assessed. Adult insects emerging from the 20 study streams were collected using emergence traps set for four weeks in a 40-meter reach during three sampling periods: August-September 2003, October-November 2003, and April-May 2004. Adult aquatic insects were identified to genus and family taxonomic levels and results were expressed as number of individuals emerging per m2 per day. Benthic samples were taken from each reach in May 2004, insects and non-insects were identified to various taxonomic levels, and results were expressed as number of individuals per m2. Ten streams were located in catchments that were clearcut to the stream bank no more than a year before sampling began; three of these streams were intermittent and seven were perennial. Intermittent streams were summer-dry and retained surface-water for a minimum of eight months during the year, while perennial streams had surface flow year-round. The other ten streams (four intermittent and six perennial) were located in forested catchments that have not been logged for at least 34 years. The physical habitat of each stream reach was assessed in August 2003. Regardless of flow-duration or season, more aquatic insects emerged from streams in logged catchments. The emergence rate of Diptera, predominantly Chironomidae, was especially high from clearcut sites. More Trichoptera also emerged from clearcut sites. Ephemeroptera and Plecoptera did not emerge at rates that varied by logging condition. Plecoptera had higher emergence from intermittent than perennial sites in spring. Taxa richness was higher at clearcut sites, driven primarily by rare taxa encountered in less than 5 of the 10 clearcut sites. Emergent insect functional feeding group composition was affected by harvest condition with collector-filterers emerging at higher rates from clearcut sites. Examination of community patterns through nonmetric multidimensional scaling (NMS) ordination analyses indicated that emergent aquatic macroinvertebrate assemblages differ by season and by harvest condition. The duration of stream flow did not strongly influence adult assemblages. Channel dimensions (active channel and bankfull width) and catchment area were correlated with ordination-axes, but were not different between logged and forested sites. The amount of riparian cover (canopy, understory, and groundcover), stand age, slash, and stream cover were all considerably different between logged and forested sites and were highly influential on emergent assemblages. Substrate size was also influential on adult assemblages. Mean water temperature in summer, fall, and spring was highly correlated with seasonal variation in assemblages. Regardless of harvest-condition, intermittent streams had higher overall benthic macroinvertebrate density. Trichoptera had higher densities at intermittent sites than perennial sites, while Diptera, Plecoptera, and non-insects had similar densities between categories of flow duration and harvest condition. Benthic macroinvertebrate functional composition was also affected by flow-duration, with collector-filterers, collector-gatherers, and predators occurring at higher densities at intermittent sites than perennial sites. The densities of scrapers and shredders did not differ between classes of flow duration or harvest condition. The majority of taxa (72%) were common to both perennial and intermittent sites; however, taxa richness was lower at intermittent sites. NMS-ordination analyses of the benthic macroinvertebrates showed that community patterns differed by harvest condition within the perennial flow-duration class. Benthic communities of intermittent streams did not differ between harvest conditions. Channel dimensions (active channel and bankfull width), mean substrate diameter, percent stream-cover, mean water temperature, elevation, and percent small riparian trees influenced benthic community assemblages. The majority of perennial-clearcut sites had macroinvertebrate community patterns more similar to intermittent-forested and intermittent-clearcut streams than to perennial-forested sites. The two perennial-clearcut sites that did not have benthic assemblages similar to the other five perennial-clearcut sites had larger diameter substrate, higher elevation, larger catchment area, and cooler mean water temperature than other perennial-clearcut sites. This study provides evidence that Oregon’s current timber harvesting practices impact macroinvertebrate assemblages of perennial and intermittent headwaters in the Central Oregon Coast Range within a year following harvest. When the studied streams were clearcut to the streambank, there was increased emergence of adult macroinvertebrates, principally midges, at clearcut sites. Benthic assemblages differed primarily between intermittent and perennial flow-duration. However, within flow-classes, assemblages of benthic aquatic macroinvertebrates in perennial streams were impacted by clearcut logging to a higher degree than intermittent streams. Perennial-clearcut streams had different benthic assemblages from perennial-mature streams and perennial-clearcut streams with coarser substrate and cooler temperatures. Intermittent streams, which generally experience fewer flushing events and accumulate finer substrates than perennial streams, may be affected to a lesser degree by any sedimentation caused by logging activity. Correlations of emergent and benthic macroinvertebrate communities with the measured environmental gradients are suggestive that reduced canopy cover and substrate composition are major influential factors. Title: Influences of clearcut logging on macroinvertebrates in perennial and intermittent headwaters of the Central Oregon Coast Range Author: Banks, Janel This research was designed to broaden the understanding of how timber-harvest affects aquatic macroinvertebrates in perennial and intermittent headwater streams. This study compared emergent and benthic macroinvertebrate assemblages from 20 headwater streams in the central Oregon Coast Range that varied by harvest condition and flow duration. Through comparison of the community and functional characteristics of the macroinvertebrates in similar streams under different harvest conditions, logging impacts on adult and immature aquatic macroinvertebrates in perennial and intermittent streams were assessed. Adult insects emerging from the 20 study streams were collected using emergence traps set for four weeks in a 40-meter reach during three sampling periods: August-September 2003, October-November 2003, and April-May 2004. Adult aquatic insects were identified to genus and family taxonomic levels and results were expressed as number of individuals emerging per m2 per day. Benthic samples were taken from each reach in May 2004, insects and non-insects were identified to various taxonomic levels, and results were expressed as number of individuals per m2. Ten streams were located in catchments that were clearcut to the stream bank no more than a year before sampling began; three of these streams were intermittent and seven were perennial. Intermittent streams were summer-dry and retained surface-water for a minimum of eight months during the year, while perennial streams had surface flow year-round. The other ten streams (four intermittent and six perennial) were located in forested catchments that have not been logged for at least 34 years. The physical habitat of each stream reach was assessed in August 2003. Regardless of flow-duration or season, more aquatic insects emerged from streams in logged catchments. The emergence rate of Diptera, predominantly Chironomidae, was especially high from clearcut sites. More Trichoptera also emerged from clearcut sites. Ephemeroptera and Plecoptera did not emerge at rates that varied by logging condition. Plecoptera had higher emergence from intermittent than perennial sites in spring. Taxa richness was higher at clearcut sites, driven primarily by rare taxa encountered in less than 5 of the 10 clearcut sites. Emergent insect functional feeding group composition was affected by harvest condition with collector-filterers emerging at higher rates from clearcut sites. Examination of community patterns through nonmetric multidimensional scaling (NMS) ordination analyses indicated that emergent aquatic macroinvertebrate assemblages differ by season and by harvest condition. The duration of stream flow did not strongly influence adult assemblages. Channel dimensions (active channel and bankfull width) and catchment area were correlated with ordination-axes, but were not different between logged and forested sites. The amount of riparian cover (canopy, understory, and groundcover), stand age, slash, and stream cover were all considerably different between logged and forested sites and were highly influential on emergent assemblages. Substrate size was also influential on adult assemblages. Mean water temperature in summer, fall, and spring was highly correlated with seasonal variation in assemblages. Regardless of harvest-condition, intermittent streams had higher overall benthic macroinvertebrate density. Trichoptera had higher densities at intermittent sites than perennial sites, while Diptera, Plecoptera, and non-insects had similar densities between categories of flow duration and harvest condition. Benthic macroinvertebrate functional composition was also affected by flow-duration, with collector-filterers, collector-gatherers, and predators occurring at higher densities at intermittent sites than perennial sites. The densities of scrapers and shredders did not differ between classes of flow duration or harvest condition. The majority of taxa (72%) were common to both perennial and intermittent sites; however, taxa richness was lower at intermittent sites. NMS-ordination analyses of the benthic macroinvertebrates showed that community patterns differed by harvest condition within the perennial flow-duration class. Benthic communities of intermittent streams did not differ between harvest conditions. Channel dimensions (active channel and bankfull width), mean substrate diameter, percent stream-cover, mean water temperature, elevation, and percent small riparian trees influenced benthic community assemblages. The majority of perennial-clearcut sites had macroinvertebrate community patterns more similar to intermittent-forested and intermittent-clearcut streams than to perennial-forested sites. The two perennial-clearcut sites that did not have benthic assemblages similar to the other five perennial-clearcut sites had larger diameter substrate, higher elevation, larger catchment area, and cooler mean water temperature than other perennial-clearcut sites. This study provides evidence that Oregon’s current timber harvesting practices impact macroinvertebrate assemblages of perennial and intermittent headwaters in the Central Oregon Coast Range within a year following harvest. When the studied streams were clearcut to the streambank, there was increased emergence of adult macroinvertebrates, principally midges, at clearcut sites. Benthic assemblages differed primarily between intermittent and perennial flow-duration. However, within flow-classes, assemblages of benthic aquatic macroinvertebrates in perennial streams were impacted by clearcut logging to a higher degree than intermittent streams. Perennial-clearcut streams had different benthic assemblages from perennial-mature streams and perennial-clearcut streams with coarser substrate and cooler temperatures. Intermittent streams, which generally experience fewer flushing events and accumulate finer substrates than perennial streams, may be affected to a lesser degree by any sedimentation caused by logging activity. Correlations of emergent and benthic macroinvertebrate communities with the measured environmental gradients are suggestive that reduced canopy cover and substrate composition are major influential factors. Close