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• 3191. [Article] Ecological effects of post-wildfire management activities (salvage-logging and grass-seeding) on vegetation composition, diversity, biomass, and growth and survival of Pinus ponderosa and Purshia tridentata

  Salvage-logging and artificial seeding of grass following wildfire are common practices in coniferous forests of the western United States, yet few studies have quantified the ecological effects of these ...

  Citation × Citation Citation Abstract Copy Title: Ecological effects of post-wildfire management activities (salvage-logging and grass-seeding) on vegetation composition, diversity, biomass, and growth and survival of Pinus ponderosa and Purshia tridentata Author: Sexton, Timothy Ogden Salvage-logging and artificial seeding of grass following wildfire are common practices in coniferous forests of the western United States, yet few studies have quantified the ecological effects of these post-fire activities. The effects of post-wildfire salvage-logging and grass-seeding on vegetation composition, aboveground biomass, and growth and survival of Pinus ponderosa and Purshia tridentata were quantified on the area burned by the 1992 Lone Pine Fire, Winema National Forest in the Klamath Basin, Oregon. Prior to the fire, the area was dominated by uneven-aged stands of Pinus ponderosa with Purshia tridentata and Stipa occidentalis in the understory. The fire was a stand-replacement disturbance, where the majority of trees, the herbaceous component, and crowns of understory shrubs were killed. Salvage logging resulted in a significant decrease in understory biomass, species richness, species diversity, and growth and survival of P. ponderosa and P. tridentata. In addition plant community composition was shifted from native forb dominance to grass dominance. In 1993, the understory biomass of salvage-logged sites was 38% of the aboveground biomass produced on nonsalvaged sites (322 kg ha^-1 vs 843 kg ha^-1). In 1994, salvage-logged sites produced only 27% of the biomass produced on nonsalvaged sites (402 kg ha^-1 vs 1468 kg ha^-1). Salvage-logging reduced species richness, species diversity, and altered species composition. The first and second years following logging, species richness was reduced by 13% (20 versus 23), and 30% (15 versus 22), respectively. In 1993 and 1994, native forb frequency on nonsalvaged sites was 80% and 77% respectively, while salvage-logged sites recorded 68% and 31% respectively. Conversely, graminoid frequency was significantly higher on salvage-logged sites. In 1994, native graminoid frequency was 35% in nonsalvaged sites and > 61% on salvage-logged sites. During the first two years following salvage-logging, mean height growth of naturally-regenerated Pinus ponderosa was significantly lower on salvaged sites (9.4 versus 7.8 cm yr^-1) as was density of natural Purshia tridentata seedlings (313 versus 530 seedlings ha^-1). Survival in salvage-logged treatments was 22% lower for planted Purshia tridentata seedlings (57% versus 45%). Height growth in salvage-logged treatments was 16% lower for planted Pinus ponderosa (4.4 versus 3.7 cm). Total aboveground biomass on nonsalvaged burned sites (controls) averaged 843 kg ha^-1 in 1993, and 1473 kg ha^-1 in 1994. In 1993, the first year following the fire, sites seeded to Secale cereale produced = 1995 kg ha^-1 total aboveground biomass; most of the biomass was S. cereale. Those seeded sites produced 89% less native forb biomass than controls (82 versus 780 kg ha^-1), and = 80% less native forb biomass than areas seeded to the native grasses Sitanion hystrix and Festuca idahoensis. In 1994, the second post-fire year, biomass on sites seeded to S. cereale was >1653 kg ha^-1, dominated by S. cereale. In 1994, no differences in total aboveground biomass were detected between S. cereale, F idahoensis, S. hystrix, and the Control, indicating that the erosion reducing benefits of grass-seeding did not last for more than one year. Treatments seeded with S. cereale produced 58% less native forb biomass than controls (350 versus 825 kg ha^-1). Seeding S. cereale also reduced by 69% the biomass ofStipa occidentalis, the most common native grass in the area (311 kg ha^-1 on control sites versus 96 kg ha^-1 on S. cereale sites). In 1993 and 1994, fewer species were recorded on S. cereale sites than on all other sites. Grass-seeded sites exhibited no significant differences in frequency of noxious weeds in either of the two years following wildfire and seeding, rejecting the hypothesis that grass-seeding reduces noxious weeds. However, native graminoid frequency was reduced on all grass-seeded treatments. There were no significant differences between grass-seeding treatments in height and density of natural P. ponderosa and P. tridentata seedlings or growth and survival of planted P. ponderosa and P. tridentata seedlings. While salvage-logging provides an economic benefit to local communities through the extraction of commercially valuable timber, there is an ecological cost. Reduction in ecosystem structure, production, species richness, diversity and alterations in species composition are important ecological consequences of salvage logging. In addition, this study demonstrates that salvage-logging retards the re-establishment and early growth of Pinus ponderosa and Purshia tridentata, two important wildfire restoration priorities. Grass-seeding also results in significant ecological changes. Alterations in ecosystem production, species richness, diversity and species composition are important ecological consequences of grass-seeding. Managers should consider these long-term influences on ecosystem composition and structure when faced with decisions concerning post-fire rehabilitation and management. Title: Ecological effects of post-wildfire management activities (salvage-logging and grass-seeding) on vegetation composition, diversity, biomass, and growth and survival of Pinus ponderosa and Purshia tridentata Author: Sexton, Timothy Ogden Salvage-logging and artificial seeding of grass following wildfire are common practices in coniferous forests of the western United States, yet few studies have quantified the ecological effects of these post-fire activities. The effects of post-wildfire salvage-logging and grass-seeding on vegetation composition, aboveground biomass, and growth and survival of Pinus ponderosa and Purshia tridentata were quantified on the area burned by the 1992 Lone Pine Fire, Winema National Forest in the Klamath Basin, Oregon. Prior to the fire, the area was dominated by uneven-aged stands of Pinus ponderosa with Purshia tridentata and Stipa occidentalis in the understory. The fire was a stand-replacement disturbance, where the majority of trees, the herbaceous component, and crowns of understory shrubs were killed. Salvage logging resulted in a significant decrease in understory biomass, species richness, species diversity, and growth and survival of P. ponderosa and P. tridentata. In addition plant community composition was shifted from native forb dominance to grass dominance. In 1993, the understory biomass of salvage-logged sites was 38% of the aboveground biomass produced on nonsalvaged sites (322 kg ha^-1 vs 843 kg ha^-1). In 1994, salvage-logged sites produced only 27% of the biomass produced on nonsalvaged sites (402 kg ha^-1 vs 1468 kg ha^-1). Salvage-logging reduced species richness, species diversity, and altered species composition. The first and second years following logging, species richness was reduced by 13% (20 versus 23), and 30% (15 versus 22), respectively. In 1993 and 1994, native forb frequency on nonsalvaged sites was 80% and 77% respectively, while salvage-logged sites recorded 68% and 31% respectively. Conversely, graminoid frequency was significantly higher on salvage-logged sites. In 1994, native graminoid frequency was 35% in nonsalvaged sites and > 61% on salvage-logged sites. During the first two years following salvage-logging, mean height growth of naturally-regenerated Pinus ponderosa was significantly lower on salvaged sites (9.4 versus 7.8 cm yr^-1) as was density of natural Purshia tridentata seedlings (313 versus 530 seedlings ha^-1). Survival in salvage-logged treatments was 22% lower for planted Purshia tridentata seedlings (57% versus 45%). Height growth in salvage-logged treatments was 16% lower for planted Pinus ponderosa (4.4 versus 3.7 cm). Total aboveground biomass on nonsalvaged burned sites (controls) averaged 843 kg ha^-1 in 1993, and 1473 kg ha^-1 in 1994. In 1993, the first year following the fire, sites seeded to Secale cereale produced = 1995 kg ha^-1 total aboveground biomass; most of the biomass was S. cereale. Those seeded sites produced 89% less native forb biomass than controls (82 versus 780 kg ha^-1), and = 80% less native forb biomass than areas seeded to the native grasses Sitanion hystrix and Festuca idahoensis. In 1994, the second post-fire year, biomass on sites seeded to S. cereale was >1653 kg ha^-1, dominated by S. cereale. In 1994, no differences in total aboveground biomass were detected between S. cereale, F idahoensis, S. hystrix, and the Control, indicating that the erosion reducing benefits of grass-seeding did not last for more than one year. Treatments seeded with S. cereale produced 58% less native forb biomass than controls (350 versus 825 kg ha^-1). Seeding S. cereale also reduced by 69% the biomass ofStipa occidentalis, the most common native grass in the area (311 kg ha^-1 on control sites versus 96 kg ha^-1 on S. cereale sites). In 1993 and 1994, fewer species were recorded on S. cereale sites than on all other sites. Grass-seeded sites exhibited no significant differences in frequency of noxious weeds in either of the two years following wildfire and seeding, rejecting the hypothesis that grass-seeding reduces noxious weeds. However, native graminoid frequency was reduced on all grass-seeded treatments. There were no significant differences between grass-seeding treatments in height and density of natural P. ponderosa and P. tridentata seedlings or growth and survival of planted P. ponderosa and P. tridentata seedlings. While salvage-logging provides an economic benefit to local communities through the extraction of commercially valuable timber, there is an ecological cost. Reduction in ecosystem structure, production, species richness, diversity and alterations in species composition are important ecological consequences of salvage logging. In addition, this study demonstrates that salvage-logging retards the re-establishment and early growth of Pinus ponderosa and Purshia tridentata, two important wildfire restoration priorities. Grass-seeding also results in significant ecological changes. Alterations in ecosystem production, species richness, diversity and species composition are important ecological consequences of grass-seeding. Managers should consider these long-term influences on ecosystem composition and structure when faced with decisions concerning post-fire rehabilitation and management. Close

• 3192. [Article] Forest macro-arthropods as potential indicators of ecosystem conditions in Western Idaho : an analysis of community composition, biological diversity, and community structure

  Adaptive ecosystem management is a new paradigm for managing federal forests which requires regular monitoring of ecosystem function and diversity to measure the effects of management. Managers need new ...

  Citation × Citation Citation Abstract Copy Title: Forest macro-arthropods as potential indicators of ecosystem conditions in Western Idaho : an analysis of community composition, biological diversity, and community structure Author: Ruby, Margaret E. Adaptive ecosystem management is a new paradigm for managing federal forests which requires regular monitoring of ecosystem function and diversity to measure the effects of management. Managers need new strategies and tools to help them assess their progress in maintaining healthy, productive and biologically diverse forests. Biomonitoring of select forest macro-arthropod species can provide useful information on the effects of management on forest biodiversity and ecosystem function. The purpose of this study was threefold: (1) to inventory the macro-arthropod community and important environmental variables in the Bear Creek and Indian Creek study area within the Payette National Forest (PNF) in Western Idaho; (2) to compare measures of community composition, diversity, and structure in forest macro-arthropod communities between patches of different sizes and treatment; and (3) to assist PNF managers in their ecosystem management efforts by providing principles to guide the use of macro-arthropods as indicators of changing forest conditions. Transects with pitfall traps were used to collect macro-arthropods at 22 sites in the Bear Creek and Indian Creek study area during the summer of 1994. Five forest patch types in Abies grandis habitat types were sampled. Intact forest patches of 100 or more hectares, and large patches of 50-100 hectares, ranged in age between 50 and 250 years old with multistoried structure. Small patches up to 10 hectares were remnants or fragments of formerly intact forest isolated by logging. A plantation patch was 15 years old with patchy understory and forb cover. Clearcut patches had little or no overstory, and variable understory, and forb layers. At each transect, soil samples were collected and six environmental descriptor variables were analyzed according to patch treatment and patch size. These site descriptors were: basal area (ft²/acre); percent canopy cover for the overstory, understory; and forb layers; litter depth (cm), and percent soil moisture content. Differences detected using an ANOVA and T-tests are discussed in the Results section. Arthropod community composition, diversity, and structure were described according to relative abundance, and four measures of diversity. They were also described by membership in seventeen orders and/or super-families; ten functional groups; two disperser classes (long or short distance); and three species indicator classes. A total of 5455 macro-arthropod individuals, representing 17 orders and/or super-families and 219 species were collected in the Bear Creek and Indian Creek study area. While macro-arthropod fauna relative abundance did not vary significantly by treatment (ANOVA p<0.3), it did vary significantly by patch size (ANOVA p<0.03). Fauna relative abundance was 35% greater in clearcut patches than in large patches (T-test p<0.09). Fauna relative abundance in small patches was twice that of intact (T-test p<0.03) and large (T-test p<0.02) patches. Taxonomic diversity (number of genera/taxa) of beetle, ant, and bug taxa differed significantly according to treatment type(each ANOVA p<0.05). For the top four taxa (beetles, ants, spiders, and bugs), taxonomic diversity was highest in the plantation and clearcut patches. Ants and bugs had their highest taxonomic diversity in the plantation patch (separate T-tests p<0.05) while the taxonomic diversity of beetles was highest in clear-cut patches (T-test p<0.05). Beetle and ant taxonomic diversity varied significantly by patch size (each ANOVA p<0.05). For beetles and bugs, small patches were twice as diverse as intact patches (separate T-tests p<0.04) and 1.5 times that of large patches. Ant diversity was similarly distributed amongst the patch sizes, with significant differences between small and intact and between small and large patches (separate T-tests p<0.05). Of the four species diversity measures employed, only two, [alpha] and JK1 (both measures of richness), were found to vary significantly by patch treatment and size. Evenness (E) and the Shannon Diversity Index (H') failed to detect differences in the majority of tests. Fauna [alpha] and JK1 differed significantly by treatment type (each ANOVA p<0.05). Richness in clearcut patches was nearly twice in intact and large patches, followed by plantation and large patches. Fauna [alpha] and JKl also differed significantly by patch size (each ANOVA p <0.001), with small patch fauna twice as rich as that in large and intact patches (separate T-tests p <0.01). Of the top four functional groups, predators were the most abundant and had the highest taxonomic diversity (number of genera/functional group), followed by herbivores, fungivores and parasites. Predators and herbivores showed increasing taxonomic diversity with decreasing patch size, from intact to large to small (ANOVA p< 0.05). Similarly, predators and herbivores exhibited increasing taxonomic diversity with increasing levels of management: from intact and large to plantation and clear-cuts (ANOVA p< 0.05). Predators and herbivores were most numerous in the managed and small patches. Fungivore taxonomic diversity was also highest in the small and managed patches, though neither patch size nor treatment differences were significant (ANOVA p<0.85). Parasite taxonomic diversity differed by patch size with highest generic diversity in the small patches (ANOVA p<0.l) and by treatment type with generic diversity highest in plantations and clearcuts followed in order by large and intact patches (ANOVA p<0.l). Twice as many genera were long distance dispersers as were short distance dispersers. Relative abundance of long distance dispersers varied significantly by patch treatment and patch size (each ANOVA p<0.0l). Long distance dispersers were most numerous in clear-cut patches, followed in order by plantation, small, large, and intact patches. Relative abundance of short distance dispersers was not significantly different between treatment types (ANOVA p<0.20) but was significantly different between patch sizes (ANOVA p<0.0l). Short distance dispersers were most numerous in small patches followed by plantation, large, and intact and least numerous in clearcut patches. An indicator species analysis of 121 Bear Creek and Indian Creek genera (Dufrene and Legendre 1997), revealed sub-groups of species with 75 to 100 percent "perfect indication" or affiliation for specific patch types. When intact and large patches were pooled and analyzed against all treated patches (plantation and clearcut patches), a list of 36 genera with 75 to 100 percent "perfect affiliation" for intact or large patches was produced (MRPP p<0.05). Small patches had 42 indicators with 75 to 100 percent "perfect indication" when compared with the pooled intact and large patches (MRPP p<0.l). Conclusions Macro-arthropod community composition, diversity and structure did vary, usually significantly, by patch treatment and size. Useful measures of generic diversity include richness estimators [alpha], [beta], and JK1. Examination of taxonomic diversity was also useful, especially for the more mobile arthropods. Pitfall traps provided copious data on the structure of the community in regards to predators and herbivores. Pitfalls, however, did not provide much information about the status of fungivores and parasites in the various different patches. Another trapping method such as the berlaise funnel, would likely provide more information about those functional groups which are likely operating at a finer scale of resolution than that tested by the pitfall trap. Employing both methods would provide a much better assessment of the community of arthropods living on the forest floor. The indicator species analysis program also provided very useful lists of species which are affiliated with particular patch conditions. Taken together, these measures could be adopted for use by forest managers to allow them to assess and monitor the effects of a management regime on the structure and composition of macro-arthropod communities as part of a comprehensive adaptive management plan. Title: Forest macro-arthropods as potential indicators of ecosystem conditions in Western Idaho : an analysis of community composition, biological diversity, and community structure Author: Ruby, Margaret E. Adaptive ecosystem management is a new paradigm for managing federal forests which requires regular monitoring of ecosystem function and diversity to measure the effects of management. Managers need new strategies and tools to help them assess their progress in maintaining healthy, productive and biologically diverse forests. Biomonitoring of select forest macro-arthropod species can provide useful information on the effects of management on forest biodiversity and ecosystem function. The purpose of this study was threefold: (1) to inventory the macro-arthropod community and important environmental variables in the Bear Creek and Indian Creek study area within the Payette National Forest (PNF) in Western Idaho; (2) to compare measures of community composition, diversity, and structure in forest macro-arthropod communities between patches of different sizes and treatment; and (3) to assist PNF managers in their ecosystem management efforts by providing principles to guide the use of macro-arthropods as indicators of changing forest conditions. Transects with pitfall traps were used to collect macro-arthropods at 22 sites in the Bear Creek and Indian Creek study area during the summer of 1994. Five forest patch types in Abies grandis habitat types were sampled. Intact forest patches of 100 or more hectares, and large patches of 50-100 hectares, ranged in age between 50 and 250 years old with multistoried structure. Small patches up to 10 hectares were remnants or fragments of formerly intact forest isolated by logging. A plantation patch was 15 years old with patchy understory and forb cover. Clearcut patches had little or no overstory, and variable understory, and forb layers. At each transect, soil samples were collected and six environmental descriptor variables were analyzed according to patch treatment and patch size. These site descriptors were: basal area (ft²/acre); percent canopy cover for the overstory, understory; and forb layers; litter depth (cm), and percent soil moisture content. Differences detected using an ANOVA and T-tests are discussed in the Results section. Arthropod community composition, diversity, and structure were described according to relative abundance, and four measures of diversity. They were also described by membership in seventeen orders and/or super-families; ten functional groups; two disperser classes (long or short distance); and three species indicator classes. A total of 5455 macro-arthropod individuals, representing 17 orders and/or super-families and 219 species were collected in the Bear Creek and Indian Creek study area. While macro-arthropod fauna relative abundance did not vary significantly by treatment (ANOVA p<0.3), it did vary significantly by patch size (ANOVA p<0.03). Fauna relative abundance was 35% greater in clearcut patches than in large patches (T-test p<0.09). Fauna relative abundance in small patches was twice that of intact (T-test p<0.03) and large (T-test p<0.02) patches. Taxonomic diversity (number of genera/taxa) of beetle, ant, and bug taxa differed significantly according to treatment type(each ANOVA p<0.05). For the top four taxa (beetles, ants, spiders, and bugs), taxonomic diversity was highest in the plantation and clearcut patches. Ants and bugs had their highest taxonomic diversity in the plantation patch (separate T-tests p<0.05) while the taxonomic diversity of beetles was highest in clear-cut patches (T-test p<0.05). Beetle and ant taxonomic diversity varied significantly by patch size (each ANOVA p<0.05). For beetles and bugs, small patches were twice as diverse as intact patches (separate T-tests p<0.04) and 1.5 times that of large patches. Ant diversity was similarly distributed amongst the patch sizes, with significant differences between small and intact and between small and large patches (separate T-tests p<0.05). Of the four species diversity measures employed, only two, [alpha] and JK1 (both measures of richness), were found to vary significantly by patch treatment and size. Evenness (E) and the Shannon Diversity Index (H') failed to detect differences in the majority of tests. Fauna [alpha] and JK1 differed significantly by treatment type (each ANOVA p<0.05). Richness in clearcut patches was nearly twice in intact and large patches, followed by plantation and large patches. Fauna [alpha] and JKl also differed significantly by patch size (each ANOVA p <0.001), with small patch fauna twice as rich as that in large and intact patches (separate T-tests p <0.01). Of the top four functional groups, predators were the most abundant and had the highest taxonomic diversity (number of genera/functional group), followed by herbivores, fungivores and parasites. Predators and herbivores showed increasing taxonomic diversity with decreasing patch size, from intact to large to small (ANOVA p< 0.05). Similarly, predators and herbivores exhibited increasing taxonomic diversity with increasing levels of management: from intact and large to plantation and clear-cuts (ANOVA p< 0.05). Predators and herbivores were most numerous in the managed and small patches. Fungivore taxonomic diversity was also highest in the small and managed patches, though neither patch size nor treatment differences were significant (ANOVA p<0.85). Parasite taxonomic diversity differed by patch size with highest generic diversity in the small patches (ANOVA p<0.l) and by treatment type with generic diversity highest in plantations and clearcuts followed in order by large and intact patches (ANOVA p<0.l). Twice as many genera were long distance dispersers as were short distance dispersers. Relative abundance of long distance dispersers varied significantly by patch treatment and patch size (each ANOVA p<0.0l). Long distance dispersers were most numerous in clear-cut patches, followed in order by plantation, small, large, and intact patches. Relative abundance of short distance dispersers was not significantly different between treatment types (ANOVA p<0.20) but was significantly different between patch sizes (ANOVA p<0.0l). Short distance dispersers were most numerous in small patches followed by plantation, large, and intact and least numerous in clearcut patches. An indicator species analysis of 121 Bear Creek and Indian Creek genera (Dufrene and Legendre 1997), revealed sub-groups of species with 75 to 100 percent "perfect indication" or affiliation for specific patch types. When intact and large patches were pooled and analyzed against all treated patches (plantation and clearcut patches), a list of 36 genera with 75 to 100 percent "perfect affiliation" for intact or large patches was produced (MRPP p<0.05). Small patches had 42 indicators with 75 to 100 percent "perfect indication" when compared with the pooled intact and large patches (MRPP p<0.l). Conclusions Macro-arthropod community composition, diversity and structure did vary, usually significantly, by patch treatment and size. Useful measures of generic diversity include richness estimators [alpha], [beta], and JK1. Examination of taxonomic diversity was also useful, especially for the more mobile arthropods. Pitfall traps provided copious data on the structure of the community in regards to predators and herbivores. Pitfalls, however, did not provide much information about the status of fungivores and parasites in the various different patches. Another trapping method such as the berlaise funnel, would likely provide more information about those functional groups which are likely operating at a finer scale of resolution than that tested by the pitfall trap. Employing both methods would provide a much better assessment of the community of arthropods living on the forest floor. The indicator species analysis program also provided very useful lists of species which are affiliated with particular patch conditions. Taken together, these measures could be adopted for use by forest managers to allow them to assess and monitor the effects of a management regime on the structure and composition of macro-arthropod communities as part of a comprehensive adaptive management plan. Close

• 3193. [Article] The geology of the Elk Mountain-Porter Ridge area, Clatsop County, northwest Oregon

  Eight Tertiary sedimentary and volcanic units crop out in the thesis area. From oldest to youngest they are the: Sager Creek formation (informal); Pittsburg Bluff Formation; Northrup Creek formation (informal); ...

  Citation × Citation Citation Abstract Copy Title: The geology of the Elk Mountain-Porter Ridge area, Clatsop County, northwest Oregon Author: Goalen, Jeffrey Scott Eight Tertiary sedimentary and volcanic units crop out in the thesis area. From oldest to youngest they are the: Sager Creek formation (informal); Pittsburg Bluff Formation; Northrup Creek formation (informal); Smuggler Cove formation (informal); Wickiup Mountain and Cannon Beach members (both informal) of the Astoria Formation; the Grande Ronde Basalt, and Frenchman Springs Member of the Wanapum Basalt, both of the Columbia River Basalt Group. Also, areally limited, unnamed sedimentary strata interbedded between flows of the Columbia River Basalt Group crop out in the study area. Quaternary deposits consist of alluvium, colluvium, and landslide debris. Rhythmically-bedded, foram-bearing, carbonaceous to micaceous mudstone and graded, fine-grained, feldspathic turbidite sandstone are the dominant lithologies of the upper Eocene (Refugian) Sager Creek formation. Plane-laminae and climbing ripple-laminae typical of Bouma b,c, and d intervals are common in the thin turbidite sandstone beds. Contemporaneous, rare, thick, sandstones may represent submarine feeder channels that supplied the more widespread, thinly-bedded overbank turbidite sandstones. Foraminiferal paleobathymetry indicates that deposition was in bathyal water depths. Sager Creek deposition was followed by a regression or offlap of the late Eocene to early Oligocene (Refugian) sea as indicated by the molluscan fossils and thick, bioturbated sandstone of the predominantly shallow-marine Pittsburg Bluff Formation. The lower part of the formation consists of outer shelf, glauconitic, fossiliferous sandstone and subordinate mudstone. Higher in the section are middle-shelf, fine-grained, bioturbated, tuffaceous, arkosic sandstones. These sandstones contain minor glauconite, wave- and storm-generated molluscan shell hash beds, carbonized wood fragments, and calcareous concretions. Deposition occurred in 20 - 50 m open-marine shelf water depths; however, the depositional environment may have shallowed to a bay-like setting (Moore, 1982, written communication). The upper part of the unit consists of thin- to medium-bedded, carbonaceous siltstone and mudstone with minor ashfall tuffs. Therefore, deposition of the Pittsburg Bluff Formation occurred as a shallowing-upward, then deepening depositional episode, punctuated by contemporaneous, intermittent eruption of nearby calc-alkaline western Cascade volcanoes. The deep-marine Oligocene to lower Miocene (Zemorrian to Saucesian) Northrup Creek formation is predominantly composed of thinly-laminated mudstone interbedded with thin, very fine-grained, graded, micaceous arkosic sandstone. Bouma c-d-e and a-b-e sequences are common in the turbidite sandstone; Bouma a-e intervals occur locally in sandstone/mudstone couplets. Paleocurrent indicators suggest that the predominant transport direction of these turbidite deposits was northeast to southwest. Abraded, carbonaceous plant debris and mica are abundant in the sandstone laminations. The upper part of the formation consists of thick, mollusk-bearing, moderately- to well-sorted, arkosic sandstone and minor polymict grit beds. A shallowing-upward, high-energy, shallow-marine shelf environment of deposition is indicated for the upper part of the formation. Contemporaneous with shelf and slope deposition of the Sager Creek, Pittsburg Bluff and Northrup Creek formations, the deep-water late Eocene to early Miocene Smuggler Cove formation was deposited as a distal or lateral correlative in a low-energy, outer shelf to slope setting. This foram-bearing unit consists of thick, bioturbated, bathyal, tuffaceous mudstone and siltstone with minor thin- to thick-bedded ashfall and current-reworked tuff. A marine onlap is indicated by the conformable relationship between the upper sandstone unit of the Northrup Creek formation and the overlying Smuggler Cove formation in the eastern part of the thesis area. The overlying lower to middle Miocene Astoria Formation contains two members in the thesis area: a high-energy, shallow shelf, fine- to medium-grained, fossiliferous, micaceous arkosic sandstone (Wickiup Mountain member), and an overlying, thinly-laminated, deepmarine mudstone (Cannon Beach member). Diatom floras indicate that a thermal "oceanographic irregularity" (water warmer than normal) may have occurred during deposition of the Cannon Beach member. At least six, and possibly eight, flows of the middle Miocene Grande Ronde Basalt (Columbia River Basalt Group) are present in the thesis area. Individual flows have been ascribed to the (N1?), R2, and N2 magnetozones. Geochemically, the flows consist of low MgO high Ti02, low MgO low Ti02, and high MgO subtypes. These subaerial to submarine flows are correlated to Mangan and others (1986) chemical subtypes 2D, 5C, 5A, and 4A of the Columbia Plateau-derived Grande Ronde Basalt of eastern Washington and eastern Oregon. The correlations are based on similarity of age, major element chemistry, stratigraphic position, and magnetic polarity. Field evidence suggests that thick, submarine pillow and breccia complexes generated sufficient pressure to autoinvasively inject into the Eocene to middle Miocene sedimentary strata of the Plympton/Porter ridge and Elk Mountain areas. This process apparently formed many randomly-oriented dike- and sill-like intrusions in the western part of the thesis area. However, in the eastern and central parts of the thesis area, three sub-parallel dikes (the Northrup, Beneke, and Fishhawk Falls dikes) extend along linear trends for tens of kilometers. This suggests that their emplacement was, in part, influenced by earlier or contemporaneous regional tectonism. At least two, and as many as five, flows of the Frenchman Springs Member of the Wanapum Basalt occur in the thesis area: one to two abundantly plagioclase-phyric Basalt of Ginkgo flow(s), and one to three Basalt of Sand Hollow flows (terminology after Beeson and Tolan, 1985). These flows consist of subaqueous pillow palagonite breccia and vesicular, columnar-jointed, subaerial basalt. No Frenchman Springs flows are invasive in the thesis area. Local middle Miocene sedimentary interbeds between flows of Grande Ronde and Frenchman Springs Basalt are lithologically and sedimentologically diverse. Common lithologies are fine- to mediumgrained, arkosic sandstone, coarse-grained basaltic sandstone, and structureless mudstone. Depositional environments represented by these strata are fluvial, marginal-marine, and shallow-marine. Thicknesses of individual interbeds range from 0.2 to 50 m. The thesis area is located on the northwest flank of the Oregon Coast Range anticline, adjacent to the Nehalem Arch. Large-scale northeast-trending oblique to strike-slip left-lateral faults coupled with northwest-trending oblique to strike-slip right-lateral faults dominate the structure of the area. These faults may have formed as conjugate shears (Riedel shear) caused by north-south compressive stress related to the oblique subduction of the Juan de Fuca Plate beneath the North American Plate. Five episodes of deformation are suggested by faults, dike orientations, unconformities, and other geological relationships within the thesis area: a late Eocene north-south compressional episode, an early Oligocene to early Miocene uplift, a middle Miocene northwest-southeast extensional episode, a post-middle Miocene to Pliocene (?) north-south compressional episode, and a north-south extensional event that occurred between the post-middle Miocene and Recent. Although crushed rock (for road and revetment construction) is currently the primary mineral resource within the thesis area, several potential fault traps on this northwest flank of the Nehalem Arch may contain significant reserves of natural gas. This conclusion is based upon field, laboratory, and subsurface (well) data. The Clark and Wilson sandstone of the middle to late Eocene Cowlitz Formation, the producing unit at the nearby Mist gas field, represents the most attractive target horizon. Additionally, the porous and permeable upper sandstone unit of the Northrup Creek formation could contain shallow hydrocarbon reserves beneath the northern part of the area. Title: The geology of the Elk Mountain-Porter Ridge area, Clatsop County, northwest Oregon Author: Goalen, Jeffrey Scott Eight Tertiary sedimentary and volcanic units crop out in the thesis area. From oldest to youngest they are the: Sager Creek formation (informal); Pittsburg Bluff Formation; Northrup Creek formation (informal); Smuggler Cove formation (informal); Wickiup Mountain and Cannon Beach members (both informal) of the Astoria Formation; the Grande Ronde Basalt, and Frenchman Springs Member of the Wanapum Basalt, both of the Columbia River Basalt Group. Also, areally limited, unnamed sedimentary strata interbedded between flows of the Columbia River Basalt Group crop out in the study area. Quaternary deposits consist of alluvium, colluvium, and landslide debris. Rhythmically-bedded, foram-bearing, carbonaceous to micaceous mudstone and graded, fine-grained, feldspathic turbidite sandstone are the dominant lithologies of the upper Eocene (Refugian) Sager Creek formation. Plane-laminae and climbing ripple-laminae typical of Bouma b,c, and d intervals are common in the thin turbidite sandstone beds. Contemporaneous, rare, thick, sandstones may represent submarine feeder channels that supplied the more widespread, thinly-bedded overbank turbidite sandstones. Foraminiferal paleobathymetry indicates that deposition was in bathyal water depths. Sager Creek deposition was followed by a regression or offlap of the late Eocene to early Oligocene (Refugian) sea as indicated by the molluscan fossils and thick, bioturbated sandstone of the predominantly shallow-marine Pittsburg Bluff Formation. The lower part of the formation consists of outer shelf, glauconitic, fossiliferous sandstone and subordinate mudstone. Higher in the section are middle-shelf, fine-grained, bioturbated, tuffaceous, arkosic sandstones. These sandstones contain minor glauconite, wave- and storm-generated molluscan shell hash beds, carbonized wood fragments, and calcareous concretions. Deposition occurred in 20 - 50 m open-marine shelf water depths; however, the depositional environment may have shallowed to a bay-like setting (Moore, 1982, written communication). The upper part of the unit consists of thin- to medium-bedded, carbonaceous siltstone and mudstone with minor ashfall tuffs. Therefore, deposition of the Pittsburg Bluff Formation occurred as a shallowing-upward, then deepening depositional episode, punctuated by contemporaneous, intermittent eruption of nearby calc-alkaline western Cascade volcanoes. The deep-marine Oligocene to lower Miocene (Zemorrian to Saucesian) Northrup Creek formation is predominantly composed of thinly-laminated mudstone interbedded with thin, very fine-grained, graded, micaceous arkosic sandstone. Bouma c-d-e and a-b-e sequences are common in the turbidite sandstone; Bouma a-e intervals occur locally in sandstone/mudstone couplets. Paleocurrent indicators suggest that the predominant transport direction of these turbidite deposits was northeast to southwest. Abraded, carbonaceous plant debris and mica are abundant in the sandstone laminations. The upper part of the formation consists of thick, mollusk-bearing, moderately- to well-sorted, arkosic sandstone and minor polymict grit beds. A shallowing-upward, high-energy, shallow-marine shelf environment of deposition is indicated for the upper part of the formation. Contemporaneous with shelf and slope deposition of the Sager Creek, Pittsburg Bluff and Northrup Creek formations, the deep-water late Eocene to early Miocene Smuggler Cove formation was deposited as a distal or lateral correlative in a low-energy, outer shelf to slope setting. This foram-bearing unit consists of thick, bioturbated, bathyal, tuffaceous mudstone and siltstone with minor thin- to thick-bedded ashfall and current-reworked tuff. A marine onlap is indicated by the conformable relationship between the upper sandstone unit of the Northrup Creek formation and the overlying Smuggler Cove formation in the eastern part of the thesis area. The overlying lower to middle Miocene Astoria Formation contains two members in the thesis area: a high-energy, shallow shelf, fine- to medium-grained, fossiliferous, micaceous arkosic sandstone (Wickiup Mountain member), and an overlying, thinly-laminated, deepmarine mudstone (Cannon Beach member). Diatom floras indicate that a thermal "oceanographic irregularity" (water warmer than normal) may have occurred during deposition of the Cannon Beach member. At least six, and possibly eight, flows of the middle Miocene Grande Ronde Basalt (Columbia River Basalt Group) are present in the thesis area. Individual flows have been ascribed to the (N1?), R2, and N2 magnetozones. Geochemically, the flows consist of low MgO high Ti02, low MgO low Ti02, and high MgO subtypes. These subaerial to submarine flows are correlated to Mangan and others (1986) chemical subtypes 2D, 5C, 5A, and 4A of the Columbia Plateau-derived Grande Ronde Basalt of eastern Washington and eastern Oregon. The correlations are based on similarity of age, major element chemistry, stratigraphic position, and magnetic polarity. Field evidence suggests that thick, submarine pillow and breccia complexes generated sufficient pressure to autoinvasively inject into the Eocene to middle Miocene sedimentary strata of the Plympton/Porter ridge and Elk Mountain areas. This process apparently formed many randomly-oriented dike- and sill-like intrusions in the western part of the thesis area. However, in the eastern and central parts of the thesis area, three sub-parallel dikes (the Northrup, Beneke, and Fishhawk Falls dikes) extend along linear trends for tens of kilometers. This suggests that their emplacement was, in part, influenced by earlier or contemporaneous regional tectonism. At least two, and as many as five, flows of the Frenchman Springs Member of the Wanapum Basalt occur in the thesis area: one to two abundantly plagioclase-phyric Basalt of Ginkgo flow(s), and one to three Basalt of Sand Hollow flows (terminology after Beeson and Tolan, 1985). These flows consist of subaqueous pillow palagonite breccia and vesicular, columnar-jointed, subaerial basalt. No Frenchman Springs flows are invasive in the thesis area. Local middle Miocene sedimentary interbeds between flows of Grande Ronde and Frenchman Springs Basalt are lithologically and sedimentologically diverse. Common lithologies are fine- to mediumgrained, arkosic sandstone, coarse-grained basaltic sandstone, and structureless mudstone. Depositional environments represented by these strata are fluvial, marginal-marine, and shallow-marine. Thicknesses of individual interbeds range from 0.2 to 50 m. The thesis area is located on the northwest flank of the Oregon Coast Range anticline, adjacent to the Nehalem Arch. Large-scale northeast-trending oblique to strike-slip left-lateral faults coupled with northwest-trending oblique to strike-slip right-lateral faults dominate the structure of the area. These faults may have formed as conjugate shears (Riedel shear) caused by north-south compressive stress related to the oblique subduction of the Juan de Fuca Plate beneath the North American Plate. Five episodes of deformation are suggested by faults, dike orientations, unconformities, and other geological relationships within the thesis area: a late Eocene north-south compressional episode, an early Oligocene to early Miocene uplift, a middle Miocene northwest-southeast extensional episode, a post-middle Miocene to Pliocene (?) north-south compressional episode, and a north-south extensional event that occurred between the post-middle Miocene and Recent. Although crushed rock (for road and revetment construction) is currently the primary mineral resource within the thesis area, several potential fault traps on this northwest flank of the Nehalem Arch may contain significant reserves of natural gas. This conclusion is based upon field, laboratory, and subsurface (well) data. The Clark and Wilson sandstone of the middle to late Eocene Cowlitz Formation, the producing unit at the nearby Mist gas field, represents the most attractive target horizon. Additionally, the porous and permeable upper sandstone unit of the Northrup Creek formation could contain shallow hydrocarbon reserves beneath the northern part of the area. Close

• 3194. [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