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4881. [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
- 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.
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4882. [Article] Umatilla Basin Natural Production Monitoring and Evaluation; Annual Progress Report 1994 - 1995
Abstract -- This report summarizes the activities of the Umatilla Basin Natural Production Monitoring and Evaluation Project (UBNPME) from September 30, 1994 to September 29, 1995. This program was funded ...Citation Citation
- Title:
- Umatilla Basin Natural Production Monitoring and Evaluation; Annual Progress Report 1994 - 1995
Abstract -- This report summarizes the activities of the Umatilla Basin Natural Production Monitoring and Evaluation Project (UBNPME) from September 30, 1994 to September 29, 1995. This program was funded by Bonneville Power Administration and was managed under the Fisheries Program, Department of Natural Resources, Confederated Tribes of the Umatilla Indian Reservation. An estimated 36.7 km (22.6 miles) of stream habitat were inventoried on the Umatilla River, Moonshine, Mission, Cottonwood and Coonskin Creeks. A total of 384 of 3,652 (10.5%) habitat units were electrofished. The number of juvenile fish captured follows: 2,953 natural summer steelhead (including resident rainbow tout; Oncorhynchus mykiss), one hatchery steelhead, 341 natural chinook salmon (0. tshawytscha), 163 natural coho salmon (0. kisutch), five bull trout (Salvelinus confluentus), 185 mountain whitefish (Prosopium williamsoni), and six northern squawfish (Ptychocheilus oregonensis). The expanded population estimate for the areas surveyed was 73,716 salmonids with a mean density of 0.38 fish/m2. The following number of non-salmonids were visually estimated: 7,572 speckled dace (Rhinichthys osculus), 5,196 sculpin (Cottus spp.), 532 suckers (Catostomus spp.) and 191 redside shiners (Richardsonius balteatus). The gross estimated density of all non-salmonids combined was 0.84 fish/m2. The estimated ratio of non-salmonids to salmonids was 2.4: 1. Relative salmonid abundance, seasonal distribution and habitat utilization were monitored at index sites throughout the basin. During index site monitoring, the following species were collected in addition to those listed above: american shad (Alosa sapidissima), smallmouth bass (Micropterus dolomieu), carp (Cyprinus Carpio) and chiselmouth (Acrocheilus alutaceus). Thirty nine sites were electrofished during the spring and summer seasons, while 36 sites were sampled in the fall season. Index sites with the. highest mean salmonid catch/minute (fish/min.) during the three sample periods were located at the following sites: East Birch Creek (3.4 fish/min.), Boston Canyon Creek (3.2 fish/min.), Spring Creek (3.1 fish/min.) and upper Squaw Creek (3.0 fish/min.). The highest electrofishing catch rates were observed in the Umatilla River tributaries above river mile (RM) 70 in the August and September sample period (Table J-2 catalogs river miles with associated landmarks). During the November sample period, catch rates were highest in Birch Creek tributaries. Most salmonids were captured in slow water near the bank during the November and March sampling periods. A study of the migration movements and homing requirements of adult salmonids in the Umatilla River was conducted during the 1994-95 return years. Radio telemetry was used to evaluate the movements of adult salmonids past diversion dams in the lower Umatilla River and to determine migrational movements of salmonids following upstream transport. Radio transmitters were placed in 30 summer steelhead, 15 spring chinook, nine fall chinook, and eight coho salmon. Salmon were released at Three Mile Falls Dam (TMD). An additional 11 summer steelhead and ten spring chinook salmon were tagged, hauled upstream, and released at either Barnhart, Nolin, Thornhollow, or Imeques C-mem-ini-kem. On average, summer steelhead required 36 days to successfully migrate from TMD to Stanfield Dam. Spring chinook required 18 days. Average passage times for summer steelhead (hours and minutes) at Westland, Feed Canal, and Stanfield Dams were 13:06, 83:24, and 2:58, respectively. Spring chinook salmon required 04:30 at Westland, 89:42 at Feed Canal, and 04:01 at Stanfield Dams. Migrational delays were observed at Feed Canal Dam at flows ranging from 563 to 1,601 cubic feet/second (cfs). Thirty-eight percent of the fish ladder at Westland Dam, 75% at Feed canal, and 31% at Stanfield Dam. Average passage times at Feed Canal Dam (1995) were more than 15 times those at Stanfield Dam in 1994 and more than 20 times those at Stanfield Dam in 1995. Data related to homing and passage needs of Umatilla River salmonids was investigated in an attempt to maximize homing to the Umatilla River. Straying rates of adult summer steelhead and spring chinook salmon were found to be low while coho and fall chinook salmon stray rates were high in some groups, particularly adult returns from subyearling smolt releases of fall chinook salmon. Attraction flows of from the mouth of the Umatilla River of at least 150 cfs were required to encourage migration and reduce straying of fall chinook and coho salmon. Significant numbers of summer steelhead entered when flows exceeded 500 cfs. Spring chinook salmon entry was variable with fish entering at flows ranging from 150 to more than 2,000 cfs. Adult anadromous salmonids potentially available to spawn above TMD from August 26, 1994 to June 27, 1995 included: 593 adult and 530 jack fall chinook salmon (1994 brood), 879 adult and 54 jack coho salmon (1994 brood), 784 natural and 509 hatchery summer steelhead (1995 brood), and 378 adult and 62 jack spring chinook salmon (1995 brood). During escapement surveys (fall of 1994), a total of 82 fall chinook salmon redds, 24 coho salmon redds and seven unidentified salmon redds (112 redds total, 2.6/mile) were enumerated along 42.3 miles of the mainstem above TMD. In 1995, we enumerated and flagged 126 summer steelhead redds (3.6 redds/mile) along 35.3 miles of lateral tributaries of the Umatilla River. Also enumerated were 90 spring chinook salmon redds (1.6 redds/mile) along 55.8 miles of the mainstem. Ninety-six percent of the adult fall chinook salmon carcasses examined had spawned while 94% of the coho had spawned; 66.8 % of the spring chinook salmon carcasses examined bad spawned. A total of 49.3% of spring chinook salmon released above TMD were sampled during spawning ground surveys and 60 coded wire tags (CWTs) were recovered from 78 adipose clipped fish. The rotary screw trap in the Umatilla River (RM 76) operated 63 of 113 days from September 21, 1994 to January 13, 1995. The trap captured 596 juvenile steelhead with a mean trap efficiency rate of 9.9%. A total of 1,368 juvenile chinook salmon were captured with a mean trap efficiency rate of 28. 8 % . The rotary screw trap at the Imeques C-mem-ini-kem site (RM 79.5) operated 43 out of 43 days from May 5 through June 16, 1995. The trap captured 304 natural juvenile steelhead with a mean trap efficiency rate of 6.6%. A total of 102 natural juvenile chinook salmon were captured with a mean trap efficiency rate of 10.5%. The rotary screw trap at the Barnhart site (RM 42,2) operated 87 out of 125 days from March 3 to June I, 1995. The trap captured 105 natural juvenile steelhead, 247 natural juvenile chinook salmon, five natural coho salmon, 6,265 hatchery juvenile chinook salmon, 467 hatchery steelhead and 16,844 hatchery coho salmon. Mean trap efficiency rates ranged from 2.3 to 5.7% . Harvest monitors estimated that tribal anglers harvested 25 hatchery and five natural summer steelhead during the spring of 1995. There was no spring chinook salmon fishery in the Umatilla River during 1995 because of the low number of returning adults. Scale analysis determined that over 85 .0% of naturally produced juvenile summer steelhead sampled during biological and index surveys were age O+ or l +. Naturally produced summer steelhead adults, returning to the Umatilla River in 1994-95, were mostly from the 1990 (46.4%) and 1991 (33.9%) brood years.