Spawning habitat of Chinook salmon (Oncorhynchus tshawytscha) was estimated upstream of Grand Coulee Dam to support the feasibility evaluations of reintroducing anadromous salmon to this blocked reach of the Columbia River. A two-dimensional depth-averaged hydrodynamic model was developed for a 76-km reach between Kettle Falls, Washington, and the US-Canada international border and used to predict water velocities and depths at 10%, 50%, and 90% flow exceedance values. Hydrodynamic model outputs were combined with calculated bed slopes and empirical and modeled data on substrate availability to estimate salmon spawning habitat availability. A probabilistic spawning model was developed to estimate suitability for spawning salmon based on habitat characteristics at the exceedance flow levels and three substrate classifications. A majority of the highest probability salmon spawning habitat was located between Northport, Washington, and the international border. The model predicted 17.6 ha of spawning habitat at the 50% exceedance flow level for areas with pebble and cobble substrates; this equates to an approximate redd capacity of 2,893 to 4,091 non-overlapping redds, depending on mean redd size. Estimated capacity of spawning adults ranged from 5,786 (assuming two fish per redd and lowest number of redds) to 32,728 (assuming eight fish per redd at highest number of redds). We conclude that suitable Chinook salmon spawning habitat is available upstream of Grand Coulee Dam. The results of this study will be useful to fisheries managers considering salmon reintroduction and ecosystem function in various processes including the modernization of the Columbia River Treaty, the Northwest Power and Conservation Council's Fish and Wildlife Program, and tribal and other natural resource conservation initiatives.

Coastal cutthroat trout [Oncorhynchus clarkii clarkii (Richardson, 1836)] from the marine waters of Puget Sound, WA, was documented as a new host for the ectoparasite Argulus pugettensis (Dana, 1852). The prevalence of A. pugettensis was 66% (49 of 74) on cutthroat trout and 0% (0 of 55) on coho salmon [O. kisutch (Walbaum, 1792)] collected during the winter of 2017/2018. Infestations occurred most frequently on the dorsal surface, with intensities ranging from 1 to 26 argulids per fish (mean intensity 3.94 ± 4.93 S.D.). In contrast, the prevalence of the common salmon louse [Lepeophtheirus salmonis (Krøyer, 1837)] was 72% for cutthroat trout and 31% for coho salmon. Relative to other native salmonids, little is known regarding the status, ecology and threats for coastal cutthroat trout. New information reported here is a first step in understanding the relationship between this wild, native trout and infestations by parasitic sea lice and should be followed by future studies aimed to identify population level consequences.

Two sources of nitrogen to Pacific Northwest riparian areas are marine-derived nitrogen (MDN) via anadromous Pacific salmon (Oncorhynchus spp.) and atmospheric nitrogen fixation via red alder (Alnus rubra). The recent removal of two large dams on the Elwha River, WA, opened up about 60 km of previously inaccessible river habitat for anadromous salmon. We used naturally abundant stable nitrogen isotopes to establish baseline data to monitor the influx of MDN to riparian zones of Elwha River tributaries post dam removal. We sampled riparian soil, overstory, and understory vegetation in sites with nitrogen-fixing A. rubra and sites with bigleaf maple (Acer macrophyllum) at an undammed reference site, and along three tributaries, one between the former dams (accessible to anadromous salmon since 2012) and the others upstream of the former dams (no anadromous salmon). Based on δ¹⁵N measurements of soil and vegetation, we did not detect MDN at any of the tributaries, including the reference tributary. However, the understory riparian vegetation between the former dams had a higher δ¹⁵N than the other tributaries, which may be due to upstream anthropogenic nitrogen sources. Although A. rubra foliage was isotopically distinct from A. macrophyllum, and A. rubra litter had higher total nitrogen, soil and understory vegetation in A. rubra and A. macrophyllum sites did not differ isotopically. Monitoring of these areas and those further upstream on the Elwha River will allow us to trace the return of MDN to the watershed, and help to clarify the role that anadromous fish play in riparian ecosystems.

Whitebark pine (Pinus albicaulis) is a long-lived tree found in high-elevation forests of western North America that is declining due to the non-native white pine blister rust (Cronartium ribicola) and climate-driven outbreaks of mountain pine beetle (Dendroctonus ponderosae; MPB). The National Park Service established a monitoring program for whitebark pine in seven parks, including Sequoia & Kings Canyon, Yosemite, Lassen Volcanic, Crater Lake, Mount Rainier, Olympic, and North Cascades National Parks. Using these data, we summarized stand structure, presence of blister rust, and MPB prevalence to provide a baseline for future monitoring. Next, we used a stochastic, size-structured population model to speculate on future trends in the seven national park populations under conditions of increased MPB activity and ongoing blister rust infection observed in Crater Lake. We found that blister rust infected 29 to 54% of whitebark pine in all the parks except the two southernmost, Sequoia & Kings Canyon and Yosemite, where infections rates were 0.3% and 0.2%, respectively. The proportion of dead trees in Sequoia & Kings Canyon and Yosemite was low (0 to 1%), while they ranged from 10 to 43% in the other parks. Model projections suggested an average population decline of 25% in the parks over the next century using Crater Lake conditions, declines which are possible if blister rust continues to spread and climate change results in a significant increase in the frequency or severity of MPB outbreaks. Overall, our study describes conditions at seven western parks and illustrates potential rates of whitebark pine decline if pest outbreaks and/or blister rust infections worsen.

Plant-microbe mutualisms can determine the success of invasive plants. Legumes (Fabaceae) are particularly successful invaders in a variety of habitats. This is partly due to their ability to access atmospheric nitrogen through microbial mutualists (rhizobia) in their root systems, which allow them to colonize a wide variety of disturbed or nutrient-poor habitats. While many plant-rhizobia mutualisms are highly species-specific, plant promiscuity with different species of rhizobia can significantly enhance the success of invasive legumes, since the availability of suitable rhizobial mutualists in a new geographic area may serve as a limiting factor. Scotch broom (Fabaceae: Cytisus scoparius) is one of the most problematic invasive legumes in the Pacific Northwest (PNW), yet very little is known about the Scotch broom-rhizobia system. We explored the rhizobial communities of root nodules of Scotch broom and sympatrically occurring legumes across three major ecoregions (coast, valley, and mountain) in the western PNW (Washington, Oregon, and California) to better understand the Scotch broom-rhizobia system in nature. We found that bradyrhizobia are the exclusive rhizobial mutualists of Scotch broom but that there is promiscuity at the species level. While there was very little overlap with rhizobial communities of sympatric native and naturalized legumes, ecoregion did influence the species composition of Scotch broom-associated rhizobial communities. Our findings suggest that Scotch broom is not reliant on sympatric legumes to provide a source of suitable rhizobial mutualists, but instead forms spatially variable associations with a range of other bradyrhizobia.

Trends and transitions in the growing season MODerate resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) time series at 250-m resolution were analyzed for the period from 2000 to 2018 to understand recent patterns of vegetation change in ecosystems of the Yukon River basin in interior Alaska. Statistical analysis of changes in the NDVI time series was conducted using the “Breaks for Additive Seasonal and Trend” method (BFAST). This structural change analysis indicated that NDVI breakpoints and negative 18-yr trends in vegetation greenness over the years since 2000 could be explained in large part by the impacts of severe wildfires, commonly affecting shrubland and forested ecosystems at relatively low elevations (< 300 m). At least one NDVI breakpoint was detected at 29% of the MODIS pixels within the Yukon River basin study area. The warmest and wettest years in the study time period were found to be associated with a sizeable fraction (30%) of NDVI breakpoints. Among pixels with no NDVI breakpoints detected, both forest and shrubland trends were strongly skewed toward positive trend values. Results from gradual NDVI trend analysis supported the hypothesis that air temperature warming has enhanced the rates of (unburned) vegetation growth in shrubland and woodlands across interior Alaska over the past two decades.

We investigated the influences of height, light availability, leaf structure, and season on bigleaf maple (Acer macrophyllum Pursh) leaf physiology in northern California to improve our understanding of productivity and carbon sequestration in western forests. Using hydrated cuttings and lab-based measurements, we found that leaf mass-to-area ratio and maximum photosynthetic capacity increased with height and distance from the bole. In situ, we measured leaf physiology throughout tree crowns from June through September and found that predawn water potential was remarkably constant, indicating sustained access to water. We also found that midday water potential generally decreased with height and distance from the bole, noticeably decreased at the end of the growing season, and did not fall below –2 MPa, suggesting ample access to water and/or stomatal regulation to maintain hydrated water status. At midday, light availability and stomatal conductance of water vapor generally increased with height and distance from the bole. Stomatal conductance peaked in the treetop in June, in the mid-crown in July and August, and in the low-crown in September, demonstrating temporal and spatial optimization of crown resources in response to changing light quality, climatic conditions, and water status across the season to maximize carbon uptake at the tree level. Together, our water potential and light measurements suggest that light availability is a stronger determinant of leaf morphology and physiology than hydraulic limitation in this species. These findings provide information on seasonal physiology in a widespread deciduous hardwood species, thereby strengthening our understanding of forest productivity in a predominantly coniferous region.

Noise from military aircraft over the Olympic Peninsula (Washington, USA), has increased in recent years with changes in operations from nearby facilities. Further increases in training activities are proposed, but lack of any data that describe current noise levels has hindered assessment of impacts on humans and wildlife. Over a one-year period, we monitored three primary and two supplemental sites to document current noise contributions of military aircraft to the soundscape.

We found that currently, 88% of audible air traffic is military. Flight training activities were concentrated during weekdays and in daytime hours, with hourly percent time audible averaging 14 to 42%. The duration of time that military aircraft were audible in any hour was correlated across sites up to 51 km apart, and the site outside the operations area experienced substantial noise, signifying a noise footprint extending well beyond the operations area. Maximum loudness of flyover events exceeded 82 dBA (A-weighted sound pressure level), and a median increase of 3 to 4 dBA (i.e., a doubling of existing acoustic energy) from ambient periods was typical in most sites and seasons. Comparison of spectral power densities indicates that military aircraft largely impact frequencies below 1.2 kHz, averaging a 20-dB increase (i.e., quadrupling of loudness) in this frequency range compared with ambient samples. Our results demonstrate that changes in military operations will play a dominant role in dictating the future soundscape of the Olympic Peninsula, and offer an empirical basis for inquiry into how the proposed increases will impact people and wildlife in this region.