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We studied responses of Columbian white-tailed deer (Odocoileus virginianus leucurus) to cattle and sheep in western Oregon because of viability concerns. We used radio-telemetry, observations from horseback, and searches with a trained dog to determine fawning habitat, dam home ranges, and habitat use by fawns. Dams (n = 12) shifted ( = 366 m, P < 0.05) their center of activity by establishing disjunct areas of use prior to fawning. Ten dams exhibited their largest Euclidian movement during May—July; 7 females undertook extended ( = 1445 m) forays during spring. Three natal sites averaged 1926 m from the center of the dam's annual home-range. Dams avoided (P < 0.05) areas with livestock during fawning; 3 fawns were encountered during 243 h of searching (1 fawn/91.4 h) in areas with livestock stocking levels of ≥2.5 animal use month/ha (AUM), whereas 39 fawns were encountered during 275 h of searching (1 fawn/7.1 h) in areas with <2.5 AUM of livestock use. Natal areas (n = 52) were in denser luxuriant vegetation, typically along a permanent stream with greater obstruction to vision. Areas with cattle (Bos taurus) or sheep (Ovis aries) had lower percent vegetative cover, less diverse herbaceous vegetation, and less concealment cover. Establishing separate home ranges during the fawning season apparently was a response to the presence of livestock or effects of grazing, which reduced the vertical vegetation profile and concealment cover. Dams likely increase fawn survival by selecting sites with nutritious, palatable forage, denser vegetation, and moderate microclimates during parturition and lactation.
White sturgeon (Acipenser transmontanus) in the lower Columbia River system were previously known to spawn in only one area; within the 12 km of mainstem Columbia River downstream of Bonneville Dam. Our work provides the first documentation of white sturgeon spawning in the Willamette River, Oregon, a major tributary of the lower Columbia River. We used artificial substrates to sample for white sturgeon eggs downstream of Willamette Falls from 18 May to 20 May 2009 and collected a total of 22 fertilized eggs. Embryonic developmental stages ranged from pigmentation change (Stage 2) to early epithelial (Stage 8), corresponding to fertilization times of approximately 5–17 hours prior to collection. We estimated that spawning occurred between 2100 hours on 19 May and 0900 hours on 20 May 2009, and that a minimum of three independent spawning events took place during that time. Results suggest that the area immediately downstream of Willamette Falls may be important white sturgeon spawning habitat, and that the lower Willamette River is likely an additional source of production for the white sturgeon population in the lower Columbia River system.
We determined nutrient export from the Yaquina and Alsea Rivers as part of a larger program for evaluating nutrient sources to coastal waters. The Yaquina and Alsea data indicated that one river typically contained twice the amount of dissolved nitrate-N, although temperature, conductivity and the concentrations of other nutrients were similar. We developed a nitrate export model using multiple linear regression (MLR) to analyze the discriminating variables that included nutrient concentrations and hardwood cover containing approximately 90% red alder (Alnus rubra), a nitrogen-fixing tree species. Using data from the Coastal Landscape Analysis and Modeling Study (CLAMS), hardwood cover was found to be most prevalent in the upper (gaged) Yaquina watershed. Estimated nitrate export was 2.02 Mg km-2 y-1 in the Yaquina and 1.24 Mg km-2 y-1 in the Alsea for 2006. However, the annual nitrate-N exported from the entire Alsea basin (1560 Mg) was slightly greater than that of the Yaquina basin (1320 Mg) since the Alsea is about twice as large with proportionally greater discharge. Various factors, including the relatively low nitrate concentrations in local rainfall and the lack of local primary anthropogenic sources, indicated that red alder density may be the primary source of higher concentrations in the Yaquina, relative to the Alsea River. The regression model developed in this study can provide a rapid estimate of nitrate-N export based on water discharge data and hardwood distribution in the Oregon Coast Range.
Two species of alkaligrass, Nuttall's alkaligrass (Puccinellia nuttalliana [Schult.] Hitch.), a native, and weeping alkaligrass (Puccinella distans [Jacq.] Parl.), an introduced species from Eurasia, are found within semi-arid regions of the United States. Recently, land managers have become concerned over the ability of these two species to colonize a wide array of soil types, but have not been able to predict which sites might be at risk of invasion. Paired plots comparing site characteristics of infested versus very close, yet uninfested sites were sampled throughout the Grande Ronde Valley, northeastern Oregon. The results of this study indicate that Nuttall's alkaligrass was most commonly associated with sodic soils (73%), whereas 85% of the sites infested with weeping alkaligrass were agriculturally ‘normal’ sites. In general, Nuttall's alkaligrass was positively associated with sodium; whereas, for weeping alkaligrass, competing vegetation was the only factor affecting establishment and abundance. Weeping alkaligrass showed traits typical of a resource generalist, establishing on a wide variety of sites and being strongly influenced by competing vegetation; whereas Nuttall's alkaligrass appears to be more niche specific. Species that behave as resource generalists are more problematic than species linked to specific site characteristics because it is difficult to predict where they will establish. Therefore, a healthy crop cover on agriculturally productive sites is the best prevention against weeping alkaligrass establishment. For sodic sites, incapable of supporting a healthy crop, diligent weed control must be practiced to prevent the spread of either species of alkaligrass within agronomic systems.
Western juniper (Juniperus occidentalis Hook.) encroachment has altered the spatial distribution of soil nutrients and plants in semi-arid systems of the northern Great Basin, forming nutrient enriched ‘resource islands’ under tree canopies. Our goal was to determine the persistence of resource island characteristics after restoration treatment (tree cutting). The study site was a privately owned grazing allotment in eastern Oregon where trees had been cut eight and fifteen years ago. In each age class and in uncut western juniper woodlands, juniper stumps or trees were randomly selected for sampling. At each bole three radial transects, set at 120° from each other, were marked and soil cores were collected to 5-cm depth at distances of 50, 100, 150 and 300-cm from the bole then combined to a single composite sample per distance class. Samples were analyzed for total C and N, soluble P, K, Ca, Fe, Al, Mg and Na and pH. Despite increases in shrub, forb and grass crops in the fifteen-year old cut treatment, western juniper resource island effects were still evident for most soil variables measured; tree island soils were significantly higher in Ctot, Ntot, P, K and Ca compared to inter-island soils. Resource island persistence was attributed to litter mats beneath relic canopies. Management efforts may be more successful at preventing establishment of undesired annuals by focusing on young juniper stands where resource islands are less developed.
We investigated the growth and feeding performance of juvenile steelhead Oncorhynchus mykiss using field measures and bioenergetics modeling. Juvenile steelhead populations were sampled from mid-June through August 2004 at study sites upstream and downstream of Hemlock Dam. The growth and diet of juvenile steelhead were determined for a warm (summer) and subsequent (late summer) transitional period at each study site. Empirical data on the growth and diet of juvenile steelhead and mean daily temperatures were used in a bioenergetics model to estimate the proportion of maximum consumption achieved by juvenile steelhead by site and period. Modeled estimates of feeding performance were better for juvenile steelhead at the upstream compared to the downstream site during both periods. The median condition factor of juvenile steelhead did not change over the summer at the upstream site, but showed a significant decline over time at the downstream site. A negative trend in median condition factor at the downstream site supported bioenergetics modeling results that suggested the warmer stream temperatures had a negative impact on juvenile steelhead. Bioenergetics modeling predicted a lower feeding performance for juvenile steelhead rearing downstream compared to upstream of Hemlock Dam although food availability appeared to be limited at both study sites during the warm period. Warmer water temperatures, greater diel variation, and change in diel pattern likely led to the reduced feeding performance and reduced growth, which could have affected the overall survival of juvenile steelhead downstream of Hemlock Dam.
Mount Adams is a large glacier-clad stratovolcano located in southern Washington, USA. We examined the area change of the 12 glaciers on the mountain during the 20th century using historical topographic maps and aerial photographs. The total glacier area decreased by 49% (31.5 km2 to 16.2 km2) from 1904 to 2006. The glaciers showed a period of retreat during the first half of the century, followed by either a slowing of retreat or an advance from the 1960s to the 1990s. Subsequently, the glaciers resumed their rapid retreat. Glaciers on Mt. Adams show similar trends to those on both Mt. Hood and Mt. Rainier. The qualitative correlation between area change and trends in winter precipitation and summer temperature indicate a largely temperature-driven glacier shrinkage as the climate warmed since the Little Ice Age of the late 19th Century. No century-scale trends were noted in precipitation but decadal-scale variations in winter precipitation appear to enhance or buffer the effects of temperature on glacier change.
Bluebunch wheatgrass (Pseudoregneria spicata [Pursh] A. Love) is a major forage species for mountain sheep (Ovis canadensis) in central Idaho. Observed condition of this forage species is high, prompting an investigation of herbivory levels and subsequently nutrient content and biomass of this species. Mean amounts of tissue removed from wheatgrass plants on a slope frequently used by mountain sheep ranged from 5.3% to 26.8% from 1992–1996. Nitrogen levels ranged from 0.7–1.4% from 1998–2007 in plants collected in late June after seed-set. Higher levels of N occurred in growth following wildfire burns. Above-ground growth of bluebunch wheatgrass ranged from 11.3 to 102.1 gm/m2 and was highly correlated with spring precipitation. While herbivory on this major forage species was low to moderate, nitrogen levels may vary enough to affect mountain sheep population trends without appreciably affecting productivity of their major forage species.