Russian knapweed and perennial pepperweed are invasive to meadow and riparian habitats in the semiarid intermountain west. Seed germination was tested to determine favored seedbed characteristics. Germination was inhibited in both species when water stress was imposed using polyethylene glycol. Knapweed achieved 60% germination after 40 d in dark and alternating light/dark environments. Pepperweed germination was greatest (30% after 14 d) in light and alternating light/ dark environments. Both species showed that germination declines when exposed to salt stress but continued to germinate under salt stress as high as 16 dSm(-1).

Growth and growth rate characteristics of diffuse knapweed and bluebunch wheatgrass seedlings were evaluated under two temperature regimes, 10 and 16 C, and two moisture regimes, - 0.01 and - 0.03 MPa, in an environmental chamber. Intra- and interspecific interference were evaluated at 10 C and at either - 0.01 or 0.03 MPa. Root-leaf ratios for bluebunch wheatgrass were greater than for diffuse knapweed at 0.01 MPa. Under moist conditions, root penetration was greater for diffuse knapweed than for bluebunch wheatgrass roots; penetration was equal in warm or dry conditions. Wheatgrass root length was greater than knapweed length under dry conditions. Intraspecific interference was greater than interspecific interference for both species. Leaf area data and root-leaf ratios suggest that diffuse knapweed is the faster-growing species under moist conditions.

Growth characteristics of diffuse knapweed (Centaurea diffusa Lam.) and bluebunch wheatgrass (Pseudoroegneria spicata (Pursch) Scribn. & Smith) seedlings were evaluated in 2 temperature regimes, 10 and 16degreesC, and 2 moisture regimes, - 0.01 and - 0.03 MPa, in an environmental chamber. In cool, wet conditions, root penetration was greater for diffuse knapweed roots than bluebunch wheatgrass roots, but penetration was equal in warm, dry conditions. Root lengths for both species were equal in cool, wet conditions; but, bluebunch wheatgrass root length was greater in warm, dry conditions. Leaf area of diffuse knapweed was greater than bluebunch wheatgrass in warm, dry conditions. Drier, but not cooler, conditions favored diffuse knapweed leaf area over bluebunch wheatgrass leaf area. Root:shoot ratios for bluebunch wheatgrass were greater than diffuse knapweed in all environmental conditions. Results suggest that bluebunch wheatgrass should be more competitive than diffuse knapweed for nutrients and water at lower depths in warmer, drier conditions. Diffuse knapweed should be more competitive for nutrients and water in wetter conditions.

Airborne infrared thermal radiography has been proposed as a tool which may be used to monitor the water temperature along the network of streams and rivers which compose a watershed. The proponents of this method correlate vegetative shadows on a stream channel with reduced infrared radiation (IR) reception in the radiographic data to suggest that the water temperature is reduced in such areas. Two methods are employed to demonstrate that this interpretation of the data is in error. First, the fundamental principles of thermodynamics are employed to show that if the stream is in fact flowing, the water affected by any cooling process cannot remain in the vicinity where it was cooled. Second, temperature data taken from a stream channel are used to show that the water flowing in the channel is essentially unaffected by the patterns of vegetative shade on the surface of the channel.

In this paper we propose two chaotic pulse-position modulation schemes (synchronous and asynchronous) for digital ultra-wide bandwidth impulse radio communication systems. In the pro- posed schemes the inter-pulse time intervals are controlled by a chaotic map. It is argued that the chaotic modulation enhances the spread-spectrum characteristics of the signal by removing most peri- odic components from the transmitted signal. Also, it is shown that the self-synchronizing properties of chaotic systems can prove useful to achieve and maintain synchronization between transmitter and receiver. Finally, maximum-likelihood estimation based on the properties of chaotic systems is dis- cussed.

Yellow starthistle germination in an environmental chamber was 74, 38, 3, and 0% at osmotic potentials of 0, −0·5, −1·0, and −1·5 MPa, respectively. Salinity levels of 0, 4, 8, and 12 dSm−1had an inconsistent effect on germination. The presence of a pappus (p-achene) was associated with an 11 and 15% increase in germination over those achenes without a pappus (np-achene) at 0 and −1·5 MPa, respectively. Field germination of p-achenes was 29 and 33% greater than np-achenes at La Grande, OR and Walla Walla, WA, respectively. Total germination (field plus lab) was not influenced by time of burial (3 months) or 1- and 2-cm burial depths. Dimorphic achenes appear to be associated with success in exploiting highly variable soil moisture regimes in semi-arid environments.

Cheatgrass (Bromus tectorum L.) and yellow starthistle (Centaurea solstitialis L.) have invaded over 250 thousand hectares throughout the Pacific Northwest, Future management of rangelands dominated by these species will require an understanding of the plant-plant interactions which contribute to the regulation of community dynamics and the establishment of desirable plants. Addition series experiments, with total stand densities ranging from 20-20,000 plants m(-2), were used to quantify the interference between cheatgrass and yellow starthistie in unrestricted soil depths on 12-day intervals throughout the growing season and in soil depths restricted to 0.2- and 0.5-m. Intraspecific interference was nearly twice as important as interspecific interference when plants were grown in unrestricted soil, Resource partitioning by cheatgrass and yellow starthistle was associated with rooting depth, When restricted to a 0.5-m depth, resource partitioning did not occur and intra- and interspecific interference were similar for both species, Restriction to a 0.(2)-m depth resulted in cheatgrass density being twice as important as yellow starthistle density for predicting yellow starthistle shoot weight, Yellow starthistle density was not important for predicting cheatgrass shoot weight, Cheatgrass appeared to have a competitive advantage over yellow starthistle in shallow soils, but the rooting depth and seed production capacity of yellow starthistle was greater than cheatgrass in deep soil.

Weed competition is a major factor causing warm-season grass seeding failures in rangeland and cropland. With a limited number of herbicides available for weed control, grazing may reduce competing vegetation in seedings and serve as an alternative to herbicides. Many immature needy forbs and grasses are palatable to cattle and contain high nutrient levels. Research was conducted (RCBD, 4 reps) comparing grazing by yearling cattle with chemical suppression [atrazine (6-chloro-N-ethyl-N’(methylethyl)-1, 3, S-triazine-2, 4-diamine)] for weed control in big bluestem (Andropogon

Published November 1994. Reprinted January 2008. Reviewed July 2013. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalog

Whitetop or heart-podded hoary cress (Cur&riir &u&z(L.)Desv.) is an Eurasian native of the Cruciferae actively invading rangelands throughout western North America. The plant is reported to be unpalatable to livestock and contain potentially toxic glucosinolates. Practical experience indicates sheep consume whitetop during its early growth stages and cattle ingest large quantities of seedheads. Chemical analysis of whole plants from rosette to hard seed, respectively, indicated the following trends: crude protein (28.8 to 7.9%), neutral detergent fiber (13.1 to 52.8%), acid detergent fiber (12.0 to 41.8%), cellulose (9.9 to 32.10/o), lignin (1.9 to 9.4%), ether extract (1.6 to 2.4%), in vitro organic matter digestibility (77.3 to 49.1%), digestible energy (2.9 to 1.8 Meal/kg), and total glucosinolates (28.4 to 84.0 pmol/g). Leaves were higher than stems in crude protein, ether extract, in vitro organic matter digestibility, and digestible energy. Analysis of 11 micro- and macroelements revealed sulfur (S) levels ranged from 0.73 to 2.69% and were therefore higher than the reported maximum tolerable level (0.4%). High S levels likely reflected the S moiety of glucosinolates and their hydrolysis products. Whitetop has some forage value, but until further research establishes the toxicity of this species to sheep and cattle, prudence suggests managers use caution when allowing animals to graze whitetop-infested rangelands by providing supplemental iodine, utilizing mature and nonlactating animals, and reducing opportunities for animals to consume the plant.

Rapid germination and root growth have been identified as important plant characteristics for establishment in arid environments. This study evaluates germination, radicle elongation, and root growth rates of two annual grasses, two forage species, and yellow starthistle. Yellow starthistle germination, radicle elongation, and root growth were faster than those of medusahead and hedgehog dogtailgrass. Subterranean clover possessed rapid seedling growth characteristics similar to those of yellow starthistle, whereas Palestine orchardgrass was most delayed.

Hoary cress germination decreased with lower osmotic potential. Knapweed germination was greatest at 0.0 and −0.5 MPa of osmotic potential. Salinity increases up to an electrical conductivity (EC) of 12 dS m-1had no effect on germination of either species. Hoary cress and knapweed root growth were reduced by decreases in osmotic potential. Hoary cress root growth was not affected by increasing salinity up to an EC of 12 dS m-1. Knapweed root growth was reduced by the initial increase in salinity (4 dS m-1), but not by higher salt concentrations.

Hypotheses are frequently posed that require comparisons among diet samples. Hierarchical cluster analysis is suited to this task, but has received little attention in food habits research. By grouping samples so that similar diets are close together and dissimilar diets are spaced farther apart, hierarchicaI cluster analysis reveals patterns in data difficult to recognize in the matrix of similarity coefficients typical of most food habits studies. We provide an example of this type of analysis, and indicate its application to mananement of laree herbivores. --_--.. .-------_-------. ----_-----~

A 2-yr study was conducted to evaluate the response of yellow starthistle density and grass biomass to combinations of newly seeded grass, picloram, and fertilizer. A combination of ‘Tualatin’ tall oatgrass or ‘Paiute’ orchardgrass with 0.14 or 0.28 kg ae/ha of picloram effectively controlled yellow starthistle and improved forage production. Grass seeded alone or combined with fertilizer neither controlled yellow starthistle nor improved forage production. Three-way combinations of grass, picloram, and fertilizer did not affect yellow starthistle density in either year but resulted in more ‘Tualatin’ tall oatgrass biomass in 1987.