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Western juniper (Juniperus occidentalis Hook.) has been actively invading shrub steppe communities during the past 120 years. The majority of these stands are still in transition, from early open juniper shrub steppe communities to closed juniper woodlands. In addition, juniper expansion has been occurring across a broad array of soils and topographic positions. Despite the high degree of spatial and developmental heterogeneity, juniper woodlands are frequently treated generically in resource inventories, management, and wildlife habitat assessments. Our goal was to evaluate the impact of western juniper encroachment and dominance on plant community composition and structure across several plant associations. This study was conducted in southeastern Oregon and northeastern California on low sagebrush (Artemisia arbuscula Nutt.), mountain big sagebrush (A. t r i d e n t a t a spp. vaseyana (RYBD.)Beetle), and aspen (P o p u l u s tremuloides Michx.) alliances. Stages of woodland development across plant associations were categorized into 1 of 4 successional phases (early, mid, late, and closed) based on tree growth and stand structural characteristics. Plant cover by species group, species diversity and richness, bareground cover, soil characteristics, elevation, aspect, and slope were measured in 108, 60 x 46 m macroplots. Twinspan was used to sort plant communities. Regression analysis was used to evaluate the relationship of tree canopy cover to shrub and herbaceous cover. Herbaceous and bareground cover were compared between early and closed stands within plant communities. Woodland structure at stand closure was different among associations varying from 19% cover and 64 trees ha-1 in a low sagebrush community to 90% cover and 1,731 trees ha-1 in an aspen community. Increase in juniper dominance had little impact on low sagebrush and an inconsistent effect on bitterbrush (Purshia tridentata Pursh.). In the mountain big sagebrush alliance, sagebrush cover declined to approximately 80% of maximum potential as juniper increased to about 50% of maximum canopy cover. Aspen (Populus tremuloides Michx.) also declined as juniper dominance increased. Herbaceous cover and species diversity declined and bare ground increased with increasing juniper dominance in the mountain big sagebrush/Thurber needlegrass association. However, herbaceous cover on the deeper soils characterized by Idaho fescue did not decrease with increasing juniper dominance. To determine the effect of juniper dominance or woodland management on community composition and structure, plant community and stage of stand development should be identified.

Growth and carbon allocation of a cool season tussock grass, Agropyron desertorum, following defoliation of newly initiated tillers in the autumn of 1988 and 1989 were investigated. Tiller density and mortality, reproductive shoot density, root density, biomass, individual tiller weight, carbon allocation, and soil water depletion were used to evaluate the response of A. desertorum to autumn grazing. Tiller recruitment was lower in the autumn-defoliated treatment in both years compared with the control because of the cessation of tiller development following autumn defoliation. Autumn defoliation also significantly reduced the movement of C to the roots in 1988 but not in 1989. Soils were cooler and drier in 1989. Other plant growth measurements and soil water depletion rates were not different between treatments. Autumn defoliation in 1988 did not influence tiller recruitment in the following autumn. Two consecutive years of autumn defoliation did not affect tiller overwinter mortality or peak standing crop in 1990.

Attempts to control the noxious weed heart‐podded hoary cress [Cardaria draba (L.) Desv.] in the Pacific Northwest have been relatively ineffective, and this species has expanded its distribution from irrigated hayland onto adjacent semiarid rangelands. The objective of this study was to define the seasonal pattern of development and biological activity of heart‐podded hoary cress growing on semiarid rangeland. The study was conducted in the field over a 2‐yr period on a terrace site that has deep Cumulic Haploxeroll soil and an adjacent upland site that has a shallow Lithic Argixeroll soil. Soil water content, phenology, xylem pressure potential and leaf conductance were measured at both sites. Aboveand belowground biomass and spring C allocation pattern, determined by labeling plants with 13C, were measured at the terrace location. Regardless of location, no heart‐podded hoary cress seedlings were found; all shoots developed from rhizome buds. The majority (76%) of heartpodded hoary cress biomass was located belowground. Although drought occurred earlier on the upland than the terrace site, phenology was similar on the two sites. Carbon was translocated to belowground tissues within 1 h of labeling and reached peak accumulation within 24 h. The greatest 13C enrichment of roots and rhizomes occurred during the flowering stage. The peak in belowground C allocation occurred at a stage when leaf conductance was declining rapidly. The short period of maximum C allocation to belowground tissue, the large proportion of belowground tissue, and the wide variation of phenology among plants at a given time may account for the difficulty in chemically controlling this species.

Summary A simple, robust and inexpensive hand‐held meter is described which senses the presence of green vegetation against brown soil by measuring the ratio of near infra‐red (0·75 μm) to red (0·65 μm) radiances: ratios are higher for green canopies than for soil, due to strong absorption by chlorophyll of red wavelength and the high near‐infrared reflectance of healthy vegetation. Field tests showed that radiance data were correlated closely with plant density and growth stage. Such spectral assessments provide a rapid, nondestructive method of monitoring changes in green‐leaf biomass. Although only small differences in radiance values were recorded from monocultures of various non‐flowering species there was a positive correlation with content of white clover in five grass/clover swards. In addition to being a research aid, these findings confirm the potential of remote sensing of agricultural targets, e.g. detection of weed patches for herbicide spraying, or gaps in swards for sowing seed.

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