Published April 2000. Reviewed January 2016. Please check for up-to-date information in the OSU Extension Service Catalog: http://extension.oregonstate.edu/catalog

Idaho fescue (Festuca idahoensis Elmer), a palatable native perennial bunchgrass, has persisted on degraded sagebrush-steppe despite invasion by alien plants, excessive livestock grazing, and increased density of woody vegetation due to fire suppression. Survival of these populations in the presence of competitive alien plants suggested 2 possibilities: 1) that Idaho fescue produces seedlings that successfully compete for soil resources with alien invaders, and 2) that Idaho fescue seedlings tolerate stress caused by resource uptake by alien neighbors. We compared germination and growth of Idaho fescue from an undisturbed population with that of conspecific populations from disturbed (grazed and invaded) sites to determine whether disturbed-site seedlings had greater potential for resource capture. Recruitment in Idaho fescue from degraded sites did not appear to be aided by rapid seed germination or greater tolerance of moisture stress during germination. A greater proportion of seeds from the undisturbed site germinated; they germinated faster, and were no more sensitive to water stress, than were seeds from disturbed sites. For both groups, decreasing water potential from 0 to -0.5 MPa had little effect on germination percentages but declined at -1 Mpa. Germination rates slowed with decreasing water potential. Though Idaho fescue from undisturbed and disturbed sites extended roots down the soil profile with equal speed, seedlings from the undisturbed site produced 3.5 times more root length, had 2.7 times greater root length density, and 3.4 times more leaf area than disturbed-site Idaho fescue. The higher growth rate and greater root length density in Idaho fescue from the undisturbed site translates to greater exploration and exploitation of the environment. The 2 Idaho fescue groups had equivalent specific root length, specific leaf area, and root weight ratio. Idaho fescue from disturbed sites showed strong, positive geotropic growth whereas branching and diageotropic growth were greater in Idaho fescue from the undisturbed site. Cheatgrass (Bromus tectorum L.) extended roots faster than did Idaho fescue, with 17 times the root length, 6 times the root length density, and 10.8 times the leaf area of undisturbed-site Idaho fescue. Cheatgrass and Idaho fescue had equivalent specific leaf area, but specific root length of Idaho fescue was nearly twice that of the alien. Roots accounted for about 31% and 55% of cheatgrass biomass. Competitive ability did not appear to promote recruitment in Idaho fescue populations on degraded rangelands. Idaho fescue seedlings from the undisturbed-site were better competitors than disturbed-site seedlings, but interference from neighboring cheatgrass most strongly inhibited shoot growth of both Idaho fescue and cheatgrass. Idaho fescue had little effect on cheatgrass shoot growth. Selection of stress-tolerant genotypes from original populations may best explain the continued existence of Idaho fescue on grazed and invaded sites. We suggest that tolerance of moisture stress combined with vegetative longevity, are mechanisms behind Idaho fescue's persistence.

The acquisition of water and regulation of its loss are important to plant 'success' in arid environments, Species existing over a range of environmental conditions should respond physiologically to varying conditions to maximize water use efficiency and avoid low tissue water potentials, Seasonal and diurnal ecophysiological responses of singleleaf pinyon (Pinus monophylla Torr, and Frem,) were investigated along an environmental gradient involving elevation, moisture and temperature in Nevada, The gradient was represented by study sites in black sagebrush (Artemisia nova A, Nels), mountain big sagebrush (Artemisia tridentata ssp, vaseyana Nutt,), and mountain mahogany (Cercocarpus ledifolius Nutt,) communities, Xylem pressure potential, conductance, and transpiration were measured over 2 growing seasons, Xylem pressure potential and leaf conductance ranged from -3.0 to -0.7 MPa and 0.01 to 0.43 cm s(-1), respectively, during the study, Carbon isotope discrimination (Delta) of needles was determined in August 1990, Differences in Delta values were not significant between sites at the lowest and highest elevations but were significant between the driest site (black sage) and the relatively wetter site (mountain mahogany), Leaf conductance was influenced by but not strongly correlated with predawn xylem pressure potentials, relative humidity, and temperature, Generally, there was little difference in water use characteristics of singleleaf pinyon along the environmental gradient in this study, Thus, it appears that singleleaf pinyon's ability to exist over a range of environmental conditions is not a function of variable ecophysiological responses but an opportunistic response to the availability of resources and conditions suitable for growth to occur.

Rangelands with histories of overgrazing are frequently depauperate of native grasses. Occasionally, remnant native grasses are found surviving in these areas. We hypothesized that these survivors have responded to livestock grazing, over the past 110 years, through development of genetically based ecotypes that are more tolerant of defoliation than populations protected from heavy use by domestic livestock. Transplanted individuals of a native grass, Idaho fescue (Festuca idahoensis Elmer), from heavily grazed and ungrazed rangelands were compared. Gardens were established in central Oregon at the Central Oregon Agricultural Experiment Station and in eastern Oregon at the Northern Great Basin Experimental Range. Plants were defoliated during the vegetative, boot, and anthesis stages in 1990 and 1991 and subsequent growth evaluated. Parameters measured were end of growing season basal area, relative biomass production, and height and phenology at about biweekly intervals. Grazing history had no consistent effect on Idaho fescue response to defoliation. There were, however, differences between the protected and grazed collections from central Oregon in that the protected population averaged greater height and relative growth than those from the grazed areas even with defoliation. While the limited number of ungrazed sources in this region limits broad speculation, these results suggest Idaho fescue survival in heavily grazed areas might be the result of differences in growth form rather than overcompensation or variation in time of phenologic development. Results also suggest that Idaho fescue from this region may elicit some grazing tolerance despite evolving historically with few large herbivores.

We investigated the influence of plant water relations on the limited expansion and dominance of Pinus monophylla (an arid land coniferous tree) into adjacent Cercocarpus ledifolius (an evergreen nonconiferous shrub or small tree) communities. Water relations and growth of both species were monitored during 2 growing seasons on a P. monophylla dominated, alluvial fan (2070 m) and a C. ledifolius dominated, exposed ridge (2745 m). In 1990, the influence of supplemental water at the lower site was investigated. Carbon isotope composition was determined from material collected in August 1990. Predawn and midday xylem pressure potentials and transpiration rates suggested that P. monophylla was more water-use efficient than C. ledifolius. Cercocarpus ledifolius had higher transpiration rates throughout the growing season and reached lower xylem pressure potentials late in the season. This suggests C. ledifolius is better able to take advantage of available water for recharging plant moisture and rapid water use. Supplemental water's only effect was a significant increase in C. ledifolius transpiration. Carbon isotope ratios (∂13C) were more negative for C. ledifolius than P. monophylla and with increasing soil water availability. Lower rates of growth and water-use patterns by P. monophylla are not an advantage in the C. ledifolius zone and contribute to its limited expansion into this zone. For. Sci. 39(4): 629-643.