Persistence of Idaho fescue on degraded sagebrush-steppe

Idaho fescue (Festuca idahoensis Elmer), a palatable native perennial bunch grass, has persisted on degraded sagebrush-steppe despite invasion by alien plants, excessive livestock grazing, and increased density of woody vegeta tion due to fire suppression. Survival of these populations in the presence of competitive alien plants suggested 2 possibilities: 1) that Idaho fescu e produces seedlings that successfully compete for soil resources with alie n invaders, and 2) that Idaho fescue seedlings tolerate stress caused by re source uptake by alien neighbors. We compared germination and growth of Ida ho fescue from an undisturbed population with that of conspecific populatio ns 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 g ermination or greater tolerance of moisture stress during germination. A gr eater proportion of seeds from the undisturbed site germinated; they germin ated faster, and were no more sensitive to water stress, than were seeds fr om 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 fe scue from undisturbed and disturbed sites extended roots down the soil prof ile with equal speed, seedlings from the undisturbed site produced 3.5 time s more root length, had 2.7 times greater root length density, and 3.4 time s more leaf area than disturbed-site Idaho fescue. The higher growth rate a nd greater root length density in Idaho fescue from the undisturbed site tr anslates 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, p ositive geotropic growth whereas branching and diageotropic growth were gre ater in Idaho fescue from the undisturbed site. Cheatgrass (Bromus tectorum L.) extended roots faster than did Idaho fescue, with 17 times the root le ngth, 6 times the root length density, and 10.8 times the leaf area of undi sturbed-site Idaho fescue. Cheatgrass and Idaho fescue had equivalent speci fic leaf area, but specific root length of Idaho fescue was nearly twice th at of the alien. Roots accounted for about 31% and 55% of cheatgrass biomas s. Competitive ability did not appear to promote recruitment in Idaho fescu e populations on degraded rangelands. Idaho fescue seedlings from the undis turbed-site were better competitors than disturbed-site seedlings, but inte rference from neighboring cheatgrass most strongly inhibited shoot growth o f both Idaho fescue and cheatgrass. Idaho fescue had little effect on cheat grass shoot growth. Selection of stress-tolerant genotypes from original po pulations may best explain the continued existence of Idaho fescue on graze d and invaded sites. We suggest that tolerance of moisture stress combined with vegetative longevity, are mechanisms behind Idaho fescue's persistence .