Persistence of Idaho fescue on degraded rangelands: adaptation to defoliation or tolerance.

Abstract

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.