EFFECTS OF LONG-TERM LIVESTOCK GRAZING AND HABITAT ON UNDERSTORY VEGETATION

the herbaceous understory stratum contuns most of the plant diversity in ponderosa pine (Pinus pon derosa P & C Lawson scopulorum Engelm) forests of the American Southwest and provides critical food and habitat for many wildlife species During thc last century this stratum has been affected by livestock grazing and by increased domnance of overstory tiees We simpled unique grazing exclosure to examine the relative importance of long term livestock grazing (grazed or ungrazed) and habit it (park or tree) on the understory community We sampled 3 plots of 192 contiguous quadrats (each qundrat at 0 5 m(2)) in each of thc 4 treatment combinations for a total of 2304 quachats Species are curses wcrc generated by aggregating quadrats into nonoverlapping are at granun sizes of 05 to 576 m(2) I he effects of habit and grazing on species density were evident at very different scales Species density was higher in park than tree plots at scales <= 32 m(2) but did not differ between habitats at Lager scales Species density differed minimally between grazed and ungrazed treatments at small grams but grazed plots continued mole species than ungrazed plots it luger grans Grazing treatments differed it smaller grans (to 4-8 m(2)) than did habitats (to 32 m(2)) with respect to density of native species and graininoids Crazed plots had moie exotic species than ungrazed plots at all gram sizes though few exotics were present twenty two species were identified is Indicator species associate with habitats and/or grazing treatments Evaluations of plant community response to treatments would be improved by accounting for the gran at which data have bccn collected and analayzed and by identifying indicator species associated with various treatments these data would unable more informed conservation and management decisions