abstract: The introduction of livestock to the vast majority of public lands may be used to simulate the conditions provided by herbivorous grazers in the past, however little data has been collected on the effects of livestock grazing in Sonoran desert habitats. Vegetative species that are characteristic of the Arizona Upland subdivision of the Sonoran desert did not evolve with extensive grazing by large ungulate populations, and therefore the response to livestock grazing is of particular interest. Four historic Parker 3-step clusters in south-central Arizona were sampled in three cohorts between 1953 and 2016 to interpret changes in rangeland health using soil coverage data, species richness and frequency, and long-term photo point comparisons. Cattle grazing was active across the allotment until 1984, allowing approximately 30 years of rest before the third and final cohort was measured. Over the entirety of this study, there was a 66.67% increase in perennial basal hits, a 56.29% increase in rock, and a 44.55% increase of forage basal hits. Decreases were seen in litter (-57.69%) and bare soil hits (-8.76%). Cluster 3 consistently had a lower percent of cover across all classes of vegetation in the 2014 cohort (-81.61%), however the average percent of cover increased by 63.16% (40 hits) across the allotment. Available species richness data from 1971 and 2014 cohorts indicates a 112% increase in unique species; however, species richness increases in the 2014 cohort are largely based on recruitment of non-palatable species (71%). Although the status of some species were undetermined, all individuals identified to species in the invader class (non-palatable) were determined to be native to the study site. Perennial grass frequency became less abundant over the duration of this study, while growth was predominantly observed in shrubs. Increases in species frequency was detected on two of the four clusters measured in the 2014 cohort; the growth was primarily observed in jojoba (Simmondsia chinensis), oak (Quercus spp.), and catclaw acacia (Senegalia greggii) in C4, and hopseed bush (Dodonaea viscosa) in C2. / Dissertation/Thesis / Masters Thesis Applied Biological Sciences 2018