Effects of Grazing Exclusion and Reseeding on a Former Uranium Mill Site in the Great Basin Desert, Arizona

Abstract

Germinable seed in the soil seed bank and vegetation were characterized at a former uranium mill site in the Great Basin desert , Arizona , 10 years after a remediation program was conducted to remove surface contamination and revegetate the site . The objective of the study was to evaluate the effectiveness of reseeding as routinely practiced to revegetate such sites . Three different conditions at the site were evaluated: (1) an area that had been bladed to remove topsoil then reseeded with exotic and native species and fenced to exclude livestock (ungrazed - bladed - reseeded) (2)a control area inside the fence that had not been bladed or reseeded (ungrazed), and (3) for further comparison , an area outside the fence that was undisturbed by the milling and remediation efforts but has received normal grazing pressure (grazed). Each condition was represented by three plots , from which soil samples and transect data were collected . The diversity of species and total number of viable seeds in the seed bank (top 5 cm of soil) were lowest in the ungrazed - bladed - reseeded plots (P < 0.05). These plots also had lower plant cover (15%) than the ungrazed plots (24%) (P < 0.05), comparable to the cover on grazed plots (11%), even after 10 years of grazing exclusion . We conclude that at this site the results of topsoil removal and replacement were not effectively remediated by reseeding . Although these methods may be effective in moister climates , more intensive efforts to reintroduce vegetation may be required in desert sites such as this .