Sensitivity to urea fertilization in three amphibian species

Forest fertilization with granular urea is a well-established management pr actice in many forested regions of the world. We hypothesize that chemical forest fertilizers may be affecting forest-dwelling wildlife. In the labora tory, we studied,the effects of fertilization doses of granular urea on thr ee species of forest-dwelling amphibians (Plethodon vehiculum, Rhyacotriton variegatus, and Taricha granulosa). In avoidance experiments, the three sp ecies avoided a substrate treated with a dose of 225 kg N/ha urea. In toxic ity experiments, we exposed amphibians to urea at doses of 225 kg N/ha and 450 kg N/ha for 4 days. The observed effects increased with time and dose, and there were significant differences in sensitivity among the species. Bo th treatment levels had an acute effect on survival of P. vehiculum and R. variegatus. At 24 h, mortality at the highest dose was 67% for P. vehiculum , and 47% for R. variegatus. In contrast, there was no mortality for T. gra nulosa at these concentrations. We suggest that environmental levels of ure a could be affecting behavior and survival of some amphibians species in fe rtilized forests.