Common mullein (Verbascum thapsus) is a non-native plant threatening the integrity of natural ecosystems throughout California. Mechanical, chemical, and biological methods have been utilized for control of common mullein. The objective of this study was to determine which of the following treatment cycles is most effective to reduce populations of common mullein at Lava Beds National Monument: annual (once per year), biennial (once every two years), or no treatment. Vegetation type, natural features, site characteristics, and human disturbance were factors considered when analyzing common mullein distribution and abundance. Forty-five pre-existing plots with populations of common mullein were visited during summer 2005. The interrelationship of common mullein with the surrounding high-desert plant communities was assessed by three vegetation sampling methods. Density, cover, and common mullein stages were measured by point-intercept transects, belt transects, and circular macroplots. Simple linear regressions were performed using common mullein density as the dependent variable with multiple independent variables such as shrub, rock, soil, and grass cover. Analysis of variance test showed no significant relationship between density of common mullein and the three treatment cycles (p > 0.05). However, trends observed imply that annual treatment reduces the population of large rosettes and reproductive stalks over no-treatment and biennial treatment. A bivariate correlation test found the circular macroplot to be similar to belt transects for measuring common mullein density (r = 0.84). / Department of Natural Resources and Environmental Management