Effectiveness of three natural biobarriers in reducing root intrusion by four semi-arid plant species.

Plant root depth, relative density, and an Intrusion Index were determined for three grass and one shrub species growing above three different natural biobarriers. High-clay content soil was the least effective barrier. Scoria (volcanic cinder) was most effective in excluding roots of crested wheatgrass and streambank wheatgrass. Root parameters for sagebrush and Great Basin wildrye were least growing over a biobarrier mixture of gravel and cobble.