Fall-Grazing and Grazing-Exclusion Effects on Cheatgrass (Bromus tectorum) Seed Bank Assays in Nevada, United States

Abstract

Cheatgrass (Bromus tectorum L.) seedlings suffer mortality if they do not occupy safe sites that provide establishment requirements. Previous research demonstrated that fall cattle grazing has strong potential for reducing invasive annual grass species dominance in winter-dominated precipitation areas of the Intermountain West. Fall cattle grazing reduces the volume of safe sites through the removal of standing dead biomass in the fall and early winter, when cheatgrass can actively germinate. This study continued an assessment of cheatgrass seed bank characteristics under fall-grazing and grazing exclusion treatments initiated by a previous study. A seed bank assay was organized into a randomized complete block, repeated measure design to assess cheatgrass seed bank characteristics from 2014 to 2017 in central Nevada. Across years, fall-grazed areas had about half the assayed seed bank levels (3 432 ± 2 513 seeds ∙ m−2) of ungrazed areas (7 187 ± 1 569), (P <0.0001). There was also a difference among years with 2015 producing higher assayed numbers in both grazing treatments. Combined plotted data from this and the previous study indicated that after several years of fall-grazing treatments, removal of fall cattle grazing for only 1 yr can result in significant increases in cheatgrass seed bank size. Conversely, reapplication of fall cattle grazing can quickly decrease cheatgrass seed bank potential.