Print PageCheatgrass (Bromus tectorum) and other non-native winter-annual plants are becoming abundant in the grasslands along the Front Range of Colorado. These species can be aggressive invaders in native grasslands, growing earlier in the spring than native plants and preempting soil resources. Currently, removal of other invasive species has benefited these winter-annuals, so effective management strategies are needed to reduce their abundance while encouraging the re-establishment of desirable native plants. We investigated whether seasonal grazing applications and seeding with native perennial grasses could limit growth of non-native winter-annuals, and benefit growth of native plants in an invaded grassland in Colorado. We established a split-plot experiment in June 2009 with three simulated grazing treatments: control, early spring grazing, and year-round grazing (early spring, mid-summer, and fall), and three within-plot seeding treatments: control, added cheatgrass seeds, and added native grass seeds. Percent cover of plant species and aboveground biomass were sampled the year following treatment manipulation. We hypothesized that native grasses would increase in plots that received early spring grazing and added native grass seed, because grazing would impact winter annuals while they were active without harming the later-growing native perennials and allow for establishment of a more desirable native grassland.
Results/Conclusions
Simulated grazing led to significantly different plant community composition in control, spring grazed, and year-round grazed plots the year after treatment initiation. In March and June of 2010, cheatgrass and other winter-annual grasses were half as abundant in both grazing treatments as in control plots, however, cover of winter-annual forbs increased two-fold in spring grazed plots and almost three-fold in year-round grazed plots relative to controls. In June and July 2010, native grasses were most abundant in spring grazed plots, and least abundant in control plots. Aboveground biomass was greatest in control plots and least in year-round grazed plots, indicating that vegetation in this grassland may not increase production in response to grazing. Adding seeds of either perennial grasses or cheatgrass did not affect percent cover or aboveground biomass in experimental plots. This lack of response indicates that seeding with natives may be ineffectual for enhancing restoration success, even in combination with grazing. Our results illustrate the strong effects that timing of grazing can have on community dynamics in grasslands. In addition, this experiment presents new possibilities for adaptive range management that targets the “temporal niche” of undesirable invasive species.
