Evaluating restoration techniques using native perennial grasses in cheatgrass (Bromus tectorum L.) invaded sagebrush-steppe ecosystems

Background/Question/Methods

In the Great Basin, cheatgrass (Bromus tectorum L.) invasion into sagebrush (Artemisia tridentata Nutt.) shrublands has dramatically altered species composition, ecosystem processes and fire regimes.  Cheatgrass produces abundant highly flammable fine fuels, creating a cheatgrass-wildfire cycle with cheatgrass promoting fire and fire promoting cheatgrass.  The key to breaking this fire cycle and preventing a type-conversion may be establishing a native understory dominated by perennial grasses.  In a field experiment conducted at Golden Spike National Historic Site, Utah, we tested the effectiveness of several non surface-disturbing restoration techniques in establishing seeded native perennial grasses.  These techniques were tested in cheatgrass near-monocultures and cheatgrass-invaded sagebrush ecosystems.  We applied treatments intended to increases the competitive advantage of seeded native perennial grasses in cheatgrass-invaded sites and seeded a mixture of five native perennial grasses.  Treatments were arranged in a 3-way factorial design and included: 1) vegetation manipulations (burning overstory species/thatch and sagebrush thinning or removal), 2) herbicide (Imazapic) application, and 3) soil amendments (sucrose and activated carbon additions).  In this study we examined the effects of 1) treatments and treatment interactions two years post treatment and 2) seeding frequency on seeded perennial grass emergence.

Results/Conclusions

In the cheatgrass near-monoculture, the burning vegetation treatment significantly enhanced perennial grass seedling densities compared to control plots.  In the cheatgrass-invaded sagebrush sites no treatments or treatment interactions enhanced perennial seedling densities.  Seeding multiple consecutive years in the cheatgrass-invaded sagebrush sites resulted in significantly higher perennial seedling densities than seeding a single year.  These results suggest that in cheatgrass near-monocultures, burning is a potentially useful restoration tool for increasing native perennial grass seeding success.  Additionally, they demonstrate that seeding success may be enhanced by multiple consecutive years of seeding.  As no treatments in the cheatgrass-invaded sagebrush experiment showed potential for use as restoration tools, future work should consider the effect of overstory dynamics and edaphic or climatic variables on seeding success in these systems.  Additionally, as many of these treatments may have a short window of opportunity for increasing success of seeding efforts, future work should address the effects of repeated treatment applications on enhancing seeded perennial grass success.