Location: Near Fort Collins, CO. 

Cheatgrass (Bromus tectorum L.) is an introduced annual grass that represents a major challenge to land managers in western North America. It is an aggressive invader of disturbed soils and is capable of transforming ecosystem processes in a way that results in near Seeding and tilling plotsmonotypic stands of cheatgrass over vast areas. Cheatgrass is especially threatening on mined land because surface disturbances create ideal footholds for cheatgrass invasion. Once established at a site, cheatgrass can foil reclamation efforts and make it difficult for operators to obtain bond release. Effective methods of cheatgrass control often involve the use of herbicides, which can be nonselective and damage desired reclamation species. The plant species that are typically planted in mined land reclamations tend to be mid- and late-seral grass species with lesser amounts of late-seral shrub or forb species. These taxa often do not compete well with cheatgrass, which is a ruderal. This often leads to further dominance of cheatgrass on these early-seral disturbed soils. The list of tools available to combat cheatgrass in mined land reclamation is thus very limited.

Our current field study is exploring an innovative approach to the control and management of cheatgrass on disturbed sites. Our approach is based on successional theory and focuses on improving ecosystem health in order to resist the invasion and dominance of cheatgrass on surface mined lands in the western US. Our specific objective is to determine if restoration of native ruderal seed banks can be used to suppress the establishment and persistence of cheatgrass and facilitate establishment of native perennials on disturbed soils. We predict that restoring the seed bank of native ruderal species on a disturbed soil will result in the competitive reduction and or exclusion of cheatgrass. Since native ruderal species share many of the same ecological characteristics as cheatgrass, an exotic ruderal species, we predict they will provide more direct competition with cheatgrass. Furthermore, ecosystem succession involves processes of facilitation whereby early-seral plants prepare the site for later-seral species. By following the natural assembly rules of the ecosystem, we predict that native reclamation species can be established where the native ruderal seed bank has been restored in adequate densities to resist reinvasion by cheatgrass.

In the fall of 2010, we initiated a field study where we established experimental plots where the seed bank of native ruderal species was Field test plots, Fall 2011 at the end of the first growing season.restored. We compared the success of seeded cheatgrass in these plots to control plots seeded only with cheatgrass or plots where a standard annual cover crop was seeded to compete with cheatgrass. We also seeded some plots with a standard reclamation mix after one growing season to see if establishing native ruderals will facilitate the establishment of the perennial reclamation species.

If this approach is successful, it will represent a new paradigm of invasive species control where emphasis is placed on restoring natural successional processes as opposed to the currently accepted single-species management approach that focuses on eliminating the weed problem. This could result in substantial cost savings to the surface-mining industry by reducing reclamation failures and improving bond release success.

Abstract of the thesis of Cassandra Kieffer Stube, presented September 19th, 2012. INTERACTIONS BETWEEN BROMUS TECTORUM L. (CHEATGRASS) AND NATIVE RUDERAL SPECIES IN ECOLOGICAL RESTORATION

Abstract:   Bromus tectorum L. is an invasive annual grass that has characteristics which make it highly successful at invading new sites, and extremely challenging to remove during revegetation efforts.   Bromus tectorum causes shifts in the mycorrhizal community that could lead to a loss of AMF species richness and abundance in a very short time period, resulting in conditions that are difficult for late-seral species to colonize.   Traditional restoration seed mixes often consist of native perennial grass species, which tend to be slower growing and less robust in disturbed sites.  Utilizing native seed mixes composed of ruderal species selected for specific functional and competitive traits, and creating seeding rates designed to increase interspecific competition with B. tectorum may provide the missing link for successful restoration of B. tectorum-invaded sites.

A study was conducted in northern Colorado to determine whether native ruderal species could suppress B. tectorum establishment and persistence in a disturbed site, and to assess the immediate effects of the establishing plant community on AMF colonization.  After one growing season, the native ruderal mix significantly reduced B. tectorum biomass.  After the second growing season, the effect was no longer detectable in biomass measurements, but was still observed as a reduction in density of B. tectorum in the native ruderal plots.  Native soils had much higher AMF colonization of the host plant species relative to soils from beneath B. tectorum.  In addition, the native host Ratibida columnifera had much higher rates of colonization than the non-native host, Sorghum bicolor, indicating that there may be some host-dependent plant-AMF relationships that are more beneficial to the native plant than the non-native plant.

The results of these studies could have important practical field applications when restoring invaded sites, particularly when the goal is to create conditions that promote development of late-seral plant communities.  Utilization of native ruderal species in revegetation mixes could provide a critical missing link for facilitation of late-seral, native plant communities through suppression of B. tectorum, as well as rapid facilitation of AMF communities that successfully colonize native late-seral host species.  Continued monitoring and assessment of this study site could lend further insight to the long-term dynamics of the native ruderal plant community with B. tectorum and development of a late-seral plant community.