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Tall Oatgrass Management

Cows grazing in the Shanahan area

What is tall oatgrass and why is it bad?

Tall Oatgrass (Arrhenatherum elatius) is a non-native, invasive bunch grass that has become an increasing threat to native prairies in the western United States. Historically grown as livestock forage and used for soil retention, tall oatgrass now plagues healthy native communities, including sensitive Open Space and Mountain Parks (OSMP) natural areas. 

  • Read a memo pdf OSMP prepared for the Open Space Board of Trustees, which includes a map of proposed fencing in the area to help manage livestock in the area.
  • Review a series of posters pdf that OSMP created for a recent community meeting. 

Why does tall oatgrass pose such a risk to OSMP natural areas? 

  • Tall oatgrass quickly forms dense spreading stands that prevent native vegetation from receiving essential light, moisture and nutrients.  
  • Its spread threatens rare and uncommon native grassland plant communities, including globally imperiled tallgrass prairie. Its spread  impacts a wide range of wildlife species --  such as grassland birds, mule deer and wild turkey -- that depend on our more diverse native plant communities.
  • Significant early summer growth of tall oatgrass creates additional fuel for wildfires, increasing fire risks for Boulder neighborhoods.
  • While tall oatgrass is found on about 350 acres of land primarily southwest of Boulder, OSMP data indicates this aggressive grass can spread at 30 to 70 acres each year and could expand to 18,500 acres if management actions are not taken.

Tall oatgrass management on open space lands is expected to be an OSMP priority for years to come. Near Boulder’s foothills, OSMP research has proven livestock grazing during the spring to be a key management tool in helping to suppress tall oatgrass while creating conditions for healthy native plant communities. To expand the use of this effective management tool while maintaining designated trail access, OSMP proposes additional fencing in the area, including replacing a fence line on OSMP’s eastern perimeter from NCAR Bear Canyon Road to the Lehigh Connector South Trail just south of several Shanahan Ridge neighborhoods. 

What is happening on Shanahan Ridge?

Shanahan Ridge falls within the area of highest tall oatgrass concentrations on OSMP lands. To limit the spread of tall oatgrass and preserve biodiversity, OSMP has::

  • Conducted monitored prescriptive spring grazing near the National Center for Atmospheric Research since 2015 to mitigate tall oatgrass and to research its usefulness on a broader scale. View a map pdf of where cattle have grazed in the past.
  • Placed additional fencing in the Shanahan Ridge area in 2019 to expand  prescriptive grazing in the area.
  • Hosted meetings and community events, including guided hikes in the area, to highlight the risks associated with tall oatgrass  to open space and Boulder neighborhoods.
  • Collaborated with CU and contractors to study tall oatgrass ecology and evaluate various management treatments.

Moving ahead, the department is planning to:

  • Expand fencing infrastructure in the area to further reduce tall oatgrass  cover while encouraging biodiversity and maintaining recreational values in the area.
  • Install educational boot cleaning stations at designated public access points to emphasize tall oatgrass containment goals.
  • Continue to invite neighbors to view cattle activities and to learn about what OSMP is doing to fight tall oatgrass spread.

Why does OSMP use cattle to mitigate tall oatgrass?

OSMP staff has been studying various non-chemical treatment methods since 2009. Weed whipping and early spring prescriptive grazing show positive results although years of treatment is needed. For the last five years, OSMP has partnered with local ranchers to use cattle to mitigate tall oatgrass expansion just south of the National Center for Atmospheric Research (NCAR). During this time, OSMP also conducted research to understand if livestock grazing can address the rapid expansion of tall oatgrass in the area. It found that: 

  • Livestock grazing during the spring reduces the amount of tall oatgrass in the area over time.
  • Livestock grazing is consistent with long-term city efforts to limit herbicides and is far more cost-effective than mowing and other mechanical options. Current estimates indicate that grazing is nearly one-third the cost of mowing.

Given the recent research, the steep terrain where tall oatgrass can be found, the high costs of mowing and Boulder's efforts to limit herbicides, OSMP believes livestock grazing is the most useful and cost-effective management technique to address and combat tall oatgass

How did tall oatgrass appear in Boulder and where is it concentrated?

Tall oatgrass is a short-lived perennial bunchgrass from northern Europe that is believed to have been introduced to the Shanahan/NCAR area in the 1950’s during ranching operations. Tall oatgrass typically becomes invasive after several decades without any grazing, forming dense stands that shade and out-compete native species for light, moisture and nutrients. Mapping efforts in 2007 and 2013 confirm the NCAR/Shanahan area is where the highest densities occur on OSMP. 

What makes tall oatgrass so invasive?

Once primarily contained to the Shanahan/Boulder Mountain Parks area, tall oatgrass has expanded to OSMP properties as far away as Lefthand Canyon, Marshall Mesa and Jay Road. Dense pockets continue to increase west of the Flatirons along Flagstaff and Bison Drive. Jefferson County Open Space identified its first occurrence this summer north of Highway 72.

  • It's spread by many vectors. Humans, vehicles, animals, wind and water all aid dispersal. This allows for rapid expansion to new areas.
  • It's 100% fall germinating. It eliminates open soil vital for less aggressive native species to germinate in spring and fall.
  • It's the first species to emerge in early spring. Reduces moisture and nutrients which native plants emerging weeks later depend on.
  • It has rapid spring growth, with 5+ feet by late June. Reduces available light, impacting native wildflower layers and associated butterflies and nectar dependent insects.
  • It has tremendous seed production by late June. Prepares itself for early fall germination, competition, and further expansion.
  • It generates excessive annual thatch and litter. Alters fire regime and intensity; decomposing thatch favors tall oatgrass over slower-growing native species.
  • Boulder’s dependable fall moisture. A perfect storm for germination, often allows established tall oatgrass plants to remain green throughout the winter.

What do we stand to lose?

  • Tallgrass prairie: Considered globally imperiled and is one of the most endangered vegetation types worldwide. Southern Boulder County and norther Jefferson County may have the largest xeric tallgrass communities remaining in Colorado and provides habitat for several Colorado Natural Heritage Program-tracked A species.
  • Ponderosa pine woodland savannas: A unique intersection of ecosystems and the open tree canopy which creates an exceptionally diverse forest understory.
  • Native grassland-dependent skippers: These skippers, all of which are tracked by Colorado Natural Heritage Program, are rare and declining. These include species dependent on big or little bluestem to complete their life cycle like Arogos Skipper, Dusted Skipper, and Ottoe Skipper.
  • Wild Turkeys: They prefer shorter stature vegetation to avoid predation.
  • Mule deer: Recent surveys indicate are avoiding areas with abundant tall oatgrass in the NCAR area.
  • Forest shrub nesting birds: They are affected by extensive tall oatgrass monocultures, which in turn impacts forest hawks that depend on this food source.
  • All of OSMP’s plant communities:  They are susceptible to tall oatgrass invasion. Occupied lands reduce biodiversity, putting most OSMP Charter goals at risk.

Moving forward: OSMP Tall oatgrass management 

Three management zones have been identified across OSMP which help guide treatment and monitoring efforts. Management zones are distinguished by tall oatgrass density and expanse on the landscape. Management zones will require different treatment strategies based on definitions and feasibility of implementation. Zone boundaries are not static and will be adjusted as various management phases are complete. 

  • The Early Detection Zone: It includes areas currently unoccupied by tall oatgrass but at risk of invasion due to their proximity to existing tall oatgrass populations and the presence of suitable habitat. Currently, most OSMP lands east of Highway 93/ Highway 7 fall within the Early Detection Zone.
    • Management Objective: Implement early detection & rapid response protocols to identify and eradicate new tall oatgrass populations. Systematic trail corridor and watershed level surveys should occur yearly to prevent establishment of tall oatgrass within the Early Detection Zone. 
  • The Containment Zone: It is the “epicenter”, the area of highest tall oatgrass concentrations, where eradication may not be feasible. This Zone includes lands from Enchanted Mesa south to the Upper Bluestem Trail and west to the Mesa Trail.
    • Management objective: Reduce existing tall oatgrass populations and prevent further spread to adjacent management zones through integrated control methods. Control strategies in the Containment Zone are predominantly non-chemical such as prescriptive spring grazing and mechanical methods with monitoring in place to measure success. Further scientific research on tall oatgrass phenology, ecology and management techniques also occur within the Containment Zone.
  • The Eradication Zone: It includes infested areas outside the containment area, where smaller tall oatgrass populations occur and have great potential to spread. These sites include intact native foothills and grassland communities that support unique plant and wildlife communities and valuable riparian areas.
    • Management objective: Eradicate tall oatgrass populations using integrated techniques and monitor treatment effectiveness. Control strategies include herbicide applications, seeding, prescriptive spring grazing and limited mechanical controls.