JACKSON, Wyo. — Preliminary data from The Nature Conservancy’s (TNC) ongoing study of cheatgrass is showing that the herbicide Rejuvra and deep furrow reseeding appear to be the most effective tools for eradicating the invasive species and supporting the regrowth of native plant populations.
According to Trevor Bloom, community ecologist with TNC in Wyoming, cheatgrass is an invasive species that poses a major threat to wildlife habitat like critical mule deer winter range and fire ecology of the American West. Bloom says cheatgrass is readily dispersed and attaches easily to wildlife, dogs, pants and boots, emerging earlier in the season and drying out faster than other plants to effectively extend the local fire season by at least six weeks.
According to Bloom, local fires that have caused evacuations in the past five years have all been cheatgrass-fueled fires. These fires compromise the sagebrush, which isn’t adapted to the short fire regime and have a mean fire return interval (MFRI) of every 100 to 300 years. This means they grow back exceptionally slower than cheatgrass, which has a MFRI of five to 10 years.
The fires and the shallower roots of the cheatgrass are also increasing the likelihood of landslides and mudslides.
“Cheatgrass is super, super concerning, and unfortunately the only way to treat it is the use of herbicides,” Bloom told Buckrail.
That’s where TNC’s study at the National Museum of Wildlife Art (NMWA) comes in, in collaboration with Teton County Weed and Pest (TCWP), Teton Conservation District, the Wyoming Game and Fish Department and the University of Wyoming. The aim of the project is to come up with a specific set of restoration best practices for Teton County and the greater sagebrush steppe involving cheatgrass control and native restoration; this is being achieved by testing the effectiveness of herbicides and reseeding.
Bloom and his colleague Charlotte Cadow, native plant technician of TNC in Wyoming, are studying subplots within three different football field-sized site blocks that are each receiving different combinations of herbicide treatments, including a control that does not receive any spray. Bloom and Cadow are also reseeding the subplots with different mixes of native species both one and two years after the herbicides are applied.
According to Bloom, those seed mixes include a control with no seeding, seed with genetics from Grand Teton National Park (GTNP), a commercially available seed and a local genetic mix that’s half from GTNP and half from a warmer, drier seed zone that’s more in line with what Jackson Hole is predicted to become as a result of climate change. The last mix is an attempt to create a more resilient strain of local plants.
At this point, Bloom says there is not sufficient data to favor any of the seed mixes, but he does say the plots seeded with any seed mix do have higher diversity and richness than the plots that were unseeded.
This study is in its third year as TCWP is in the process of spraying its second round of Rejuvra, also known as indaziflam, to treat cheatgrass in Teton County. While Bloom admits he was initially skeptical of the recently adopted herbicide, he says the preliminary results for the use of Rejuvra are very promising.
“Rejuvra is reducing cheatgrass cover to less than five percent, in some cases completely gone, and maintaining the diversity of native plant species almost as well as the untreated controls,” Bloom tells Buckrail. “In fact, it’s actually increasing the cover of native species by reducing the competition. That’s really, really promising compared to some of the older herbicides that were used.”
While results so far have shown that the native plants are coming back after herbicide treatment and the cheatgrass is not, there is preliminary evidence to suggest that the use of Rejuvra does lower diversity of early season forbs, a primary food source for greater sage grouse. However, Bloom says it’s difficult to quantify at what stage that’s detrimental to wildlife.
According to Cadow, in the reseeded plots the highest emergence success comes from seeds applied directly into deep furrows dug below the top one to two inches of soil. Broadcast seeding has shown a relatively low success rate of plants coming up compared to the amount of seeds dispersed, primarily due to wind, birds and seed to soil contact. This is particularly striking when Cadow talks about sagebrush; out of hundreds of thousands of sagebrush seeds over the past few years, only about 30 have successfully started to grow.
Sagebrush planted from plugs, which are seeds that start growing in a greenhouse and are then transferred to the site, show about 75 percent survival success after three years; however, the cost of this method is notably higher than broadcast seeding and, even with plugs that are successful, Bloom confirms it will take 50 to 75 years to get an intact sagebrush community back.
“Cheatgrass has the potential to change the composition of the Greater Yellowstone Ecosystem and it’s literally happening right in front of our eyes.”
Trevor Bloom, community ecologist with TNC in Wyoming
“This highlights the importance of conserving sagebrush habitats we have now and tackling cheatgrass immediately,” Bloom says. “Cheatgrass has the potential to change the composition of the Greater Yellowstone Ecosystem and it’s literally happening right in front of our eyes.”
The final phase of the project will unfold in the next 18 months, after which Bloom expects to start publishing results in the fall of 2024. However, Bloom notes he’d love to be able to understand what’s happening with the cheatgrass in a more long-term study, seeing if it grows back in 10 to 15 years and tracking more year to year variation.
