Effects of Ventenata dubia removal on rangelands of northeast Wyoming

Abstract

Ventenata dubia (Leers) Coss is one of several annual grass invaders of the western US. Ventenata dubia is documented reducing the forage availability for livestock and wildlife as well as lowering biodiversity in the Great Basin. This species has recently spread to the Great Plains, where it could bring these impacts with it. We attempt to answer questions on whether or not conservation practices, in this case removal of V. dubia with herbicide, results in recovery of forage resources and biodiversity. We answer these questions by measuring biomass, cover, and nutrient content one year post treatment at eleven sites in Sheridan County, Wyoming, conducted in two years. Perennial grasses have higher crude protein and total digestible nutrients than V. dubia and removal of V. dubia resulted in a positive perennial grass response both years. Further, the differences in pattern of growth between perennial and annual species, with annual grasses quickly senescing early in the year, make perennial grasses a more dependable forage base with higher available nutrients. Interestingly, total biomass and nutrient mass did not change after V. dubia removal due to equal replacement with perennial grasses. Species richness and diversity were unaffected by removal of V. dubia. Our results suggest that managing invasive annual grasses, particularly V. dubia, in the northern Great Plains can improve forage resources for livestock and wildlife while maintaining species diversity. Therefore, proactive monitoring and management efforts to prevent spread should be prioritized in this region.

Indaziflam reduces downy brome (Bromus tectorum) density and cover five years after treatment in sagebrush-grasslands with no impact on perennial grass cover

“…Consistent with this explanation, perennial grass cover at 33 MAT at Site 1 showed a positive response at intermediate and high indaziflam rates (Figure 1C), where B. tectorum density and cover were also lowest at this time (Figure 1A and B). These data support previous studies demonstrating that the positive perennial grass cover responses we observed probably resulted from reduced B. tectorum competition (Clark et al 2020;Hart and Mealor 2021;Sebastian et al 2017a).…”

“…We expected indaziflam treatments to have no observable impact on the cover of co-occurring perennial grasses based on previous research (Clark et al 2020;Hart and Mealor 2021;Sebastian et al 2016Sebastian et al , 2017a. Consistent with our expectation, we did not observe any negative effects on perennial grass cover (Figures 1C and 2C).…”

“…At Site 1, the wildfire that occurred in August 2019 likely precluded our ability to detect treatment effects on perennial grass cover at 45 and 57 MAT. Our findings add to a growing number of studies demonstrating that indaziflam can selectively control annual grasses with minimal risk to established perennial plants (Clark et al 2019(Clark et al , 2020Fowers and Mealor 2020;Hart and Mealor 2021;Sebastian et al 2016Sebastian et al , 2017aSeedorf et al 2022), but future research should evaluate the potential for longer-term impacts to native perennials with repeated treatments. Impacts to P. spicata and A. tridentata seedlings have been observed in a grow room study (Clenet et al 2019), and grazing managers have long understood the importance of allowing perennial grasses to complete their reproductive cycles in at least some years (Burkhardt and Sanders 2012), which suggests that the potential for longer-term impacts from repeated indaziflam treatments may be different.…”

“…Positive effects on perennial grass biomass following indaziflam treatment have been observed in some studies (Clark et al 2020;Hart and Mealor 2021;Sebastian et al 2017a), and resource preemption by B. tectorum is relatively well understood and can have substantial negative effects on perennial grass growth and vigor (Melgoza et al 1990;Nasri and Doescher 1995;Ploughe et al 2020). Consistent with this explanation, perennial grass cover at 33 MAT at Site 1 showed a positive response at intermediate and high indaziflam rates (Figure 1C), where B. tectorum density and cover were also lowest at this time (Figure 1A and B).…”

“…Further, because it typically provides 3 or more years of control, and B. tectorum seedbanks are generally short-lived in the field (≤5 yr; Burnside et al 1996;Sebastian et al 2017b;Smith et al 2008), indaziflam could deplete B. tectorum seedbanks with a single application or a sequence of applications spaced several years apart. While non-target impacts to native annual plants have been observed (Courkamp et al 2022), field trials across the western United States have demonstrated indaziflam's effectiveness for controlling invasive annual grasses with no apparent impacts to established perennial plants (Clark et al 2019(Clark et al , 2020Hart and Mealor 2021;Sebastian et al 2016Sebastian et al , 2017a.…”