Invasive Species
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We imposed spring-applied annual grass control treatments followed by fall seeding of a perennial bunchgrasses and then measured vegetation response for the next 3 yr in cheatgrass and medusahead-invaded communities. Spring treatments that included imazapic application (at a low rate), followed by fall seeding of perennial bunchgrasses, successfully controlled annual grasses and substantially increased perennial bunchgrass cover and density. Spring burning and glyphosate herbicide application, without imazapic, were not successful in promoting substantial increases in perennial bunchgrass cover. Spring burning before imazapic application was the most successful treatment for rehabilitation seeding. By the third yr after seeding, perennial bunchgrass cover was 17% in the spring burn-imazapic treatment, greater than what is generally found in intact Wyoming big sagebrush-bunchgrass communities in this region. The results of this study provide strong evidence that spring-applied control treatments including imazapic can be part of successful revegetation efforts, thereby decreasing some of the logistical challenges associated with revegetation of annual grass−invaded sagebrush rangelands.
Webinar recording.
Sam “Jake” Price and Matt Germino, USGS Forest & Rangeland Ecosystem Science Center, present findings from their recent publication on the Soda Fire fuel breaks and how they might help to break the annual grass-fire cycle. Q&A to follow the presentation.
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This study specifically analyzed how the abundance of non-native plants after fire was related to fire characteristics and environmental conditions, such as climate, soil, and topography, in 26,729 vegetation plots from government networks and individual studies. Non-native plant cover was higher in plots measured after wildfires compared to prescribed burns or unburned plots. The post-fire cover of non-native species varied by plant functional type, and only the cover of short-lived (i.e., annual and biennial) forbs and short-lived C3 grasses was significantly higher in burned plots compared to unburned plots. Cool-season short-lived grasses composed most of the non-native post-fire vegetation, with cheatgrass (Bromus tectorum) being the most recorded species in the dataset. Climate variables were the most influential predictors of the cover of non-native short-lived grasses and forbs after fires, with invasion being more common in areas with drier summers and a higher proportion of yearly precipitation falling in October through March. Models using future projected climate for mid (2041–2070) and end (2071–2100) of century showed a potential for increasing post-fire invasion risk at higher elevations and latitudes. These findings highlight priorities for mitigation, monitoring, and restoration efforts to reduce post-fire plant invasion risk across the western United States.
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Invasive annual grasses have long been known to increase wildfire danger in shrublands and woodlands of the American West. Ventenata (Ventenata dubia) is one such grass. First reported in North America in 1952 in Washington state, it is now expanding into previously invasion- resistant forest landscapes. Unlike cheatgrass, another invasive grass, ventenata can grow in sparsely vegetated rocky meadows. These forest scablands, often embedded within a forested landscape, have historically served as natural fire breaks. Lacking sufficient fuels, the scablands usually stopped fire from spreading into neighboring fireprone forests. However, when ventenata invades scablands and other open areas, it can create a highly flammable bridge between adjacent forested areas and act as a “ fire conveyor belt” that facilitates the spread of fire across a landscape.
Virtual workshop recordings and resources.
Invasive annual grasses–such as cheatgrass, medusahead, and ventenata–are the leading cause of degradation and loss of America’s sagebrush grasslands, reducing forage and habitat, fueling more frequent and larger wildfires, and threatening rural economies. While invasive grasses are widespread, there remains a generational opportunity to proactively address this threat. However, many land managers may not be equipped with the information needed to plan and implement effective treatments.
In this one-day virtual workshop, participants will learn about guiding principles, strategic planning processes, tools, and tactics for managing annual grass invasion in sagebrush country. Participants will be introduced to the proactive “defend and grow the core” management philosophy, which emphasizes protecting intact and functioning native plant communities, and expanding them through improved management techniques, rather than initially starting with the most degraded areas. This workshop seeks to inspire participants and start conversations across the sagebrush biome on how to meet the invasive annual grass problem head on in their own watersheds. We hope this information will be especially useful to any land manager, landowner, or conservation practitioner working to conserve and protect the sagebrush biome.
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Fuel-treatments targeting shrubs and fire-prone exotic annual grasses (EAGs) are increasingly used to mitigate increased wildfire risks in arid and semiarid environments, and understanding their response to natural factors is needed for effective landscape management. Using field-data collected over four years from fuel-break treatments in semiarid sagebrush-steppe, we asked 1) how the outcomes of EAG and sagebrush fuel treatments varied with site biophysical properties, climate, and weather, and 2) how predictions of fire behavior using the Fuel Characteristic Classification System fire model related to land-management objectives of maintaining fire behavior expected of low-load, dry-climate grasslands. Generalized linear mixed effect modeling with build-up model selection was used to determine best-fit models, and marginal effects plots to assess responses for each fuel type. EAG cover decreased as antecedent-fall precipitation increased and increased as antecedent-spring temperatures and surface soil clay contents increased. Herbicides targeting EAGs were less effective where pre-treatment EAG cover was >40 % and antecedent spring temperatures were >9.5 °C. Sagebrush cover was inversely related to soil clay content, especially where clay contents were >17 %. Predicted fire behavior exceeded management objectives under 1) average fire weather conditions when EAG or sagebrush cover was >50 % or >26 %, respectively, or 2) extreme fire weather conditions when EAG or sagebrush cover was >10 % or >8 %, respectively. Consideration of the strong effects of natural variability in site properties and antecedent weather can help in justifying, planning and implementing fuel-treatments.
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Invasion by nonnative annual plants that form prolific seed banks, including cheatgrass, throughout western North America is a major natural resource concern. Even with known economic and ecological implications, soil seed banks and their potential to impact ecological restoration in arid and semiarid ecosystems are poorly understood. Quantifying the regenerative potential of the soil seed bank—the living seeds in the soil profile and on the soil surface—can help natural resource managers make decisions to increase the likelihood of restoration success. We analyzed the germinable soil seed bank composition and distribution of a rangeland site in western Colorado that experienced a wildfire in 1994 and is dominated by cheatgrass. We collected soil seed bank samples from 118 points in a 100 × 110 m grid to a depth of 5 cm. Each sample was split by depth from 0 to 2 cm and from 2 to 5 cm, and the seed bank was quantified using greenhouse emergence methods. We found that seeds of native species were more dense and evenly distributed (3391 seeds ⋅ m−2than seeds of nonnative species were (1880 seeds ⋅ m−2) in the 0–5 cm seed bank across the site. We also found that seeds of both native and nonnative species were concentrated in the 0–2 cm layer of the seed bank but that native and nonnative seeds were present in substantive densities in the 2–5 cm layer. These findings suggest that the soil seed bank of the site is resilient, and a targeted approach to specifically deplete the seed bank of nonnative annuals could facilitate restoration by the in situ native seed bank.
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The invasive annual grass, medusahead, infests rangelands throughout the West, from the Columbia Plateau to the California Annual Grasslands and the Great Basin. Dominating secondary succession in the sagebrush steppe, medusahead can degrade the habitat of threatened species such as the greater sage-grouse. This research explores the potential of dormant season grazing as an applied management strategy to reduce the negative impacts of medusahead while promoting recovery of perennial vegetation at the landscape scale. In particular, it assessed grazing with four treatments from 2018 to 2020: traditional grazing (May–October), dormant season grazing (October–February), traditional + dormant season grazing (May–February), and no grazing. After 2 yr of grazing treatments, biomass, density, cover, and fuel continuity did not differ between treatments (P > 0.05). However, biomass measurements were significantly different between years, which is likely due to greater than normal precipitation in 2019 and 2020. Between 2018 and 2019, annual grass biomass increased by 81% (666–1 212 kg ha−1) and perennial grass biomass increased by 165% (118–313 kg ha−1). Litter biomass decreased by approximately 15% in every year since 2018 (2 374, 2 012, and 1 678 kg ha−1 in 2018–2020). There were not significant differences in cover or density of annual and perennial grasses between treatments and years. Our results indicate that 2 yr may not be adequate time for dormant season grazing treatments to be effective in reducing the abundance of medusahead and that after 2 yr of treatments, dormant season grazing does not have a detrimental effect on perennial vegetation.
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Reestablishing perennial vegetation dominance in ventenata (Ventenata dubia)– and other annual grass-invaded rangelands is critical to restoring ecological function and increasing ecosystem goods and services. Recovery of perennial dominance in ventenata-invaded rangelands is challenging and constrained by a lack of established best management practices; however, preemergent herbicides can, at least temporarily, reduce ventenata. Indaziflam is a preemergent herbicide that has longer soil activity than other commonly used preemergent herbicides that needs evaluated to determine if it offers multiple-year control of ventenata and to determine its effects on residual perennial vegetation. Some ventenata-invaded rangelands may not have enough residual vegetation to occupy the site after ventenata control, but longer soil activity with indaziflam likely limits establishment of seeded species. However, incorporating seeds in activated carbon pellets, which can limit herbicide damage, may be a strategy for establishing perennial vegetations simultaneously with indaziflam application. We evaluated 1) applying indaziflam to control ventenata and 2) broadcast-seeding perennial grass seed incorporated in activated carbon pellets with a simultaneous indaziflam application at two sites for 3 yr post treatment. Indaziflam controlled ventenata for the 3 yr sampled. Perennial grasses increased with indaziflam at the site that had more residual perennial grasses before treatment. At the other site, perennial forbs increased with indaziflam. Indaziflam offers multiple-year control of ventenata; however, plant community response depends on composition before treatment. Seeding perennial grass seeds incorporated in activated carbon pellets while indaziflam controlled ventenata did not increase perennial grass abundance. Though this was likely associated with low establishment due to below-average precipitation post seeding and because broadcast seeding is often an ineffective seeding method, we cannot rule out nontarget herbicide damage. Further evaluations of activated carbon technologies used in conjunction with indaziflam are needed to determine if this can be an effective management strategy.
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Aims Invasion by annual grasses (IAGs) and concomitant increases in wildfire are impacting many drylands globally, and an understanding of factors that contribute to or detract from community resistance to IAGs is needed to inform postfire restoration interventions. Prefire vegetation condition is often unknown in rangelands but it likely affects variation in postfire invasion resistance across large burned scars. Whether satellite‐derived products like the Rangeland Analysis Platform (RAP) can fulfill prefire information needs and be used to parametrize models of fire recovery to inform postfire management of IAGs is a key question. Methods We used random forests to ask how IAG abundances in 669 field plots measured in the 2‐3 years following megafires in sagebrush steppe rangelands of western USA responded to RAP estimates of annual:perennial prefire vegetation cover, the effects of elevation, heat load, postfire treatments, soil moisture–temperature regimes, and land‐agency ratings of ecosystem resistance to invasion and resilience to disturbance. Results Postfire IAG cover measured in the field was % and RAP‐estimated prefire annual herbaceous cover was %. The random forest model had an R² of 0.36 and a root‐mean‐squared error (RMSE) of 4.41. Elevation, postfire herbicide treatment, and prefire estimates from RAP for the ratio of annual:perennial and shrub cover were the most important predictors of postfire IAG cover. Threshold‐like relationships between postfire IAG cover and the predictors indicate that maintaining annual:perennial cover below 0.4 and shrub cover below <10% prior to wildfire would decrease invasion, at low elevations below 1400 m above sea level. Conclusion Despite known differences between RAP and field‐based estimates of vegetation cover, RAP was still a useful predictor of variation in IAG abundances after fire. IAG management is oftentimes reactive, but our findings indicate impactful roles for more inclusively addressing the exotic annual community, and focusing on prefire maintenance of annual:perennial herbaceous and shrub cover at low elevations.