Invasive Species
Workshop webpage.
In this two-day field and classroom workshop in Sheridan, WY, participants will build upon the information presented in the Level 1 Virtual Workshop: Defending and Growing the Core by Breaking the Cycle of Annual Grass Invasion. This hands-on workshop is designed to take a more in depth look at how you can strategically plan for and manage invasive annual grasses (IAG). Participants will visit various sites including intact core areas and growth opportunity areas where we will discuss potential management approaches in each situation. This is also a great opportunity for participants to see multiple management tactics and their effects on rangeland plant communities over time. We will explore various monitoring techniques and discuss strengths and weaknesses. Through this field workshop, participants will become familiar with different management practices and improve their capacity to determine which management tactics will best suite their needs in different situations.
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Chemical herbicides increased soil mineral nitrogen in proportion to their negative effects on plant cover for 2 years after treatments in all sites and increased soil water and net N mineralization (measured at one site) but did not affect total carbon, nitrogen, or organic matter. Invertebrate responses to herbicides varied by site, and invertebrates increased with chemical herbicides at the highest, wettest site. We show that herbicide treatments can exacerbate pulses of mineral nutrients, which previous studies have shown can weaken ecosystem resistance to invasion. Thus, restoration strategies that increase the likelihood that desired plants can capture mineralized nutrients after herbicide application will likely be more successful.
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Predicted fire-moderation benefits over the first 4 years of fuel break implementation were modest and variable, but, generally, increases in exotic annual grasses and their associated fire risks were not observed. Nonetheless, ancillary evidence from shrublands would suggest that treatment-induced shifts from shrub to herbaceous fuel dominance are expected to improve conditions for active fire suppression in ways not readily represented in available fire models.
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We evaluated the effects of controlling medusahead with prescribed burning and imazapic application followed 1 yr later with drill-seeding large perennial bunchgrasses at two seeding rates (medium and high) for more than a decade post seeding. Large perennial bunchgrass cover and density was > 16- and > 4-fold greater in revegetation treatments compared with the untreated control 11 yr after seeding, respectively. Invasive annual grass abundance was ∼twofold greater in the untreated control compared with the revegetation treatments. These results suggest that revegetation efforts in medusahead-invaded rangelands can have persistent ecological benefits (increased perennials and decreased invasive annuals). The high seeding rate resulted in more perennial bunchgrass and less invasive annual grass compared with the medium seeding rate over the duration of the study, suggesting that high seeding rates may be needed to maximize benefits. Revegetation of medusahead-invaded rangelands can have long-lasting effects, though high establishment of perennial bunchgrasses is likely necessary for success.
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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.