Invasive Species
View this webinar recording for a science-management discussion on the latest herbicide findings from three published papers on risks and rewards of indaziflam, applying indaziflam and imazipic together, and a review of post-fire seeding and herbicide treatment effectiveness, and will discuss implications for management.
See also answers to unanswered attendee questions remaining at the conclusion of the webinar.
Topics and presenters:
Brynne Lazarus, Botanist, USGS Forest and Rangeland Ecosystem Science Center, will discuss Risks and rewards of pre-emergent herbicide (indaziflam) to defend core sagebrush-steppe ecosystems under suboptimal precipitation. Link to paper: https://www.sciencedirect.com/science/article/pii/S1550742425000715
Christie Guetling, Range Technician, USDA-ARS Eastern Oregon Agricultural Research Center, will discuss Does applying indaziflam and imazapic together improve restoration of annual grass-invaded rangelands? Link to paper: https://www.sciencedirect.com/science/article/pii/S1550742425000703
Matt Germino, Supervisory Research Ecologist, USGS Forest and Rangeland Ecosystem Science Center, will discuss A systematic review and meta-analysis of post-fire seeding and herbicide treatment effectiveness for controlling exotic annual grasses in the sagebrush biome. Link to paper: https://research.fs.usda.gov/treesearch/69871
View article.
To assess the role of current and source environments in explaining variation in flowering phenology of Bromus tectorum, an invasive annual grass, we conducted a replicated common garden experiment using 92 genotypes collected across western North America. Replicates of each genotype were planted in two densities (low = 100 seeds/1 m², high = 100 seeds/0.04 m²) under two different temperature treatments (low = white gravel; high = black gravel; 2.1°C average difference) in a factorial design, replicated across four common garden locations in Idaho and Wyoming, USA. We tested for the effect of current environment (i.e., density treatment, temperature treatment, and common garden location), source environment (i.e., genotype source climate), and their interaction on each plant’s flowering phenology. Flowering timing was strongly influenced by a plant’s current environment, with plants that experienced warmer current climates and higher densities flowering earlier than those that experienced cooler current climates and lower densities. Genotypes from hot and dry source climates flowered consistently earlier than those from cool and wet source climates, even after accounting for genotype relatedness, suggesting that this genetically based climate cline is a product of natural selection. We found minimal evidence of interactions between current and source environments or genotype-by-environment interactions. Phenology was more sensitive to variation in the current climate than to variation in source climate. These results indicate that cheatgrass phenology reflects high levels of plasticity as well as rapid local adaptation. Both processes likely contribute to its current success as a biological invader and its capacity to respond to future environmental change.
View article.
Local adaptation may facilitate range expansion during invasions, but the mechanisms underlying successful invasions remain unclear. Cheatgrass (Bromus tectorum), native to Eurasia and Africa, has invaded globally, with severe impacts in western North America. We aim to identify mechanisms and consequences of local adaptation in the North American cheatgrass invasion. We sequence 307 range-wide genotypes and conduct controlled experiments. We find that diverse lineages invaded North America, where long-distance gene flow is common. Nearly half of North American cheatgrass comprises a mosaic of ~19 locally adapted, near-clonal genotypes, each seemingly very successful in a different part of North America. Additionally, ancestry, phenotype, and allele frequency-environment clines in the native range predict those in the invaded range, indicating pre-adapted genotypes colonized different regions. Common gardens show directional selection on flowering time that reverse between warm and cold sites, potentially maintaining clines. In the USA Great Basin, genomic predictions of strong local adaptation identify sites where cheatgrass is most dominant. Our results indicate that multiple introductions and migration within the invaded range fuel local adaptation and success of cheatgrass in western North America. Understanding how environment and gene flow shape adaptation and invasion is critical for managing ongoing invasions.
View article.
We compared vegetation recovery spanning 20 yr following prescribed fire on mid-succession and late-succession western juniper woodlands on Steens Mountain, Oregon. Our objective was to evaluate vegetation dynamics between early (first decade) and later successional (second decade) time periods after fire. The first decade after fire vegetation on burned mid-succession sites were codominated by native herbaceous perennials and sprouting shrub species and on late-succession sites vegetation was codominated by nonnative cheatgrass and snowbrush. During the second decade after fire, vegetation composition converged and both mid-succession and late-succession sites were codominated by herbaceous perennials, mountain big sagebrush, round-leaf snowberry, and snowbrush. Herbaceous and shrub vegetation composition of both burned woodland phases proved to be highly resilient to fire, the difference was that native shrub-herbaceous recovery on late-succession sites required about twice as much time as mid-succession sites. The resilience of both mid-succession and late-succession woodland sites was likely a product of ecological site characteristics (e.g., elevation and precipitation zone) that affords a competitive advantage for native perennial species over invasive annuals.
Webinar recording.
We will begin with a brief overview of weed biocontrol, and then discuss how climate change may impact biocontrol systems at different stages of planning and implementation. Our speakers will highlight as examples the control agents and their host dynamics for Hypericum perforatum, Lythrum salicaria, and Reynoutria spp.
This event will also serve as the launching point for a working group to address knowledge gaps around Northwest biocontrol in a changing climate, including modeling population dynamics and geographic distributions of agents under different climate scenarios and developing a framework for collecting data to disentangle climate impacts from other drivers of population dynamics. Other potential working group topics include disruption in the phenological synchrony of agent and host and evolutionary changes in response to climate change.
View article.
Restoration of annual grass-invaded rangelands is often a management priority. Pre-emergent herbicides are an effective restoration tool to reduce annual grasses but can negatively impact seeded vegetation. Hence, seeding is often delayed until herbicide activity has abated. With indaziflam, a pre-emergent with longer soil activity, seeding may need to be delayed for several years. It would be advantageous if seeded species could establish while indaziflam controls annual grasses, as competition with annual grasses would be limited, and forage production and vegetation cover of the soil surface would recover sooner. Seeding deeper in the soil may allow seeded species to largely avoid herbicide activity, but seeded species may struggle to emerge from greater seeding depths. We investigated seeding squirreltail and crested wheatgrass at 1-, 3-, 5-, and 7-cm seeding depths just prior to a fall indaziflam application at two sites in 2 yr. Seeding at ∼1-cm is the recommended practice for both bunchgrasses. Seedling density in late June was greater at the 3 and 5 cm seeding depths and likely greater at the 7 cm depths than at the 1-cm depth. Seedling height was greater at the 3-, 5-, and 7-cm depths than at the 1-cm depth. Seedling density and height did not vary among the 3-, 5-, and 7-cm depths. This suggests that indaziflam largely did not penetrate below the first centimeter or two of the soil the growing season after application. Seeding at depths of 3–7 cm is likely a viable strategy for allowing some seeded species to establish while indaziflam controls annual grasses. Additional evaluations across a gradient of soil and site characteristics, with different plant species and functional groups, and other pre-emergent herbicides are needed to refine this restoration strategy and identify its benefits and limitations.
View article.
The goal of restoration actions in these communities is to control the annual grasses and promote co-occurring perennial vegetation. Indaziflam and imazapic, applied as pre-emergent herbicides, have both been used for this purpose. Indaziflam often has less than desired control in the first year but can control annual grasses for multiple years. In contrast, imazapic has effective control in the first year, but control is short-lived. Land managers have recently started tank-mixing these two herbicides to potentially alleviate their individual shortcomings and theoretically achieve more effective, long-term annual grass control. However, little is known about the effectiveness of aerially applying these herbicides together, particularly compared with just applying indaziflam, and the effects on co-occurring perennial vegetation. We investigated the effects of applying indaziflam individually and in combination with imazapic at three sites (two in Oregon and one in Washington). Applying indaziflam and imazapic in tandem provided better control of annual vegetation and promoted perennial vegetation, although site differences influenced treatment effects. Applying indaziflam individually controlled annual vegetation but did not generally generate a response from perennial vegetation. Tank-mixing indaziflam and imazapic improved first-year control compared with only applying indaziflam, but control was still better in the second year after treatment, suggesting that a greater rate of imazapic than used in this study may be needed to achieve better first-year control. The results of this study suggest that applying indaziflam and imazapic in tandem may be an effective strategy for controlling invasive annual grasses and promoting co-occurring perennial vegetation.
View article.
While substantial efforts have been made to conserve critical mule deer habitat, less attention has been given to mule deer habitat affected by invasive annual grasses (IAGs) and there is limited information about how mule deer respond to IAG invasions. We evaluated mule deer resource selection in a sagebrush grassland community impacted by IAGs in northeast Wyoming. We then used empirical model estimates to forecast how IAG management could impact mule deer habitat in the future following a strategic IAG framework focused on defending and growing sagebrush core areas most threatened by IAGs. We found that mule deer responded to IAGs in a nonlinear pattern across all seasons and strongly avoided areas once cover exceeded approximately 20%. When projecting results 20 yr into the future, we found that over half of the study area is expected to experience significant declines in mule deer habitat quality if IAGs continue to spread at the same rate observed over the past two decades. However, with targeted IAG treatments, we predicted widespread improvements in mule deer habitat, particularly in priority areas where ecological integrity can be restored with future IAG management. Our findings reinforce the emerging notion that ecosystem-based frameworks designed to defend and grow intact sagebrush steppe through strategic management efforts also have the potential to benefit species of conservation interest. As current conservation efforts to mitigate IAGs are not progressing fast enough to address the magnitude of the IAG problem in sagebrush across the west, strategic management efforts will be necessary to maintain important habitats for numerous sagebrush occurring wildlife.
View factsheet.
Ventenata and medusahead are winter annuals that emerge in late fall, winter, and spring. These grasses mature early in the summer providing fine fuels for wildfires.Ventenata and medusahead are frequently found together where conditions allow. These invasive annual grasses increase wildfire danger in shrublands and woodlands of the American West.
- Fine, highly flammable fuel loads facilitate larger and more frequent fires.
- Relatively high silica content make these grasses less palatable for grazing (unlike cheatgrass which is palatable in its green phase), and creates a build-up of litter on the soil surface.
- These species can spread throughout areas that once acted as natural fire breaks.
View article.
We created a regional-scale chronosequence of areas that burned only once from 1984 to 2017 using Landsat-derived burned area products, and collected species composition data across a gradient of 4–32 years since fire. We used linear mixed models to look for evidence of native plant recovery, and used indirect gradient analysis and joint species distribution models to examine the response of species occurrence to a) fire occurrence and timing and pre- and post-fire climate; and b) topography, grazing, and annual grass dominance.
Native diversity and perennial herbaceous cover were unrelated to time since fire and negatively associated with annual grass cover. The occurrence of a single fire had mostly negative associations with native species and mostly positive associations with non-native species. Grazing intensity did not affect the dominant post-fire annual grass, but non-native annual forbs sorted along a gradient towards two groups based on grazing intensity, annual grass cover, and topography.
Annual grass competition will likely maintain the post-fire invasive-dominated plant community even if management interventions successfully stop the grass-fire cycle.