Invasive species have caused and will continue to cause numerous problems to the sagebrush ecosystem. Although 30 or more species of plants can be considered invasive in the range of the sage-grouse (see Miller et al. 2011, table 10.4), the two primary species of concern to fuels managers are the invasive grasses cheatgrass and medusahead. These grasses were introduced into the sagebrush ecosystem in the late 19^th century and have spread ever since. Although more dominant in the western (Great Basin) range, these species are at least a local threat throughout Greater Sage-Grouse range. Some of the essential points to remember concerning invasive grasses, fire, and the sagebrush ecosystem are:

fires exceeding 100,000 acres

Since 2000, individual fires exceeding 100,000 acres in the sagebrush steppe have become a near annual occurrence in the Great Basin. These fires, occurring under conditions of long-term drought, extreme fire hazard, high winds, low humidity, and multiple starts make direct attack and control very difficult. Recent observations suggest many megafires are linked to cheatgrass-dominated areas which serve as primary ignition points and facilitate spread within large, contiguous stands of sagebrush (Maestas et al. 2016).

Wildfires Expand quickly

Wildfires in the sagebrush steppe expand quickly and can affect hundreds of thousands of acres of sage-grouse habitat in a matter of days; the Long Draw (2012) and Buzzard Complex (2014) fires in southeastern Oregon both had multiple hundred-thousand-acre runs in a single burning period with a rate of spread between 10 and 15 miles per hour. This map (from Chambers et al. 2017, Figure 7) shows the distribution of fires over a 15-year period in the Great Basin.

Click on map for a printable PDF version.

fire return interval

In lower elevations of the Northern Great Basin sagebrush steppe (below 4000 ft), the fire return interval has been reduced from 50 to 100 years to less than 10 years in some places (Great Basin Factsheet Series #5).

Expanding Annual Grasses

Making the problem even worse going forward, annual grasses that typically invade lower elevation sagebrush communities are now expanding into mid elevations following wildfire (Great Basin Factsheet Series #5).

Depleted native Grasses

As fires gradually deplete native perennial grasses and forbs, these previously more resistant sagebrush communities have become susceptible to conversion to invasive annual plant dominance (Davies et al. 2011), as shown in the photos from Miller et al. (2014).

A Wyoming big sagebrush/bluebunch wheatgrass-Indian ricegrass system with a severely depleted understory and cheatgrass cover near 5% (left photo, taken in 2008). Following a prescribed fire invasive annuals dominate the understory (right photo, taken in 2010). Resilience and resistance to invasive annuals and potential seeding success is low with a Resilience and Resistance score = 9.

Tipping Point

Sagebrush ecosystems are at a tipping point when invasive annual grasses dominate the herbaceous understory. There are limited management options and few science-based solutions to these situations.

Grass-Wildfire Feedback Cycle

The invasive grass-wildfire feedback cycle has serious potential negative consequences for sage-grouse populations in the next several decades. In this video, Pete Coates discusses the current rate of burning and sage-grouse population forecasts.

Begin by watching Matt Germino describe techniques and emerging science to combat the invasive annual grass threat.

Emerging science on various aspects of invasive grasses, their control, and restoration techniques offer some hope of solving the fire/invasives problem and breaking the cycle. These include:

• Techniques to help the establishment of perennial grasses;
• Better weather prediction tools to help predict seed germination and survival to establishment;
• Seed coatings to accelerate or delay germination to increase establishment;
• Use of seed transfer zones to obtain plant materials better adapted to local sites;
• Use of herbicides to help eradicate of exotic annuals, including where, when and why and avoiding collateral damage;
• Development of weed-suppressive bacteria (e.g., Pseudomonas fluorescens) to reduce the competitiveness of invasive annual grasses;
• How soon grazing should be allowed after fire and seeding;
• Soil health restoration (e.g., restoration of cryptobiotic crusts) that can inhibit cheatgrass germination.

Given projected climate change and longer fire seasons across the western United States, fuels management represents a proactive approach for modifying large fire trends. A key toward successful application of fuels management techniques in systems invaded by invasive annual grasses is the concept of Resistance and Resilience.

This concept is more fully explained in the Lesson on Resistance & Resilience, but we need to understand how resistance and resilience applies specifically to systems invaded by annual grasses. The concept of Resistance and Resilience is also critically important when designing fuels treatments and considering their long-term consequences, especially in warm and dry sites with low resistance and resilience. In this video, Rick Miller discusses the concept of resistance and resilience.

The sage-grouse habitat resistance and resilience matrix (Chambers et al. 2017, Table 8) can be used to develop general management strategies for invasive plant species (Chambers et al. 2017).

The sage-grouse habitat resilience and resistance matrix is based on resilience and resistance and Greater Sage-Grouse breeding habitat probabilities. The rows show the ecosystem’s relative resilience to disturbance and resistance to invasive annual grasses (1 = high resilience and resistance; 2 = moderate resilience and resistance; 3 = low resilience and resistance). The columns show the landscape-scale sage-grouse breeding habitat probability (A = 0.25 to < 0.5 probability; B = 0.5 to < 0.75 probability; C = ≥ 0.75 probability).

Click the image to view a PDF the matrix and associated instructions and information.

The feedback cycle between recurring wildfires and annual grass expansion has been repeatedly cited as one of the dominant threats to sage-grouse persistence range-wide (USFWS 2013, Knick et al. 2011). Recent research (Coates et al. 2015) provides context on current wildfire and sage-grouse trends across the Great Basin. Specifically, this research examined the relationship between the locations of fires, the location of highly valued habitats (lek clusters), and patterns of Resistance and Resilience. This work also projected likely future trends for sage-grouse populations based upon different rates of burning and precipitation scenarios.

Some of the important findings from this research are summarized here:

The primary management implications related to “core” areas are illustrated in Coates et al. 2015, Figure 12, which illustrates projected sage-grouse population change from 2015 to 2045.

The projections were modeled under three different scenarios of decreased rates of burning in core areas (columns; 25%, 75%, or 99% reduction in annual cumulative burned area), under three different levels of annual precipitation (rows; low, medium, and high precipitation). The black horizontal line in each graph represents stable population trends in that scenario. The blue bands represent populations in core areas, while the red bands represent populations outside of core areas.

The key take home messages are:

• Reducing the rate of annual cumulative burned area by only 25% in defined ‘core areas’ (left column) did little to prevent population declines under any of the modeled precipitation conditions.
• Reducing the rate of annual cumulative burned area by 75% (middle column) in core areas slowed the rate of population decline under below-average precipitation conditions (top), stabilized population growth under normal precipitation conditions (middle), and resulted in population growth under above-average precipitation conditions (bottom).
• A near complete cessation of fire in core areas (right column) resulted in increased population growth under all precipitiation conditions, especially for normal (middle) and high precipitation (bottom).

The research related to invasive annual grasses clearly shows:

• The frequency and size of wildfires has increased across the Great Basin, driven strongly by post-fire invasive annual grass (primarily cheatgrass) dominance.
• The distribution of sage-grouse and their breeding habitats are highly clustered. Protecting core areas where birds are concentrated is an important conservation strategy to improve long-term sage-grouse persistence.
• At current rates of burning, continued declines in Great Basin sage-grouse populations are expected over the next three decades under most climate scenarios.
• Effective fire suppression, which constrains cumulative area burned in core areas, is an essential management tool over the next three decades.
• During this period, failure to constrain cumulative area burned by 75% or more in core areas is projected to result in large-scale declines in sage-grouse populations across the Great Basin.
• Successful post-fire Emergency Stabilization and Rehabilitation following fire can offset losses resulting from wildfire and is not incorporated into the projections.

Click Play to listen to Pete Coates' conclusions from his research.

Next explore the Land Management Tools section to learn about tools for managing invasive annual grasses and associated wildfire.