TOPIC 2 Resistance and Resilience,
An Introduction: Science


This section introduces you to the science of resistance and resilence. Scoll down the page to read each sub-section, or click the Science drop-down navigation to go directly to a sub-section.


This figure (Chambers et al. 2017, Figure 21) shows conceptual models of:

  1. Resistance to invasive annual brome grasses.
  2. Resilience to disturbance over typical soil moisture and temperature gradients in the sagebrush ecosystem.

The horizontal axis demonstrates a continuum from relatively warm (soil temperature) and summer moist (soil moisture) on the left (in this case with Wyoming big sagebrush, silver sagebrush, and cool season grasses with a minor component of warm season grasses) to cold and summer moist on the right with a mixture of cool and warm season grasses and silver sagebrush. Although resistance varies between species of annual grasses (compare cheatgrass, Bromus tectorum, the dashed line in A, to field brome, Bromus arvensis, the solid line in A), resistance to annual grasses and resilience to disturbance generally increase in most areas as the climate regime changes to cool/moist (to the right in the graph).

The type, characteristics, and natural range of variability of stress and disturbance strongly influence both resilience and resistance. Disturbances like overgrazing of perennial plants by livestock and atypical fire regimes are outside of the natural range of conditions and can reduce the resilience of sagebrush ecosystems. This is illustrated in (B), where, for a given position on the environmental gradient (the horizontal axis), resilience is reduced at disturbed or altered sites.


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Figure 21: Click on chart for a printable PDF version.


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Table 2: Click on chart for a printable PDF version.

Vegetation and fuels management projects planning processes are informed by three different scales (Chambers et al. 2017, Table 2). Most assessments are conducted at the mid-scale: the scale of individual or multiple Management Zones because of differences or similarities in environmental characteristics, ecosystem threats, and management strategies as well as the availability of higher resolution data. These Management Zone assessments are used at the sagebrush biome scale for budget prioritization and to ensure range-wide consistency in resource allocation. These assessments are also used to prioritize local planning areas for targeted management activities. At the local and site planning area scale, local data and expertise are used to select project sites and determine appropriate management activities within prioritized planning areas. Treatments are local scale management actions that directly manipulate vegetation to achieve a vegetation or habitat objective (e.g., conifer removal, invasive annual grass control, fuel treatments, or seeding).


Soil Temperature and Moisture Regimes

Soil climate regimes (combinations of temperature and moisture) integrate several different climate variables including mean annual temperature and precipitation and seasonality of precipitation, thus providing a means of assessing climatic differences among ecoregions and effects on vegetation. These regimes can be mapped at appropriate scales to provide an extremely useful tool to help determine the appropriate vegetation treatments and the potential success of such treatments. The soil temperature and moisture regimes that characterize sagebrush ecosystems in the eastern range vary due to the large latitudinal differences and elevation gradients that the area encompasses as well as the variation in seasonality of precipitation (Chambers et al. 2017, Figure 6; Maestas et al. 2016).

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Figure 6: Click on map for a printable PDF version.


In general, higher Resilience and Resistance occurs with cool to cold (frigid to cryic) soil temperature regimes and moist (udic), winter moist (xeric) or predominantly summer moist (ustic) soil moisture regimes. Lower Resilience and Resistance occur with warm (mesic) soil temperatures and relatively dry (aridic) or summer moist bordering on dry (ustic bordering on aridic) soil moisture regimes (Chambers et al. 2017). High soil moisture typically equates to elevated productivity and increased resilience, while cold soil temperatures typically limit growth and reproduction of nonnative invasive annual grasses and thus increase resistance to these species. Timing of precipitation also is important because cheatgrass and many other invasive annual grasses are particularly well-adapted to climates with cool and wet winters and warm and dry summers. In contrast, areas that receive regular and relatively abundant summer precipitation often are dominated by warm and/or cool season grasses that likely create a more competitive environment and result in greater resistance to annual grass invasion and spread.

This type of product can also be used to build simplified, but very useful, landscape rapid assessment (or triage) tools for land managers to use across large landscapes (Maestas et al. 2016). For example, this table categorizes each soil temperature and moisture regime in the western Great Basin in one of three categories of Resistance and Resilience (high, moderate, or low) along with a “common name” for the temperature/moisture regime and the typical type of sagebrush found at the site.


When combined with other data layers, such as priority habitat areas and existing sagebrush land cover, the Resistance and Resilience rating allows the assessment of relative risks to important habitats across large areas and the targeting of appropriate management strategies for potential project areas. For example, sites with relatively low Resistance and Resilience located in and around important sage-grouse habitats could be a priority for installation of strategic fuel breaks, pre-positioning of firefighting resources, and post-fire rehabilitation, because these sites are most likely to suffer severe impacts from fire and invasive annuals. In contrast, areas with moderate-to-high Resistance and Resilience could be prioritized for conifer removal to prevent loss of understory perennial vegetation due to woodland encroachment and to maintain resilient landscapes.

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Click on map for a printable PDF version.

Sage-Grouse Breeding Habitat Model

The breeding habitat model was developed to more accurately portray important breeding areas for the Greater Sage-Grouse (Doherty et al. 2016). The model uses sage-grouse 2010-2014 lek data as a proxy for landscapes important to breeding birds, because leks are central to the breeding ecology of sage-grouse and the majority of nests occur within 4 miles of leks. The model evaluates characteristics such as vegetation, climate, landform, and disturbance variables around leks (within a radius of 4 miles) and provides an estimate of the probability of occupied breeding habitat based on habitat characteristics for each sage-grouse Management Zone (Chambers et al. 2017, Figure 25).

The breeding habitat probabilities were used to develop three categories of breeding habitat probability for prioritizing management actions on the landscape. The categories were based on the probability for areas near leks to provide suitable breeding habitat and included:

  • Low (0.25 to < 0.50);
  • Moderate (0.50 to < 0.75); and
  • High (0.75 to 1.00).

Areas with probabilities of 0.01 to < 0.25 were considered to be unsuitable for breeding habitat, but these areas may provide habitat during other life stages or linkages between areas of suitable breeding habitat.


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Figure 25: Click on map for a printable PDF version.

Connectivity between Areas for Conservation of Sage-Grouse

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Figure A.8.1: Click on map for a printable PDF version..

Maintaining connectivity between conservation areas for sage-grouse (and other species) is important for many reasons, primarily to avoid disruption of the current population structure that could lead to greater isolation and potentially initiate or accelerate population declines. A recent effort to model potential movement between identified conservation areas (Crist et al. 2017) revealed important movement pathways and habitat connections as shown in this map (Chambers et al. 2017, Figure A.8.1).

These areas of habitat connections between priority areas can help land managers target conservation actions to help ensure seasonal and dispersal movements (Crist et al. 2017). Areas of high movement potential (blue and green in the figure) can be used to identify locations where movement is constrained. If resources are limited, sagebrush restoration efforts that improve or expand habitat areas at these “pinch points” between existing Priority Areas for Conservation might create or enhance potential corridors and preserve the likelihood of population persistence by facilitating movements that sustain or augment populations and for dispersal and gene flow.

Managing for Climate Change in the Sagebrush Ecosystem

Although exact predictions on how, what, and where the sagebrush ecosystem will respond to climate change depend greatly on the specific model used, it is clear that building resistance, increasing resilience, and facilitating a response to changing environmental conditions will be necessary. Chambers et al. (2017), Appendix 10, present some preliminary management strategies which could be used to adapt to climate change in the sagebrush. The concepts of Resistance and Resilience will be key in deciding when to apply these strategies and how to prioritize where they should be performed.

  • Maintain or restore soil quality and nutrient cycling by re-evaluating the timing and intensity of land use practices such as livestock grazing
  • Maintain or restore hydrologic and geomorphic processes following stress and disturbance
  • Develop appropriate land use plans and policies to protect habitat and prevent fragmentation
  • Secure conservation easements to prevent conversion to tillage agriculture, housing developments, etc., and maintain existing connectivity
  • Manage conifer expansion to maintain connectivity among populations and facilitate seasonal movements
  • Suppress fires in targeted areas where altered fire regimes are resulting in fire sizes and severities that are resulting in alternative states that increase landscape fragmentation and impede dispersal, establishment, and persistence of native plants and animals
  • Expand existing reserve boundaries to buffer and replicate the diversity within the core of the reserve and to increase the overall variation in species within the expanded reserve
  • Identify and maintain ecosystems that are on sites that may be better buffered against climate change and short-term disturbances and contain communities and species that are at risk across the greater landscape
  • Prioritize and protect existing populations on unique sites and sensitive or at-risk species or communities
  • Establish artificial reserves for at-risk and displaced species
  • Reduce fuel loads and fuel continuity to: (1) decrease fire size, alter burn patterns, decrease perennial grass mortality, and maintain landscape connectivity; (2) decrease competitive suppression of native perennial grasses and forbs by woody species; and (3) lower the longer-term risk of dominance by invasive annual grasses and other invaders
  • Use prescribed fire in areas with moderate resilience and little or no presence of invasive annual grasses and with high resilience to create fuel mosaics and promote successional processes
  • Suppress wildfires in low to moderate resilience and resistance sagebrush-dominated areas to prevent conversion to invasive annual grass states
  • Suppress wildfires adjacent to or within recently restored ecosystems to promote recovery and increase capacity to absorb future change
  • Use fuel breaks in carefully targeted locations along existing roads where they can aid fire suppression efforts and have minimal effects on ecosystem processes
  • Limit anthropogenic activities that facilitate invasion including surface disturbances, altered nutrient dynamics, and invasion corridors
  • Use Early Detection and Rapid Response for emerging invasive species of concern to prevent invasion and spread
  • Manage livestock grazing to promote native perennial grasses and forbs that compete effectively with invasive plants
  • Actively manage invasive plant infestations using integrated management approaches such as chemical treatment of invasives and seeding of native perennials
  • Manage grazing to maintain soil and hydrologic function and the capacity of native perennial species, especially grasses, to effectively compete with invasive plant species
  • Reduce conifer expansion to prevent high severity fires and maintain native perennial species that can stabilize geomorphic and hydrologic processes and minimize invasions
  • Restore disturbed areas with functionally diverse mixtures of native perennials and shrubs with capacity to persist and stabilize ecosystem processes under altered disturbance regimes and in a warming environment
  • Use seeds, germplasm, and other genetic material from across a greater geographic range
  • Favor existing genotypes that are better adapted to future conditions because of pest resistance, broad tolerances, or other characteristics
  • Increase diversity of nursery stock to provide those species or genotypes likely to succeed
  • Monitor both native and invasive species at range margins to provide advanced warning of range shifts
  • Implement assisted migration in areas with high rates of climate change
  • Practice adaptation measures such as reduced grazing during droughts, conservation to facilitate species persistence, and seeding and transplanting techniques proven to work during drought
  • Anticipate and respond to species declines such as may occur on the southern or warmer edges of their geographic range
  • Favor or restore native species that are expected to be better adapted to the future range of climatic and site conditions
  • Protect future-adapted regeneration from inappropriate livestock grazing
  • Avoid seeding introduced forage species that out-compete natives
  • Spread ecological types over a range of sites and conditions, both existing and new, to increase combinations of locations, site conditions, and species aggregations

Take-home Message about Resistance and Resilience

Before moving on, watch Mike Pellant discuss why the resistance and resilience must be paired with site evaluations to help determine site priorities and potential treatments.


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