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A Working Lands for Wildlife tool

Invasion Severity Index

Plan, prioritize, and monitor invasive annual grass treatments across the sagebrush biome.

Launch the ISIWhat is the ISI?
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Why it matters

“Cheating” The West Of Its Future

Cheatgrass, medusahead, ventenata, and other invasive annual grasses (IAG) are taking over America’s sagebrush biome — fueling larger and more frequent wildfires, degrading wildlife habitat, reducing forage for livestock, and threatening rural ways of life.
01

#1

Threat to the sagebrush biome

Invasive annual grasses are the top threat to core sagebrush areas.

02

2×

Risk of wildfire

Having invasive annual grasses on the landscape doubles the risk of wildfire occurrence.

03

70%

Loss of forage

Converting from perennial sagebrush rangelands to annual grasslands can reduce forage production by up to 70%.

A spatial tool for planning and monitoring treatments

Introducing The Invasion Severity Index

Effective management of invasive annual grasses requires not only understanding the distribution and extent of the invasion, but also what desired plants will fill the void once invasives are removed.

The ISI was created to help conservationists on the front lines of treatment planning gauge the extent of IAG invasion relative to site recovery potential, while accounting for variations in productivity across the sagebrush biome.

Built for treatment scale

The ISI complements broader-scale prioritization and planning tools with the data field conservationists and land managers need to design and monitor land treatments. With this tool, users can:

  1. Create a rapid baseline inventory of herbaceous conditions to inform treatment prioritization, delineation, and prescriptions — as a starting point to verify in the field.

  2. Better communicate with landowners, land managers, and stakeholders about conditions, goals, alternative treatments, and management expectations.

  3. Remotely monitor treatments to assess efficacy and the need for follow-up management.

ISI map of a treatment unit with areas marked for spot spray and broadcast spray
01 / 03 · Plan

ISI under the hood

From Satellite To Severity

The ISI combines three Rangeland Analysis Platform (RAP) 10-m indicators — invasive annual grass cover, perennial forb and grass cover, and bare ground cover — into a single, continuous metric of invasion severity.
Sentinel-2 scan — sagebrush biomeOne pixel · 10 × 10 mScoring the pixelInvasion severity · 10-m resolution

IAG

0%

PFG

0%

BGR

0%

Other cover

0%

ISI=ln(IAG 4+ εPFG 21+BGR 24+ ε)=−2.42
Less invadedMore invaded

1Satellite imagery

Sentinel-2 satellites image the sagebrush biome every few days at 10-m resolution. RAP turns that imagery into vegetation cover estimates for every 10 × 10-m pixel, about half a tennis court of ground.

2Vegetation cover

Each pixel's cover is split into the three components that matter for invasion: invasive annual grasses (IAG), the desired perennial forbs and grasses (PFG), and bare ground (BGR) — rock, soil, and litter.

3Calculate the index

The ISI is the log ratio of IAG to perennials and bare ground — a single, continuous measure of how far invasion has progressed relative to what the site can recover to. Higher values mean greater severity.

4Severity map

Scored for every pixel, every year from 2018 to present, severity becomes a map: five management-linked levels from Very Low to Severe, ready for treatment planning and monitoring.

Right practices, right places ↓

ε is a small constant that keeps the ratio defined when cover values approach zero. Higher ISI values indicate greater invasion severity.

1: Very Low2: Low3: Moderate4: High5: Severe

Linking severity to management

Right Practices, Right Places

The real power of ISI is helping conservation practitioners put data into action. ISI maps are presented in five levels linked directly to typical management strategies and actions — simplifying complex environmental conditions into meaningful categories for delineating treatments, selecting appropriate actions, setting site-appropriate goals and expectations, and tracking change through time.

Breakdown of five Invasion Severity Index (ISI) levels with associated descriptions and management strategies. Strategies are suggestions and may differ based on conditions, values, and resources available.

Management actions

What Each Strategy Looks Like On The Ground

Each severity level points to a typical management strategy. These are the practices behind them — starting points to adapt to site conditions, values, and resources available.

Maintain

  • Person pressure-washing a tractor's rear tire to clean field equipment.

    Prevention

    Keep IAG out of intact sites: clean vehicles and equipment, use weed-free seed and feed, and limit new disturbance.

  • Field crew surveying grasses and sagebrush across a green hillside.

    Early detection–rapid response

    Find new, small infestations and eradicate them while they are still cheap and quick to remove.

  • Field crew using backpack sprayers to spot-treat vegetation on a rocky hillside.

    Spray-and-release (spot)

    Spot-treat IAG patches with pre-emergent herbicide, releasing the perennial grasses and forbs already on site.

Improve

  • Helicopter spraying sagebrush rangeland below snow-covered hills.

    Spray-and-release (broadcast)

    Broadcast pre-emergent herbicide across the unit where enough perennials remain to recover on their own.

  • Green and dry grasses growing among lichen-covered rocks.

    Repeated treatments

    Follow-up treatments over several years to deplete the IAG seed bank and head off reinvasion.

  • Young grass seedlings emerging from dry soil scattered with plant litter.

    Localized seeding

    Seed desired perennials in patches where too few remain to fill the space treatment opens up.

Revegetate or contain

  • Rows of green grasses growing in open rangeland beneath distant hills.

    Site prep and seeding

    Where perennials are largely gone, prepare the site and seed widely to rebuild the plant community.

  • Aerial view of a wide fuel break along a gravel road through sagebrush rangeland.

    Fuel breaks

    Break up continuous fine fuels so wildfire starting in invaded ground is less likely to reach intact habitat.

  • Cattle grazing on sagebrush rangeland beside a gravel road and blue water troughs.

    Targeted grazing

    Graze to reduce fine fuels and fire risk where restoration is not yet feasible.

Turning data into action

Prioritize, Plan, And Monitor Treatments

Integrate invasive annual grass cover data with site recovery potential to inform strategic management — so you can explore and analyze invasion and recovery potential at a treatment scale.

Invasion severity maps

See severity anywhere in the sagebrush biome.

Seamless 10-m index severity maps for any single year from 2018 to present, or a smooth multi-year average, over satellite, street, topo, or dark basemaps. Non-vegetated, cultivated, and ≥50% tree-cover areas are masked out.

Cover components

Look behind every ISI value.

The three RAP indicators the index is built from — invasive annual grass, perennial forb and grass, and bare ground cover.

Severity levels

Turn a continuous metric into a decision.

Five management-linked classes, from Very Low to Severe, each tied to a typical strategy and set of actions.

Treatment-scale summaries

Get numbers for the ground you manage.

Query a single pixel, or delineate an area by hand or by upload, and summarize ISI and cover across the 2018-to-present record, then download the data for your own GIS.

Management context layers

Place severity in the context that drives decisions.

Threat-Based Ecostates, Sagebrush Conservation Design tiers, the IAG Management Framework, and land ownership boundaries.

Fire history

See which pixels burned and when.

MTBS fire perimeters from 2000 to 2024, overlaid on severity so you can read invasion against recent fire.

Brought to you by

Built By And For The Conservation Community

Working Lands for WildlifeUniversity of MontanaUSDA Natural Resources Conservation Service

Partners: ISI is derived from Rangeland Analysis Platform 10-m cover indicators and provided by ARS Jornada Experimental Range and USDA ARI.

Let’s talk

Put Invasion Severity Data To Work On Your Landscape

Explore and analyze IAG invasion and recovery potential at a treatment scale, or get in touch with the team behind the tool.

technology@wlfw.org —