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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 exotic annual grasses 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.
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Threat to the sagebrush biome

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

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Risk of wildfire

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

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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 annual grass 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. Plan

    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. Communicate

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

  3. Monitor

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

ISI under the hood

From Satellite To Severity Map

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. Follow one pixel — about half a tennis court of rangeland — from orbit to a management decision.
Landsat scan — sagebrush biomeOne pixel · 10 × 10 mScoring the pixelInvasion severity · 10-m resolution

IAG

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PFG

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BGR

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Other cover

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ISI=ln(IAG 38+ εPFG 21+BGR 24+ ε)=-2.63
Less invadedMore invaded

1Satellite imagery

Landsat satellites have imaged the sagebrush biome for four decades. The Rangeland Analysis Platform (RAP) turns that archive 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 invasives 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.

Five levels, five ways to act ↓

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

Five Levels, Five Ways To Act

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 treatment delineation, selecting appropriate actions, setting site-appropriate goals and expectations, and tracking change through time.

* ISI = ln( (IAG + ε) ⁄ (PFG + BGR + ε) )

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

Platform outputs

What You Can See And Analyze

Explore and analyze annual grass invasion and recovery potential at a treatment scale.

Invasion severity maps

See severity anywhere in the sagebrush biome.

Continuous 10-m ISI for any single year from 2018 to 2025, or a smoothed 2023–2025 average.

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 2018–2025 record.

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.

A spatial tool for planning and monitoring treatments

See the invasion. Plan the recovery.

Turning data into action

Prioritize, Plan, And Monitor Treatments

Integrating 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.

Map the invasion

Visualize 10-m resolution ISI data anywhere in the sagebrush biome, for any year from 2018 to present.

  • Single years 2018–2025, or a 2023–2025 average
  • Adjustable layer opacity over satellite, street, topo, or dark basemaps
  • Masking that removes non-vegetated, cultivated, and ≥50% tree cover

Area-of-interest summaries

Click a point or draw an area to summarize invasion severity and RAP cover across your treatment unit.

  • Query a single pixel, or delineate a polygon by hand or by upload
  • ISI and RAP cover trends across the full 2018–2025 record
  • Download data for use in your own GIS platform

Customize your view

Layer in the management context that matters for your decision, then filter down to the pixels you care about.

  • Threat-Based Ecostates, Sagebrush Conservation Design, IAG Management Framework
  • Land ownership boundaries
  • MTBS fire perimeters, 2000–2024, to see which pixels burned and when

Brought to you by

Built By And For The Conservation Community

Working Lands for WildlifeUniversity of Montana

Project partners

USDA Natural Resources Conservation ServiceUSDA Agricultural Research Service

Data partner: ISI is derived from Rangeland Analysis Platform 10-m cover indicators.

Let’s talk

Put Invasion Severity Data To Work On Your Landscape

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

technology@wlfw.org —