Study Name

Wild Horse Island

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Location

Wild Horse Island, Flathead Lake, Montana

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Overview

Wild Horse Island, a 2,163-acre Montana State Park in Flathead Lake, is home to a world-renowned population of bighorn sheep. In recent years, invasive annual grasses such as cheatgrass, Japanese brome, and ventenata have begun to replace native perennial grasses—threatening wildlife habitat, forage quality, and ecosystem resilience.

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This case study examines how NutraFix® Micronutrient Fertilizer was used to improve perennial grass cover and species diversity on the island’s south-facing slopes.

Background: A Critical Habitat Under Pressure

Located within the Confederated Salish and Kootenai Tribes’ reservation, Wild Horse Island has played a significant role in bighorn sheep conservation—providing more than 560 sheep for reintroduction programs across Montana and Oregon.

However, long-term monitoring from the Rangeland Analysis Platform shows a concerning trend:

• Perennial grass cover decreased from 50% → 40%

• Annual invasive grasses increased from 15% → 20%
   

Traditional herbicides can reduce annual grass cover but may harm non-target native species and require yearly applications. Montana Fish, Wildlife & Parks and the Wild Sheep Foundation partnered to test a non-chemical, soil nutrient–based approach to habitat restoration using NutraFix.

The Problem

The island’s south-facing slopes—critical forage areas for the bighorn sheep herd—were shifting from diverse native plant communities to annual grass dominance. This change threatens:

• Forage quality

• Soil health

• Wildfire risk

• Long-term habitat stability
   

A sustainable restoration solution was needed.

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🔗 Rangeland Analysis Platform

Site Challenges

Restoration work had to account for:

• Multiple invasion patterns (disturbed, native, forest-edge sites)

• Highly variable vegetation response from year to year

• No clear “threshold” for when treatment becomes necessary

• Steep slopes where invasives spread rapidly

• Sensitive native plants, such as arrowleaf balsamroot and rough fescue
   

Researchers selected three representative sites—including Eagle Cove—to evaluate nutrient-based restoration.

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Application Rates & Methods

In September 2018:

• NutraFix® Micronutrient Fertilizer was applied to test plots at:

  • Low rate: 212 lbs/acre

  • High rate: 424 lbs/acre

• Granular fertilizer was applied with a hand broadcast spreader

• Each research plot measured 1,600 sq ft

• No herbicides were used during the application phase
   

Learn more about application methods:
🔗 How NutraFix Works