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CASE STUDY 3 
Wild Horse Island, Flathead Lake Montana

LOCATION:

Location:  Northwest Montana

PROPERTY OWNERSHIP:

Public Wildlife Management Area

BACKGROUND:

Wildhorse Island is renown for its iconic wildlife include wild horses and bighorn sheep.  The populations are protected in part by their island refuge which is managed for wildlife.  The largest bighorn sheep skull in the world was found on the island in the year 2016 kindling excitement for the conservation of bighorn sheep in this natural environment.

PROBLEM:

Annual grasses have begun to encroach on the south-facing grasslands used by bighorn sheep for forage leading to concern for habitat quality and parallel bighorn sheep fitness. The Rangeland Analysis Platform (https://rangelands.app/) was used to estimate the cover of both perennial and annual grasses on the south-facing slopes and suggests that perennial grasses have declined from 50% to 40% since 1984 while annual grass have replaced them and increased from 15 to 20% during the same period.

APPROACH:

Three application rates and three habitat types were selected to demonstrate the effectiveness of micronutrient fertilization in promoting the growth of perennial grasses. The sites selected were a disturbed site where the soil was previously tilled by homesteading, a south-facing natural grassland (Eagle Cove Site) and a ponderosa pine understory community dominated by rough fescue.

GOAL:

Demonstrate that innovative fertilizer-based treatments can be used to promote the growth of perennial grasses allowing them to outcompete annual invasive grasses.

APPLICATION RATES:

Granular  350 pounds fertilizer/acre

Granular  Low Rate (175 pounds/acre), Medium Rate (350 pounds/acre), High Rate (525 pounds/acre) 

APPLICATION METHOD:

Granular fertilizer was applied using a hand broadcast spreader to 1600 square foot plots in September 2018.

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