Forage Value of Invasive Species to the Diet of Rocky Mountain Elk

Abstract

The winter range of Rocky Mountain elk (Cervus canadensis) throughout the Intermountain West is threatened by invasive plant species including spotted knapweed (Centaurea maculosa) and cheatgrass (Bromus tectorum). These species have direct impacts on pasture and grasslands resulting in substantial forage losses and costs associated with prevention and mitigation. Invasive species cost the United States $120 billion annually, with knapweed estimated to cost $14 million annually to the economy of Montana. Knapweed and cheatgrass are aggressive invaders, and are generally more common in disturbed sites resulting from overgrazing, fire, cultivation, or other forms of ground disturbance, but can invade and transform relatively undisturbed rangeland. The biochemical and physiological characteristics of knapweed allow it to outcompete native plants through greater resource acquisition and inhibition of native plant growth and seed germination. Similarly, cheatgrass may inhibit native grass germination by rapidly outcompeting natives for soil moisture and nitrogen and increase fine dry fuels leading to increased fire intervals that favor cheatgrass dominance.