The Problem = Encroachment of noxious weeds:
This problem is not just an Agricultural issue, it’s a societal issue. Non–native invasive plants are the number one environmental threat to western wildlands. These plants have quadrupled their range in the last 10 years. If allowed to spread at their current rate for the next 100 years, they will be the dominant plants on the western rangelands. It is estimated that more than 17 million acres of public lands have serious weed infestations and that an additional 5000 acres become infested each day. Encroachment of non–native weeds reduces forage availability for wildlife and livestock.
- Montana Knapweeds: Identification, Biology, and Management
- Leafy Spurge: Biology, Ecology and Management
Forbs are a critical source of food supply for wildlife species, and noxious weeds nearly eliminate the forb component of the landscape. As a result, wildlife food sources are significantly limited. This has an indirect impact on wildlife–associated recreation opportunities and expenditures in most states. This secondary impact on the economy is unknown, but is estimated to range between $200 to $300 million each year.
Noxious weeds gradually replace grass species until the landscape diversity is significantly compromised. The influence of leafy spurge, alone, drastically affects cattle grazing utilization. When leafy spurge patches exceed an infestation level of approximately 40% — ranchers observe little utilization by cattle (J. Range Mange, 45:405). This results in a loss of land usage and value, as there is minimal available cattle/wildlife grazing and the use of chemicals to control invasive plants exceeds the value of the land.
The Solution = Utilization of sheep for management of noxious weeds:
The Montana Sheep Institute (MSI) has repeatedly demonstrated that sheep can be used to control non–native noxious weeds. Selective grazing of unwanted plants helps control their growth. As their growth is limited, their roots and strength are compromised. As a result, the lesser grazed native plants are able to grow larger root bases and plants and gradually re–establish themselves.
Sites involved in controlled sheep grazing demonstrate that sheep will selectively graze leafy spurge and knapweed. For example, in studies examining the utilization of leafy spurge by grazing sheep, there was a 60–70% utilization of leafy spurge and a 30–40% utilization of grass. In similar studies looking at knapweed — there was a 50–60% utilization of knapweed, 30–40% utilization of grass, and 10% utilization of forbs. Over time this type of grazing weakens the weed species and favors the re–establishment of grass and forb species.
Most of the sites involved in the MSI program have been depredated by weeds to a state that most traditional weed control methods (herbicides) are economically impractical. Therefore, utilizing sheep provides a cost effective means of controlling weeds on these lands.