About

The purpose of this workshop was to bring together all the diverse interests involved with sheep and goat grazing for weed control along with the wildlife specialists who have concerns about the possible impacts of this practice.  The workshop was a success in establishing dialogue and mutual understanding among all interests.  Hopefully, the communication started at this workshop will continue.  We offer all the presentations from the workshop so that those interested in these issues can continue to refer to all the useful information presented during the workshop.

Grazing by domestic sheep and goats can be an effective tool for controlling noxious weeds on private and public lands; however, there are certain potential complications including impacts on native predators and the possibility of disease transmission.  Sheep and goats are most commonly used to control leafy spurge (Euphorbia esula) and spotted knapweed (Centaurea maculosa) but have also been used to graze toadflax (Linaria vulgaris), hound’s-tongue (Cynoglossum officinale), and tansy (Tanacetum vulgare).  Many other weed species can also be grazed.  To be effective, grazing must be managed intensively, taking into account the length of time grazed, season, density of grazers, species of grazers, phenology, target species, and desired species.  Clear objectives for success should be agreed upon before grazing begins and progress should be monitored closely.  Revegetation may be necessary to rehabilitate/restore certain areas of heavy weed infestation if site availability, native seed availability, and/or species performance limit native plant establishment. 

When livestock are used to graze weeds in the Intermountain West, they provide a prey source and potential attractant to predators such as coyotes, wolves, grizzly bears, black bears, and mountain lions.  Wolves and bears are particularly likely to depredate sheep.  This causes economic losses to the producer and biological losses to the ecosystem as the predators are generally either relocated or removed from the wild.  There are many ways to limit these losses such as grazing during certain seasons, removing livestock carcasses, using a full-time herder, guard dogs, and portable electric fencing in bedding grounds.

Domestic sheep can also affect wildlife through disease transmission.  Wild bighorn sheep are susceptible to several diseases carried by domestic sheep and goats and epidemics can decimate wild sheep populations.  There are fewer options to limit this type of impact on wildlife populations but the general consensus among wildlife biologists and veterinarians is that grazing of domestic sheep and goats in wild sheep habitat should either be done in a very controlled manner (with a full-time herder to ensure no contact with wild sheep) or not at all.

Lastly, grazing by domestic livestock can affect wildlife habitat through direct competition for desired forbs and grasses.  Conversely, grazing may enhance wildlife habitat through weed control.  This type of detrimental competition is more easily controlled than other problems through clear identification of management objectives, wildlife species of interest, and livestock species used for grazing.

Overall, the use of domestic sheep and goats to control noxious weeds is a promising additional tool to restore ecosystem health through weed control.  Care should always be taken to assure that the grazing does not have significant detrimental impacts. Sometimes, grazing may be the only tool necessary for weed control, but at other times, it might be beneficial to use other methods such as hand-pulling, herbicides, prescribed burns, etc. in conjunction with or in place of grazing.  In the end, every weed infestation is site-specific and weed control must be integrated into a unified management strategy considering the biology and ecology of domestic animals and the maintenance of healthy native plants and animals in the target area. 

Thanks to everyone who participated!

Chris Servheen, US Fish and Wildlife Service

College of Forestry and Conservation 

University of Montana

grizz@umontana.edu