On both rangelands and forested areas, invasive plants crowd out more desirable and nutritious forage, cause soil erosion, and poison some livestock. Public land ranges and family ranches are rendered nearly useless for grazing. Unfortunately, the proliferation of weeds is causing an ever increasing degradation of this habitat. As weed infestations become severe, diversity declines and wildlife habitat quality degenerates. Studies in Montana show that spotted knapweed invasions reduced available winter forage for elk between fifty and ninety percent.
Weeds reduce land values, causing damaging economic impacts to local communities.
Numerous studies and repeated landowner experiences show that weeds commonly reduce livestock carrying capacity between thirty-five and ninety percent. Weeds cause abandonment of wildland recreation sites and trails. Hunters and bird dogs are reluctant to use land infested with thistles and weeds diminish the enjoyment of recreationists along trails and near campgrounds. For example, float boaters encountering the spines of thistles and the stickery knapweeds, frequently have a difficult time finding a suitable campsite to place their tents and sleeping bags. Similarly, fishing along stream banks is often impossible because of the pain inflicted by thistles.