McGrath, there are huge regions of land here being invaded by non-native plants that take over the habitat, crowding out native plants and destroying wildlife and livestock forage. Kudzu was referred to earlier in the thread. Two of the main noxious weeds in Montana are spotted knapweed and leafy spurge. Sometimes non-native plants are poisonous to livestock, sometimes they just choke out all the healthy native plants. More info at this site CLICK "Areas dominated by leafy spurge receive much less use by deer (3 times less use) and bison (4 times less use) compared with similar uninfested areas. On native bunchgrass sites in Montana, dense spotted knapweed populations reduce available winter forage for elk by 50 to 90 percent."