3. Invaders— Annual Weeds 



Canada Thistle 



Curly Cup Gumweed 



If continued heavy use also forces the in- 

 creasers out of a plant community, invader 

 plants will come in to fill their place. In- 

 vaders may not be present at all in the cli- 

 max community, or if present they make 

 up less than 2 1/2 percent of the total com- 

 munity. Invaders are usually not palatable 

 to animals and some in fact may be poison- 



Salsify 



ous, or have thorns or stickers. In Montana 

 some of these low quality grasses are salt- 

 grass, little bluestem, and wild rye. Annual 

 weeds, such as spotted knapweed, baby's 

 breath, salsify, bindweed, curly cup gum- 

 weed, lambsquarter, and Canada thistle of- 

 ten invade grasslands that have been 

 overgrazed or disturbed (figure 3). 



