Final answer:
Cheatgrass colonization affects the climax community by outcompeting existing grasses and leading to decreased species diversity. It creates a transient climax community that is maintained by grazing and fire.
Step-by-step explanation:
When cheatgrass colonizes rangelands in western North America, it outcompetes existing grasses, leading to decreased species diversity. This happens because cheatgrass has thin blades that can dry out over time, allowing it to thrive in dry conditions. The invasion of cheatgrass creates a transient climax community, meaning it disrupts the existing equilibrium of the ecosystem. These invaded communities end up being maintained by a combination of grazing and fire.