Pioneer

A pioneer is the first plant to colonize a new site, which is often seen with western yarrow on over forged sites.

A pioneer is the first plant to colonize a new site or being the change from one stage of succession to another.

For example, western yarrow is often a pioneer species and considered an increaser where the forage resource has been over utilized. It is seldom regarded as a problematic opportunist except on heavily disturbed, arable sites with favorable environmental conditions.