Researchers also recorded various environmental site conditions that may influence the recruitment rate. In a set of randomly located plots within areas where black oaks were known to occur in the Valley, all black oaks were inventoried, and assigned to one of several size classes. Recruitment Rate StudyĪnother study looked at the recruitment rate-essentially the “birth” and retention rate-for oak seedlings and saplings. In a healthy population, there should be many oak tree seedlings.