In eastern forests, openings dominated by grasses, forbs, or shrubs are areas of conservation concern because they typically contain endemic, threatened, and rare plants. Understanding the ecology and mechanisms of tree encroachment would be valuable for conservation managers and would add to a substantial body of literature on forest openings. In this study, we worked in grass-dominated forest openings on Buffalo Mountain, Virginia using a method that combined dendrochronology and belt transects to assess tree encroachment. We discovered both stable ecotones and areas where trees were invading the formerly grass-dominated openings. Both gradual and episodic patterns of tree encroachment were identified; however, successful tree establishment always initiated from the edge of the forest-grass ecotone and progressed towards the center of the opening rather than occurring across the entire forest opening. This spatial pattern of recruitment implies that successional facilitation is necessary for tree encroachment in forested openings at Buffalo Mountain.