Influence of legacy-tree retention on group-selection opening persistence

Single-tree selection, a common uneven-aged silvicultural technique, has been known to simplify stand structure and reduce species richness over time. Alternative techniques, such as group selection and biological legacy-tree retention, have the potential to achieve more ecologically based management objectives such as enhancing species diversity and stand structural complexity. Forty-nine harvest gaps ranging in area from 200 to 1500m ² and 20 reference sites were evaluated in 2004 and 2011. Group-selection openings were assessed to determine whether the range of gap sizes considered would persist long enough for regenerating mid-tolerant tree species to successfully recruit into the overstory. We estimated gap closure rates based on observed rates of lateral crown expansion into the openings by border trees and legacy trees. Canopy gaps were projected to remain open for 41-91years depending on legacy-tree retention and initial opening size. Centrally located legacy trees reduced opening longevity most substantially in small openings, but only minimally impacted medium and large gaps. Openings larger than 500m ² were projected to persist long enough for mid-tolerant tree species to successfully recruit into the overstory. Legacy trees responded vigorously to full-crown release (exhibiting nearly a 3-fold increase in diameter increment versus reference trees) and experienced a relatively low mortality rate of 1.17%year ^-1.