Converting plantations to uneven-aged stands: Effects of harvest type, group opening size, orientation, and canopy position on residual tree development

Abstract

Uneven-aged silviculture is becoming increasingly popular as a tool to restore and manage forests for multiple benefits. However, there are few studies that evaluate the growth response of shade intolerant pine species in the southeastern United States to regeneration harvests during stand conversion process. We utilized an existing long-term, operational scale, replicated stand conversion trial in the southeastern United States to evaluate the effects of two initial stand conversion harvest treatments (uniform shelterwood and group cuttings) and an uncut control on the growth of residual slash pine (Pinus elliottii Englm.) trees over a 7-year period. In addition, we explored the influence of group opening size, canopy position and distance from group opening border on residual tree growth. Tree growth, measured as basal area increment (BAI), was significantly affected by harvest treatment, canopy position, group opening size, and distance of tree from group opening border. Uniform shelterwood harvest led to significantly higher mean tree BAI (25.04 cm2) than group cuttings (16.56 cm2) and uncut control (11.88 cm2), and group cutting harvest had significantly higher mean BAI than the uncut control (p < 0.001). Within the group cutting treatment, 0.1 ha group opening had significantly less mean BAI (13.33 cm2) than all other group opening sizes (0.2 ha -17.81 cm2, 0.4 ha - 17.80 cm2, and 0.8 ha -17.92 cm2). Residual trees located within 0–5 m from the group opening border had significantly higher mean BAI than trees found further away (5–10 m or 10–15 m) from the group opening border (p < 0.001). However, the orientation of trees around the group opening (i.e., North, South, East, and West sides) did not have a significant effect on mean BAI (p = 0.813). Overall, canopy position influenced growth significantly, with dominant and codominant trees exhibiting statistically greater growth response than intermediate and suppressed trees (p < 0.001). Understanding how residual trees respond to harvests during stand conversion is critical for fully assessing the efficacy of these systems with slash pine. The findings of this study will assist land managers in predicting slash pine ingrowth to larger size classes in uneven-aged systems with varying harvest gap size.