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Understory and overstory growth responses to structural retention of mature eastern white pine (Pinus strobus l.)1

Abstract The retention of overstory trees in a shelterwood-with-reserves regeneration method provides structural legacies, but at an unknown cost to white pine regeneration growth. Height, breast height diameter, and basal diameter growth responses of 12–15 year-old naturally regenerated eastern white pine (Pinus strobus L.) to partial overstory removal and pathological pruning (i.e., the removal of lower branches that are most susceptible to blister rust infection) were monitored over four growing seasons in a 110-year-old red pine (Pinus resinosa Ait.) - white pine stand. A two-cut shelterwood-with-reserves system with an average basal area of 23 m2 ha−1 initiated white pine regeneration in 1983. Partial overstory removal in the winter of 1998/99 followed by the July 4th 1999 blowdown event retained an average basal area of 4.5 m2 ha−1 (± 2.3). Five-year white pine seedling growth responses were independent of the level of overstory retention and pruning. Damage from white pine weevil and white pine blister rust were minimal. Residual red and white pines also increased radial growth in response to partial overstory removal. We conclude that a two-cut shelterwood-with-reserves system enhances the structural heterogeneity of the stand without reducing short-term growth of the regeneration. Given low blister rust infection rates, pruning 12–15 year-old white pine under a partial canopy may be unnecessary.