Growth responses of Abies amabilis advance regeneration to overstory removal, nitrogen fertilization and release from Vaccinium competition

Abies amabilis advance regeneration may take several years to acclimate to overstory removal, and poor performance has been attributed to unfavorable microclimate, nutrient stress, and competition from ericaceous vegetation. Our objective was to examine potential factors limiting growth of advance regeneration of Abies amabilis on a montane site in coastal British Columbia. In 1996, 72 experimental plots were established at the Montane Alternative Silvicultural Systems site, Vancouver Island, to provide a design with 12 plots within each of 2 replicate blocks of 3 overstory removal treatments [clearcut (CC), shelterwood (SW), green tree retention (GT)]. Two plots within each replicate block were randomly allocated to each level of 3 nitrogen (N) treatments (0, 100, 250 kg ha-1, applied as urea) × 2 Vaccinium treatments (shoots present or removed).The three overstory removal treatments differed in the amount of solar radiation received beneath the canopy, in the order CC > GT > SW. Three to five growing seasons after treatment, advance regeneration in the GT and CC treatments exposed to >70% incoming solar radiation had the greatest height, stem diameter, and dry weight. N content, new N uptake (inferred from uptake of applied 15N), and allocation of uptake to new shoots were greatest in the CC followed by the GT and SW treatments. N fertilization had no effect on seedling growth. Removal of Vaccinium shoots increased stem diameter of advance regeneration, and increased new shoot dry weight in the GT treatment. Allocation of N to new shoots was greatest in advance regeneration from plots where Vaccinium was removed.