Impact of three silvicultural treatments on weevil incidence, growth, phenology, and branch-level dynamics of Pinus strobus from large and small populations

Our goal was to quantify tree- and branch-level components of growth response to three silvicultural treatments (STs), and weevil incidence in white pine (Pinus strobus L.) from large, central populations in Ontario (ON) versus small, isolated populations in Newfoundland (NL). Light levels were 100%, 42.0%, and 20.4% transmittance for the full-sun, intermediate-shade, and high-shade STs. After 8 years, the overall incidence of weevil infestation was 42.1%, 23.4%, and 13.7% for the full-sun, intermediate-shade, and high-shade STs, respectively (P < 0.001). Weevil impact on total height and volume averaged -13.2% and -11.8%. Analysis of dominant lateral shoots showed that ON populations had 32% longer shoots than the NL populations. Bud set difference was a primary determinant of shoot-length growth differences between regions: Julian days 171 and 184 for the NL and ON populations, respectively. The primary determining factors related to shoot length were the number of needle bundles and region, driven by light levels and day length, respectively, and the internode length, probably through inbreeding effects. Total height and diameter showed a positive curvilinear relationship to light level. To maximize fitness, NL conservation strategies should also now consider introducing adaptive trait variation in the context of anticipated climate change.