Effects of climate on growth of lodgepole pine and white spruce following site preparation and its implications in a changing climate

Site preparation and vegetation control can be used to mitigate climate change effects on early plantation growth in boreal forests. In this study, we explored growth of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) and white spruce (Picea glauca (Moench) Voss) in relation to climate and site preparation using 20 years of data collected from studies in British Columbia. Results indicate that up to 45% of the variation in spruce growth and up to 37% of the variation in pine growth over this 20-year period can be explained by selected climatic variables. Monthly climate variables showed a stronger relationship to conifer growth than seasonal and annual variables. Climate variables related to the preceding year accounted for more than half of the variables in the final equations, indicating a lagged response in conifer growth. Future projections indicated that height growth of young lodgepole pine plantations in the subboreal zone could benefit (in the short term) from longer growing seasons by up to 12% on untreated stands. Untreated young white spruce plantations in the boreal zone may suffer height growth decreases of up to 10% due to increased drought stress. Vegetation control and mechanical site preparation treatments appear to mitigate effects of climate change to some extent.