The effect of temperature on site index in western Canada and Scandinavia estimated from IUFRO Pinus contorta provenance experiments

Site index was calculated for 78 experimental plantations in western Canada and northern Finland and Sweden, representing a wide range of site environments where lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) is considered as a potential afforestation species. The plantations and provenances belong to the International Union of Forest Research Organizations' international provenance testing program, and estimates of site index (projected 50-year height) were based on height growth of recommended provenances. The estimated site indices were used in regression analyses with temperature data and estimated soil fertilities to predict the change in forest production due to a warmer climate, which may follow an expected rise in atmospheric CO2. The influence of temperature was strong and considerably stronger in northern Finland and Sweden than in Canada. The relationships differed between the two continents and between sites located north of 56°N and south of that latitude. Soil fertility had a small but significant influence. Estimates of increases in site index and potential productivity in different scenarios for increases in temperature sum and average July temperatures are given.