To assess the long-term effects of the projected climatic change on Scots pine and Norway spruce in Finland, observations were made on the timing of bud burst in provenance experiments established in 1931-1932 and in 1978. Significant differences in the timing of bud burst were found between seed origins. The northernmost origins flushed earlier than origins from southern regions. However, no correlation was found between the effective temperature sum at which bud burst took place and the annual mean temperature sum at the original location, probably because the experiments included origins from southerly high-altitude sites. When the degree days before bud burst in the 1931 and 1978 Norway spruce experiments at Punkaharju were compared, it appeared that, in the older experiment, the populations had adapted to the environment at the new site as a result of selective thinning.

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Old provenance experiments with Scots pine and Norway spruce in Finland were used for assessing the long-term effects of the projected climatic change on forest trees. The northernmost origins showed an increase in wood production when transferred southwards into a climate with an annual mean effective temperature sum close to that which is expected in northern areas as a result of the projected climatic change. A model is constructed with the estimated changes in wood production as a function of the annual mean temperature sum at the original location and the change in the annual mean temperature sum caused by the geographical transfer. The major changes in wood production are expected to occur in the northernmost areas of tree growth.

Impacts of elevated tropospheric ozone and soil nitrogen amendment on two native European aspen ( Populus tremula L.) and eight hybrid aspen (P. tremula L. × Populus tremuloides Michx.) clones were studied in a free-air ozone exposure system. Potted saplings were exposed to ambient (ca. 20 ppb) or 1.5× ambient ozone and two levels of soil nitrogen (39 and 78 kg N·ha–1·year–1 in the first year, 60 and 140 kg N·ha–1·year–1 in the second year for low-nitrogen and high-nitrogen treatments, respectively) over two growing seasons. The plants were measured for photosynthesis, chlorophyll fluorescence, and biomass accumulation. Ozone decreased leaf-level net photosynthesis (Asat) in particular early in the growing season and maximum quantum yield of photosystem II (Fv/Fm) at the end of the growing season. Nitrogen amendment increased the growth of all plant parts and mitigated the adverse ozone effects. There were significant differences in ozone responses among the clones, and we were able to cluster the clones into sensitivity groups based on their growth responses. The most ozone-tolerant genotypes were hybrid aspen clones, indicating that populations that have already experienced selection for ozone-tolerant genotypes should be used to cross-breed with ozone-sensitive populations to achieve tolerance of a climate with increasing tropospheric ozone concentrations.

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