XVI International Botanical Congess

The timing of bud burst and frost damage risk for leaves of Betula sp. under climatic warming in Finland was examined using two models. In the first the completion of dormancy starts ontogenetic development. The second assumes an additional signal from the light climate to trigger ontogenetic development in the spring. Both models fitted the observed phenological data well, but gave varying results when observed temperatures were adjusted to simulate climatic warming. The estimates for change in average bud burst dates were 2.6 and 5.2 days per 1C of warming for the light climate and dormancy models, respectively. Especially the estimates of frost damage risks diverged: the dormancy model estimated the annual risk to reach 54% in the next 150 years, while the light climate model forecasted almost no risk. Further empirical tests and biochemical studies are required to ascertain the mechanisms controlling phenology, so that credible model extrapolations can be undertaken.