Regularities and patterns in the spring phenology of some boreal trees

Phenological time series of flowering and bud burst of Populus tremula (L.) and Betula sp., and the flowering of Pinus sylvestris (L.), Alnus glutinos a (L.) and Alnus incana (L.) were constructed from data collected in Finlan d during the period 1896-1955. The resulting combined time series were exam ined with two aims in mind: first, to determine the phenological regulariti es between different species and, second, to detect patterns of spring adva ncement over a geographically large area. The results indicate that the geo graphical pattern of spring advancement is rather uniform from year to year , and between different species. Furthermore, the mechanisms regulating the timing of phenological events in different species seem to function in a s imilar way, suggesting an unanimous optimal response to climatic conditions .