Impact of landscape features on spring phenological phases of maple and bird cherry in Estonia

We analysed the spatial distribution of the pollination of maple (Acer platanoides L.) and bird cherry (Prunus padus L.) in Estonia on the basis of phenological data from the time series for 1948-1995, in 27 observation points, and from the special field observation programme 1996-1999, in 46 observation points. Phenological maps show that these springtime phenophases spread in the landscape at a rate of 3-6 days per 100 km, with different rates in early and late springs. The maple has a steeper gradient on northeastern islands and the bird cherry on the western islands; the values of standard deviation have a similar spatial pattern. The distribution of phenological phases in Estonia is influenced by differences between the temperature regimes of the Baltic Sea and inland areas, different climatic conditions in north-eastern Estonia, local altitude-impact of uplands with an absolute height of 150-300 m asl, and the effects of bigger lakes and wetland areas. On the basis of spring phenology, three seasonally different landscape types can be determined in Estonia: (1) Relatively continental South-East Estonian Plain and uplands - have the earliest spring with the smallest deviations and stable intervals between phases, (2) Central, western and northern Estonian plains - with temperate influence of the temperature regime of the Baltic Sea, and big variations from year to year. Large variability is caused by the presence and duration of ice cover on the sea in cold springs, and direct access by warm air masses in early springs. (3) North-east Estonia - has the most boreal climate with longer snow cover and very late spring, influenced by arctic air masses, local influence of the Baltic Sea, uplands, and large wetlands.