Climatic factors governing plant phenological phases along a Norwegian fjord

In the present project, the time of leaf budding and flowering, and partly also of fruit ripening, was studied over 3 years in different cultivated and native plants on a gradient along a western Norwegian fjord about 300 km long, from oceanic to relatively continental regions. In the plants investigated, flowering of the red currant was most strongly favoured by oceanic conditions in the outermost part of the fjord. On the other hand, flowering of the apple was earliest in the middle district, as were flowering of the common lilac and raspberry, while differences were small between the districts for flowering of the plum and pear. In the inner district, leaf budding of the apple was about 1.5 weeks earlier than flowering of the red currant, while these two phenophases, on average, occurred on the same day in the oceanic district. The time from 1 April to flowering was generally lengthened by increased precipitation in the pear, apple, lilac and raspberry, but not in the red currant and plum. By contrast, the period from leaf budding to flowering was significantly shortened in the plum by high precipitation. The present studies also indicated that leaf budding of the birch was favoured by the high minimum temperature and the relatively high precipitation normally found in the oceanic district. Partial correlations showed that increased precipitation delayed the flowering of both rowan and bird cherry trees; there was also a week effect on bud break in the same two species. The clear conclusion of the present study, therefore, is that various plant species react differently to various climatic factors ("phenological interception"), even in different phenophases within the same species. This means that the various species are best fitted to certain climatic regions and should preferably be planted there if other growth factors are satisfactory.