Short-term forecasts and long-term regional scenarios of climate change effects on Swedish forest phenology

Comprehensive forest phenology data from the Swedish National Phenology Network has been used to produce forecast models of the seasonal phenology on tree species, wild berries and insects, which are made available to the public. One model forecasts the onset, maximum appearance and ending of the budburst and leaf/shoot elongation of the most common tree species in Sweden; Silver birch ( Betula pendula Roth), Downy birch ( B. pubescens Ehrh.), Norway spruce ( Picea abies [L.] H. Karst.) and Scots pine ( Pinus sylvestris L.). Furthermore, a model for the onset, maximum appearance and ending of flowering and ripening of the most common wild berries in Sweden; Cowberry ( Vaccinium vitis-idaea L.) and Bilberry ( V. myrtillus L.), and a model for the timing of the swarming of the Eurasian spruce bark beetle ( Ips typographus Linnaeus, 1758) for the mother generation and, more interestingly, for the coming generations during the same season, are also available. Daily air temperature data from the sites where phenology observations has been undertaken, is used to produce critical accumulated temperatures for when target phenological phases appear. Current year’s weather data, for estimation of the current status, and long-term averages, for predicting the near future, are used to produce seasonal forecasts predicting the timing of e.g. budburst, berry ripening and swarming of first generation offspring that may establish a second generation of beetles. The assigned critical temperature sums for phenological phases to appear in the forecast models have also been applied on scenario temperature data, to explore possible long-term effects of climate change in the Swedish forests. The scenarios predict broadleaf trees to have a 9–41 days earlier start of the season in the period 2070–2099, compared to the reference period 1970–1999, depending on the applied scenarios (average of all sites and species, shortest for RCP2.6 and longest for RCP8.5). A general pattern is that the spruce bark beetle may be able to produce two new generations on one season at the end of the century, in the south this can be the new normal, in the north only occasionally and only under the strongest climate change scenario (RCP8.5). Northern Sweden and local continental areas are expected to experience the least change, compared to southern Sweden and, especially, the maritime west coast area, at least for some of the tested treats.