Impacts of stressful weather events on forest ecosystems in south Sweden

Abstract: Coniferous as spruce (more specifically Norway spruce, Picea abies) and deciduous species like European beech (Fagus sylvatica) and oak (Quercus spp.) co exist in south Sweden. In perspective of climate change, species composition of Swedish forests is assumed to change. Observed climate on the period 1950-2010 prove that a general warming trend is occurring in southern Sweden, and that vegetation growth period is getting longer. From the observed weather data, annual precipitation and minimum temperature in spring are highlighted in order to analyse the response of the three tree species. Extreme years are distinguished. Responses from the trees are studied in terms of onset and end of vegetation period and length of vegetation period, for each species, using observations from satellite data (MODIS) for the period 2000-2009. Variations observed during extreme years constitute the basis for an interpretation of the species-specific response to climate events, qualified as stressful for the vegetation. Further on, the discussion is relating stressful weather events with tree defence capacity and biotic stresses (e.g insect outbreaks) and their role in a disturbance system. Links to forest ecosystem are made through processes like regeneration, competition and migration. Climate change projections are analysed in order to study the potential reactions of the three species in South Sweden with climate shifts according the observations made in the previous parts.