Nutritional ecology of selected Scandinavian tree species with special emphasis on hardwoods

Sammanfattning: This thesis considers several important aspects of nutrient dynamics and allocation in adult stands of Swedish forest tree species (Quercus robur L., Tilia cordata Mill., Fraxinus excelsior L., Betula pendula Roth., Fagus sylvatica L. and Picea abies (L.) Karst) planted on the same soils. Differences between species in macro- (N, P, K, Ca, Mg, S), and micro- (B, Cu, Fe, Mn, Zn) nutrient levels in aboveground biomass, in re-translocation and in fluxes of the elements prior to leaf senescence (via litterfall and throughfall) and in their interactions with soil chemistry were examined. With the exception of Fe in spruce stemwood, nutrient levels in the foliage were considerably higher than in stemwood. Differences between the species in terms of stemwood concentrations only partly corresponded to foliar differences between the species, indicating that nutrient mobility and allocation differed between the species. An investigation of nutrient fluxes in a deciduous forest during the period of leaf senescence showed that, with the exception of K in an ash stand, the nutrient input to the soil surface via leaf litterfall was considerably higher than the throughfall fluxes. The amounts of elements in the throughfall per unit stand leaf area showed a clear dependency on the original amounts in the leaves and on the species’ susceptibility to foliar leaching, which was highest in ash leaves. Nutrient resorption prior to leaf senescence was high for N, P, K and S (accounting for 30-70% of the green leaf contents). Cu and Fe were the most efficiently resorbed micronutrients. Inter-specific differences in nutrient resorption efficiency were also observed. The study clearly demonstrated that stands with different species planted on former agricultural land had differing impacts, after just 40 years of growth, on the chemical characteristics of the uppermost layer of the mineral soil. The most prominent differences were between lime stands (which had considerably higher pH, base saturation, base cations and boron pools) and spruce stands (which had the most acidifying effect on the mineral topsoils). Among the deciduous species, beech had the most similar effect to spruce on topsoil chemistry. Differences in nutrient dynamics in studied species should be taken into account when using trees of different species in environmental monitoring and when assessing their nutrient status. The differences are also of particular importance for evaluating the effects of different forest management strategies on long-term nutrient sustainability.