Effects of three species and nutrient application on distribution and budgets of base cations in Swedish forest ecosystems

Previous studies have revealed that a depletion of pools of exchangeable base cations (Ca, Mg, K) has taken place in southern Swedish forest soils over recent decades. Unless compensated for, such depletion could endanger the maintenance of natural site productivity levels. This thesis investigates i) the effects of tree species and NP fertilization on nutrient uptake, ii) effects of uptake on nutrient pools in soils, iii) effects of tree species on base cation budgets, and iv) effects of wood ash application on nutrient and acidity pools in the soil. Effects of tree species and wood ash application were determined in two experiments for each factor, one in NE Sweden and one in SW Sweden, respectively. A supplementary budget investigation of the tree species site in SW Sweden was conducted using a weathering model and literature data. Effects of long-term NP fertilization were investigated at the Straasan experiment in Central Sweden. Results showed that tree species may differ considerably in nutrient uptake at similar production levels. At both sites, Norway spruce had a high Ca and K uptake in relation to species with similar production. In stands with higher tree uptake of base cations, either due to species-related differences or as a result of fertilization, a greater depletion in the soil pools was detected in most cases. Species-related differences were found only in the upper soil horizons. The budget study of the SW tree species experiment indicated that higher uptake rates were correlated with lower leaching rates. The NP fertilization study indicated that the increased uptake of base cations induced by the fertilization prevented leaching losses. After two years, addition of granulated wood ash had increased base cation pools and decreased acidity mainly in the upper layers of the soils. It was concluded that the remedial rate of wood ash application for a site would partly depend on species. In areas where the availability of mobile anions is high, base cation losses from the ecosystem could be minimized if a high tree uptake is maintained, and whole-tree harvest and proper ash recycling is carried out.