Spatial variability of throughfall chemistry and selected soil properties as influenced by stem distance in a mature Norway spruce (Picea abies,Karst.) stand

Our aims were to investigate the spatial variability of throughfall chemistry and soil parameters as influenced by stem distance and to evaluate the implication of the observed systematic and random patterns for the sampling strategy.One hundred throughfall samplers with a sampling area of 106 cm² each were established in a systematic grid around 5 trees in a mature Norway spruce; site of the Fichtelgebirge (Germany). One hundred soil cores were taken with an auger of 50 cm² next to the throughfall samplers. Soil samples were stratified according to genetic soil horizons and analysed for pH, exchangeable NH₄⁺, SO₄^2– and total-S. Throughfall samples were collected over a period of 6 months. For each sampler an aliquod sample was mixed over the observation period and analysed for major ions.The spatial variability of the element concentrations in throughfall, expressed by the coefficient of variance, was 21–164%, depending on the element considered. For precipitation volume, the coefficient of variance was only 3%. The distance to the stem influenced most element concentrations in throughfall with increasing concentrations approaching the stem. Steepest gradients were observed in case of SO₄^2– and H⁺.The spatial variability of the investigated soil parameters was also very high with the exception of pH. The SO₄^2– content of the forest floor reflected the gradients observed in throughfall, while for the other investigated soil parameters and soil horizons no significant relations to stem distance were found.To determine site representative throughfall concentrations and soil properties with the sample volumes and time intervals we used, the number of samples required to get a statistical error of less than 10% (with 95% probability) can be very high. In case of throughfall, more than 100, and in case of the soil parameters, more than 300 replicates would be required.