Changes in forest-floor chemistry caused by a birch admixture in Norway spruce stands

The aim of this study was to determine how soil chemistry and the distribut ion of fine roots (<1 mm) in the organic and upper mineral soil horizons we re affected by an admixture of birch (Betula pendula Roth and B. pubescens Ehrh.) in Norway spruce (Picea abies (L.) Karst) stands. The surface organi c horizons (LF and H) and mineral soil were characterized to a depth of 10 cm on three sites in southern and central Sweden. On these sites, replicate d plots had been established that contained either ca. 30-year-old birch gr owing as a shelter over similar-aged spruce (mixed plots) or spruce only. T he treatments had been created 8-11 years before this study was done. A fou rth site, with plots containing ca. 90-year-old spruce or birch/spruce, and a fifth site, with 30-year-old spruce and a low admixture (12% by basal ar ea) of birch, were also included in the study. Concentrations of Ca and Mg and pH in the LF layer were significantly higher in plots with a birch admi xture. In the H-horizon, concentrations of K, Ca and Mg were significantly higher in mixed plots than in plots with pure spruce. Consequently, base sa turation was higher in mixed plots than in pure spruce plots. A shelter of birch decreased the total amount of spruce fine roots (<1 mm), as revealed at one of the sites. Total fine root biomass (birch + spruce) in the organi c and mineral soil horizons (to 10 cm) did not differ significantly between the pure spruce stands and the spruce stands with a birch shelter. (C) 200 0 Elsevier Science B.V. All rights reserved.