Distribution and diversity of tree species with respect to soil electrical characteristics in Finnish Lapland

Soil dielectric permittivity (epsilon), which is dependent on soil water content (theta(v)), and electrical conductivity (sigma), which is dependent on soil solute concentration, were measured in the immediate vicinity of 7596 mature trees naturally established on glacial deposits across granitoid and greenstone assemblages in Finnish Lapland (67 degrees 30'N-68 degrees 40'N). The proportions of the main timber species Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.), and downy birch (Betula pubescens Ehrh.) or the diversity of tree species were not affected by the temperature sum (between 750 and 600 degree-days), but the occurrences were strongly influenced by the soil's electrical characteristics. Scots pine and silver birch (Betula pendula Roth) were found to only occupy dry soils (fixed effect estimates epsilon(p) = 8.5 and epsilon(sb) = 8.3) with low solute concentration (sigma(p) = 0.64 mS(.)m-1 and sigma(sb) = 0.56 mS(.)m-1), while Norway spruce, downy birch, aspen (Populus tremula L.) and sallow (Salix caprea L.) occupied sites with higher soil moisture (epsilon(s) = 17.0, epsilon(db) = 14.7, epsilon(a) = 16.7, and epsilon(sa) = 16.7) and solute concentration (sigma(s) = 0.96 mS(.)m-1, sigma(db) = 0.90 mS(.)m-1, sigma(a) = 1.07 mS(.)m-1, and sigma(sa) = 0.93 mS(.)m-1). Species diversity was found to be at its highest with the following soil parameters: 12 < epsilon < 15 and 0.8 < sigma < 1.2 mS(.)m-1. Scots pine was concentrated on tills derived from granitoid rocks. Norway spruce dominated sites on tills particularly derived from the mafic metavolcanic rocks of the Greenstone Belt but did not occur on tills derived from granulite. The edaphic constraint for pine appeared to be theta(v) > 0.27 cm3.cm(-3) (epsilon > 15) and for spruce sigma < 0.5 mS(.)m-1, respectively.