Question: Do beech and hornbeam differ in undergrowth species diversity, and could these differences be explained by mass
of the organic layer, pH or soil moisture? Could species richness under beech and hornbeam be explained by differences in
Location: Ancient forests dominated by beech and hornbeam in Luxembourg, on decalcified and lime-rich parent
Methods: Species composition and soil characteristics, i.e. mass of the organic layer, pH, moisture content,
bulk density and air-filled pore space, were determined under beech and hornbeam on decalcified marl and limestone, and analysed
with cluster analysis, correspondence analysis and ANOVA, with tree species and parent material as independent factors. Net
N mineralization, nitrification and N in soil and microbial biomass were determined in a laboratory incubation experiment
over a pH gradient, and correlated with species richness.
Results: Species richness was lower under beech than under hornbeam
on both decalcified marl and on limestone. Mass of the organic layer was higher under beech in all cases, but pH and soil
moisture only differed between tree species on decalcified marl. Species richness increased with soil N, microbial N and nitrification
in the mineral topsoil, but was not correlated with net N mineralization, and was negatively correlated with nitrification
in the organic layer and with efficiency of N mineralization per unit microbe.
Conclusion: Litter quality affected species
richness on both limestone and decalcified marl via the organic layer, but only on decalcified marl in terms of pH or soil
moisture. Species richness did not seem to be stimulated by high overall net N mineralization or high nitrate availability
in the organic layer, but only by high nitrate in the mineral topsoil.