Impact of Tilia Platyphyllos Scop., Fraxinus excelsior L., Acer pseudoplatanus L., Quercus robur L. and Fagus sylvatica L. on earthworm biomass and physico-chemical properties of a loamy topsoil

Impact of hardwoods of different humus forms on earthworm biomass and physico-chemical properties of the topsoil of a loamy acid brown forest soil after a time-span of 60–65 years was examined in the Forest of Halle near Brussels. Three sites were selected in which homogeneous stands of mull-forming tree species (Tilia platyphyllos Scop., Fraxinus excelsior L. and Acer pseudoplatanus L.) were compared with adjacent stands of Fagus sylvatica L. and/or Quercus robur L. where a mullmoder had developed. Total earthworm biomass was conspicuously higher at the sites that supported Tilia and Acer as mull-forming hardwoods. Study of soil acidity revealed that there were marked differences in pH and base saturation in the A- and E-horizon between hardwoods developing different humus forms. The topsoil beneath mull-forming hardwoods was generally higher in pH and base saturation with the largest differences being displayed between Tilia and Fagus/Quercus. C/N ratios were significantly lower in the topsoil under Acer. Significant differences in physical soil properties among humus form were also evident. The A-horizon under mull-forming species was higher in total porosity, aeration porosity and saturated hydraulic conductivity. The bulk density was only significantly lower under Fraxinus. The E-horizon of the mull stands was lower in bulk density and higher in aeration porosity but this was linked by a reduction in water-filled porosity. The study indicated that mull-forming tree species differed in ability to improve or maintain productivity of the studied soil type.