Soil Animals and Litter Quality as Key Factors to Plant Species Richness, Topsoil Development and Hydrology in Forests on Decalcified Marl

Abstract

Animal activity and litter quality play a key role in forests on decalcified Steinmergelkeuper marls. The dominant trees hornbeam and beech clearly differ in litter quality, which affects earthworm activity and soil formation. Trees were even more important to topsoil characteristics than the subsoil. Under hornbeam, with high-palatable litter, organic layers were thinner, species richness higher and topsoils wetter and less acidic than under beech with more recalcitrant litter. In decalcified marl, lateral clay eluviation leads to differentiation in silty topsoils and clay-rich, water-impermeable Bg-horizons. Depth of the impermeable layer was shallower under hornbeam than under beech. Under hornbeam, formation of silty topsoils is probably counteracted by erosion. High animal activity leads to increased denudation of the surface, macropore systems with pipe flow in the soil, and approximately ten times higher export of soil particles than under beech. Under the low-palatable beech, leaching can continue without interruption, due to protective litter covers, low macroporosity, and throughflow with loss of base cations and clay particles rather than silt and sand. The two trees also showed habitat preferences, which extend their presence in particular habitats beyond the lifespan of individual trees. Hornbeam seedlings were only found under hornbeam, and are probably better adapted to wetness with superficial fine roots. Beech seedlings established everywhere, but further growth may be hampered in wet places due to three-dimensional fine root systems. Hornbeam and beech thus act as ecosystem engineers, with different litter quality and animal activity leading to more suitable habitat conditions for themselves, and development of wet and dry subsystems in the forest.