The ecological effects of grassland afforestation have been investigated in a comparative study between different tree species on a sandy-loam substrate. After 20 yr of forest, the earthworm communities and litter decomposition rates differed considerably, depending on the quality and quantity of the litter fractions produced. Under Quercus palustris, earthworm biomass diminished, and litter accumulation and soil acidification had begun. The results have practical consequences for the choice of tree species in new forest plantations.