Tree species differ in their effects on soil properties and biogeochemical cycles. The supply of nitrogen typically differs by two-fold under the influence of different species on the same soil types, and rates of trace gas fluxes (including NO, N20 and CH4) may differ even more. The influence of global changes on soils (and feedback between soils and the atmosphere) will depend more strongly on changes in the distributions of tree species across landscapes, than on direct effects of climate on soils. This book examines the state of knowledge of the effects of tree species on soils, considering evidence from broad natural gradients in species distributions, and from 'common garden' experiments where several species have been planted on the same site. Topics include the influence of the chemistry of forest litter on soil biogeochemistry, the dependence of soil biotic communities on tree species, and the interactions of physical, chemical and biological factors in determining the overall effects of different species. Case studies from across North America, Europe, Russia, South America and Australia illustrate the key role played by tree species in determining long-term development and sustainability of soils.