Forest humus forms as a playground for studying aboveground-belowground relationships: Part 2, a case study along the dynamics of a broadleaved plain forest ecosystem

A set of research studies has been performed over a period of 10 years on the silvicultural cycle of an even-aged beech forest in Normandy, France. The striking results about both soil functioning (litter decomposition, N cycling, soil C stock) and soil biota (microorganisms, mesofauna, and macrofauna) are presented with the goal of developing an empirical model of the successional patterns of aboveground-belowground relationships in forests. Our purpose was to test the hypothesis stating that the best performance of this forest ecosystem, as high organic matter recycling and low biogenic element losses, is achieved in an ecological stage exhibiting limiting similarity in functional traits and maximizing traits complementary for both plant and soil communities. The present synthesis showed that this hypothesis seems to be confirmed for a late successional stage, i.e., a mature even-aged forest with a closed canopy. The most organized communities, on the basis of ecological requirement similarity, were found in 130 year-old stands. These stands also support the greatest values in microbial functional diversity, in soil C stock and in nitrogen mineralization. Nitrogen losses were the lowest in 95 year-old stands. We also provide some methodological advices for using humus forms for the study of aboveground-belowground relationships in forest ecosystems.