The floor of a deciduous forest consists typically of “brown earth”, a kind of soil characterized by a relative abundance of iron compounds that are responsible for its brown hue. The predominant pedogenetic process (accordingly called brunification) determines the formation of clay-humic complexes where the two components are bound together by iron deriving from the geochemical alteration of the parent rock. The process of brunification of soil is characteristic of temperate climate zones, which do not have extremes of temperature or lack of atmospheric moisture. The litter layer is rich in nutrients and easily degradable.
Brown earth is fertile, with abundant nutrients in the litter layer, rich in humus and home to a large variety of ground-dwelling animals. It is very stable and allows for an easy recovery of the vegetation when removed. For these reasons, brown forest soil supports the ecosystem’s ability to recover its normal structure and function after a disturbance (“resilience”). Furthermore, thanks to its porosity and high degree of soil infiltration capacity and water holding capacity, brown soil can retain large amounts of water and delay runoff during heavy rain falls (water flow regulation capacity).
Brown earth is the result of a slow decomposition and humification process triggered by bacteria, fungi and arthropods that feed on wood and other organic matter that is mixed with the mineral components of rocks broken down through the action of climate and living organisms. The length of time required for soil to form depends on factors such as rainfall, temperature, and parent material, but in deciduous forests the processes of decomposition and humification of organic matter are relatively rapid, normally performed by abundant colonies of bacteria and earthworms, and helped by good aeration, favorable temperature, availability of nutrients, good drainage, and easily degradable litter.