Humus structure during a spruce forest rotation: quantitative changes and relationship to soil biota

Temporal dynamics of edaphic communities affect numerous processes in forests and also strongly influence the soil's organic matter status. We have linked long-term changes in the formation of organic matter (using humus micromorphological analyses) to changes in the soil's community structure during a spruce forest cycle on acid soil. The study was carried out at four sites of different age-classes in the Tharandter forest, Germany. The composition of the deeper humus layers (OH, A) was stable. Herbaceous litter, recent spruce litter, fragmented spruce litter, decomposed litter and faeces and fungi, which contributed to the organic layer (OL and OH horizon), significantly changed during the forestry cycle, especially with the shift from the early stage to intermediate stages. Parallel changes of the faunal assemblage of the soil showed quantitative relations between major stages of the forest development, humus dynamics and soil community composition. The herbaceous litter was correlated with surface-dwelling Collembola and microbial properties with faeces and fungi. Our results suggest that the long-term stability of deep organic layers provides a refuge for decomposers and detritivores that allows a rapid response to both adverse and favourable conditions, taking place in OL and OF layers. Furthermore, the opening of the canopy in mature stands allows the decomposers to adapt to changes in resource input long before the collapse of the forest.