Humus Forms of Moist and Wet Forest Stands. A Review

The organic layer of forest soils (forest floor) provides important ecosystem functions and serves as a habitat for soil organisms. This review provides an overview of research on humus forms of moist and wet forest stands based on a systematic literature review. Detailed information was collected from around 80 articles and books. It was examined whether the articles include the chemical, physical, or biological properties of humus forms. In addition, selected topics associated with and often used in relation to moist or wet humus forms, like information on morphological properties or information on specific classification systems, are considered. In general, it was found that many articles include the importance of moist or wet humus forms in their classification system. However, there was less or insufficient explanation on morphological properties. The humus forms on poorly drained or even waterlogged sites differ from humus forms on well-drained sites because the water factor affects the processes and thus the morphology very much. High soil moisture (=water saturation) means periodically anaerobic conditions in mineral soil and also very often in organic layers. Hence, soil organic carbon and soil organisms are affected. Especially, the recent literature often deals with climate change and soil organic carbon in moist and wet forest stands.