mullbänkens

Mullbänken is a term used in Swedish soil science to describe a bench-like, humus-rich layer that forms within forest soil profiles. The word combines mull, meaning a well-decomposed organic layer, with bänken, implying a distinct horizontal surface or terrace. In practice, mullbänken refers to a relatively stable, organic-rich horizon that sits near or at the upper part of the mineral soil and can extend as a horizontal band along a slope or terrace.

Formation and environment

Mullbänken forms through the accumulation and organization of organic matter from litter and root activity, aided by soil fauna and microbial processes. It is commonly observed in cool, moist boreal and temperate forests where litter decomposition is active and erosion is limited enough to allow organic material to accumulate and persist at a specific depth. Physical processes such as slight soil creep, freeze–thaw cycles, and root growth help produce the characteristic bench-like appearance by concentrating organic matter at a relatively discrete interface between the litter layer and the mineral soil.

Ecological and forestry significance

The mullbänken influences important soil properties, including water infiltration, aeration, pH, and nutrient availability. Its presence can indicate a relatively stable site with ongoing organic matter turnover, and it may affect root distribution and seedling establishment. In soil classification and site assessment, mullbänken serves as a reference horizon for interpreting past disturbance, fertility potential, and drainage characteristics.

Variations and terminology

The thickness and rough appearance of mullbänken vary by site, with darkest, most humified intervals marking the typically organic-rich zones. It is related to other humus forms in soil science, such as mor and moder, and to the broader concept of soil horizons that describe organic-mineral interfaces within a profile.