metsänpohjan

Metsän pohja, commonly referred to as the forest floor, is the uppermost part of a forest ecosystem that lies above the mineral soil. It consists of organic material such as freshly fallen needles, leaves, and twigs (the litter layer), partially decomposed organic matter (the humus layer), living ground cover like mosses and small herbaceous plants, and sometimes decaying wood. The exact thickness and composition vary with tree species, climate, soil conditions, and disturbance history.

The forest floor plays a key role in ecosystem processes. It is central to nutrient cycling, as organic matter decomposes and releases nutrients that become available to plants. It also stores moisture, influences soil temperature, and provides a critical seedbed for new seedlings. The floor hosts a diverse community of organisms, including fungi, bacteria, insects, and other invertebrates, many of which form important ecological relationships such as mycorrhizal networks with trees.

Variation is notable between forest types. Coniferous forests often have a thick, acidic litter layer and a moss-rich surface, whereas deciduous forests may exhibit faster litter decomposition. Management practices, such as harvesting and residue handling, can alter the thickness and composition of the forest floor, affecting regeneration, biodiversity, and soil health. The forest floor thus reflects both natural dynamics and human influence, serving as a visible indicator of forest condition.

See also: humus, litter layer, soil horizon, forest ecology.