Mor humus

Mor humus is a form of forest floor humus occurring mostly in coniferous forests. Mor humus consists of evergreen needles and woody debris that litter the forest floor. This litter is slow to decompose, in part due to their chemical composition (low pH, low nutrient content), but also because of the generally cool and wet conditions where mor humus is found. This results in low bacterial activity and an absence of earthworms and other soil fauna. Because of this, most of the organic matter decomposition in mor humus is carried out by fungi.

Mor humus is one of three classifications of forest floor humus, along with Moders and Mulls. Each class corresponds to a scale of increasingly colder conditions, decreasing biological diversity and activity, and decreasing nutrient availability. Mor humus ranks at the bottom of this scale and is characterized by very slow decomposition and accumulation of plant material.