Lehtikerros

Lehtikerros, in forest ecology, refers to the uppermost organic layer on the forest floor, consisting mainly of recently fallen leaves and other plant debris such as needles, fruits, and twigs. The layer sits atop the mineral soil and is commonly associated with the litter or O horizons in soil profile classifications. It forms as leaves shed by deciduous and coniferous trees accumulate during autumn and throughout the growing season, and it changes in thickness with species composition, climate, and disturbance history.

Decomposition in lehtikerros is carried out by fungi, bacteria, and soil fauna, releasing nutrients back to the soil and contributing to the formation of humus. The layer buffers soil temperature and moisture, reducing evaporation and protecting seeds and small seedlings from temperature extremes. It also influences the rate of nutrient cycling and soil fertility.

Ecological significance of lehtikerros includes its large reservoir of organic carbon, its role as habitat for a diverse community of invertebrates and microorganisms, and its effect on seed germination and regeneration by providing a microhabitat with varying light and moisture conditions. The properties of the layer are influenced by stand structure, soil moisture, and land-use practices. For example, conifer-dominated stands may exhibit slower decomposition and thicker litter layers, whereas deciduous stands often show quicker turnover in autumn.

Disturbances such as logging, fire, or heavy rainfall can modify litter depth and composition, with downstream effects on soil temperature, moisture, and nutrient cycling. Researchers measure lehtikerros by assessing litter mass per unit area or litter depth, and study decomposition using litterbags or long-term soil monitoring.