Leaf litter

Western Hemlock litter

Leaf litter is dead plant debris, mostly leaves from trees or shrubs, that has fallen to the ground. This includes pine needles, leaves, dead or cut grass, and even decaying moss. Leaf litter is an important part of ecosystem, as it serves as shelter and as a food source for many keystone species. Due to leaf litter containing life depending nutrients they are crucial for many species including arthropods, fungi, small vertebrates, and even other plants.

Leaf Litter in Wetlands

Leaf litter is a source by which wetland ecosystems can recycle scarce nutrients that were already consumed. This is part of how wetlands can support diverse communities of organisms, from microbes to fish to frogs and beyond. When the litter comes in contact with water, some of the organic material dissolves due to it being soluble. This initial breakdown of litter is a process called leaching. After this process organisms begin to further the breakdown of the material. Microbes and macroinvertebrates, such as shredders, will physically tear and break the material apart into more digestible fragments, thus accelerating decomposition. Through decomposition, nutrients held within the litter are able to be mineralized, or further broken down into the essential building blocks of life. For stream ecosystems, leaf litter is the largest source of organic matter, thus composition, or chemical makeup, of the litter has a great influence on the available nutrients in freshwater ecosystems.

Leaf litter decomposition releases essential nutrients including nitrogen and phosphorus back into the water. These nutrients support primary producers and differences among plant species lead to variation in nutrient release, affecting ecosystem productivity and biogeochemical processes. In many ways, leaf litter is the energy base for food webs. In many freshwater ecosystems, leaf litter is the dominant source of organic matter. Microorganisms such as fungi and bacteria colonize submerged leaves, initiating decomposition. Detritivorous invertebrates consume this conditioned leaf material. The energy from the leaf litter is therefore transferred to the shredders, and on to higher trophic levels such as fish and amphibians that consume the shredders.

Water Quality Regulation

Decomposition of litter releases dissolved organic carbon (DOC), which influences water color, pH, and light penetration. Tannins and phenolic compounds from leaves can darken water and reduce UV exposure for sensitive organisms. Leaf litter also helps moderate temperature and slow erosion in stream channels by stabilizing sediments.

Decomposition Processes

Leaf litter decomposition in wetland ecosystems occurs through:

• Microbial conditioning, especially by fungi that soften leaves
• Invertebrate shredding: breaking leaves into smaller particles
• Mineralization: converting organic matter into inorganic nutrients

Factors affecting decomposition include temperature, oxygen availability, leaf chemistry, and microbial community composition.

Importance to Biodiversity

Many aquatic species depend directly or indirectly on leaf litter. Shredder invertebrates such as crabs and amphipods rely on it as a food resource, while predators such as fish and larger invertebrates feed on shredders. Amphibians, crustaceans, and small fish use litter as cover from predators and as breeding or feeding grounds.

Mineralization

Mineralization of leaf litter releases the nutrients from the litter in an inorganic form which can then be used by other organisms. This is how leaf litter can be recycled within an ecosystem to produce ready to use nutrients.