Leaf litter includes several different types of materials, but its chief components are the fallen leaves of deciduous trees in various stages of decomposition. Leaf litter also includes other organic material, such as dead plant stems, small twigs and fallen fruits, nuts and berries, according to About.com.
Decomposing leaf litter adds valuable nutrients to the soil and helps it to retain moisture. The material is a biodiverse layer on the forest floor, providing a rich growth medium for plants and a home to small invertebrates, such as earthworms, spiders, snails and microscopic organisms that help to break down the organic material. Leaf litter also attracts birds to an area as it provides all the birds' basic needs, including food, water, nesting sites and shelter.
Human interference often decreases the biodiversity of leaf litter. Raking and bagging leaves to keep a lawn tidy eliminates the nutrients as well as the organisms that often live in this layer on the forest floor. Fertilizers, pesticides and herbicides affect the natural biodiversity. According to Scientific American, "A low biodiversity is unfavorable because these ecosystems take longer to recover from environmental changes." Adding leaf litter to a lawn helps to reverse these effects while also improving the health of the grass.