Decomposers, such as worms, fungi bacteria and other invertebrates play a critical role in nutrient recycling. Elements, such as carbon and nitrogen are in limited supply, so decomposers break dead dead things, animal droppings and other forms of natural litter to release this back into the atmosphere, which will eventually be processed through their natural cycles (see; Carbon cycle, etc) and can be reused, although this does take a long time. They also act as sort of a natural clean up system.