Leaves falling off the trees signal the end of the summer, but it is also the beginning of spring. Leaves and other falling debris supply the raw materials needed for next year’s growth of new leaves. Going from dead leaves to nutrients that can be taken up by the tree requires a recycling system of decomposition.
Plants need certain chemicals to grow and produce food that sustains the entire forest ecological system. Calcium, nitrogen, phosphorous, and many other elements are taken up from soil by plant roots. These elements enter the soil through the recycling of dead vegetation, animal carcasses and animal wastes that accumulate on the ground as organic litter. A complex community of bacteria, fungi, protozoans, and many different kinds of micro-beasties that live in the soil carry out the vital task of decomposition that ultimately leads to what is called biogeochemical cycling. This is where organic material is finally broken down to individual atoms that can move from the soil and be taken up by plants.
The carpet of dried leaves, twigs and other plant debris that covers the forest floor is called the litter layer, and here is where recycling begins. If you dig into this litter you will note that the upper layer is made up of leaves that are more or less intact. Newly fallen leaves contain a great deal of potential food energy that is tapped by the many inhabitants in the soil.
As you dig deeper in the litter layer, the leaves will become increasingly moist and flimsier. Deeper still the litter becomes increasingly skeletonized, where all the softer tissue has been consumed, leaving only the tougher veins and stem. Decomposing leaves become darker in color and feel slimy due to a coating of microorganisms. If you look close you may notice thin, white threads growing on the leaf surfaces, produced by the many funguses that consume dead material. On down, the leaves become broken up and unrecognizable. The litter here is dark, gritty and moist. This is the humus layer, and is where organic matter from formerly living things finally becomes the simple chemicals that can be taken up by plants to make them go.
I don’t mean to sound overly profound, but in the forest, death is as important as life. And while decaying things may smell bad and are often shunned by us humans, without this important recycling process, life as we know it could not exist.
Steve Roark is the area forester in Tazewell, Tennessee for the Tennessee Department of Agriculture, Forestry Division.