Forest Litter

Autumn is a time of year when many changes take place in forests in northern Illinois.  Leaves change color and fall off the trees; numerous species start their annual migration; and other species get ready to overwinter here.  The forest floor forms a rich habitat, covered with several layers of litter including fallen leaves, dead wood, plant debris, exposed roots, and other organic matter.

Very few of the leaves that grow in a forest during spring and summer are eaten before they fall off the trees.  A majority of the forest biomass litters the forest floor in autumn, providing a large amount of potential food for bacteria, fungi, and other decomposers living in the forest litter.

The top layer of forest litter contains newly fallen leaves.  At lower levels, leaves and other debris become wetter.  Small holes appear in leaves and around their edges, made by minute insects and mites.  These allow bacteria and fungi to enter the interior of the leaves and begin the process of decomposition.  As vegetation breaks down it becomes darker in color, and surfaces feel slimy due to the large number of microorganisms living on them.

Deeper in the litter, leaves have lost much of their soft tissue, leaving only veins and petioles.  In bottom layers, leave are often unrecognizable.  The organic matter has changed into dark, gritty, moist humus.  Complex organic matter, once living, has been broken down to simple, non-organic chemicals and nutrients that are absorbed into the soil.  Calcium, potassium, nitrogen, phosphorous, magnesium, and sodium are recycled from decomposing vegetation and animal remains.

Fungi feed on organic matter.  Fungi are often not visible, either living underground or are microscopic in size.  They produce fruiting bodies in the form of mushrooms, mold, and yeast.  Fungal fruits are at the peak of their showiness after autumn rains.  Fungi reproduce from spores, grown in the fruit, and released by wind, water, or contact with passing animals, to be spread throughout their habitat.

The most recognized fruits are the many mushroom varieties that appear in autumn.  Mushrooms are most often grouped by physical characteristics.  Some found in our area include:

Gilled mushrooms are pale white to highly colorful.  They tend to grow from the ground or from decomposing stumps and logs, and may be poisonous.  They are important field and forest decomposers     by DonArnold, Sep 2022          

Brackets grow by attaching to decomposing logs or tree trunks.  They are dark red to deep brown and  may grow singly or in clusters.  They are hard and woody allowing them to a long time. Brackets by DonArnold, Sep 2022

Cup fungi are brightly colored with upturned edges or deep furrows, such as morel.

Jelly fungi are brightly colored, pale white to red.  Although they appear to be shiny and slimy, they have a dry surface and a rubbery texture.  They look like a clump of jelly or laid out in ribbons on branches and logs.  Following a wetting from rain, spores appear on the surface to be lifted away by the wind.

On your next forest walk, be sure to watch for mushrooms along the trail, on fallen logs, and on tree trunks and branches.  Next week we will take a closer look at what else may be living in the rich habitat beneath your boots!