Wednesday, November 3, 2010

Fall Leaf Decomposition

Nature Watch

By Susan Thurn,
Cable Natural History Museum

“Scrunch,” “scrunch” went the crunch of dry leaves under my feet. The brown, dead leaves have been a delight for many that love to walk through leaf litter while kicking up fall leaves. For others, the leaves are perhaps part of a fall routine as people rake them from their lawns. For nature, decomposition is the natural process for leaves as they fall to the ground, creating new building blocks of life recycled over again. Right now in the forest this recycling is a job filled by invertebrates, fungi and bacteria.

Decomposition of leaves occurs through many different means. Invertebrates and earthworms break leaves into smaller fragments. This process allows the leaf pieces to have more surface area to support the next step of decomposition, bacteria and fungi. Rain also filters through the leaves, dissolving chemicals and nutrients. Bacteria grow better when the leaf fragments are smaller. The organic matter is broken down to carbon, nitrogen and other minerals.

Certain species of fungi also aide with the decomposition of leaves. Fungi hyphae fibers spread through dead leaf litter just under the forest floor, extracting nutrients the fungi need to survive. These hyphae develop into matted carpets that we sometimes see when leaf litter is moved. The speed at which decomposition occurs depends on moisture, temperature and composition of the leaf matter. Lower temperatures make decomposition occur more slowly. Leaves with low nitrogen also slow decay because the fungi cannot gain enough nitrogen from the organic matter to make necessary proteins. Lower oxygen environments also slow decomposition.

Waste not, want not is the perfect description of our leaf decomposers. Without them, nitrogen and other nutrients would be locked in the dead leaves, not leaving enough for living plants and their needs in making new leaves and seeds. Those bacteria and mushrooms are such “fun-guys!”

For over 42 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility and exhibit, On Lake Owen: The Art of Walter Bohl, in Cable at 13470 County Highway M. Also find us on the web at to learn more about our exhibits and programs. Post your own stories on the Nature Watch blog at

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