By Maria Cristina Alves
Evergreens, like the loblolly pines you find at CBEC, can hang onto their leaves through winter, because their foliage or needles have a waxy coating and a special liquid inside that protects them against freezing. The cold temperatures and frigid winds would damage the unprotected leaves of broadleaf plants, so trees have to reduce themselves to their toughest parts — stems, trunks, branches, bark. In the fall, a corky layer at the base of the colorful leaf seals it off from the tree, sending it to its beautiful death.
The broadleaf trees in the Eastern deciduous forests can drop 2–3 tons of leaves per acre per year in preparation for the winter. These fallen leaves still have a key ecological role in the survival of the trees and the forest as a whole. Thanks to the natural process called decomposition, dead leaves and other organic matter rots and breaks down, so that their nutrients are recycled back into the environment. Without decomposition, the planet would be covered with dead bodies of animals and plants. There would be no new plant growth because nutrients would not be returned to the soil. There would be no food for animals and we would be unable to survive.
Fortunately, dead plants and animals quickly are transformed by other organisms who feed on them. A group of animals called scavengers will promptly eat dead things. Scavengers break down dead material by chewing and excreting it. Foxes, badgers, opossums, vultures, crows, blowflies and various beetles will eat the flesh of dead animals. Sow bugs, carpenter ants, bark beetles, and termites are common scavengers that eat or burrow through decaying wood.
Another group of organisms, called decomposers, will work to break down any dead plant or animal tissue even more. They transform the dead organism into organic matter and nutrients that can again be used for the growth of new organisms. These include fungi, slime molds, bacteria, slugs, snails, woodlice, springtails, earthworms, flies, maggots, beetles and their larvae. Although they are mostly tiny and work out of sight, and may seem ugly or repulsive, their work is gigantic. Through recycling of organic matter, they guarantee the continuation of life in all of the earth’s ecosystems. Decomposers are, in fact, nature’s real recycling heroes.
Animals and plants are decomposed in distinct manners, and you can tell them apart with your nose! The decomposition of plant material is aerobic, meaning that it needs to take place in the presence of oxygen in the air. When people make compost in their garden, they are using the same decomposition process of nature, but accelerating it by concentrating the organic matter in a pile or container. When oxygen is present, bacterial action on the leaves generates heat and accelerates decay. When the temperature of the compost begins to decrease it is time to turn the pile for addition of oxygen. If the oxygen supply gets too low the process becomes anaerobic and the pile begins to smell bad. The pile needs to be turned for addition of oxygen and continuation of the process. Leaf compost can be used as rich soil conditioner to improve fertility level of soil in a yard or garden.
In nature, decomposition takes time, with different decomposers involved at different times, and for different types of plants. The voluminous leaves and stems of deciduous trees are generally decomposed within a year of falling on the forest floor. Leaf litter is quickly invaded by the hyphae of fungi – the white thread-like filaments that are the main body of a fungus. Mushrooms appear mostly in late summer and autumn, and are merely the fruiting bodies of fungi trying to spread their growth during fall and winter. The hyphae draw nutrients from the litter and break down the dead plant material. As the decay becomes more advanced, bacteria, as well as various invertebrates, including springtails, slugs and snails play a role, with earthworms arriving in the last stages.
Trees and other woody plants are much tougher to break down. Depending on the chemical components and amount of fibers in the species, decomposition might sometimes take several years or even decades. Fungi are also the first decomposers to attack the fibers of logs, dead trees or snags, by feeding on the tough cellulose and lignin and converting those into softer tissues. The growth of the fungi hyphae helps other decomposers, like bacteria and beetle larvae, gain access to the woody material. As these penetrate and open the wood even more, the galleries produced by beetle larvae let in more moisture. Earthworms and springtails can be seen when the wood becomes very wet and falls apart. More invertebrates, such as woodlice and millipedes arrive to feed on the softer wood material. Centipedes, beetles, spiders, robber fly wasps and other predators feed on the sow bugs, millipedes, and other scavengers that eat logs.
Don’t think though, that those fallen logs and snags are important only for nutrient recycling. They provide food and shelter for decomposers and several other groups of organisms. Because of their nutrient richness, you may also see lichen, trees, bushes, and moss growing out of the rotting logs. These logs and snags house insects and serve as a rich food source for woodpeckers and other animals that, by their turn, will also help to break down the wood. Cavities on logs and snags also make them good habitat for spotted owls, box turtles, snakes and other animals. Newts and salamanders often spend hot days hiding in the cool, damp log. So, the next time you see a “dead” tree or log, remember how full of life it is!
If you are walking on that trail and smell that awful scent of decaying meat, you just got a hint about the work of bacteria decomposing the body of a dead animal. Animal decomposition is different than that of plants because most of the decomposers are other animals and bacteria.
When an animal like a deer dies, scavengers such as blowflies and crows quickly start to consume the fresh carcass that for them is very appetizing. Dead animal bodies, also called carrion, are valuable sources of food, with a high concentration of energy and nutrients that need to be recycled to keep scavengers alive in the ecosystem. In the warmer seasons, blow-flies are the first to lay their eggs around places like the nose and ears, to give their larvae easy access to the inside of the body. Then, bacteria take over. In the absence of air and oxygen inside the body, bacteria cause decay and anaerobic decomposition. This produces gases that smell like spoiled meat. In the next and most stomach-turning phase of animal decomposition, the skin is broken, liberating the stench of the gases. The blowfly’s larvae or maggot eat the soft tissue and grow.
Predators like wasps, ants, beetles and birds also arrive, to feed on the blowfly larvae. Only cartilage, skin, bones and hair remain. A different group of flies and beetles, plus their respective parasites and predators take over the decomposition process. The only thing remaining after a year are the bones, teeth and hair. Although these may stay around for a few years, mice and voles like to chew on the bones, seeking their calcium content. The rate of dead animal decomposition depends on the time of the year death occurs. It is slow during fall and winter, when many things like blowflies are missing, so it will take several months to get started.
When the time comes to rake leaves from your yard, where the space is probably too small for you to let decomposition happen naturally, think of how much work the decomposers have to go through in order to keep the planet clean and alive! In fact, I hope you think twice and do not rake so fastidiously. Leave a corner or two of your yard with the leaves on the ground for our recycling heroes. I also hope a renewed appreciation of their importance will inspire us to recycle more, too!
Resources and information
- Yahner, R. 1995. Eastern Deciduous Forest: Ecology and Wildlife Conservation. Pages 37-38; 178. University of Minnesota Press. 2nd ed. Minneapolis, MN.
- Weidensaul, S. 1992. Seasonal Guide to the Natural Year: A month by month guide to natural events – Mid-Atlantic. Pages 240-54; 255-257. Fulcrum Publishing. Golden, Colorado.