Exploring a Woodlot's Ecosystem
"The land is one organism. Its parts, like our parts, compete with each other and cooperate with each other. The competitions are as much a part of the inner workings as the cooperations." - Aldo Leopold
Ever since I was a toddler, I have enjoyed exploring in my wooded backyard. Every walk through the woods was an adventure for me. I always found it exciting to learn something new about the wonders my backyard held. To this day, I still marvel at my wooded sanctuary, different from the manicured lawns and city lots of my friends. The aura of my backyard captures my senses and sends me to a whole new place, a place of uniqueness and diversity. I decided to take an inventory of the plants, wildlife, and the non-living components of my backyard to document the diversity and the vast number of different species in my woodlot (see Inventory at end of essay). After I studied my inventory, I could not help asking myself, "Are all these various woodlot components connected? If so, how are they all connected?" I looked for some reference in the vast field of ecology to guide me in my search for answers. Ecology is a branch of biology that studies the relationships between the organisms and their environment. I learned that in the early 1970s, ecologist Barry Commoner summarized the study of ecology into four basic tenets: "Law No. 1 -- Everything Is Connected to Everything Else; Law No. 2 -- Everything Has to Go Somewhere; Law No. 3 -- Everything Is Always Changing; and Law No. 4 -- There Is No Such Thing as a Free Lunch." Come along with me as I investigate the inner relationships of the many living and non-living components of my wooded backyard's ecosystem.
Commoner's First Law: Everything Is Connected to Everything Else
"When we try to pick out anything by itself, we find it hitched to everything else in the universe." - John Muir
While exploring my wooded backyard, I have noticed a variety of relationships, including symbiotic relationships, which are close connections between two organisms of different species. I recognize three symbiotic relationships: interspecific competition, predation, and parasitism. An interesting example of interspecific competition I have observed is house wrens and chickadees competing for the same sources of food, such as cankerworms and caterpillars. The intense competition I have observed between wood ducks, gray squirrels, flickers, and screech owls for the same nesting sites in my backyard is more evidence of interspecific competition. Similarly, all the woodlot animals compete for limited water supplies during dry weather. Another symbiotic relationship I have observed is predation, such as when the screech owl and sharp-shinned hawk consume chickadees and other small birds for the nutrients these predators need to exist. An example of parasitism, the third symbiotic relationship I have observed, is when fungi, such as the hen of the woods, feed on trees and rot the underground parts of them.
Intraspecific competition between two organisms of the same species and the relationships between living and non-living things may not be symbiotic, but they are just as much a part of the ecosystem of the woodlot. For instance, when chickadees compete with other chickadees for the same territory or nesting sights, they demonstrate intraspecific competition. The same is true of gray squirrels competing with each other for nesting sites, acorns, and hickory nuts. An example of a relationship between living and non-living things is that which exists between dead leaves and living trees. This is important because the layers of dead leaves on the forest floor decay and enrich the soil that nourishes the living trees. In another instance, decaying logs and the roots of dead trees support the growth of fungi and even seedlings, supplying them with all the nutrients they need.
Intricate food webs and food chains connect everything in the woodlot. I have observed the red fox during his frequent visits to my backyard. The red fox's diet includes small rodents, rabbits, and young opossums. In the same way, adult opossums may raid great horned owls' nests and eat the owlets, as I sadly discovered early one morning last March. Through examination of the many sporobolus the owls leave behind, I have discovered that their diet consists of rabbits, small rodents such as mice and moles, garter snakes, and small birds. Further down the food chain, rabbits regularly consume vegetation, including grasses and wild flowers. These grasses and wild flowers need the sunlight to produce their food. These examples of the food web and food chain clearly demonstrate the connectedness of the ecosystem.
Commoner's Second Law: Everything Has to Go Somewhere
Have you ever wondered where the garbage you "throw away" goes? It has to go somewhere because it does not just disappear. Depending on your disposal method, your garbage may be recycled or placed in an overflowing landfill. This concept that everything has to go somewhere is associated with ecology in more ways than one. For instance, scientific findings show that plants and animals need certain nutrients to grow. Nitrogen is among the most important nutrients plants and animals need to survive. The nitrogen cycle is important to the continued health of my ecosystem, because without nitrogen, plants and animals would not be able to build nucleic acids, structural proteins, and enzymes. All these things are necessary for life. For example, nitrogen from the air is converted into a compound that plants can use by the bacteria on the roots of the white clover found in my backyard. Plants, such as the white oak tree, use this nitrogen compound to make protein. A chipmunk eats the white oak's protein found in its acorn. The chipmunk passes the nitrogen to the red fox when the red fox consumes the chipmunk. When the fox dies, his decaying body releases the nitrogen into the soil. Young sugar maples extract the nitrogen from the soil. The cankerworm eats the sugar maple's leaves and picks up the nitrogen the maple used to make the amino acids it needed. The nitrogen cycle continues when the chickadee eats the cankerworm, and it, in turn, is eaten by the screech owl. The nitrogen continues to be passed through the ecosystem when the great horned owl eats the screech owl. Finally, the great horned owl's sporobolus decays and releases the nitrogen back into the soil, where it is used once again by the white clover (as diagrammed and included in my "Illustrations and Field Observations").
Likewise, everything is connected by the energy flow through the woodlot's ecosystem. The organisms in the ecosystem rely on sunlight as their ultimate source of energy. Producers, or plants, such as the sugar maple, use the sun's energy to produce their own food through photosynthesis. The primary consumers, or herbivores, such as the cankerworm, eat the plant's tissues to get the nutrients they need. Similarly, as the herbivores eat the plants to gain the nutrients they need, secondary consumers, or carnivores, such as the chickadee, eat the herbivores to obtain the nutrients they need. The chain lengthens when the tertiary consumers, or top carnivores, such as the screech owl, eat the small carnivores. The amount of energy at each succeeding level decreases (as illustrated in my "Illustrations and Field Observations"). The energy decreases from one level to the next because much of the energy is unusable at succeeding levels.
Commoner's Third Law: Everything Is Always Changing
At family reunions my relatives always say, "My, how you have grown." They see how much I have changed from the last time they visited with me. In the same way that I am always changing, so is the ecosystem in my wooded backyard. Today my backyard woodlot is reaching its climax stage. It used to be predominantly nut-bearing trees, with many oaks and hickories. However, there is interspecific competition between the nut-bearing trees and the sugar maple trees. When the woodlot was still young, the oaks and hickories thrived in the full sunlight. As they matured, they created a canopy that shaded the young trees, allowing only shade-tolerant trees to grow. As I explore my woodlot today, I see that only shade-tolerant maples make up the undergrowth. When the mature oaks, hickories, and walnut trees die, only the maples will remain.
Commoner's Fourth Law: There Is No Such Thing as a Free Lunch
"We abuse land because we regard it as a commodity belonging to us. When we see land as a community to which we belong, we may begin to use it with love and respect." - Aldo Leopold
The phrase, "There is no such thing as a free lunch," is very familiar to me. When my parents tell me this, they mean that there is a price we have to pay for everything. Throughout my course of investigation, I have seen this tenet come into play many times. For example, when my parents built their home in the woods, there was a big price to pay with regard to the woodlot's ecosystem. First there was the loss of woodland habitat. Many trees, some old and some very young, were cleared to make room for the house. One shagbark hickory tree that was cut down had 152 growth rings. Removing the tree eliminated a source of food and shelter for squirrels and other woodlot animals. Today, the use of stains and preservatives on the house introduces chemicals into the woodlot's ecosystem. To balance the negative costs, my family and I have tried to make positive impacts on my backyard's ecosystem. We have added nesting sites, shelters, feeders, and water sources for our backyard wildlife. Because great horned owls do not build their own nests, they rely on old squirrel or hawk nests to raise their young. My father has seen too many occupied owl nests fall apart, so he built a nesting platform that the great horned owls use every season. He also built many large nesting boxes that are regularly occupied by wood ducks, screech owls, and squirrels. As a family, my parents and I have made a further positive impact on the ecosystem by leaving our discarded Christmas tree out in our backyard until late spring. We learned that the little orange-faced screech owl we call "Orange Face" likes to roost in the old Christmas tree during the day to hide from the sharp-shinned hawk who also inhabits our neighborhood. Since the Christmas tree turns reddish-brown, little "Orange Face" blends in perfectly, camouflaged safely from his predators. Our family tradition of hanging bird feeders in the winter and hummingbird feeders in the summer has also made a positive impact on our ecosystem because the birds we attract spread native species of seeds from trees and other plants around the woodlot. This adds diversity and attracts even more wildlife.
I never originally thought of my backyard as an "ecosystem," but this expedition has helped me see how all living and non-living things are connected through intricate relationships. Through my observations and discoveries, I can conclude that in my wooded backyard, everything is connected! In addition, I have discovered that Barry Commoner's four laws are applicable to my wooded backyard's ecosystem. I would like to further my research to learn how my backyard is connected to the larger ecosystem of the world. For instance, how do outside environmental influences such as pollution, use of pesticides, global warming, and acid rain affect my backyard?
"The outstanding scientific discovery of the 20th century is not television, or radio, but rather the complexity of the land organism. Only those who know the most about it can appreciate how little is known about it." - Aldo Leopold
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Commoner, Barry. The Closing Circle: Nature, Man and Technology. New York: Knopf, 1972.
Leopold, Aldo. A Sand County Almanac and Sketches Here and There. Oxford University Press, 1949.
The World Book Multimedia Encyclopedia. Chicago: 1998.
Towle, Albert. Modern Biology. Chicago: Holt, Rinehart and Winston, 1993.
Zim, Herbert S. and Clarence Cottam. Insects: A Guide to Familiar American Insects. New York: Golden Press, 1956.
Zim, Herbert S. and Ira N. Gabrielson. Birds: A Guide to the Most Familiar American Birds. New York: Golden Press, 1956.
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