Signs of Summer 1: Our Yard Ecosystems (part 1)

Photo by M.O.Stevens, Wikimedia Commons

(Click to access an audio version of this blog)

Each of us who owns a house manages the ecosystem that surrounds it. We make choices about what plants we want to grow in our home-ecosystems, and we make choices about how controlled we want those ecosystems to be.

The most prominent feature of a yard-ecosystem is usually the lawn. On average, 75 to 80% of a house lot area is set aside for grass. Most lawns are closely trimmed and densely vegetated with tightly packed grass plants. Fescue and bluegrass are the dominant grasses. Most lawns are extremely controlled monocultures: no clover, no dandelions, no ground ivy, and no “weeds” of any kind. A monoculture, be it lawn or cornfield, is an unstable ecosystem. Successional forces and waves of opportunistic, invading plant species (the “weeds”) exert immense pressures on the system. These forces would very quickly change a lawn- grass system into a system dominated by annual weeds. A great deal of energy has to be

Photo by D. Sillman

employed to keep these successional forces at bay.

The grass manager (i.e. the home owner) has to set up a regime in which the grass plants are vigorously stimulated to grow (by the addition of water, fertilizer, lime etc.), and in which less desirable plants (the “weeds”) are selected against by the frequent plant tissue destruction caused by mowing (and the more you “feed” and water a lawn the more you have to mow it!), by the very occasional direct removal of “weeds,” and by the very frequent, broad application of herbicides designed to kill non-grass plants. These steps are the only ways to insure that a lawn remains a singular grass ecosystem.

The cost of this control is astounding. Here are some numbers for lawns in the United States (derived primarily from EPA, Audubon Society, and The Garden Club of America publications and web sites):

1. 54 million people mow their lawns each summer weekend, 800 million gallons of gasoline are used in gas lawn mowers each year,
2. 17 million of these gallons of gasoline are spilled during refueling mishaps,
3. mower exhaust and the volatile organic chemicals from the gas spills contribute to lower atmospheric ozone production (“smog”) all summer and also generate about 5 % of the nation’s total air pollution,
4. 78 million pounds of herbicides/pesticides/fungicides are used on lawns each year (with almost no oversight or control),
5. 3 million tons of fertilizers are applied to lawns each year (again, with almost no oversight or control),
6. 50 to 70% of the total residential water volume is used for landscaping (mostly to water lawns),
7. a total of $30 billion is spent annually on lawns (installation, care, and maintenance).
8. lawns in the United States cover approximately 50,000 square miles. This area represents the largest single, irrigated “crop” grown in the United States.

The growing economic and environmental cost of maintaining lawns, especially in regions of low rainfall, have begun to raise serious questions about the sustainability of this phenomenon. Added to these concerns are the realizations that the grass plants themselves that have assumed such a dominating presence in our urban, suburban, and rural landscapes are, in fact, non-native, and, frequently, invasive plant species. Even “Kentucky” bluegrass is a plant native to Europe, Asia, and northern Africa! These plants are invading and upending our natural floral ecosystems!

Norway maple, J. Billinger, Wikimedia Commons

The most common trees in the yards of my neighborhood are Norway maples, blue spruces, Norway spruces, and silver and sugar maples. The spruces are often of substantial sizes (more than a foot in diameter and 40 to 50 feet tall) with broad growth forms with little branch shading or limb pruning. Only in a very few cases are any of the trees in branch contact with each other. For the most part, the trees are widely separated and quite isolated. There are also some yellow and European white birch, yellow poplar, cherry, and crab apple trees growing in these home-ecosystems along with a variety of shrubs including rhododendron, azalea, burning bush, yew, privet, Rose of Sharon, forsythia, lilac, and a variety of forms of arbor vitae.

Now without getting too preachy or picky about the subject, it is important to consider the idea of “native” vs. “non-native” plants with regard to these tree and shrub species. The three most abundant trees are introduced, exotic species. The Norway maple is native to eastern and central Europe and has been, primarily because of its tolerance of a wide range of site conditions, extensively planted throughout the eastern United States.  The Norway maple, though, because of its prodigious production of seed and its tendency to form dense thicket masses in untended ecosystems, is classified by the National Park Service as an alien, invasive plant that should be avoided. The escape of this species into the wild has done a great deal of damage to native plants throughout the eastern United States.

Norway spruce, Photo by D. Sillman

The Norway spruce (which is native to northern Europe) and the blue spruce (which is native to western North America) have also both been widely planted as ornamental trees throughout the United States. Their respective reproductive and growth patterns do not generate invasive or destructive responses in unmanaged ecosystems, although both have “escaped” extensively from their landscape systems into surrounding forests and both have, undoubtedly, had some negative impacts on competing, native tree species.

Rhododendron, arbor vitae, and some (but not all) of the azalea types are native plants in our region. Burning bush (from northeast Asia), privet (there is a European form, a Japanese form, and a Chinese form), Rose of Sharon (from southeast Europe and southwest Asia), lilac (from Europe and Asia), forsythia (from eastern Asia), and yew (from England) are all exotic, introduced shrubs. Of these plants only the lilac and the English yew are classified as “non-invasive,” although both are recognized as having frequently “escaped” into surrounding ecosystems.  The other species (burning bush, privet, Rose of Sharon, and forsythia) have not only widely escaped but also have caused, according to the U. S. Forest Service, via their dense and destructive growth patterns, widespread declines in many native plant species.

Photo by K. Andrew, Flickr

Flower beds often border the home-ecosystem swath of lawn. Some typical home-ecosystem flowers include roses (a very old domesticated flower which probably originated in the Middle East thousands of years ago), crocuses, daffodils, and tulips (which are from southern Europe, North Africa, and Asia).  The “top ten flowers” planted in the United States (as listed by topteny.com) include lilies, sunflowers, tulips, roses, pansies, sweet peas, nigellas, marigolds, California poppies and Dianthus varieties (the “pinks,” sweet William and carnations). Of these only sunflowers and California poppies are native to the United States (there are some native lilies, but most garden varieties are from Asia). For potted plants the USDA indicates that chrysanthemums (Asia), orchids (mostly tropical species), geraniums (eastern Mediterranean), and poinsettias (Mexico) are the dominant plants sold in the United States. These flower represent (according to statisticbrain.com) about 46% of the $31.3 billion generated each year by floral products industry!

So, from our grasses to our trees to our flowers, we have made and sustain (and pay steeply for!!) an ecological node of invasive plants all around our houses.

(next week: some animals of our home-ecosystems!)