Human Impact and Intervention

By clearing land for agriculture or logging, large formerly-forested areas of the Middle-East and Europe have been turned into deserts. This also causes major soil erosion which is one of our major ecological problems, worldwide. Problems here in the U. S. caused the Dust Bowl in the 1930s. These problems were subsequently partially overcome by people on small, family farms planting windbreaks, rotating crops, etc. However, the large, post-WWII corporate farms went back to monoculture and tore out the windbreaks that were in the way of big machines, thereby bringing the erosion problems back, even worse than before. I recall reading about an area of, I think it was, Spain that originally had been a lush, forested area, but for much of recent history was a hot, nearly-inhospitable, desert-like area. A local man undertook it as his life’s work to re-plant as many trees as he could, and to encourage others to do the same. Now, a generation or two later, the climate of the area has changed noticably. The presence of trees changed not only the localized microclimate, but influenced the overall climate in the area, including temperature and humidity.
Human Destruction

Human Destruction

Human Destruction--Smashed Christmas Fern
  Here in the U. S., the timber industry typically clearcuts forests, then burns the stumps to totally kill everything, then reseeds with a monoculture of commercial, nursery-grown species. Also, dead trees (snags) are removed in the process. These, however, provide homes/nests for a variety of wildlife. Logging is a problem in tropical rainforest areas because desirable species of trees are few and widely-spread, and loggers end up having to cut a lot of other trees to make roads to haul out even one desirable tree. Often forest destruction also allows “weedy” plants and insect pests to proliferate in newly-cleared, agricultural areas. Some, less-drastic tree-harvesting methods include division of a forest into strips, and cutting only the desirable trees in only every third strip at a time.

Urbanization is a major problem. Cities and their suburbs take the place of both wild land and agricultural areas. More and more land is paved over as roads or covered with buildings, etc. Especially in the inner city, most species are “weedy” exotic species that are invasive and can tolerate urban conditions. Waterways are frequently rerouted and often channelled through concrete “ditches” or metal pipes, making it impossible for native wetland species to survive there. Some species of human-introduced “landscape” plants (Garlic Mustard, Amur Honeysuckle, Multiflora Rose, Euonymus, Russian Olive) have escaped and are outcompeting local, wild species.  
Ohio River

Burning of fossil fuel, and other activities in cities change the local climate. Winter weather (snow) is usually not as “bad” in the center of a city as in the surrounding rural areas. City temperatures often average 6 to 8° C higher than in nearby rural areas. Usually, things like tornados do not occur as frequently in big cities as in rural areas, probably also due to the difference in air temperature.

Human Destruction--Smashed Christmas Fern
  Dwindling numbers of small family farms typically grow a variety of crops surrounded by hedgerows, windbreaks, and pockets of remaining forest and thus, animals like rabbits, quail, and (exotic) pheasants. Today’s agribusiness monoculture of large expanses of corn/soy has eliminated this diversity. Hedgerows, etc. on farms can provide edge/ecotone areas and support more wildlife.

Draining of wetlands for agriculture or urban sprawl causes loss of habitat and of species/species diversity. A settlement of houses and “cabins” around the shores of a lake is the “beginning of the end,” and the accompanying motorboats are detrimental to aquatic wildlife. Dams are constructed to cause major changes in the watercourse of a given river-system.

Pollution is a major human-induced problem. Pesticides, herbicides, and fertilizers are washed into local water systems. Litter, landfills, and improperly-treated sewage may potentially leach a variety of chemicals and pathogenic bacteria into the surrounding environment. Remember the previously-discussed example of DDT adversely affecting production of Peregrine Falcon egg shells? Also, burning of coal, and other fossil fuels releases sulfur and nitrogen compounds into the air. The sulfur compounds form sulfuric acid, and the nitrogen forms nitric acid. These fall with the precipitation as “acid rain.” Acid rain, when absorbed into the soil, can alter the pH of the soil, therefore the solubility of various chemical ions used as nutrients. We are increasing low-altitude O3 levels which shouldn’t be, and by releasing chloroflurocarbons (CFCs) into the air, are decreasing the high-altitude O3 that protects us all from too much sun. We are also releasing large quantities of toxic, heavy metals (mercury, cadmium, chromium, selenium, lead) into our soils. A brand-new problem is genetically-engineered corn with BT genes in it. Bacillus turingensis is a bacterium that invades/kills caterpillars. Its genes were incorporated into a certain variety of corn to try to make the corn more resistant to attack by corn borers (a type of non-descript moth). However, it has been noted that if pollen from this corn settles on local, wild plants the BT genes in the pollen may cause the death of any caterpillars which normally feed on those plants. This could, then, have a negative impact on the populations of local butterflies.

Growth after Burn in Lynx Prairie
Some ecosystems depend on fire to maintain their usual flora, so humans setting fires (accidentally?) can be both good and bad. This is bad because a fire could destroy a habitat if it is started during the wrong time of year, but good for the habitat if started at the proper time of year when fire-susceptible species are killed off and growth of fire-resistant species is encouraged. In some habitats (such as the Adams Co. prairie preserves), humans have realized the necessity of fire and have set controlled fires on purpose. People have recognized that in areas where fire is needed to maintain the ecosystem, human suppression of fire can be harmful to habitats that depend on it for regeneration, seed germination (for example, Lodgepole Pine, Pinus contorta in Yellowstone), and killing of “invaders.”


Students Rescuing Fern
  A number of years ago, in Papua, New Guinea, an attempt to introduce Western farming methods failed miserably because it was so foreign to the way the people there did things. However, this area is home to several species of large, showy butterflies called birdwing butterflies. These are greatly-prized by insect collectors, and were overcollected to the point of being endangered. Some entomologists went to that country and studied the birdwing butterflies, discovering the specific plants eaten by the caterpillars. Based on that information, a very successful butterfly farming “industry” was started. On their small, family “farms,” local people plant gardens that are a mixture of wild plants with flowers to attract adult butterflies and wild plants that are used as caterpillar food. Wild butterflies find these gardens and lay eggs on the host plants. The people monitor the growth of any resulting caterpillars, and when these turn into chrysalises, they are carefully transferred to a protected, screened-in area (maybe a porch of the people’s homes) until the butterflies emerge. When the butterflies emerge, a very small percentage are “harvested” for sale to insect collectors, and the rest are released back into the wild. This “butterfly farming” has had several positive results. The people in that country are able to use farming methods that philosophically and physically “work” in that situation and that don’t destroy the local ecosystems, the number of birdwing butterflies available for sale on the international market has increased and this has provided a significant source of income for that country and its citizens, and perhaps most importantly, the numbers of these once-endangered butterflies have increased significantly,

Yosemite National Park



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