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Disturbances Defined
T.S.A. Pickett and P.S. White define ecological disturbances as a "relatively discrete event in time that disrupts ecosystems, community or population structure, and changes resources, substrate availability or the physical environment." Disturbances are natural geological phenomenon, such as earthquakes, floods, hurricanes, volcanoes and tsunamis, and biogenic, or biological, disruptions.
Biogenic Disturbances
Biogenic disturbances can be natural or man-made. Biological events include invasive species not introduced by man and disease, such as the American chestnut blight that decimated the existing population of trees. Man-made, or anthropogenic, disturbances include invasive species, clear-cut timber, building roads or dams, and strip mines.
Anthropogenic Disturbances
Anthropogenic disturbances can be accidental or intentional. In the case of logging, industry or mining, they are intentional. It was also intentional when Gypsy moths were introduced to the United States in 1869 by Etienne Leopold Truvelot. He imported the moths in hopes of improving the silkworm industry. The moths escaped and are slowly migrating south and west, eating up forest leafs as they travel.
Invasive Species
Invasive species events involve the introduction of plants or animals to an area where they have not existed previously. They may be introduced by birds, wind or man. In 1988, Zebra mussels were introduced to the Great Lakes. Their invasion has almost eliminated the natural clam population of the region. They also have clogged the water intakes on power plants and water supply companies. It is believed they were introduced on ship hulls.
Forest Fires
Forest fires are another example of an ecosystem disturbance. They may be started by lightning, from a camper's fire or intentionally by an arsonist. In 1988, fires swept through Yellowstone National Park. According to the National Park Service, 1.2 million acres were scorched, about 793,000 of them in Yellowstone. On Aug. 20, 1988, 150,000 acres burned. Some of these fires were caused by lightning and some by man.
Ecosystem Services
Ecosystem services are the benefits provided by ecosystems, such as food, water, natural resources and entertainment. Disturbances interfere with these services. For example, the 2011 Japanese tsunami disrupted fisheries, flattened towns and scoured the landscape of vegetation. Drinking water and food production become limited, and resources needed to be supplied from outside the area.
Recovery
Whether disturbances are good or bad remains to be determined. Author Douglas Spieles says such disturbances are good because they increase the biodiversity of an area, especially, if that area had reached maturity, thus supporting fewer species. This seems to be supported by evidence after the Yellowstone fires. However, the U.S. government is funding other studies on disturbances. Thirty years after the Mount St. Helens volcanic eruptions, the U.S. Forest service is still studying its effects, and the NASA-CASA project is looking at environmental effects on global disruptions.