What Happens if Something Disrupts the Ecosystem?

Ecosystems are dynamic, ever-changing communities of interdependent organisms and their environment. When disaster strikes, natural ecosystems can be affected just as humans communities are. Natural and human-caused disturbances and disasters can alter or devastate an ecosystem temporarily or for an extended period of time. But like human communities, natural ecosystems quickly rally forces to put things back together, whether to restore things as they were or to give birth to a whole new ecological community.

Natural disasters are caused by meteorological, geological or biological forces in nature. When a natural disturbance hits an ecosystem, it can instantly leave tremendous damage and chaos in its wake. Fires, hurricanes, tornadoes, floods, droughts, insects and diseases, earthquakes, tidal waves and volcanoes can destroy much of the flora and fauna and sometimes shatter land forms. In a severe storm, trees in forests may be toppled or uprooted, animal homes destroyed, vegetation removed and animals slain. Volcanic eruptions can remove mountaintops, fire and volcanic eruptions can burn and destroy many acres of vegetation, and insects can denude all plants in an area.

A natural disaster doesn't necessarily mean the end to a healthy ecosystem. After a disruption or disaster, nature begins to repair itself. If widespread disease wipes out many members of a species, those that survive will continue to grow and reproduce until the population bounces back, while other species affected by its loss -- predators of that species, for example -- must meanwhile adjust. If an entire species dies out, another similar species might eventually move into its niche to take its place. When a tornado or storm fells trees in a forest, the new space and light are quickly inhabited by plants that thrive with more sunlight. If much of the vegetation in an area has been destroyed, new plants called pioneers take the first steps toward restoring life.

The succession of organisms that return to a damaged area, called a sere, follows a particular pattern and order in particular environments. For example, after a forest fire in the western United States, secondary succession begins: Pioneer fireweed, other forbs, and grasses sprout, followed by shrubby plants and trees. Years later, the forest may eventually return to a climax community. Some plants in fire-prone areas depend on fire to thrive; lodgepole pine cones need the heat of fire to open, for example, and fire may stimulate the growth of other plants. Following widespread fires in 1988 in Yellowstone National Park, aspen trees appeared where they had not been before, and lush initial growth of pioneer plants sprouted in the new open areas and high-nutrient ash soils. After disruptions that remove soil as well as plants, such as volcanism, glaciers and tsunamis, primary succession begins with organisms such as lichens, which can grow on bare rock, and recovery takes much longer than with secondary succession.

Many disturbances to ecosystems today are human-caused and continuous, and ecosystems have little opportunity to recover. The clear-cutting of forests, draining of marshes or removal of native vegetation for development and agriculture; pollution from industries, residences, automobiles and ships; strip mining and mountaintop removal mining – all of these disruptions can put tremendous, long-lasting strains on ecosystems. Sometimes even good intentions harm instead of help ecosystems. After the U.S. Forest Service spent years preventing most forest fires, they discovered forests became unhealthy “tinderboxes,” littered with debris and vulnerable to hotter, more damaging fires. Perhaps most ominous, carbon emissions that raise average annual temperatures worldwide threaten to alter ecosystems irreversibly with more severe storms, increased flooding and droughts, the melting of polar ice, loss of islands and shorelines to rising oceans, more widespread disease and extinctions of species.