Effects on the Biosphere

Modification of Habitats

As humans establish cities, they disturb habitats and destroy others. But at the same time, they import new species of plants and animals and create habitats for other unintended species.

Modifications can take place in many ways. Natural ground cover is replaced with grasses and decorative plants, with native plants sometimes allowed to remain. With non-native grasses and decorative plants, fertilizers are used to provide essential nutrients that are not found natively, theses spread across lawns, and find their way into river channels where it promotes the growth of more plants at the expense of aquatic species. Additionaly, waste dumped into streams lowers oxygen levels during its decay and causes the death of plants and animals. Sometimes, urbanization promotes the growth of native species populations, such as squirrels and raccoons, and population size increases far above the natural equilibrium.

Waterfowel, such as these ducks, have adapted to urbnaization around Boulder Creek

River diversions help to prevent flooding around underpasses,
but disturb movement of fish poplutions and other aquatic species.


created 3/9/2002; last revised 5/1/2002 - Matt Kuhn & Andreas von der Dunk