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On Sunday, May 18, 1980, Mount St. Helens blew its top. The volcano erupted with the force of several atomic bombs.
Just a two-hour drive from downtown Seattle, it blew down and scorched 230 square miles of forest. In many places, nothing survived. By now, lots of plants and animals have come back. It will be another 200 years before hardwood forests dominate the area again. But, as it turns out, the volcano’s destruction was one of nature’s many ways of renewing itself.
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Succession
After being destroyed by a volcano, forest fire, or other natural disaster, an area goes through a process that ecologists call succession.
Recovery and Renewal
Grasses, ferns, and weeds cover the once lifeless ground. Small animals, such as groundhogs, mice, and rabbits, return. Because there’s so little life around, the food chain is very short.
Every ecosystem has its limits. A forest can support only so many badgers, a river only so many fish. This limit is called its carrying capacity. Ecosystems tend to have a balance among plants, the animals that eat them, and predators. For instance, plenty of grass means more deer will be born—and more wolves will be born to hunt them. A lack of grass will cause both deer and wolves to die off. ▶
◀ Humans clear wild areas for farming or housing. This stops the process of succession. The longer an area is cleared of its natural habitat, the more its original plants and animals die out or move away.
▲ It’s often difficult to see the benefits in a natural disaster like a volcano or forest fire. But from the planet’s perspective, volcanoes are an absolute necessity. They help recycle rocks and minerals that are vital for life. Most of the molecules in your body came out of the ground through a volcano at one time or another. Here’s how it happens: Weather wears away rock particles, which, over time, become part of the soil. Soil also contains organic material. Plants take up nutrients from the soil through roots, and those nutrients become part of the plant tissue. When you eat a plant, the nutrients become part of you.
▲ The animals that adapt best are the ones that survive. These adaptations include slight physical changes—perhaps in size or eyesight. Over three and a half billion years, such changes have created a rich variety of life on Earth. Ecologists call this biodiversity. For instance, nobody mistakes a chimpanzee for a human. Yet, humans and chimps share 98.5 percent of their genetic coding. That makes them close cousins genetically.
▲ Biodiversity is important, because each plant and animal has its niche. Remove bees from an area, and flowers can’t be pollinated and reproduce. Remove snakes, and the mouse population soars. Removing any species can destroy or weaken other species. This causes ripple effects throughout an ecosystem.
◀ Each plant and animal has its own unique niche in its community. At first glance, some animals seem to share the same niche. But look more closely. For instance, cheetahs and lions both hunt antelope. But cheetahs are weaker, so they go for young antelope and other smaller animals. Lions, being stronger, tend to go for larger animals, such as zebras.
