precipitation Water that falls to the earth in the form of rain, snow, sleet, hail.
runoff Water that is not absorbed by the soil that eventually returns to streams and rivers.
transpiration Process by which water leaves a plant by evaporating from the leaves.
Points to Consider
- Do ecosystems change over time? Why or why not?
- Can you think of an example of a ecosystem changing over time?
24.3 Lesson 24.3: Ecosystem Change
Lesson Objectives
- Explain the process of ecological succession.
- Distinguish between secondary and primary succession.
- Describe a climax community.
Check Your Understanding
- What is a biome?
- What is the most abundant element in living things?
- How do humans obtain nitrogen?
Introduction
When you see an established forest, it’s easy to picture that the forest has been there forever.
This is not the case, however. Ecosystems are dynamic and change over time. That forest
may lie on land that was once covered by an ocean millions of years ago. Or the forest
may have been cut down at one point for agricultural use, then abandoned and allowed to
re-establish itself over time. During the ice ages, glaciers once covered areas that are tropical
rainforests today. Due to both natural forces and the influence of humans, ecosystems are
constantly changing.
Primary Succession
If conditions of an ecosystem change drastically due to natural forces or human impact,
the community of plants and animals that live there may be destroyed or be forced to