Succession After Human-Caused Disturbances In North America, land cleared for farming and then abandoned often passes through succession that restores the original climax community. But this is not always the case. 
Ecosystems may or may not recover from extensive human-caused disturbances. Clearing and farming of tropical rain forests, for example, can change the microclimate and soil enough to prevent regrowth of the original community.
Studying Patterns of Succession Ecologists, like the ones seen in Figure 4–15, study succession by comparing different cases and looking for similarities and differences. Researchers who swarmed over Mount Saint Helens as soon as it was safe might also have studied Krakatau, for example. In both places, primary succession proceeded through predictable stages. The first plants and animals that arrived had seeds, spores, or adult stages that traveled over long distances. Hardy pioneer species helped stabilize loose volcanic debris, enabling later species to take hold. Historical studies in Krakatau and ongoing studies on Mount Saint Helens confirm that early stages of primary succession are slow, and that chance can play a large role in determining which species colonize at different times.
FIGURE 4–15 Studying Succession These Forest Service rangers are surveying some of the plants and animals that have returned to the area around Mount Saint Helens. The volcano erupted in 1980, leaving only barren land for miles.
4.3 Assessment
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Review What effects do pioneer species have on an environment undergoing primary succession?
Explain Why do communities change over time?
Apply Concepts When a whale or other large marine mammal dies and falls to the ocean floor, different waves of decomposers and scavengers feed off the carcass until nothing remains. Do you think this is an example of succession? Explain your reasoning.
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Review What is a climax community?
Relate Cause and Effect What kinds of conditions might prevent a community from returning to its predisturbance state?
VISUAL THINKING
Look at the photo below. If you walked from this dune in a straight line away from the beach, what kinds of changes in vegetation would you expect to see? What sort of succession is this?
Table of Contents
- Formulas and Equations
- Applying Formulas and Equations
- Mean, Median, and Mode
- Estimation
- Using Measurements in Calculations
- Effects of Measurement Errors
- Accuracy
- Precision
- Comparing Accuracy and Precision
- Significant Figures
- Calculating With Significant Figures
- Scientific Notation
- Calculating With Scientific Notation
- Dimensional Analysis
- Applying Dimensional Analysis