Exercises: Ecological Succession

Define ecological succession in your own words. Then name the two main types of succession.

After a volcano erupts and leaves only bare rock, living things slowly begin to return. Decide whether this is primary or secondary succession, and name one type of organism that is usually the first to arrive.

A wildfire burns a forest in California, but the soil stays in place. Decide whether the recovery that follows is primary or secondary succession. Give one reason for your answer.

A farmer in Kansas stops mowing a field. Over the next 30 years, the field changes from grasses to shrubs to small trees. Identify the type of succession, and explain why it is usually faster than succession on bare rock. Mention what is already present in the soil.

The table shows the number of plant species found on a lava flow in Hawaii at different times after the lava cooled.

Describe the trend in species diversity. Then explain how early organisms such as lichens and mosses help make it possible for new species to arrive.

Mount St. Helens erupted in 1980. Some areas were buried under thick ash and rock, while other areas kept some soil and surviving plants. Explain why the two kinds of areas may recover at different speeds. Name the type of succession in each area.

A town clears a forest to build a parking lot. Years later the lot is abandoned, and cracks in the pavement slowly fill with weeds, then shrubs. Marcus says this is primary succession because humans caused the change. Aaliyah says it is secondary succession. Evaluate both claims. Decide who is correct, and justify your answer using what defines each type of succession. Then predict how the number of species and the kinds of populations will change over many decades.

Two sites in the same region were disturbed. Site 1 was scoured down to bare rock by a glacier-fed flood. Site 2 was a pine forest destroyed by a wildfire. After 20 years, Site 2 has 25 plant species and Site 1 has 6. After 200 years, both sites have mature communities with similar numbers of species. Compare how populations and species diversity changed at each site, and explain why Site 2 recovered faster. Then describe how a second disturbance, such as another fire at Site 2 after 10 years, would likely affect its diversity compared with no second disturbance.