Ecological Succession
The biomes we see today are the result of a sequence of changes that occurred as ecosystems were changed by the organisms living within them. Organisms are capable of changing their environment so drastically that they can no longer survive there! Other species may take over, and they in turn will cause further changes. Ecological succession is the sequence of change that occurs in an ecosystem’s biotic community over a very long period of time.
Primary succession occurs where no life existed before, such as on a newly formed volcanic island, or on newly exposed rock.
For example, in many regions of Ontario, the first step of primary succession begins with lichens, which are blown into cracks in the rock. Over the centuries, they produce acids that break the rock down into small particles which form a thin layer of soil when they combine with dead lichen material. Mosses can grow there and build up more soil. As more centuries pass, grasses replace the mosses, and these in turn are replaced by shrubs. Each stage of succession is identified by the predominant types of plants, with each plant population generally growing to be taller than the one that preceded it. Next come deciduous trees and finally, if conditions allow, a permanent boreal coniferous forest appears. For example, white birch acts as a parasol for spruce trees which can survive in their shade. The spruce trees grow to be taller than the birches, which can’t survive in the shade. The spruce population ultimately replaces the birch population. When these coniferous plants die, they are replaced with the same types of plants. In any ecosystem, the final stage of succession is called the climax community, and it tends to be very stable. The type of climax community depends on the climate.
Secondary succession occurs where life existed previously, but was disrupted by a catastrophic event such as a flood or a forest fire. It may also occur if land is cleared for agriculture and then allowed to return to its natural state. Secondary succession usually takes less time than primary succession – one or two centuries, rather than thousands of years. The climax community will be just like the one that was originally there.
Ecological Succession: Questions
Answer these questions in complete but brief sentences.
1. How are stages of natural succession identified?
2. Differentiate between the terms primary succession and secondary succession.
3. Briefly describe the events that occur when primary succession occurs in a typical rocky Ontario location. Use the terms acids, coniferous, deciduous, grass, lichen,
moss, shrubs, and soil. You may present your answer as a flow chart.
4. Explain what is meant by the term climax community.
5. Complete this table:
Primary Succession / Secondary SuccessionWhen does it
occur?
How long does
it take?
What is the
final result?