Ecological succession is the gradual change in a community of organisms over time as species arrive, interact, and alter the environment. Primary succession begins where no soil exists, such as on bare rock left by a glacier or new lava flow. Secondary succession begins where a disturbance removes many organisms but leaves soil behind, such as after a fire, flood, or abandoned farm field.
Comparing the two helps explain how ecosystems recover and why soil is such an important starting resource.
Key Facts
- Primary succession starts on bare rock or new surfaces with little or no soil.
- Secondary succession starts after disturbance in an area where soil, seeds, roots, or microbes often remain.
- Pioneer species are the first organisms to colonize a disturbed or lifeless area, such as lichens on rock or grasses in soil.
- Soil formation in primary succession often begins when lichens and mosses break down rock and add organic matter.
- Seral stages are the intermediate community stages between pioneer species and the climax community.
- Rate comparison: secondary succession is usually faster than primary succession because soil is already present.
Vocabulary
- Primary succession
- Primary succession is ecological succession that begins on a surface with no developed soil, such as bare rock.
- Secondary succession
- Secondary succession is ecological succession that begins after a disturbance in an area where soil remains.
- Pioneer species
- Pioneer species are the first organisms to colonize an area and begin changing conditions for later species.
- Seral stage
- A seral stage is one of the temporary community stages that appears during succession.
- Climax community
- A climax community is a relatively stable mature community that can persist until the next major disturbance.
Common Mistakes to Avoid
- Saying primary and secondary succession both start with soil is wrong because primary succession begins where soil is absent.
- Thinking pioneer species are always large plants is wrong because early pioneers are often lichens, mosses, grasses, or microbes that tolerate harsh conditions.
- Assuming succession follows the exact same path every time is wrong because climate, soil, available species, and disturbance history affect the sequence.
- Treating a climax community as permanent is wrong because storms, fires, disease, human activity, and climate change can disturb it and restart succession.
Practice Questions
- 1 A lava flow creates 2 square kilometers of new bare rock. If soil develops at an average rate of 1.5 millimeters per decade, how many millimeters of soil form in 80 years?
- 2 After a forest fire, grasses cover 60% of a field in 3 years. If the coverage increased at a constant rate from 0%, what was the average percent cover gained per year?
- 3 A glacier retreats and exposes bare rock, while a nearby farm field is abandoned after many years of use. Identify which site will undergo primary succession and which will undergo secondary succession, and explain the main reason.