Earth Science Ecology

Disturbance and succession: examples of ecological disturbances, and the role of wildfire in ecosystems!

In this post, you’ll learn about ecological disturbance and succession, starting with definitions and examples of disturbances. We will cover the differences between primary succession vs. secondary succession, as well as the steps of the ecological succession process. Finally, you’ll read about why disturbances like wildfire can be important and natural processes in ecosystems!

forest on fire
Wildfire is one example of an ecological disturbance.

What is a disturbance?

What is a disturbance in ecology?

A disturbance is some sort of event that causes a large and rapid change in an ecosystem. Disturbances may abruptly change the ecological community – the plants, animals, fungi, etc. in an ecosystem. Disturbances may also impact non-living features of an ecosystem such as the soil and water. Examples of disturbances in nature include wildfires, parasitic insect outbreaks, landslides, avalanches, volcanic eruptions, and floods.

What is ecological succession?

Succession is the natural and gradual change in an ecosystem over time. Different species may live and thrive in an environment depending on how far along the ecosystem is in the succession process.

What are the types of ecological succession?

There are two main types of ecological succession. Primary succession, and secondary succession. Primary succession occurs when species are colonizing a new habitat that was previously devoid of life. An example of primary succession is the formation of an ecological community atop newly formed igneous rocks after a volcanic eruption. Because the rocks just formed, the community is forming on them for the first time (hence, primary succession). Secondary succession happens after a disturbance that caused a sudden change in an existing ecosystem, such as a wildfire or flood. Such disturbances may (temporarily) wipe out or scare off many of the species living there before the disturbance.

The Steps of Ecological Succession

  1. Disturbance: A disturbance is an event that causes a large and rapid change in an ecosystem. Natural disturbances include wildfires, insect infestations, landslides, avalanches, volcanic eruptions, and floods.
  2. Post-Disturbance: After a disturbance, there are significant changes to the ecological community (plants, animals, fungi, etc.) as well as to non-living features such as the soil and water. Some severe disturbances may leave behind little more than bare rock.
  3. Pioneer Species: Pioneer species are the first to grow in the post-disturbance landscape. These usually include hardy lichen, fungi, and plant species that can survive in rocky soils without many nutrients. Pioneer plant species are often introduced to a disturbed area when wind or water carries in seeds from nearby. As the pioneer species live and die, they help make a nutrient-rich topsoil, which allows for more plants to grow.
  4. Intermediate (shade intolerant) species: Intermediate plant species include grasses, shrubs, and some trees that can survive in thin topsoil. Intermediate species often include shade-intolerant plants which thrive in the relatively open, post-disturbance landscape. As more and more plant species become established, they help create habitats for different animal species to return to.
  5. Climax (shade tolerant) species: Climax species are the last species to return to an area following a disturbance. Climax species require a thicker layer of nutrient-rich topsoil to grow. Climax species often include shade-tolerant tree species, which can grow from seedlings beneath a canopy of shade-intolerant trees, as well as any animals that rely on these tree species.

Why are ecological disturbances important?

Ecosystems naturally experience a cycle of disturbance and succession. We call the natural timing and magnitude of disturbances in an ecosystem a disturbance regime. Maintaining a natural disturbance regime helps keep an ecosystem healthy! For example, regular, small wildfires can clear out diseased trees and overgrown brush, which helps prevent more severe fires and insect outbreaks from happening later on! Additionally, natural disturbances create the conditions for new trees to grow. Interestingly, some tree species even have cones that only open to release their seeds when they are exposed to extreme heat during wildfires!

How do humans impact disturbance and succession?

Humans impact the cycle of disturbance and succession in many ways. Humans create unnatural disturbances such as clearcutting forests. Humans sometimes introduce invasive species that take the place of native species during the succession process. Humans also alter the timing of disturbances, causing disturbances to take place more or less often than they should naturally. Humans often try to prevent disturbances like fires, floods, and landslides because they damage our buildings, roads, and homes. However, altering natural disturbance regimes has a history of coming back to haunt us. For example, preventing small, natural fires can lead to a larger, more damaging fire later on. For this reason, forest managers now set and closely supervise controlled burns over small areas, to mimic natural disturbances in a safer way.

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References and Further Reading

  1. Free Fire Ecology Curriculum for multiple grade levels, from!
  2. Project Learning Tree’s STEM activities about forest fires!
  3. Forest Ecology Basics from Michigan Tech
  4. Wildlife Ecology Basics from Michigan Tech

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