Disturbance

Lightning

When a wildfire sweeps through a stretch of forest, our first instinct is to put the blaze out.  Fires are scary, destructive and dangerous, especially when a fire gets too close to people’s homes. 

However, fire is also a natural part of ecosystems. Forests and grasslands have actually evolved to deal with an occasional fire in a historic cycle of growth, dieback and growth. Fire is one of the many natural disturbances that effect ecosystems every year. 


What is a Natural Disturbance?

A disturbance is any event that causes a disruption to the current state of an ecosystem. Disturbances can be localized – only impacting a small patch of land – or they can affect an entire forest or wetland.   The results of a disturbance can be short-lived or long-term. Sometimes it takes a few months for an ecosystem to bounce back and other times it can take decades. 

Natural disturbances are caused by forces of nature, including weather, geology and biological fluctuations. 


Types of Natural Disturbances

  • Fire
  • Flood
  • Wind
  • Disease
  • Severe Storms
  • Insect Swarms
  • Volcanic Activity
  • Drought
  • Long term Freezing
  • Earthquake

What Happens to an Ecosystem After a Natural Disturbance?

After a fire or a flood impacts an ecosystem, there can be devastation. Plants die, animals are displaced from their former homes and tracts of land may have no wildlife at all.  But these situations are temporary. If you had a time-lapse camera to watch the long-term aftermath of a disturbance, you would see a lot of positives come from a seemingly negative event. 

Healthy ecosystems have an amazing ability to bounce back from a disturbance. Sometimes the ecosystem will go back to its former structure, with the same plant and animal species. Other times, the disturbance will create something new by allowing new species to move in. Only time will determine the effects of each disturbance. It could take days or decades, but eventually, the ecosystem will recover. 

For example, imagine a new disease spreading among a particular mouse species. The disease could greatly reduce the mouse population or even cause it to go extinct in that area. The consequences of this disturbance are felt throughout the ecosystem, because all the predators and prey of the mouse must adapt to the new conditions. The hawk and snake predators must find new sources of food, while the grasses the mice fed on will spread to new areas. Even if the mouse population never rebounds, the ecosystem will eventually adjust to the new conditions.

Forest Fire in Eldorado National Forest

Natural Disturbances are Healthy for Ecosystems

Natural disturbances are not a new thing. They have been around since the beginning of time, shaping ecosystems and species. Disturbances are bound to happen, and ecosystems are adapted to an occasional disturbance. 

Some ecosystems depend on disturbances. The threatened longleaf pine ecosystems of the Southeast depend on fire to control the growth of understory plants. Without fire, young longleaf seedlings are outcompeted by other plants and have difficulty reaching maturity. Similarly, silver maple trees can spread and grow after a flood, because they are flood-tolerant. When other trees die, silver maple can grow. 


Human Disturbance

Not all disturbances are natural. Human actions have contributed to a lot of the disturbances we see in ecosystems today. While natural disturbances happen on occasion, human disturbances are putting constant pressure on ecosystems and dramatically impacting species. 

Human disturbances, including clear-cutting, habitat fragmentation, and pollution, are continuously affecting ecosystems. The moment the ecosystem begins adjusting to one stress, another appears. Many ecosystems that we depend on are not given enough time to adapt to the new conditions. The natural cycle of disturbances – growth, dieback and growth – cannot properly function, because too many disturbances are putting pressure on the ecosystem at once.

 

National Wildlife Magazine Articles:
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