Lesson 23: Ecosystem Responses to Disturbance
In this lesson, we will look at ecological succession, fire climax ecosystems,
and the twenty-six Long Term Ecological Research sites around the world. We
will also learn about resilience and feedback loops.
After a disturbance like a fire or volcano, new plants grow from the soil, new
trees sprout, and eventually a new forest replaces the old. This process is
called ecological succession: Ecological Succession is the process of
transition from one biotic community to another.
There are 2 stages to
ecological succession. Primary succession occurs right after the event
(volcanic eruption, fire or other) where one biotic community invades the area
and starts growing. With an empty environment like bare rock, not much life can
be supported initially. However, mosses can develop in this area. As moss
grows, soil accumulates. As soil accumulates, plants can grow. Eventually,
bigger shrubs and trees can develop.
Secondary succession begins after soil has taken root. In this stage, plants,
animals and human beings move into the area.
Fire climax ecosystems are ecosystems that
depend upon the recurrence of fire to maintain their existence. Fire is often
started by lightning and acts as a natural abiotic factor to preserve the
balance in ecosystems. Fire can help release nutrients from dead organic
matter. Some plant species like lodgepole pine will not release seeds until
scorched by fire.
In 1980, crown fires occurred in
Yellowstone because the area was too dry, even though there was not a lot of
deadwood. Crown fires, while scary at the time, helped to clear out sickly
trees and debris, release nutrients, and provide a fresh start to the
ecosystem. Burned areas turned into productive meadows. Periodic crown fires
thus create a series of meadows and forests at different levels of succession
with a variety of habitats.
Long Term Ecological Research (LTER) consists of 26 sites to study different
ecosystems in the world. The studies conducted at these sites help in
understanding climate change, land-use change, and invasive species, to provide
insight and ways to prepare for changes in systems.
Resilience is the ability of an ecosystem to return to normal functioning after
a disturbance such as a fire or flood. Fires appear to be very destructive, but
can also release nutrients and improve the entire landscape through new growth.
Feedback loops involve the process of either amplifying (positive loops) or
dampening (negative loops) the behavior of a system. For example, predator-prey
cycles function as negative feedback loops that keep both populations from
exploding. If you removed the predator, this could result in a positive
feedback loop for the prey with too much prey overgrazing and destroying their
own food supply.