Disturbance Why Ecosystems Change Explain why disturbance is
Disturbance Why Ecosystems Change
§ Explain why disturbance is a natural part of biological communities § Describe the impacts of major disturbance types and how these affect community composition § Analyze how human activities can lead to decreases or increases in disturbance Objectives
Every community undergoes some type of disturbance Disturbances can be natural or human caused…or both.
Disturbances occur naturally at semi-regular intervals. Some disturbances are frequent and some like this forest blowdown are much more unusual. Forest Blowdown – Berthoud Pass, Colorado 2020
Fire is critical to community structure and ecological function Some examples: • Many pine-cones are Serotinous meaning they release seeds after a trigger event which is often fire. This is critical to pine reproduction. • Fires open up canopies to light allowing other species to grow • Fires kill off old trees and reduce forest density & can reduce the likelihood of disease spread
Many human management techniques mimic aspects of disturbance Forest harvest (fire or tree death) Agriculture (herbivory or pest removal of crops) Prescribed fire (natural fire) BUT Forest regrowth after logging Most harvest-oriented human dominated systems substitute individual species for more complex communities
Communities change after disturbance Succession – covered in a different video Some plant species expand some become less common. Food sources and habitat becomes more diverse Biodiversity is maintained or increases because of the variation across the landscape. Successional change following forest clearing and fire
Summary § Disturbance is important in virtually all communities because it can affect reproduction, habitat, and because it changes in the physical environment. § Many major disturbances such as fire or insect outbreak allow new populations of plants and animals to thrive. This can lead to higher levels of ecosystem scale biodiversity § Human management of ecosystems can profoundly alter disturbance. Suppression of fire, logging, introduction of pest species and many other actions change the frequency and severity of disturbances.
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