Disturbance (ecology)
Disturbances often act quickly and with great effect, to alter the physical structure or arrangement of biotic and abiotic elements.
Disturbance forces can have profound immediate effects on ecosystems and can, accordingly, greatly alter the natural community’s population size or species richness.
[3] The scale of disturbance ranges from events as small as a single tree falling, to as large as a mass extinction.
[1] Natural fire disturbances for example occur more often in areas with a higher incidence of lightning and flammable biomass, such as longleaf pine ecosystems in the southeastern United States.
[6] Wildfires, droughts, floods, disease outbreaks, changes in hydrology, tornadoes and other extreme weather, landslides, and windstorms are all examples of natural disturbance events that may form a cyclical or periodic pattern over time.
Logging, dredging, conversion of land to ranching or agriculture, mowing, and mining are examples of anthropogenic disturbance.
Human activities have introduced disturbances into ecosystems worldwide on a large scale, resulting in widespread range expansion and rapid evolution of disturbance-adapted species.
[14] Although disturbance types have varied on ecosystems, spatial scale likely influences ecological interactions and community recovery from all cases because organisms differ in dispersal and movement capabilities.
With the passage of time following a disturbance, shifts in dominance may occur with ephemeral herbaceous life-forms progressively becoming over topped by taller perennials herbs, shrubs and trees.
Pine forests in western North America provide a good example of such a cycle involving insect outbreaks.
[18] Environmental stresses can be described as pressure on the environment, with compounding variables such as extreme temperature or precipitation changes—which all play a role in the diversity and succession of an ecosystem.
They, as well as some other pine species, have specialized serotinous cones that only open and disperse seeds with sufficient heat generated by fire.
However these shifts may not reflect the progressive entry to the community of the taller long-lived forms, but instead, the gradual emergence and dominance of species that may have been present, but inconspicuous directly after the disturbance.
The success of a wide range of species from all taxonomic groups is closely tied to natural disturbance events such as fire, flooding, and windstorm.
If fire is suppressed, douglas fir (Pesudotsuga menziesii), a shade tolerant species, eventually replaces the pines.
Douglas firs, having dense crowns, severely limit the amount of sunlight reaching the forest floor.
Fire, in this case, is important not only to the species directly affected but also to many other organisms whose survival depends on those key plants.
[19] The interplay between disturbance and these biological processes seems to account for a major portion of the organization and spatial patterning of natural communities.
[26] Disturbance variability and species diversity are heavily linked, and as a result require adaptations that help increase plant fitness necessary for survival.
