Exam 1: Succession
Secondary succession
Secondary succession is one of the two types of ecological succession of plant life. As opposed to the first (primary succession), secondary succession is a process started by an event (e.g. forest fire, harvesting, hurricane) that reduces an already established ecosystem (e.g. a forest or a wheat field) to a smaller population of species, and as such secondary succession occurs on pre-existing soil whereas primary succession usually occurs in a place lacking soil. Secondary succession is usually much more rapid than primary succession, due to the presence of pre-exisitng soil beneath the damaged area (e.g. beneath the surface of a forest burnt by a forest fre) but also due to the presence of pre-existing spores and seeds already in the soil (which may germinate when the appropriate cionditions occur).
An example of Secondary Succession by stages (see picture below):
*example of a community = a forest of trees and undergrowth plants, inhabited by animals and rooted in soil containing bacteria and fungi, constitutes a biological community
Secondary succession
Secondary succession is one of the two types of ecological succession of plant life. As opposed to the first (primary succession), secondary succession is a process started by an event (e.g. forest fire, harvesting, hurricane) that reduces an already established ecosystem (e.g. a forest or a wheat field) to a smaller population of species, and as such secondary succession occurs on pre-existing soil whereas primary succession usually occurs in a place lacking soil. Secondary succession is usually much more rapid than primary succession, due to the presence of pre-exisitng soil beneath the damaged area (e.g. beneath the surface of a forest burnt by a forest fre) but also due to the presence of pre-existing spores and seeds already in the soil (which may germinate when the appropriate cionditions occur).
An example of Secondary Succession by stages (see picture below):
- A community* of interacting populations of different species
- A disturbance (a fire) destroys the forest
- The fire burns the forest to the ground
- The fire leaves behind empty, but not destroyed soil
- Grasses and other herbaceous plants grow back first due to the seeds still in the soil
- Small bushes and trees then begin to colonize the public area
- Fast growing evergreen trees develop to their fullest, while shade-tolerant trees develop in the understory
- The short-lived and shade intolerant evergreen trees die as the larger deciduous trees overtop them.
- The ecosystem is now back to a similar stable state (equilibrium) to where it began = climax community
*example of a community = a forest of trees and undergrowth plants, inhabited by animals and rooted in soil containing bacteria and fungi, constitutes a biological community
Example 2:
Oak and Hickory forest
A classic example of secondary succession occurs in oak and hickory forests cleared by wildfire. Wildfires will burn most vegetation and kill those animals unable to flee the area. Their nutrients, however, are returned to the ground in the form of ash. Thus, even when areas are devoid of life due to severe fires, the area will soon be ready for new life to take hold. Before the fire, the vegetation was dominated by tall trees with access to the major plant energy resource: sunlight. Their height gave them access to sunlight while also shading the ground and other low-lying species. After the fire, though, these trees are no longer dominant. Thus, the first plants to grow back are usually annual plants followed within a few years by quickly growing and spreading grasses and other pioneer species. Due to, at least in part, changes in the environment brought on by the growth of the grasses and other species, over many years, shrubs will emerge along with small pine, oak, and hickory trees. These organisms are called intermediate species. Eventually, over 150 years, the forest will reach its equilibrium point where species composition is no longer changing and resembles the community before the fire. This equilibrium state is referred to as the climax community, which will remain stable until the next disturbance.