Ecological Succession Changing Ecosystems

Biodiversity  Biodiversity is the variety of organisms in a given area.  Physical factors (abiotic) have a big influence on biodiversity.  Ex: Low temp or Low water = Low biodiversity Sahara Desert Forest

Resistance to Environmental Damage  The biodiversity of habitats and ecosystems varies widely.  When ecosystems have high biodiversity, they are more resistant to damage.  Systems with low biodiversity can be severely damaged easily.

Succession  When we observe an ecosystem, it may look like an unchanging feature of the landscape.  However, all ecosystems change.  The replacement of one kind of community by another in the same location is called succession.

Primary Succession  The arrival of life in an area where no community previously existed.  Ex: Volcanic eruptions of lava  Rock weathers and produces soil where there wasn’t any before.

Pioneer Species  The first organisms to appear in a newly made habitat.  Often small, fast- growing species that reproduce quickly.  These change the habitat in such a way that other species can live. Lichens and mosses are often the first to colonize a bare area of rock. These break down rock and help form soil so that other plants can live.

Secondary Succession  Occurs in areas that previously had life.  Ex: Damage from severe storms, plowing with bulldozers, forest fires.  Occurs faster than primary succession because soil is already present as well as seeds from previous plants.

Secondary Succession A recently cleared patch of ground (in Britain). The same ground 2 years later, now covered in grasses and low flowering plants.

Equilibrium  If a major disruption strikes a community, many of the organisms may be wiped out.  But the ecosystem will respond to the change in such a way that equilibrium will be restored. Forest recovery is more effective when left to natural processes, as illustrated by the successful regeneration in Yellowstone National Park after the fires in 1989 (left) and nine years later (right).

Climax Community  Ecologists refer to the final, highest stage of ecological development in an area as the area's climax community.  That term refers to a relatively stable community that is environmentally balanced.  The type of climax community depends on the climate

Maintained by Fire  When fire sweeps through a forest, the fire destroys just about everything in its path.  Fire can actually be a good thing for certain communities, however.  In fact, fire is important for preserving many plant communities and the animals that depend on them.

Fire Lovers  Some plants benefit from fire.  Fireweed is one such plant.  It gets its name because it quickly colonizes burned land without competition from other species.

Fire Aides Reproduction of Certain Species  The jack pine and the loblolly pine can release their seeds only after they have been exposed to the intense heat of a forest fire. Loblolly Pine Jack Pine

Controlled Burns of Forest Ecosystems  Firefighters often light fires on purpose.  This firefighter is setting a controlled burn fire because burned vegetation helps bring nutrients to the soil.

Fire Used for Forest Management  Forest managers may prescribe a controlled burn to reduce the brush present in the ecosystem.  Too much undercover brush may lead to a more catastrophic forest fire later.

Controlled Burns to Reduce Non-native species Invasion  Ecologists may also use a prescribed burn to reduce the number of introduced species in an area.  This may allow the native species to repopulate the land with less competition. The goal is to remove non-native grass thatch and seed and provide a weed-free planting window for restoration to diverse, native coastal bluff scrub vegetation.