Ecological Succession Succession refers to the normal gradual

Ecological Succession • Succession refers to the normal, gradual changes that occur in the types of species that live in an area. • Succession is a process by which one biotic community is replaced by another until a climax community develops.

Succession from Rock to Forest Some 240 years ago a glacier began retreating in Glacier Bay, Alaska The glacier left behind a rocky terrain completely devoid of organic matter The process that begins in a place without any soil is called Primary Succession

An Example of Primary Succession: Glacier Bay, Alaska

Primary Succession Pioneer organisms such as microbes, lichens, and mosses are the first to inhabit a rock promoting soil formation.

Primary Succession Eventually, enough soil is built up so that grasses can succeed the pioneer organisms.

Primary Succession Grasses are replaced by shrubs, which are replaced by fast-growing trees.

Primary Succession Coastal Sitka Spruce Forest, Southeast Alaska

Succession occurs differently in different places around the world. The types of grasses, fastgrowing trees, and climaxcommunity plants vary with the location and climate of an area.

A Climax Community Is Not Truly Final Humans or nature can destroy it.

A Climax Community Is Not Truly Final In this case, succession starts over with grasses as Secondary Succession.

Secondary Succession After a forest fire, not much is left except dead trees and ash-covered soil. However, these places do not remain lifeless for long.

Secondary Succession • The topsoil, which may • • have taken 1000’s of years to form, is not destroyed. Spores and seeds which lie dormant are then allowed to develop. Sequence may be crabgrass, tall grass and horseweed, softwood then hardwood.

Secondary Succession • The soil already contains the seeds of • weeds, grasses, and trees. More seeds are carried to the area by wind and birds. • Other wildlife may move in. • Succession that begins in a place that already has soil and was once the home of living organisms is called secondary succession.

Secondary Succession Secondary succession occurs faster and has different pioneer species than primary succession because soil is already present. The cause may be a natural disturbance such as a forest fire or farming. In 1850, Connecticut was almost entirely open land cleared for farming or timber. Today, Connecticut has been mostly reforested through the process of secondary succession as farming has left the state since the 1800's.

Climax Communities • A community that has reached a stable stage of ecological • • succession is called a climax community. It is a combination of plants and animals that use the available resources most efficiently. Diversity and balance are maintained in a climax community because as trees die, they provide nutrients for new communities of organisms.

How do ecosystems change over time? • Ecosystems change over time by a process know as succession in which one biotic community is replaced by another until a climax community develops. • Succession is often caused by changes in the environment brought about by the current community. • Succession can also occur because of changes in climate and natural catastrophes such as fire, hurricanes, floods, and volcanic eruptions. • Humans cause succession by cutting down forests, polluting the environment and overdeveloping an area.

How do new communities begin in areas without life? • By a process known as primary succession. Pioneer organisms such as microbes, lichens, and mosses are the first to inhabit a rock promoting soil formation. • They survive drought, extreme heat and cold, and other harsh conditions and start the soil-building process. • Soil begins to form as lichens and the forces of weather and erosion help break down rocks into smaller pieces. • When lichens die, they decay, adding small amounts of organic matter to the rock. • Plants such as mosses and ferns can grow in this new soil. • Thus begins the process for higher order plants.

How do pioneer species compare to climax communities? Pioneer species are the first organisms to occupy an area and do not need soil to survive. Examples of pioneer species would be organisms such as microbes, lichens, and mosses. Climax communities are the last communities to occupy an area. Climax communities are a combination of plants and animals. They tend to be stable and self-perpetuating.