Download Ecological Succession

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.