Transcript Succession powerpoint

Succession
Ecological succession is the gradual process by which
ecosystems change and develop over time. Nothing
remains the same and habitats are constantly changing.
Life Span of a Lake
Lakes, like all things, change over time. Even a
lake has a life span like people do - there are
young lakes, middle-aged lakes and old lakes.
Many of the lakes in British Columbia are still
quite young because they were formed by the
last ice age that carved our northern landscape.
As our lakes age, many of them will slowly
shrink. Land naturally takes over at the edge of
a lake. It's very slow, but it happens. This is
called “lake succession,” and this is how it
works.
Each year trees and shrubs along the edge of a
lake shed leaves and debris into the water that
then settle to the bottom. This debris slowly
decays to form new habitat for grasses, rushes
and sedges. The grasses take root quickly and
stabilize the new ground for dry land species.
Some day shrubs and small trees will grow
where lily pads once floated.
As the lake becomes smaller and smaller, it
may not be able to provide enough oxygen or
food for some fish. But this happens so slowly
that they have plenty of time to move on to
other lakes, if the lake is connected to the rest
of the watershed by a stream.
•Primary Succession
follows the formation of
new land surfaces
consisting of rock, lava,
volcanic ash, sand, clay,
or pavement, NOT SOIL
•Secondary
Succession follows
the destruction or
partial destruction of
the vegetation (plant)
area by some sort of
disturbance, like a fire,
windstorm, or flood
that leaves the soil
intact.
http://www.kscience.co.uk/as/module5/succession/index.htm
Some organisms are
able to environments
where there is no
stable soil. They
have to be able to
extract nutrients
from the air and to
attach themselves to
the surface. As they
grow and produce
dead matter, they
start to develop soil
and weather the
surface. Other
colonizers then start
to grow in the area
and the pioneers are
rapidly out
competed. Lichens
are an example of
pioneers of bare
rock.
Animals are often able to avoid fires or
survive them in a number of ways. The ant
nest was in an area that had burned the day
before. The ants quickly dug themselves out
and moved their pupae and young to a new
nest about 10 feet away .
In the drought year of 1988, huge fires swept
through Yellowstone National Park (above
and left). After years of fire suppression in the
park, the forest floor was loaded with potential
fuel, and the resulting fire burned hotter than it
would have if more frequent, patchy fires had
been allowed to take their natural course. The
pictures above were taken in 1999; 11 years
after the fires. The slow regrowth is in part due
to the cold temperatures there; average annual
temperature in Yellowstone is only about 1°
C. To the left, a pine sapling struggles to
regrow after the fire. In Yellowstone, the fires
moved the community away from its climax and
set secondary succession into motion.
The good thing about
replanting is that we
have more trees. The
bad thing is that they
are all the same type
and the same age –
not giving much
diversity for animals
who rely on different
kinds of trees.
This old pasture is
reverting back to forest.
Grasses are gradually
being replaced by flowers
and weeds. Next will come
shrubs and small trees.
Finally, larger trees will
sprout up and grow,
creating a mature forest
or CLIMAX
COMMUNITY.
In 1980, Mt. St. Helens in Washington
erupted, essentially destroying all life in a
large blast zone. Trees were killed (left)
and the ground was covered with ash.
Above: A nurse log in a temperate rainforest shows
many of the stages of succession, with mosses and other
plants taking roots. Tree seedlings will also grow here, and
eventually the nurse log may give rise to 2 or 3 full-size
trees.