Transcript Ecological Succession

Ecological Succession
Ecological Succession
• Series of changes that occur during the
development of an ecosystem
• the gradual replacement of one community
by another until a stable long-lasting stage
is reached
Changes in the Community
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
What determines what the final
Community will be????
• 1. Climate (temperature & moisture) and
Soil Quality
• 2. In the U.P., the climate is pretty much
the same, so differences in soil type
influence the community type.
Four Basic Communities
•
•
•
•
A. Pine
B. Boreal Forest
C. Northern Hardwoods
D. Bog/Swamp
Why does Succession Happen?
• Each community alters the physical features
of a site making it less favorable for its
members and more favorable for
competitors.
• In other words, each community brings
about its own demise.
How long does Succession Take?
• Succession depends on the size of the
ecosystem but generally takes hundreds to
thousands of years.
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
Types of Succession
• Primary Succession – soil building occurs
on previously uninhabited site
• Examples:
– Bare rock  lichen  moss  herbs  trees
– Sand  dune grass  blueberry 
cherry/poplar trees
Pioneer Species
• The first species to occupy a bare site
• Characteristics:
- tough (can endure extremes of temperature
- lack of moisture
- lack of nutrients
Secondary Succession
• Occurs on a site on which the established
community has been removed
(soil already present)
• Disturbances include:
–
–
–
–
–
Fire (commonly used to control undergrowth)
Farming
Logging
Over-grazing
Urbanization
Climax Community
• The eventual community that occupies the
site after the disturbance – it will remain
that way unless it is disturbed.
• If a forest is removed, secondary succession
begins with perennial weeds, poplar and
cherry trees, and sometimes pine. Often
fireweed is an indicator species of the stage.
• If the disturbance is severe enough, it may
set it back to primary succession – may take
a tremendously long time for climax
community to be reached.
• In general, as succession proceeds, food
chains are replaced by food webs, there is
more biomass and species diversity, and the
ecosystem is more stable – what might
destroy an early stage does not cause as
great an effect at later stages
Make Up of a Community
• Depends on tolerances of the species involved
• Tolerance
– 1. Shade tolerant species – can photosynthesize
adequately at very low levels of light ex. Maple,
oak seedlings, certain species of fern
– 2. Shade intolerant species – require bright light to
photosynthesize enough to survive ex. Cherry,
poplar, grass
How Does Succession Happen?
• Cherry/poplar seedlings colonize a
disturbed site. As they grow, they shade the
ground. Young cherry and poplar seedlings
cannot grow in the shade but oak/maple
seedlings thrive there. Eventually,
oaks/maples shade the cherry and poplar
trees, reducing the light to below the
compensation intensity, and those trees die.
Indicator Species
• Species that live only in certain stages of
succession or under very specific conditions
• Examples:
– Yew – an evergreen shrub found
only in mature hardwood forests
– Sphagnum moss – found only in
bogs and swamps
Disclimax Community
• Artificial communities that are maintained
only by constant intervention by man -----they are never allowed to reach the climax
stage of succession
• Examples: park, farmer’s field, lawn
QuickTime™ and a
decompressor
are needed to see this picture.
QuickTime™ and a
decompressor
are needed to see this picture.
Ecotone
• The transition zone
between two adjacent
communities
• Example: Where a field
blends into a forest often there is a greater
diversity of life in an
ecotone, because the
more tolerant species
from each community
can be found there
The End