Transcript Community Dynamics

Disturbance and Succession
Primary succession is a process that generally involves:
1) the accumulation of organic matter- wind blown debris,
insects migrating in, etc.
2) Small plants (long-distance dispersal, small seeds)
3) Accumulation of more material, deeper rooted species- more
habitats for wildlife
4) Continued increase in organic matter, the formation of
rudimentary soil, eventually “real” soil, vegetation and the
accompanying animal species.
A sequence of species
colonize the blocks,
replacing each other in
an apparently
predictable way…
Henry Chandler Cowles- Lake Michigan Dunes, 1899
Glacier Bay
Secondary succession
http://www.youtube.com/watch?v=rFeufWFPVm4
Fire is a spectacular, and sometimes scary
process, but ecologically this is very often
essential to the functioning of the system. It is
almost never a “disaster” from an ecological
perspective
Fire influences ecosystems by:
1)
2)
3)
4)
5)
6)
Reducing competition
Altering seed bed characteristics
Changing soil nutrient environment
Creating/Perpetuating a mosaic
Reducing forest floor mass (fuels)
Many others
Dendroecological reconstruction of fire history
First- what is a tree ring?
-A record of tree growth, created by a tree’s seasonal access to
resources and/or by cold weather.
Summer
Winter
Temperature-derived tree rings:
-In the summer, it is warm and wet, the trees grow rapidly.
-In the autumn, temps drop, trees lose their leaves.
-In the winter, in freezing temps, the trees are “dormant”.
Summer
Winter
- This process is recorded in the wood as an “annual ring”
- “Annual”- because it happens every year.
- This means we can date the trees with great accuracy
One year
Winter
Winter
Tree-ring analysis can be used to
reconstruct fire history:
- When fire passes near a tree the heat
kills the cambium.
- The tree closes the wound and
therefore, encapsulates that injury in the
wood.
- The wounds are found in a tree-ring
series, so they can be dated.
-Fire scars give information about the
frequency of fires in the forest.
-If you collect many samples in a
forest you can also reconstruct
spatial patterns of fire.
-If have old trees, you can develop
long histories.
A)
B)
D)
C)
Prescribed Fire
Early successional species
vs.
Late successional species
Some theories of succession…
equilibrium forces, facilitation,
inhibition and tolerance…
Equilibrium forces (succession)
Non-equilibrium forces (disturbance)
Question:
Why to later species replace earlier species?
Some theories of succession1)
Facilitation- Each species creates opportunities for the next
species. The system cycles through species until a species no
longer provides this opportunity and become dominant.
2)
Inhibition- Species hold onto the site via competition (and other
negative interactions) and only give way to other species due to
disturbance or death.
3)
Tolerance- Species that make up the final composition of the
community are those best able to tolerate environmental conditions.
They are neither hindered (inhibition) or helped (facilitation) by other
species
Implications of succession…
Implications of succession- ecosystem processes…..
Disturbance and Succession