Transcript Disturbance Ecology

Disturbance & 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.
12.16 Lava field on Hawaii, showing a young tree fern that has colonized the bare ground
12.8 The 1980 eruption of Mount St. Helens lead to primary succession
Henry Chandler Cowles- Lake Michigan Dunes, 1899
Glacier Bay
Secondary Succession
12.5 A large Dipteryx panamensis has created a gap
Gap formation & colonization
are important for maintaining
biodiversity.
-Forest floor heterogeneity
-Increased light at forest floor
-Colonization space for shade
intolerant species
12.6 Locations of all tornadoes recorded the United States from 1981 to 1990
http://www.youtube.com/watch?v=rFeufWFPVm4
Tornado damage
“Oak Openings”
12.9 Disturbance and early succession in a forest in northern lower Michigan (Part 1)
12.9 Disturbance and early succession in a forest in northern lower Michigan (Part 3)
12.11 Annual growth rings show clearly in this cross section of the trunk of a white pine
10
300
Quercus macrocarpa
6
200
4
Release Extent (%)
Ring Width (mm)
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2
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Quercus macrocarpa
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6
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Release Extent (%)
Ring Width (mm)
0
10
2
100
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Quercus macrocarpa
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6
200
4
2
0
1650
1700
1750
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1850
Year
1900
1950
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Release Extent (%)
Ring Width (mm)
0
10
Some theories of succession…
equilibrium forces, facilitation,
inhibition and tolerance…
F. E. Clements
Put forth the idea that ecosystems arrive, ultimately,
at a stable composition/structure, that is dictated by
climate. The “Climatic Climax” community. When
to exhaustive lengths describing the orderly phases
ecosystems move through prior to arrival at the
climax.
Was influenced by vegetation zonation, where if you
at a certain elevation and aspect you see the same
vegetation type over, and over, again across the
landscape.
This idea is a predecessor to the idea of “Equilibrium
Communities.” A more nuanced idea, to be sure,
because it implies “balance” but, still emphasizes a
deterministic process leading to a stability
http://people.wku.edu/charles.smith/chronob/CLEM1
1 & 2 are “equilibrium concepts.”
In number one the systems is passing
through an orderly series of stages
arriving at a common endpoint (box
D) after that point the system does
not change.
In two, the system is a bit less
orderly, but still arrives at a stable
endpoint.
Another way to think about
equilibrium is a ball and cup model.
Manipulating ecosystem dynamics is
an essential part of ecological
restoration.
In many cases, you start from a
system that is complete disarrayequilibrium forces are what you need
to manage to drive the system
toward the desired state.
But, what if the system has multipleequilbria as demonstrated in 4 (or in
a ball and cup diagram)?
Or, what if the system had no
equilibrium! This is demonstrated in
3, (or via a ball and cup diagram)
In fact, the idea of a climax community and equilibrium
conditions has been all but annihilated in the ecological
literature. Clements has been over-simplified and is now
something of a joke. As an ecologist it is a bit embarrassing to
be caught in something that smacks of being Clementsian!
Many have put for the idea that ALL ecosystems are
disequilibrium communities. There are no stable enpoints, and
things are constantly changing.
This is particularly prevalent among paleoecologists who point
out that ecosystem drivers are in constant flux. Climate and
anthropogenic processes have been dynamic for 15,000 years
in eastern North America and ecosystems are constantly
reacting to them.
Nevertheless, there are some real distinct patterns(Ecosystems near Dayton pretty much want to turn into
hardwood forest… for instance.)
Equilibrium forces (succession)
Non-equilibrium forces (disturbance)
12.14 Predictable and unpredictable successional trajectories
Convergence, Divergence and Stability…
Is succession deterministic or stochastic?
12.13 F. E. Egler’s theories of succession diagrammed for a hypothetical abandoned field in NC (1)
12.13 F. E. Egler’s theories of succession diagrammed for a hypothetical abandoned field in NC (2)
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
12.12 A saguaro cactus grows in the shade of its nurse plant, a palo verde tree
Watts Model of Vegetation Dynamics
Implications of succession…
Implications of succession- ecosystem processes…..
Disturbance & Succession