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Plant succession
The Concept
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Succession is the natural, orderly change
in plant and animal communities that
occurs over time. If left undisturbed, an
open field may become an "aging" forest in
150-300 years. However soil conditions,
climate, permafrost, topography, and
natural and unnatural forces may affect the
pattern of succession
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Weather, fire, flood, insects, and human
activity can disrupt the forest, altering the
pattern of succession
The Stages
Herb Stage
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In this stage it contains seed plants whose
stems wither away to the ground each
winter.
insects and small rodents feed on the
grasses, herbaceous plants, and seeds
As the diversity of plants increases so does
the variety of wildlife species.
Shrub Stage
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usually low woody plants with several
permanent stems instead of a single trunk
Larger variety of wild-life attracts predators
Young Forest Stage
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the quantity and diversity of shrubs and
herbaceous plants decreases
With less variety in food available, the
number of wildlife species decreases.
birds of prey nest in the trees of a young
forest
Mature Forest Stage
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hardwood trees begin to die, opening the
canopy for the growth of spruce
Shrubs return and make more food and
cover available to songbirds, game birds,
and rodents.
Climax Forest Stage
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dead trees called snags provide homes for
woodpeckers and other cavity-nesting
birds. Porcupines, squirrels, spruce grouse,
and several songbird species are typical of
old stands of spruce trees.
Types of Succession
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Primary
Secondary
Allogenic
Autogenic
Progressive
Retrogressive
Primary
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Establishment of plants on land previously
not cultivated.
Secondary
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Invasion by plants on land that that was
previously vegetated.
Possible causes include natural or human
such as fire logging, cultivation or
hurricanes
Allogenic
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Change in Environmental conditions
E.g.. Salt marsh to woodland.
The environmental changes the
composition of the plant community
Autogenic
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Where both plant community and
environment change
Caused by the activities of plants over time
E.g.. Eruption of Mt. St.Helens
Progressive
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Where community becomes more complex
with time
Contains more species
Contains more biomass over time.
Retrogressive
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The community regresses.
Becomes more simplistic
Contains fewer species and less biomass
Some retrogressive successions are
allogenic in nature
E.g. Introduction of grazing animals results
in degradation of farmland.
The Facilitation Model
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"pioneer species" establish a presence on the site
of a disturbance.
They modify a site, for instance, by regenerating
the soil with organic material making the area
more attractive for invasion by other species.
Eventually, new species move in, edging out the
pioneers.
This process may repeat itself several times, until
the ecosystem reaches the climax stage.
The Tolerance Model
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all species involved in succession are equally
capable of establishing themselves on a recently
disturbed site
but those capable of attaining a large population
size quickly are likely to become dominant
Unlike the facilitation model, the tolerance model
does not depict earlier inhabitants as preparing
the site biologically.
this model is more akin to natural selection.
The Inhibition Model
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all species have equal opportunity to
establish populations after a disturbance
some of the early species actually make
the site less suitable for the development of
other species
An example of this is when plants secrete
toxins in the soil, thus inhibiting the
establishment and growth of other species
Climax
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When a biological community reaches a state of stability and
is in equilibrium with environmental conditions
Dominant species in a climax community are those that are
tolerant of the biological stresses that come with competition
frequent enough events of disturbance within small sections
of the biological community may prevent climax from even
occurring
Once reached change will slow down bringing an end to the
stages of succession.
Climax remains a theoretical notion.
What can cause Succession
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Seismic Events: earthquakes, tidal waves, or
volcanic eruptions
hurricanes or tornadoes.
the movement of glaciers or even of plates in
Earth's crust
wildfires or sudden infestations of insects
Humans causes such as plowing up ground,
logging, clearance for construction even by
causing explosions on a military reservation or
battlefield