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Patterns of Succession
Succession is:
• Non-seasonal, directional change in plant
species living in a particular place through
time.
• Involves:
– Colonization
– Establishment
– Ultimate local extinction
• Initiated by a disturbance that opens up
space and resources
Types of Succession
• Primary: Occurs when new bare rock is
generated by geologic activity (no
organic material)
– Mt. St. Helens, Krakatoa, glacial retreat
• Secondary: vegetation invades areas
that have been previously occupied, but
has been removed due to disturbance
(fire, agriculture, etc)
Primary Succession after
glacial retreat
Example of primary
succession:
lichensmoss small
forbsshrubstrees
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Lichens and moss growing on
rock (primary succession)
Secondary Succession
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Secondary Succession in YNP
after 1988 fires
Classic Study: Billings (1938)
• Studied succession from old field to oak
forest (150 years)
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Annual plants = pioneer species
Biennial plants, grasses
Perennial plants, shrubs
After about 15 years: softwood trees
After about 50 years hardwood trees, primarily oak
“Old-field Succession”
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Successional Progression
• Annuals: Pioneer Species
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Tolerate low nutrient soils, need high light
Good dispersers
Grow rapidly, short life span (1 year)
Produce many offspring
• Biennial plants, grasses
– Share attributes with pioneer species, but longer
lived, grow more slowly
• Perennials and shrubs
– Slower growing, longer lived
– Can reproduce asexually as well as sexually
– Better competitors
• Softwood trees (Pines)
– Slow growing
– Eventually produce canopy
– Shade out light-loving shrubs and perennials in
understory
– Also shades out new baby pines
• Hardwood trees (Oaks and hickory)
– Longer lived
– Better competitors
– Eventually dominated forest as softwood trees
died.
Oak forest in this case = climax
community
Climax Communities
• Final successional stage: self-replacing,
persistant over very long periods of time
• Idea of climax community controversial these
days because of recognition of role of
disturbance
– Shifting mosaic steady state model:
• Majority of patches in habitat in some stage of recovering
from disturbance
• Landscape is in a steady-state because roughly constant
portions of landscape are in each stage of succession
• Thus there is a dynamic equilibrium across the
landscape
Disturbance Specialists: Often
Weeds
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Mechanisms of Succession
Connell and Slayter, 1977
1. Facilitation
- Changes in abiotic conditions are
caused by the plants currently
occupying an area
- These changes favor new invaders over
the current occupants (current
occupants pave the way for future
occupants)
Examples: Lichens make soil, nitrogenfixing plants enrich soil, nurse plants
support others
2. Tolerance
• Plants in different stages of succession
don’t have much impact on each other
• Position in the scheme of succession
depends on their different life histories
• Example: Old field Succession
3. Inhibition
• Members of one stage of succession
resist invasion of later stages
• Succession proceeds when one stage
dies
Example: Allelopathy
Succession and Chemical
Cycling
• Biomass, production, diversity and
chemical cycling change during
succession
• Biomass and diversity peak in midsuccession, increasing at first to a
maximum, then declining and varying
over time.
K-selection and r-selection
• Pioneer species generally have
particular set of characteristics - all
together these are called r-selected
traits
• Climax species generally have different
set - represent a different life history
strategy
Succession and Plant
Diversity
Succession and Diversity
Just focusing on woody
plants:
Corresponding changes in
animal species
Succession in the Intertidal
Diversity through Succession
in Intertidal
Succession in Streams
Points to Consider:
• Change through time is a natural
characteristic of most ecosystems - when
thinking about conservation need to
incorporate understanding of natural
disturbance regimes
• Mosaic of Patches in different stages of
succession maximizes habitat heterogeneity
and thus diversity
Ecological Restoration
• Attempt to return impacted land to natural
state
• What exactly should be returned?
• Increasingly are trying to replace the original
disturbance regime so that succession can
occur naturally
– Need to restore disturbance and succession
processes both temporally and spatially
– What area of land is big enough to encompass
these processes?
Stream Restoration
• What ecosystem functions/services need to
be restored?
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Habitat
Conduit
Barrier
Filter
Source
Sink
• Processes need to be restored, not just
individual components
– Hydrologic functions:
• How much flow, how deep, timing
– Geomorphological functions
• Stream profile, sedimentation patterns, erosion
– Physical and Chemical Properties of Water
• Toxins?
• Nutrients
• PH
– Biological Processes (eg large woody debris,
habitat structure, heterogeneity in stream)
– Role of Disturbance/Dynamic Equilibrium