Patterns of Succession

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Patterns of Succession
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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

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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)

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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)
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Secondary Succession
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Secondary Succession in YNP after 1988 fires
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Classic Study Billings (1938)

• Studied succession from old field to oak forest
  (150 years)
• Annual plants pioneer species
• Biennial plants, grasses
• Perennial plants, shrubs
• After about 15 years softwood trees
• After about 50 years hardwood trees, primarily
  oak

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Old-field Succession
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Successional Progression

• Annuals Pioneer Species
• 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

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• 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

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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

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Disturbance Specialists Often Weeds
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Mechanisms of SuccessionConnell 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, nitrogen-fixing
  plants enrich soil, nurse plants support others

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2. Tolerance

• Plants in different stages of succession dont
  have much impact on each other
• Position in the scheme of succession depends on
  their different life histories
• Example Old field Succession

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3. Inhibition

• Members of one stage of succession resist
  invasion of later stages
• Succession proceeds when one stage dies
• Example Allelopathy

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Succession and Chemical Cycling

• Biomass, production, diversity and chemical
  cycling change during succession
• Biomass and diversity peak in mid-succession,
  increasing at first to a maximum, then declining
  and varying over time.

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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

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Succession and Plant Diversity
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Succession and Diversity
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Just focusing on woody plants
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Corresponding changes in animal species
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Succession in the Intertidal
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Diversity through Succession in Intertidal
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Succession in Streams
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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

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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?

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Stream Restoration

• What ecosystem functions/services need to be
  restored?
• Habitat
• Conduit
• Barrier
• Filter
• Source
• Sink

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• 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