How do plant communities change over time

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How do plant communities change over time? Plant
Succession is a process of colonization to climax.
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Succession communities in an area change over
time into a different community Community
populations of all species living interacting
in an area Association certain species commonly
found together
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Plant Succession

• PRIMARY vs... SECONDARY
• PRIMARY starts with bare rock/mineral soil
• (no organic material i.e. lava flows, sand
  dunes, volcanoes, mines, landslides, bulldozers)
• SECONDARY partial disturbance
• (tree falls, fire, disease/insect impacts,
  storms)
• Question is, how much disturbance what type?

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Glaciers covered the Puget Sound about 12,000
years ago
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Glaciers scraped the surface clean and lands
recolonized
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Big Fires can kill all life 1. succession
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• Primary Succession means
• No living plants
• No organisms in the soils
• No Organic material in soils

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Which Organisms Take Over?

• First to arrive (Colonizers)
• Tolerance of environment
• Early Colonizers tend to
• grow rapidly sun loving
• mature quickly
• reproduce with small seeds in large numbers

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Early Successional species include mosses
lichens
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Mosses lichens capture windblown seeds soil,
allowing herbs grow
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Colonizers change habitats

• Hold soil/seeds windblown
• create soil with decomposition
• (add organics)
• create shading/cooler/hold moisture
• add biomass
• This allows new species with different habitat
  requirements

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Many annual perennial herbs are early
successional species
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Non-native Species

• Tend to be early successional
• Tend to have no predators
• (chemical defenses/interactions)
• Aggressive and Fast growing
• Can be extremely disruptive to ecosystems
• Examples cheatgrass, Himalayan blackberry,
  English ivy, clematis, holly

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Young trees growing in a field
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SECONDARY SUCCESSION disturbances such as
tree falls, fire, diseases, insects, impacts,
storms may only partially disturb a community
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Small fires may only remove some of the
vegetation this is 2. succession
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Some species of plants are only found after a fire
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Some species of plants survive fires better
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Late Mid- Early Forests Shrubs Herbs
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Species Characteristics

• EARLY
• Sunloving
• Fast growing
• Fast to reproduce
• Lots of small seeds
• Smaller biomass
• Broad niche
• Biodiversity low
• Interactions low
• Ecosystem stability low

• LATE
• Shade tolerant
• Slow growing
• Slow to reproduce
• Larger seeds
• (more stored food)
• Larger biomass
• Narrow niche
• Biodiversity high
• Interactions high
• Ecosystem stability high