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Succession
“An understanding of succession provides a basis for resolving man’s conflict with nature.”
Eugene P. Odum
Ecological Succession
Bare land usually does not stay bare for long.
Plants will colonize forming a community
Other communities replace that
This is Succession
Succession: a natural increase in the complexity of the structure and species composition of a community over time
• Occurs when there are no traces of the original community remaining,including vegetation and soil
• Pioneer species, such as lichens, are the first to colonize.• The environment changes as new species move in, adding nutrients andgenerating habitat.
Primary Succession
Primary Succession Cont.
Primary succession occurs after new land is either created or uncovered Examples: River Deltas, volcanic lava fields, sand dunes or
glacial deposits
Each stage of succession adds something that the next stage needs, allowing one stage to flow into the next
Pioneer Species: first to colonize adapted to live in limiting environments
Climax Community: Final stage of succession Stable and self perpetuating
Primary Succession
Northern Europe Example
Ecological Period Years ago Community
Pre‐Boreal 10000‐9500 Tundra with patches of willow, birch and pine
Boreal 9500‐7500 Hazel, pine
Atlantic 7500‐5000 Hazel, oak, elm, lime ash alder
Sub‐Boreal 5000‐2500 Mixed oak wit many cleared areas either being farmed or abandoned and returned to woodland
Secondary Succession Occurs when an already established community is suddenly destroyed
Following flood, or fire or after human activity, such as ploughing
Secondary Succession: occurs in soils already developed and ready to accept seeds carried by wind Often some seeds left from previous community Shortened number of stages
Secondary Succession
Changes Occurring During a Succession
Size of organisms increase, with trees creating more hospitable environment
Energy flow becomes more complex as simple food chains form webs
Soil depth, soil fertility, water‐holding capacity, mineral content and cycling all increase
Biodiversity increases (more niches), fall as climax is reached
Productivity rises and then falls
Species Diversity in Successions
Early stages have few species in the community
Number of species found increases and succession moves through the stages
Pioneer species usually are not totally replaced
Diversity increases and then levels out once niches are filled
Mt. St. Helens Example: species diversity increased for 10 years, leveled after 20
Disturbance
Even climax communities are subject to periods of disturbance
In forests, trees age, die and fall over leaving gaps
Communities can also be affected by natural hazards Flood, fire, landslides, earthquakes, hurricanes, etc Make gaps that can be colonized within the surrounding
community Adds to productivity and diversity
Some ecosystems never reach climax due to frequent disturbance (Equilibrium Communities or Subclimax Communities)
Arrested and Deflected Successions
Succession can be stopped by: Abiotic factors: soil conditions, water logging Biotic factor: heavy grazing
Causes Subclimax community, will only continue development if limiting factor is removed
Plagioclimax Community: succession arrested by humans Pasture, arable farmland or plantations (reduced
biodiversity) Can still develop into climax community if our
activity ceases
Significance of Changes
Agriculture conflicts with succession
We want high productivity, simple system and maximum yield
Natural System wants increased complexity and biodiversity
Changes if we value ecosystem services