How do plant
communities
change over
time?
Plant
Succession is
a process of
colonization
to climax.
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
Different Wildlife use Different Stages
of Successional Environments
Species Characteristics
• EARLY
• LATE
•
•
•
•
Sunloving
Fast growing
Fast to reproduce
Lots of small seeds
•
•
•
•
•
•
•
•
•
Smaller biomass
Broad niche
Biodiversity low
Interactions low
Ecosystem stability low
•
•
•
•
•
Shade tolerant
Slow growing
Slow to reproduce
Larger seeds
(more stored food)
Larger biomass
Narrow niche
Biodiversity high
Interactions high
Ecosystem stability high
EASTERN U.S.
SUCCESSION HAS
DECIDUOUS
TREES AS CLIMAX
(NORTH WESTERN
forests have conifers
as climax type)
Bare Soil
Colonizing
Old Field
Forest
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
Seed Dispersal is a Critical Component
of Soil Colonization
Colonizers change habitats
• Plants hold windblown soil + seeds
• create soil with decomposition
(add organics + biomass)
• create shading/cooler/hold moisture
• This allows new species with different
habitat requirements to come in
Early Successional species
include mosses + lichens
• Facilitation: The organisms at a given successional
stage make the environment more suitable for later
successional stages.
• Examples: lichens breaking down rock into soil,
nitrogen-fixing plants
Mosses + lichens capture
windblown seeds + soil,
allowing herbs grow
Many annual + perennial
herbs are also early
successional species
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
Shrubs and young trees invading
a field continue succession
Early-successional habitats are declining
due to development, loss of farmland, natural plant
succession and the absence of fire. They are also
degraded by the invasion of non-native plants
Cottonwood trees in a mid successional forest
Climax: the end point of a successional sequence, a
community that has reached a steady state under a
particular set of environmental conditions.
Oregon “old growth” climax forest
Climax Steppe-Shrub in Eastern
Oregon – Go Sagebrush!
Plant Succession
PRIMARY vs... SECONDARY
• Primary succession = sequence of communities
developing in a newly exposed habitat devoid of life
• starts with bare rock or newly exposed mineral
soil (no organic material, no seeds)
i.e. lava flows, sand dunes, volcanoes, mines,
landslides, bulldozers
Glaciers covered the Puget Sound
about 12,000 years ago
Glaciers scraped the surface
clean and lands recolonized
Colonizing a bare slope
.
Big Fires can kill all life = 1 succession
Primary Succession means:
•No living plants
•No organisms in the soils
•No Organic material in soils
SECONDARY = partial disturbance
• sequence of communities taking place
on sites that have already supported
life
• ie. Abandoned farms, clearcut forests,
burned areas, etc.
• i.e. tree falls, small fires, disease/insect
impacts, storm damage.
Disturbance: an abrupt event that removes individual organisms or
biomass and opens up space (or frees resources) which can be
exploited by other organisms.
Disturbances vary in spatial scale, intensity, frequency, and type.
SECONDARY SUCCESSION =
•Question is, how much disturbance =
what type? Primary or Secondary?
http://www.youtube.com/watch?v=CQ2Xl6ZqzRI
Small fires may only remove some of
.
the vegetation = this is 2 succession
Some species of plants only
reproduce after a fire
Species Characteristics
• EARLY
• LATE
•
•
•
•
Sunloving
Fast growing
Fast to reproduce
Lots of small seeds
•
•
•
•
•
•
•
•
•
Smaller biomass
Broad niche
Biodiversity low
Interactions low
Ecosystem stability low
•
•
•
•
•
Shade tolerant
Slow growing
Slow to reproduce
Larger seeds
(more stored food)
Larger biomass
Narrow niche
Biodiversity high
Interactions high
Ecosystem stability high