Welcome!
 Please read the board
completely.
 Please get out your
Ecology objectives #15 and review with
your neighbor for the
quiz. (add review
ideas in a different
color!)
Succession – Change in
Ecosystems
Case Study: Enchanted Rock, TX
Enchanted Rock, State Park
 15 mi NW of
Fredricksberg
 Granite batholith
surrounded by
limestone
.
Succession: the orderly
replacement of one ecosystem by
another.
Primary Succession
Secondary
Succession
Primary succession begins with
bare rock.
The granite rock cracks and breaks off as it is heated
and cooled each day and season. This is the first
step in the formation of soil.
Dust, rain, and soil particles are trapped in the depressions,
allowing grasses to grow. The first species to appear in an
area are referred to as pioneer species.
Characteristics of early
successional or pioneer plants:
 Grow close to
ground
 reproduce
quickly
 can survive harsh
conditions
 short lives
Plants live, die and are decomposed, adding to
the soil depth. This allows more seeds to
germinate and grow.
Cacti can grow here, too and are a good example of
midsuccessional species.
As communities grow, abiotic conditions are altered,
allowing new communities to take hold.
How would soil development change the amount of
moisture available to plants? How would the growth
of plants change the amount of wind at ground level?
Climax communities represent the final stage of
succession. These climax communities will remain
in this spot until they are disrupted.
Characteristics of climax or late
successional communities
 Slow growing
 can tolerate shade
 tall (or at least taller than pioneers)
Climax communities differ by ecoregion, but they
generally include long-lived and woody species.
Climax communities are described by their
vegetation, but remember that animal communities
will change as succession proceeds, too.
Factors affecting succession
patterns and rates
 Facilitation –

one species makes an area suitable for species
with different requirements.
 Inhibition –

early species hinder the establishment and
growth of other species
 Tolerance –

late successional plants are largely unaffected
by plants at earlier stages of succession
Secondary Succession begins with a
disturbance in an existing ecosystem.
 Clear cutting
 Abandoned agricultural field
 Fire!
Some Climax species are fire
adapted!
 Humans don’t like disturbances, but some
ecosystems need them!

Fire wars – 17-31
What can you add now?
Primary succession
Secondary succession
Fire is critical to prairie and forest
ecosystems
 Returns nutrients to soil
 Helps certain seeds
germinate
 Forest – clears underbrush
/fuel
 Prairie – kills trees
 Light can reach soil
 Help control
pathogens/insects
Intermediate Disturbance hypothesis
Fire Suppression
 1944 – US Forest
Service
 1988 – fires in
Yellowstone shocked
nation
 1990 – fire policy
change
Yellowstone 1988 1.4 million acres
burned; May - Nov
US Forest fire policy




Extinguish arson
Manage lightning strikes
Protect people
Application of improved scientific
understanding in succession
Succession is a pattern
 Nature doesn’t always
fit human categories
 Many scientists doubt
the usefulness of the
concept of succession
 Succession does help
predict what changes
may occur in an
ecosystem over time