Welcome! §Please read the board completely. §Please get out your Ecology objectives #1- 5 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 SuccessionSecondary 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 – l one species makes an area suitable for species with different requirements. § Inhibition – l early species hinder the establishment and growth of other species § Tolerance – l 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 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