1. How do plant communities change over time?
Plant Succession is a process of colonization to climax.

2. 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

3. Different Wildlife use Different Stages of Successional Environments

4. 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

5. EASTERN U.S. SUCCESSION HAS DECIDUOUS TREES AS CLIMAX
(NORTH WESTERN forests have conifers as climax type)

6. Bare Soil
Colonizing
Old Field
Forest

7. 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

8. Seed Dispersal is a Critical Component of Soil Colonization

9. 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

10. Early Successional species include mosses + lichens

11. 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

12. Mosses + lichens capture windblown seeds + soil, allowing herbs grow

13. Many annual + perennial herbs are also early successional species

14. 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

15. Shrubs and young trees invading a field continue succession

16. 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

18. Cottonwood trees in a mid successional forest

19. Oregon “old growth” climax 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

20. Climax Steppe-Shrub in Eastern Oregon – Go Sagebrush!

21. 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

22. Glaciers covered the Puget Sound about 12,000 years ago

23. Glaciers scraped the surface clean and lands recolonized

24. Colonizing a bare slope

25. Big Fires can kill all life = 1. succession

26. Primary Succession means:
No living plants
No organisms in the soils
No Organic material in soils

27. 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.

28. 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.

29. SECONDARY SUCCESSION =
Question is, how much disturbance = what type? Primary or Secondary?

30. Small fires may only remove some of the vegetation = this is 2
Small fires may only remove some of the vegetation = this is 2. succession

31. Some species of plants only reproduce after a fire

32. 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