Chapter 19 Section 2

Describe the process of succession

Contrast primary and secondary succession

Explain how mature communities develop

Records were set in 2000 and 2002 for the largest areas of the US burned by wildfires in 50 years

More than 4 million acres were burned in 2002 during a period of severe drought

Like living things, ecosystems are born, develop, and mature.

Events can disrupt ecosystems and set off a chain reaction of events called: succession

Events:◦ Fires, storms, volcanic eruptions…

Succession: the gradual development of a community over time

Can take place in all communities not just forests

Ex: Forest fires in 1988 at Yellowstone National Park◦ http://www.yellowstone-bearman.com/yfire.html

A small community starts to grow in an area where no organisms had previously lived

No soil in the area, only bare rock

Organisms live and die on the rock and eventually form soil

Pioneer species: the first organisms to live in an area

1. Retreating glacier exposes bare rock

2. Lichens help to start the formation of soil

3. After many years, soil and mosses grow and insect being to live there

4. Soil deepens, mosses are replaced by ferns, grasses , and wildflowers; shrubs and small trees may grow

5. 100’s or 1000’s of years pass and the soil is deep enough to support a forest

http://image.tutorvista.com/content/biotic-community/lithosere-trends-sucession.jpeg

Sometimes an existing community is destroyed by a natural disaster

Causes: fire, flood, farmer stops farming an area

If the soil is left intact, the original community can regrow

1. First year a farmer stops growing crops, weeds start to grow (crab grass 1st)

2. Second year, new weeds appear (horseweed is common)

3. In 5-15 years, small conifer trees grow among the weeds, forest may form after ~100 years

4. As older conifers die, may be replaced by hardwoods (oak, maple) if the climate is right

http://www.rpdp.net/sciencetips_v2/images/L12C2_4.gif

All species in a new community are vulnerable to disease, competition, and disturbances

Community becomes dominated by a well-adapted, slow-growing climax species

Over time more species become established Variety of species in an area is called: biodiversity

A mature community: has organisms that are well adapted to live together in the same area over time

Ex: plants of the Sonoran Desert in Arizona

http://www.deserttortoise.org/image/2006cat7bos.jpg

Fire is a necessary part of the life cycle of forest communities

Prescribed burning (controversial)

Fire can assist in the recycling of nutrients, regulation of plant succession, help in maintaining biological diversity, reducing biomass, helping to control the insect population…

Describe the main difference between primary and secondary succession

Describe how pioneer species prepare an area for other living things