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