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How do Ecosystems Respond to Change?
Name_____________________
Directions: Read all the directions and background information thoroughly.
Ecological Succession - Change in the species composition of a community over time
Succession progresses in stages from pioneer species to a climax community. The entire process
from bare rock to climax is called a SERE that progresses through SERAL STAGES
Early seral stages – low diversity, simple structure, wide niches
Later seral stages – climax communities – higher diversity, complex structure, narrow niches
Pioneer Species – initiate recovery in both primary and secondary succession
 Provide soil stabilization
 Soil nutrient enrichment (organic matter and biological nitrogen fixation)
 Increased moisture holding capacity
(1) Primary Succession – progression of species after the formation of new land (NO SOIL –
mixture of mineral material, decaying organic material, and living organisms))
 Ex: River deltas, lava fields, sand dunes, glacial deposits)
 Pioneer species - lichens and mosses
 Early successional plant species - grow close to the ground; help break up rock
and make more soil
 Midsuccessional plant species - herbs, grasses and low shrubs
 Late successional plant species – trees
 If primary succession starts on land it is a xerosphere
 If it starts in water (a pond) it is a hydrosphere
(2) Secondary Succession – when an existing community is destroyed but the SOIL REMAINS
 Ex: fire, flood, abandoned farmland, polluted streams
 Occurs on soils that are already developed and ready to accept seeds carried in
by the wind or those that are already stored in the soil
 This shortens the number of seral stages the community goes through
Good examples of secondary succession have been studied in abandoned form land in North
Carolina. The farmland had become infertile through not enough nutrients being returned after
crops had been harvested and through wind erosion. As the land became unproductive and
uneconomical to farm, farmers simply abandoned the land. This left patches of former farmland
of various ages.
Energy Flow
During succession Gross Primary Productivity tends to increase through the pioneer and early
wooded stages and then decreases as climax community reaches maturity. This increase in
productivity is linked to growth and biomass.
Early seral stages
 rapid growth and biomass accumulation (grasses, herbs, shrubs)
 GPP is low, but NPP a large proportion of GPP as there is little
biomass and low respiration to start with
Later seral stages
 Woodland – biomass and productivity have increased
 GPP high, NPP a lower percentage of GPP as respiration rates
have increased
Climax community
 Tree growth slows, biomass decreases as canopy prevents ground cover
 Older trees are less photosynthetically efficient and more energy is allocated to structural
biomass (root systems) so NPP approaches zero, ratio of NPP to R approaches 1
Biodiversity
 Early seral stages – fewer species
 Subsequent seral stages – number of
species increases
 Climax community – little additional
increase in diversity
Climax Communities
 Determined by climate and edaphic (soil)
factors
 Frequently disturbed by human factors –
fire, agriculture, grazing, habitat destruction
Name__________________________________
Visit the web link: http://www.nps.gov/kefj/naturescience/plant-succession.htm
1. Describe the succession that has occurred in this ecosystem. Describe the order that
species appear and why.
Visit the web link: http://www.countrysideinfo.co.uk/successn/hydro.htm
2. Describe the succession that has occurred in this ecosystem. Describe the order that
species appear and why.
3. Is this an example of primary or secondary succession? Why?
Fire Succession in San Diego County Click on each of the links and answer the associated
questions
Chaparral→ http://interwork.sdsu.edu/fire/resources/chapparal-charecteristics.htm
4. How are some plants adapted to the fires of the chaparral?
5. What has been the impact of fire suppression strategies in the chaparral?
6. According to the article, what might happen if human population in chaparral areas
continues to increase, and the frequencies of wildfires become more prevalent?
Mixed Coniferous Forest→ http://interwork.sdsu.edu/fire/resources/conifer-forest.htm
Read the 1st section: The Burning of Cuyamaca Rancho State Park
7. How have fires benefitted this biome?
8. How have fire suppression efforts in coniferous forest influenced shade tolerant plants?
9. In National Forests, government policy has been to suppress forest fires whenever
possible for the last century. Now some regions are starting to allow fires to burn. Based
on what you know about succession, what impact do you think this might have in the
mixed coniferous forests of San Diego and areas like it?
Click on the link→ http://www.fire-ecology.org/education/doc1.htm (Fire Ecology)
10. What are some of the adaptations common to plants and trees in fire prone areas?
11. According to the article, how does wildfire and the wildfire recovery process influence
animal biodiversity?
12. List the six major U.S. fire-adapted ecological communities.