1. Succession and Stability
Seals

2. Reduced snowfall in ice field sources
Warmer temp. during winter
Reduction in cloud cover and rain in summer

3. Outline Introduction Primary Succession Secondary Succession
Disturbance
Ecosystem Recovery
Mechanisms of Succession
Community and Ecosystem Stability

4. Introduction
Succession: Gradual change in plant and animal communities in an area following disturbance.
Primary succession on newly exposed geological substrates.
Secondary succession following disturbance that does not destroy soil.
Climax Community: Late successional community that remains stable until disrupted by disturbance.

5. Primary Succession at Glacier Bay
Reiners et.al. studied changes in plant diversity during succession.
Total number of plant species increased with plot age.
Species richness increased rapidly in early years of succession and more slowly during later stages.
Not all groups increased in density throughout succession.

6. Margerie Glacier

8. Primary Succession at Glacier Bay

9. Secondary Succession in Temperate Forests
Oosting found number of woody plant species increased during secondary succession at Piedmont Plateau.
Johnston and Odum found increase in bird diversity across successional sequence closely paralleled increase in woody plant diversity observed by Oosting.

10. Secondary succession occurs where a plant community has been disrupted
Secondary succession occurs where a plant community has been disrupted. A common example is when abandoned farmland is allowed to revert to the wild. In deserted farm fields, the pioneer plants are often grasses, shrubs, weeds, and tree saplings. Eventually, taller trees move in and alter the environment by creating moist and shaded conditions. Ultimately, a relatively stable climax community will be attained.

12. Buell- Small Succession Study

13. Succession in Stream Communities
Fisher studied rapid succession in Sycamore Creek, AZ.
Evaporation nearly equals precipitation - flows generally low and intermittent.
Subject to flash floods.
Observed rapid changes in diversity and composition of algae and invertebrates.
Invertebrates found refuge because many adults in aerial stage.
Re-colonized after flooding.

14. Ecosystem Changes During Succession
Chapin documented substantial changes in ecosystem structure during succession at Glacier Bay.
Total soil depth and depth of all major soil horizons show significant increase from pioneer community.
In addition, organic content, moisture, and N concentrations all increased.
Physical and biological systems are inseparable.

15. Ecosystem Changes During Succession

16. Four Million Years of Ecosystem Change
Chronosequences (seq. of ages represented at study sites) such as that found at Glacier Bay are limited.
Hawaiian Islands have formed over hot spots on the Pacific tectonic plate, forming an island chain varying greatly in age.
Hedin et.al. found differing patterns of nutrient distribution across the chronosequence.

17. Recovery of Nutrient Retention Following Disturbance
Bormann and Likens found felling trees in Hubbard Brook substantially increased nutrient losses.
Herbicide used to suppress regrowth.
When application stopped, succession proceeded, nutrient losses decreased,and primary production increased.

18. Mechanisms of Succession
Clements
Facilitation
Connell and Slayter
Tolerance
Inhibition

19. Facilitation
Proposes many species may attempt to colonize newly available space.
Only certain species will establish.
Colonizers “Pioneer Species” modify environment so it becomes less suitable for themselves and more suitable for species of later successional stages.

20. Tolerance
Initial stages of colonization are not limited to pioneer species.
Early successional species do not facilitate later successional species.

21. Inhibition
Early occupants of an area modify the environment in a way that makes it less suitable for both early and late successional species.
Early arrivals inhibit colonization by later arrivals.
Assures late successional species dominate an area because they live a long time and resist damage by physical and biological factors.

22. Mechanisms of Succession

24. Successional Mechanisms in Rocky Intertidal Zone
Sousa investigated mechanisms behind succession of algae and barnacles in intertidal boulder fields.
If the inhibition model is in effect, early successional species should be more vulnerable to mortality.
Results showed early successional species had lowest survivorship and were more vulnerable to herbivores.

25. Community and Ecosystem Stability
Stability: Absence of change.
Resistance: Ability to maintain structure and function in face of potential disturbance.
Resilience: Ability to recover from disturbance.

26. Park Grass Experiment Hertfordshire, England
Studied effects of fertilizer treatments.
Continued for 150 years.
Silverton investigated ecosystem stability.
Used community composition variability as measure of stability.
Represented composition as proportion of community consisting of each plant form.

27. Park Grass Experiment
Dodd showed that although community stability is present, populations of individual species can change substantially.
Stability depends on resolution an area is investigated at.

28. Disclimax
Disclimax or "disturbance climax" describes a community that is held at an earlier successional stage by repeated but unpredictable disturbances that prevent succession from reaching the climax community that might be expected for the climate of the area.
The original prairies of Illinois are examples of disclimax communities. The early successional grass and perennial plants are fire tolerant because of their underground roots and stems. Repeated fires destroy shrubs, young trees, and other plants that would change the environment and result in further successional changes that would eventually result in the establishment of a deciduous forest.
Agricultural practices are essentially an artificial form of maintaining disclimax. Crops like corn and soybeans as well as the common weeds found in agricultural fields have the characteristics of pioneer species and require repeated soil disturbance.

29. Chapter 20