Patterns of Succession

1. Patterns of Succession

2. Succession is: • Non-seasonal, directional change in plant species living in a particular place through time. • Involves: • Colonization • Establishment • Ultimate local extinction • Initiated by a disturbance that opens up space and resources

3. Types of Succession • Primary: Occurs when new bare rock is generated by geologic activity (no organic material) • Mt. St. Helens, Krakatoa, glacial retreat • Secondary: vegetation invades areas that have been previously occupied, but has been removed due to disturbance (fire, agriculture, etc)

4. Primary Succession after glacial retreat Example of primary succession: lichensmoss small forbsshrubstrees

5. Lichens and moss growing on rock (primary succession)

6. Secondary Succession

7. Secondary Succession in YNP after 1988 fires

8. Classic Study: Billings (1938) • Studied succession from old field to oak forest (150 years) • Annual plants = pioneer species • Biennial plants, grasses • Perennial plants, shrubs • After about 15 years: softwood trees • After about 50 years hardwood trees, primarily oak

9. “Old-field Succession”

10. Successional Progression • Annuals: Pioneer Species • Tolerate low nutrient soils, need high light • Good dispersers • Grow rapidly, short life span (1 year) • Produce many offspring • Biennial plants, grasses • Share attributes with pioneer species, but longer lived, grow more slowly • Perennials and shrubs • Slower growing, longer lived • Can reproduce asexually as well as sexually • Better competitors

11. Softwood trees (Pines) • Slow growing • Eventually produce canopy • Shade out light-loving shrubs and perennials in understory • Also shades out new baby pines • Hardwood trees (Oaks and hickory) • Longer lived • Better competitors • Eventually dominated forest as softwood trees died. Oak forest in this case = climax community

12. Climax Communities • Final successional stage: self-replacing, persistant over very long periods of time • Idea of climax community controversial these days because of recognition of role of disturbance • Shifting mosaic steady state model: • Majority of patches in habitat in some stage of recovering from disturbance • Landscape is in a steady-state because roughly constant portions of landscape are in each stage of succession • Thus there is a dynamic equilibrium across the landscape

13. Disturbance Specialists: Often Weeds

14. Mechanisms of SuccessionConnell and Slayter, 1977 1. Facilitation - Changes in abiotic conditions are caused by the plants currently occupying an area - These changes favor new invaders over the current occupants (current occupants pave the way for future occupants) Examples: Lichens make soil, nitrogen-fixing plants enrich soil, nurse plants support others

15. 2. Tolerance • Plants in different stages of succession don’t have much impact on each other • Position in the scheme of succession depends on their different life histories • Example: Old field Succession

16. 3. Inhibition • Members of one stage of succession resist invasion of later stages • Succession proceeds when one stage dies Example: Allelopathy

19. Succession and Chemical Cycling • Biomass, production, diversity and chemical cycling change during succession • Biomass and diversity peak in mid-succession, increasing at first to a maximum, then declining and varying over time.

21. K-selection and r-selection • Pioneer species generally have particular set of characteristics - all together these are called r-selected traits • Climax species generally have different set - represent a different life history strategy

22. Succession and Plant Diversity

23. Succession and Diversity

24. Just focusing on woody plants:

25. Corresponding changes in animal species

26. Succession in the Intertidal

27. Diversity through Succession in Intertidal

28. Succession in Streams

29. Points to Consider: • Change through time is a natural characteristic of most ecosystems - when thinking about conservation need to incorporate understanding of natural disturbance regimes • Mosaic of Patches in different stages of succession maximizes habitat heterogeneity and thus diversity

30. Ecological Restoration • Attempt to return impacted land to natural state • What exactly should be returned? • Increasingly are trying to replace the original disturbance regime so that succession can occur naturally • Need to restore disturbance and succession processes both temporally and spatially • What area of land is big enough to encompass these processes?

34. Stream Restoration • What ecosystem functions/services need to be restored? • Habitat • Conduit • Barrier • Filter • Source • Sink

35. Processes need to be restored, not just individual components • Hydrologic functions: • How much flow, how deep, timing • Geomorphological functions • Stream profile, sedimentation patterns, erosion • Physical and Chemical Properties of Water • Toxins? • Nutrients • PH • Biological Processes (eg large woody debris, habitat structure, heterogeneity in stream) • Role of Disturbance/Dynamic Equilibrium