1. Disturbance and Succession

3. Aerial view
Of 1989
Yellowstone
Fire

4. Disturbance
Disturbance - any agent which causes complete or partial destruction of the community resulting in the creation of bare space
Disturbance agents: both physical and biological processes may cause disturbances, though we usually focus on physical processes -
Physical - fires, ice storms, floods, drought, high winds, landslides, large waves
Biological - severe grazing, predation, disease, things that inadvertently kill organisms - digging and burrowing

5. Wind Damage – July 4, 1999 Derecho

6. Wildfire – Southern California
October 22, 2007

7. Intermediate Disturbance Hypothesis
Disturbance maintains communities in a "non-equilibrium state" (never reach equilibrium) and by renewing colonizable space, disturbance allows the persistence of species that might otherwise go extinct due to competitive exclusion. – from Joe Connell

9. Rocky coast near Santa Barbara, CA

10. Intertidal boulder field - California

11. Waves, boulders and disturbance
Wayne Sousa

12. Species diversity on intertidal boulders with
different degrees of disturbance – from Sousa

13. Species diversity on intertidal boulders with different degrees of disturbance – from Sousa
Boulder size
Small
Medium
Large
turnover chance
49% / month
9 % /month
0.1%/ month
bare space
most
medium
little
diversity
low - mostly Ulva
high - several species
low - mostly Gigartina

14. Tree fall in Gabon

15. In an ecosystem, disturbance
1) clears space and interrupts competitive dominance
2) changes relative abundance of species
3) is a source of spatial and temporal variability
4) is an agent of natural selection in terms of life history characteristics

16. Succession
Succession is the non-seasonal, directional and continuous pattern of colonization and extinction on a site by populations of species - this definition incorporates a range of successional sequences that occur over widely different time scales and have very different mechanisms.

17. Types of Succssion
Primary - succession on a site that has not experienced life before - extremely severe disturbance may have killed all life so no seeds or roots or individuals survive - lava flow, volcanic explosion, glacial retreat, landslides, weathering of bare rock
Secondary - succession on a site that may have remnants of previous life on it - some survivors of the disturbance - fire, floods, windstorms, wave battering, severe grazing 
Degradative - succession in which the substrate is decaying and being exploited by various organisms - succession of decomposers on carcass, rotting log, etc.

18. Body Farm – University of Tennessee
FBI Forensics Class

20. Facilitation Succession
Early species change community or ecosystem in a way that allows later species to move in and changes the system so that the early species can no longer survive there.

24. Retreat of Muir Glacier

25. Retreat of Muir Glacier – 1941 – 1950 - 2004

26. Retreat of Pederson Glacier – Kenai Fjords NP - 1930-2005

27. Succession at Glacier Bay

28. Glacier Bay terminal moraine

29. Terminal Moraine – Close Up

30. Early succession – Moss on bare soil

31. Fireweed at Glacier Bay

32. Dryas - herbal rose at Glacier Bay

33. Alder thicket – Glacier Bay

34. Sitka spruce seedlings

35. Mature Spruce–Hemlock Forest – Glacier Bay

36. Tolerance Succession
All species arrive at start of succession, but longer lived individuals eventually outlive short lived species and grow to dominate in the succession - long lived species can tolerate shade and competition early in life.

37. Old Field Succession

38. Old field succession – bare ground

39. Old field succession – annual weeds

40. Old field succession – perennials

41. Old field succession – pine invasion

42. Old field succession – hardwood forest

43. Inhibition Succession
First species to arrive occupies space and prevents the settlement of later arriving species - the first species are replaced only after they die.

44. Ulva – above and
Gigartina overgrowing Ulva – right

45. Typical Succession
In most successional sequences, all three mechanisms operate at different times in the sequence.

47. Henry C. Cowles (center) about 1920

48. Lake Michigan sand dune ecosystem

49. Marram grass establishment

50. “Blow-out” in sand dune ecosystem