Consequences of Disturbance for Diversity

1. Consequences of Disturbancefor Diversity Jennifer Skene Kristen Baker Margaret Metz

2. Disturbance? • Just about anything except: • Agriculture (not including forestry) • Climate change • Common disturbance types: • Hurricanes • Volcanoes

3. So what is diversity? • Genetic • Species • Spatial/temporal/structural • Landscape

4. And how did we do things? • Focus on review papers to facilitate synthesis across systems • Rocky intertidal zones and coral reef systems • Temperate, terrestrial systems: forests and grasslands • Tropical systems: do these systems respond differently due to inherently high diversity?

5. Consequences of Disturbance for Diversity The Intermediate Disturbance Hypothesis and Examples from Marine Environments

6. Intermediate Disturbance Hypothesis Connell 1978

7. The X axis • Frequency • Time since disturbance • Succession • Size • Small disturbances: encroachment and regrowth of individuals on the edge • Large disturbances: new recruits from outside, depends on propagule dispersal • Severity • Low severity: regrowth from remaining individuals • High severity: new recruits

8. Dynamic Equilibrium ModelHuston 1994 Or Productivity

9. Coral Reefs

10. Disturbance Agents in Coral Reefs • Hurricanes (cyclones) and storm waves • Freshwater floods • Smothering by sediments • Herds of predators Connell 1978

11. Coral Reefs in Australia Connell 1978

12. Storms cause a decrease in % cover, but this does not necessarily correspond to a change in diversity Rogers 1993

13. Effect of storms changes with depth • Deep reef zones experience fewer/less intense disturbances than shallow reef zones • Maximum H’ values and maximum species richness occur in deep reef zones -- perhaps because low light levels prevent shallow zone dominants from outcompeting other species Rogers 1993

14. Changes in Community Structure Over TimeHughes and Connell 1999

15. Susceptibility to damage depends on disturbance history. This can vary over regional scales.Hughes and Connell 1999

16. Rocky Intertidal

17. Rocky Intertidal

18. Disturbance Agents in the Rocky Intertidal • Storm waves • Drifting logs, cobbles • Tectonic uplift • Extended aerial exposure • Volcanic activity • Algal whiplash • Ice • Landslides Sousa 2001

19. Algae of the Rocky Intertidal Ulva sp. Early successional species Chondracanthus canaliculatus (formerly Gigartinia canaliculata) Late successional species

20. Rocky IntertidalSousa 1979 Algal density is highest for boulders of intermediate size, which require intermediate force to be overturned

21. Rocky IntertidalSousa 1979

22. Effect of species diversity on resistance to or recovery from disturbance • “Does the aggregate response of a multi-species assemblage to a disturbing force, in terms of lost cover or biomass, differ from what would be the sum of independent responses by the member species?” - Sousa 2001 • Are there higher order effects of species diversity?

23. Effect of species diversity on resistance to or recovery from disturbance • No evidence for this: The differences in species’ responses can be explained by their physiological and life history characteristics • Sousa 1980 - responses of boulders of different successional stages can be explained by algae characteristics • Allison 1997 - resistance to heat of algal aggregations of differing diversity can be explained by physiological characteristics

24. Local and Regional DiversityPaine and Levin 1981 • Disturbance creates patches within mussel beds, which are filled by a variety of species • “Environments exposed to intermediate disturbance levels should contain a richer mix of sites than environments with benign conditions or total destruction.” • Asynchronies in disturbance or colonization events increase the richness of pattern • Seasonality and size of disturbance determine the species that can colonize the patch • Regional diversity is maintained

25. Anthropogenic Logging Herbicides Insecticides Grazing by domestic livestock Research related (ie to study effect of disturbance) Natural Hurricane Volcanoes Wind Fire Windstorm Ice storm Insects Pathogens Herbivores Other mammal damage Avalanche Temperate, terrestrial systems

26. Disturbance intensity • High intensity disturbance tends to “set back” succession, reducing species diversity in the short term, maintaining or increasing it in the long term • Low intensity may increase or maintain • Ectomychorrizal communities in boreal forests following fire (Dahlberg 2002).

27. Janzen-Connell hypothesis • Maintenance of high diversity in tropical forests….temperate too? • Soil pathogen in mature black cherry adversely affects survival of seedling black cherry….effect disappears away from mature tree (Packer and Clay 2000) • Maintaining forest diversity?

28. gap gap nongap nongap gap border gap border Brokaw and Busing 2000 • In the Great Smoky Mountains, USA, relative abundances similar between gaps and understory. Higher richness observed in large gaps largely explained by greater stem density. • Niche availability not increased.

29. Herbicide use • Glyphosphate • No reduction in richness or diversity, sometimes increased • Intermediate disturbance? Control/treatment comparison Control Sullivan and Sullivan 2003

30. Grazing and the intermediate disturbance hypothesis • Soil, climate, and other disturbances likely have greater affect on species diversity • Little effect on native spp richness or exotic spp spread Stohlgren at al. 1999

31. More grazing (plus fire!) • California grassland replaced by coastal sage scrub replaced by chaparral and oak woodland….in presence of fire • Predicted high directional change in absence of grazing or fire – based on 40 years of change Callaway and Davis, 1993

32. Other critters • Moose browsing affects diversity at a variety of scales (Edenius et al. 2002) • Patch/plant level, stand level and landscape level • Ice depressions and goose grubbing (Belanger and Bedard 1994) • Human removal of biomass • Logging (ie McRae et al. 2001) – decrease genetic diversity, alter successional pathways • Hot spring algal community (Kullberg and Scheibe 1989)

33. Abrams and Scott, 1989

34. Foster et al. 1998

35. Peterson et al. 1998 Disturbance size: More diversity in seed dispersers (lg. and sm.) results in much different landscape pattern, affecting distribution and abundance of trees dispersed by mammals (model predictions) Not temperate: Kibale Forest in Uganda Whitebark pine: temperate, bird dispersed pine

36. Cascading effects • Whitebark pine as example • Decreasing in high elevation forests • Considered a keystone species • Large nuts offer high value food source for birds (Clark’s nutcracker), squirrels and grizzly bears • Disappearance of WBP on diversity?

37. Interacting disturbances • Fire, avalanche, bark beetles • Fire spread influenced by avalanche pattern (return interval almost annual), bark beetles influenced by both fire and avalanche • Results in non-overlapping distributions Veblen et al. 1994

38. Human alteration of disturbance regime • Logging and fire • Pin cherry abundance highest under short rotation harvesting, seed bank depletion under longer cycles decreases dominance following disturbance (Tierney and Fahey 1998) • Increase in angiosperm abundance in Fennoscandian boreal forest led to increase in moose population led to ….already discussed • Fire suppression: decrease landscape heterogeneity and result in less diversity?

39. Consequences of Disturbancefor Diversity Examples from Tropical Forests

40. Disturbances Resulting inPrimary Succession • Landslides • Volcanoes • Mobile rivers • Hurricanes • Logging Whitmore & Burslem, 1998

41. Disturbances Resulting in Secondary Succession • Treefalls • Severe windstorms • Shifting cultivation • Lightning • Fires Whitmore & Burslem, 1998

42. Hurricanes in NicaraguaVandermeer et al. 2000

43. Logged Borneo ForestsCannon et al. 1998

44. Cyclones - Solomon IslandsBurslem et al. 2000

45. Cyclones - Solomon IslandsBurslem et al. 2000

46. Small-Scale Disturbances • Early ideas of niche differentiation in gaps • soil • light • Treefalls are main form of canopy turn-over Orians, 1982

47. Growth-Survivorship Trade-off Wright, 2002

48. Richness in/out of Gaps Schnitzer and Carson 2001

49. Advance RegenerationUhl et al. 1988 • 97% of trees ≥1m four years after gap were present as seeds/seedlings before gap • Annual mortality: 8% for already established seedlings vs. 16% for post-treefall establishments

50. Dispersal Limitation:Decoupling Disturbance & Diversity