1. Fire Effects on Aquatic Ecosystems
guest lecture by
Christine May

2. Fire Effects on Aquatic Systems
How can fire affect fish?
When and where does fire or fire management pose a threat?
What management alternatives are most likely to benefit aquatic systems?

3. Dunham et al. 2003

4. Direct Effects Mortality (causes are largely unknown)
Water temperature
Chemical toxicity from smoke or ash
Absorption of smoke gases into surface waters can cause ammonium levels to increase > 40-fold.
Leaching of aerially deposited ash can increase phosphorus levels.
Fire retardant is highly toxic to many aquatic organisms

5. Indirect Effects
Physical
Chemical
Biological

6. Physical Effects Hydrological Geomorphic Elevated water temperatures
Increased water yield
Geomorphic
Accelerated erosion rates
Changes in channel morphology
Elevated water temperatures
Dependant upon removal of riparian canopy cover

7. Factors that Influence Watershed Responses
Burn severity
Proportion of the watershed burned
Relative proximity of the burned area to the stream channel
Slope steepness
Soil type / erosivity

8. Chemical Effects
Rivers: increases in nutrient and chemical concentrations typically have a short duration and are flushed through the system with the first pre-fire precipitation events.
Lakes: inputs are often diluted but may be more persistent.

9. Biological Effects
Often associated with a short-term increase in biological productivity:
Increased light and nutrient availability = greater primary productivity.
Food web dynamics = algae → invertebrates → fish
Shift in functional feeding groups from shredders and collectors (associated with litter input) to grazers.

10. Minshall conceptual

11. Why is the Historic Range of Variation Important?
Without prior exposure to a particular frequency, magnitude, or type of disturbance there is no evolutionary basis for an individual or a community to respond.

12. Vulnerability of Fish to Fire
Quality of the affected habitats
Amount and spatial distribution of habitat
(habitat fragmentation)
Position in the drainage network
Habitat specificity
Mobility
Life history diversity

13. Which populations are the most vulnerable?
Relatively immobile species with a narrow range of habitat requirements in highly degraded or fragmented systems.

14. Metapopulation Dynamics

15. Metapopulation Dynamics
Network of habitat patches potentially interconnected by dispersal.
Driven by local extinction and recolonization.
Population recovery is faster in sites closer to sources of recolonization and free from migration barriers.

16. Dunham et al. 2003

17. Dunham et al. 2003

18. Dunham et al. 2003

19. Dunham et al. 2003

20. Dunham et al. 2003

21. Dunham et al. 2003

22. Dunham et al. 2003

23. Isolated Populations
In some cases, local extinctions have been observed in response to fire.
Particularly in small, headwater streams.
Example: fire-related mortality halted de-listing of the endangered Gila trout.

24. Dunham et al. 2003

25. Dunham et al. 2003

27. modified from Dunham et al. 2003
HABITAT
FRAGMENTATION
MOBILITY
ISOLATION
VULNERABILITY
HABITAT SPECIFICITY
HABITAT SIZE
HABITAT DEGRADATION
modified from Dunham et al. 2003

28. Dunham et al. 2003

29. Pre-fire Management
A proactive approach, which addresses factors that render fish populations vulnerable to fire-related disturbance
Likely to be the most effective!

30. Fire Management
Consideration for vulnerable populations in fire suppression or let burn policies.
Placement of fire lines.
Toxicity of fire fighting chemicals.

31. Post-fire Management
Reactive approach that attempts to speed recovery of a system.
Most expensive and outcomes are uncertain.
Salvage logging.

32. Research & Monitoring
Adaptive management recognizes that management plans are made with imperfect information and understanding, and management decisions often lead to unintended or unsuspected consequences.

33. Trajectories of Disturbance & Reorganization

39. Intermediate Disturbance Hypothesis
Species Diversity
Disturbance Frequency

40. Intermediate Disturbance Hypothesis
Species Diversity
Fast Recolonizers &
Rapid Reproducers
(Inferior Competitors)
Disturbance Frequency

41. Intermediate Disturbance Hypothesis
Competitive
Exclusion by
A Few Species
Species Diversity
Fast Recolonizers &
Rapid Reproducers
(Inferior Competitors)
Disturbance Frequency

42. Intermediate Disturbance Hypothesis
Competitive
Exclusion by
A Few Species
Species Diversity
Fast Recolonizers &
Rapid Reproducers
(Inferior Competitors)
Disturbance Frequency
Biotic Interactions
Dominate
Stochastic, Abiotic
Processes Dominate

43. Patterns of Recovery
Dependant upon the frequency, magnitude, and composition of the disturbance.
Population size
Species pool

44. Questions??

45. Question for the class:
If you are planning a prescribed fire, what are some factors that should be considered for protecting or restoring aquatic ecosystems?

46. Question for the class:
Do you think large, low severity fires or small, high severity fires have a greater affected on aquatic ecosystems?