Fire Effects on Aquatic Fire Effects on Aquatic EcosystemsEcosystems

guest lecture by

Christine May

Fire Effects on Aquatic SystemsFire 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?

Dunham et al. 2003

Direct EffectsDirect 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

Indirect EffectsIndirect Effects

1. Physical

2. Chemical

3. Biological

Physical EffectsPhysical Effects

• Hydrological• Increased water yield

• Geomorphic• Accelerated erosion rates

• Changes in channel morphology

• Elevated water temperatures• Dependant upon removal of riparian canopy cover

Factors that Influence Watershed Factors that Influence Watershed ResponsesResponses

• Burn severity

• Proportion of the watershed burned

• Relative proximity of the burned area to the stream channel

• Slope steepness

• Soil type / erosivity

Chemical EffectsChemical 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.

Biological EffectsBiological 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.

Adapted from Minshall (1989)

Why is the Historic Range of Why is the Historic Range of Variation Important?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.

Vulnerability of Fish to FireVulnerability of Fish to Fire1. Quality of the affected habitats

2. Amount and spatial distribution of habitat (habitat fragmentation)

3. Position in the drainage network

4. Habitat specificity

5. Mobility

6. Life history diversity

Which populations are the most Which populations are the most vulnerable?vulnerable?

Relatively immobile species with a narrow range of habitat requirements in highly degraded or fragmented systems.

Metapopulation DynamicsMetapopulation Dynamics

Metapopulation DynamicsMetapopulation 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.

Dunham et al. 2003

Dunham et al. 2003

Dunham et al. 2003

Dunham et al. 2003

Dunham et al. 2003

Dunham et al. 2003

Dunham et al. 2003

Isolated PopulationsIsolated 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.

Dunham et al. 2003

Dunham et al. 2003

HABITAT DEGRADATION

HA

BIT

AT

SIZ

E

ISO

LA

TIO

NHABITAT

FRAGMENTATION

VULNERABILITY

HA

BIT

AT

SPE

CIFIC

ITY

MO

BIL

ITY

modified from Dunham et al. 2003

Dunham et al. 2003

Pre-fire ManagementPre-fire Management

• A proactive approach, which addresses factors that render fish populations vulnerable to fire-related disturbance

• Likely to be the most effective!

Fire ManagementFire Management

• Consideration for vulnerable populations in fire suppression or let burn policies.

• Placement of fire lines.

• Toxicity of fire fighting chemicals.

Post-fire ManagementPost-fire Management

• Reactive approach that attempts to speed recovery of a system.

• Most expensive and outcomes are uncertain.

• Salvage logging.

Research & MonitoringResearch & Monitoring

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

Trajectories of Disturbance & Trajectories of Disturbance & ReorganizationReorganization

Intermediate Disturbance HypothesisIntermediate Disturbance Hypothesis

Disturbance Frequency

Spe

cies

Div

ersi

ty

Intermediate Disturbance HypothesisIntermediate Disturbance Hypothesis

Disturbance Frequency

Spe

cies

Div

ersi

ty

Fast Recolonizers &Rapid Reproducers(Inferior Competitors)

Intermediate Disturbance HypothesisIntermediate Disturbance Hypothesis

Disturbance Frequency

Spe

cies

Div

ersi

ty

Fast Recolonizers &Rapid Reproducers(Inferior Competitors)

CompetitiveExclusion by A Few Species

Intermediate Disturbance HypothesisIntermediate Disturbance Hypothesis

Disturbance Frequency

Spe

cies

Div

ersi

ty

Fast Recolonizers &Rapid Reproducers(Inferior Competitors)

CompetitiveExclusion by A Few Species

Biotic InteractionsDominate

Stochastic, AbioticProcesses Dominate

Patterns of RecoveryPatterns of Recovery

• Dependant upon the frequency, magnitude, and composition of the disturbance.

• Population size

• Species pool

Questions??Questions??

Question for the class: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?

Question for the class:Question for the class:

Do you think large, low severity fires or small, high severity fires have a greater affected on aquatic ecosystems?