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Fire Effects on Aquatic Ecosystems. guest lecture by Christine May. 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?. Dunham et al. 2003.
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Fire Effects on Aquatic Ecosystems guest lecture by Christine May
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?
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
Indirect Effects • Physical • Chemical • Biological
Physical 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 Responses • Burn severity • Proportion of the watershed burned • Relative proximity of the burned area to the stream channel • Slope steepness • Soil type / erosivity
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.
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.
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.
Vulnerability of Fish to Fire • Quality of the affected habitats • Amount and spatial distribution of habitat (habitat fragmentation) 3. Position in the drainage network • Habitat specificity • Mobility 6. Life history diversity
Which populations are the most vulnerable? Relatively immobile species with a narrow range of habitat requirements in highly degraded or fragmented systems.
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.
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.
HABITAT FRAGMENTATION MOBILITY ISOLATION VULNERABILITY HABITAT SPECIFICITY HABITAT SIZE HABITAT DEGRADATION modified from Dunham et al. 2003
Pre-fire Management • A proactive approach, which addresses factors that render fish populations vulnerable to fire-related disturbance • Likely to be the most effective!
Fire Management • Consideration for vulnerable populations in fire suppression or let burn policies. • Placement of fire lines. • Toxicity of fire fighting chemicals.
Post-fire Management • Reactive approach that attempts to speed recovery of a system. • Most expensive and outcomes are uncertain. • Salvage logging.
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.
Intermediate Disturbance Hypothesis Species Diversity Disturbance Frequency
Intermediate Disturbance Hypothesis Species Diversity Fast Recolonizers & Rapid Reproducers (Inferior Competitors) Disturbance Frequency
Intermediate Disturbance Hypothesis Competitive Exclusion by A Few Species Species Diversity Fast Recolonizers & Rapid Reproducers (Inferior Competitors) Disturbance Frequency
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
Patterns of Recovery • Dependant upon the frequency, magnitude, and composition of the disturbance. • Population size • Species pool
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: Do you think large, low severity fires or small, high severity fires have a greater affected on aquatic ecosystems?