Where we re going today: Start integrating previous lecture information with the effects of fire as a disturbance factor in forested ecosystems Revisi

Transcription

1 Fire Regimes and Pyrodiversity ESPM 134 Spring 2008 Rick Everett

2 Where we re going today: Start integrating previous lecture information with the effects of fire as a disturbance factor in forested ecosystems Revisit Fire Regimes Pyrodiversity Fire as a formative agent in biological systems Set up for Prescription fires & management, Restoration

3 5 Components: Fire Frequency Seasonality Fire Severity Dimensionality (SIZE) Interactive Syntax Fire Regimes What other disturbance factors contribute to the regime? Insects Disease Climate

4 Fire Regimes Agee, James K Fire Regimes and Approaches for Determining Fire History (Attached to your handout, and on the web.ppt) Fire Regimes Defining using severity: Low Moderate High

5 Agee, continued Fire Histories Point Frequencies Low to moderate fire frequencies Area Frequencies Moderate to very high fire frequencies stand replacement events Nt Natural lfi Fire Rotation Rtti Fire rotation is the time required for an area equal to the entire area of interest to burn and is expressed in terms of years per area (125 years for a 40,000 ha area). Fire Cycle Average stand age of a forest whose age distribution fits a mathematical distribution Usually a Weibull, non-parametric distribution

6 Fire Frequency # of fires per unit time in a specific area Example: 10 fires in 100 ha every 100 years

7 Seasonality Description of the time of the year that fires occur: Spring, Summer, Fall Only can be an estimation of Season, not a calendar date Immense effect on plant ecosystem Fire during unexpected period (plant hasn t developed a life history which h handles fire during a given season) Even holding fire intensity constant, mortality can be greatly increased Affecting: Phenology (leafing & buds) Water availability & uptake Organism activity (especially arthropods)

8 Fire Severity Degree of alteration of vegetation & soils by fire Relative varies by system Usually thought of as: Amount of crown scorch Height of bark char Amount of plant consumption (live & dead fuels) Plant mortalities

9 Low severity: unburned duff, cone, match!

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11 Fire Severity Individual tree damage: Foliage & Bud Damage Cambial kill bole & leaders Root Damage poorly studied (mycorhizal, too) 60º C kills tissues (we blister plant vascular tissues die

12 Larger Scale damage: Soils Heating & sterilization Volatilization & Hydrophobicity Bulk Density Chemistry (Nitrogen export) Water Changes local water potenital Loss of photosynthetic crown : commensurate rise in watertable Changes in percolation, holding capacitance Mudflows & Runoff

13 Dimensions Size of fire (hectares or acres) Another Dimension : Unburned area within fires Degree of patchiness Low and moderate severity fires in coniferous non- stand replacement systems probably bl left a varied patchy mosaic of burned & unburned areas, leading to: Uneven aged stand structure Unburned Patches: Wildlife Refuge Seed source

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15 Interactions with other disturbance agents Insects, pathogens, drought, etc. Before Fire Insects, pathogens & other agents may increase mortality, leading to increased aerial & ladder fuels increasing intensity After Fire Insects often key into dead or wounded trees Fire-related related stresses in plants may increase pathogen susceptibility In general: hard to predict, but large-scale & important

16 Lake Arrowhead, SBNF July 2003

17 Prehistoric Fire Intervals prehistoric generally refers to fire regimes seen prior to 1850 in California Reconstructed using fire-scar dendrochronology Both season, and date, can be developed from Fire-scar dendrochronology Reconstructed using geomorphologically-derived Carbon-dates Phytoliths Generally driven by ignition sources.

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19 Lightning Current theory: High negative charge builds up in clouds Electrons stripped off of water & snow droplets as they are repeatedly lifted & descend within the cloud. Stepped leaders form every 50 meters Ultimately seek high positive charge near ground Up to 2 km from flux source Nasty: 40 Kiloamperes Bolt Temperature: 30000º C, nearby air temperature 10000º C 1 gigavolt, 100 terwatts So: no problem with providing a source of ignition & push for a fire regime

20 North American Aboriginals Large influences on fire regimes Most cultures have some evidence of fire use Major influences in most plant communities except sub-alpine & alpine Decreased intervals Diversified & increased annual seasonality of burning (lifted the lightning season limit)

21 Fire return intervals in California Vegetation Area (ha) mfri Spruce/cedar Cedar/Doug fir Mixed conifer Redwood Red Fir Lodgepole Pine-Cypress Ponderosa Great Basin Pine Pinyon-juniper Juniper steppe Calif mixed evergreen

22 Other kind of communities Vegetation Area (ha) mfri Chaparral Montane chaparral Coastal sagebrush Coastal sage Oak wd Oak Woodlands Great Basin Sagebrush Fescue Oatgrass California Steppe Tules

23 Fire Rotations Vegetation Average Fire rotation Cedar Douglas fir 61 Mixed Conifer 27 Red Fire 63 Lodgepole 46 Great Basin Pine 23 Chaparral 70 Pinyon-Juniper 440

24 Historic Fire Intervals Fire Histories based on written or oral Eurocentric culture records Major decrease seen throughout western US & California after 1905 Golly! 1905: Transfer Act Creation of modern day USFS & start of aggressive fire suppression

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27 Pyrodiversity Prehistorically (key word: heterogeneity): Diverse regimes Differing sizes Differing severities Differing intervals Fairly regular seasonality Variability in fire regimes : variable effects of ecosystems Promoted biodiversity Broader amplitude of habitats & niches for the entire suite of organisms in a community

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29 Fire suppression policies have altered prehistoric fire regime This should now be familiar: Most small ll& moderate sized fires have been suppress Now, only the most large & severe burn plant communities These fires do not promote biological diversity

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