Fire Regimes and Pyrodiversity ESPM 134 Spring 2008 Rick Everett
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
5 Components: Fire Frequency Seasonality Fire Severity Dimensionality (SIZE) Interactive Syntax Fire Regimes What other disturbance factors contribute to the regime? Insects Disease Climate
Fire Regimes Agee, James K. 1996. 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
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
Fire Frequency # of fires per unit time in a specific area Example: 10 fires in 100 ha every 100 years
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)
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
Low severity: unburned duff, cone, match!
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
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
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
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
Lake Arrowhead, SBNF July 2003
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.
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
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)
Fire return intervals in California Vegetation Area (ha) mfri Spruce/cedar 2004 100 Cedar/Doug fir 806278 25 Mixed conifer 5522676 8 Redwood 928102 10 Red Fir 761396 35 Lodgepole 860378 45 Pine-Cypress 49290 30 Ponderosa 678043 5 Great Basin Pine 19636 7 Pinyon-juniper 985407 70 Juniper steppe 363867 70 Calif mixed evergreen 1359693 10
Other kind of communities Vegetation Area (ha) mfri Chaparral 3400234 30 Montane chaparral 229220 30 Coastal sagebrush 989414 20 Coastal sage Oak wd. 256470 5 Oak Woodlands 3821807 3 Great Basin Sagebrush 740558 20 Fescue Oatgrass 351484 3 California Steppe 5288897 3 Tules 743764 5
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
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
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
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