Woody Plants BI237
Week 5
FIRE REGIME – the definition of regime has three components
Type: Surface, Ground (in O.M.), or Crown
Frequency: How often?
Severity: Impact on site. Stand replacement?
Influenced by: weather (wind, heat, moisture), vegetation type, dead O.M.
EFFECTS OF FIRE ON ECOSYSTEM
1. Burns O. M.
A. reduces incidence of future crown fires (in most systems)
B. releases nutrients
Releases carbon dioxide and nitrogenous gasses to the atmosphere.
Deposits minerals in the form of ash -- very soluble!
pH also rises because of higher occupation of sites by mineral cations.
Nutrients available to plants and microbes immediately, but may be washed away.
2. Soil heating –
Usually doesn't heat up much below surface.
Exception is “slash” piles (woody debris left from logging; branches, etc.)
Can bake the soil to such an extent that the structure is ruined and water can't penetrate.
3. Preparation of seedbeds -- mineral soil good for germination
4. Reduction of competing vegetation
Tends to retain fire-resistant species.
ADAPTATIONS TO FIRE
1. Avoid fire damage
 Thick, insulated bark (many pines and oaks, giant sequoia, redwood)
 Buried buds protected by soil (aspens, many shrubs)
 Rapid juvenille growth -- crown grows above surface-fire zone (pines)
2. Recover following damage
 Deep rooting -- tap root in young plants (upland oaks and hickories)
 Sprouting -Root collar or crown (oaks, paper birch, black cherry)
Burls -- large swellings near ground contain dormant buds (redwoods)
3. Colonize sites after fire
 Light, windborne seeds (Betula, Populus, Salix, Tsuga, Larix)
 "Serotinous" cones or fruits -- opening triggered by fire (jack, pitch, lodgepole and
other pines; cypresses in arid California, Banksia in Australia)
 Heat-induced germination from seed bank -- western species of Arctostaphylos,
Ceanothus
Woody Plants BI237
Week 5
A COMPLEX CONUNDRUM: Fire is a disturbance; fire exclusion is also a disturbance.
1. Fire exclusion can cause fire-resistant species to be overtaken (see photos p 423-424).
2. Fire exclusion can reduce diversity at the landscape level; no more mosaic of stands.
( but Native Americans used fire for ~ 10,000 years. What is “natural”?)
3. Build up of fuel can potentially lead to increase in severity when fire does occur.
(Some experts think that fire exclusion isn’t even possible for some habitat types, and
catastropic fires are inevitable.)
See website for
 A list of historically significant fires.
 Map of historic fire regimes.
 Map of FRCC (Fire Regime Current Conditions)
1 = within historical conditions
2 = frequency departed by > 1 return interval
3 = frequency departed by multiple return intervals.
Alteration of key ecoystem components such as species composition, structural stage,
stand age, or canopy closure.
May have been caused by fire exclusion, timber harvesting, grazing, exotic plants,
insects/disease, etc.
Will cause changes in fire size, frequency, intensity, severity, or landscape patterns.
Restoration may be necessary before fire can be used to restore the historical regime.
Case Studies:
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Redwoods in in northern coastal California
Hardwood forest in the Allegheny Plateau in northern PA & southwestern NY
Southern pines (esp Longleaf) in coastal Georgia & Florida
Lodgepole pine in central Colorado and western Wyoming
For each case -Identify Historical Natural Fire Regime
Identify Fire Regime Current Condition Class
How “natural” is a stand-replacing fire for that ecosystem?
How much care needs to be taken to restore the historical regime?
What undesirable consequences could follow from either intervening in the system or
failing to intervene?
Be able to compare and contrast the four cases.