FIRE

I. Causes of fire

A. Natural -- lightning and volcanism

B. Anthropogenic -- (importance recognized by C.O. Sauer and Omer Stewart)

Aboriginal use of fire for:

1. Warfare

2. Religion

3. Hunting tool

4. Vegetation management (e.g. forage improvement)

5. Accidental

II. Types of fire

A. Surface fires

B. Ground fires

C. Crown fires (wild fires)

III. Fire effects on the environment depend on intensity and spread

A. Fire intensity depends on:

1. Amount of fuel (grams per square meter); a function of productivity and decomposition.

2. Heat yield (kcal per gram of fuel) as determined by fuel quality (chemical and physical properties).

B. Rate of spread (m/sec) as determined by weather and topography

IV. Fire effects on soil

A. Effects on soil organic matter

combustion of organic matter (e.g. 85% lost at 250EC)

decline in CEC

loss of organic matter reduces porosity, increases bulk density, etc.

B. Physical effects on soil:

1. decline in water holding capacity

2. possible changes in soil "wettability" (can translocate water repellant chemicals towards greater depth)

C. Effects on soil pH and on soil microorganisms

Short-term increase in pH.

Generally fungal pathogens decline (due to lack of litter) and bacteria increase (due to less acid conditions).

ADAPTATIONS TO FIRE

Two alternatives:

a. Survival of fire (e.g resistance)

b. Population recovery following fire

1. Post-fire germination (scarification of seed, ability to germinate and survive in open post-fire sites)

2. Fire-resistant foliage (e.g. low resin content)

3. Thick fire-resistant bark

4. Evanescent lower branches

5. Sprouting behavior

latent buds on tree bole (epicormics)

root collar or stump sprouting

new shoots from lateral roots (suckering)

new shoots from lignotubers (partially buried swollen stem)

6. Cone serotiny

7. "Grass stage" of longleaf pine (Pinus palustris)

8. Fire-induced flowering of some herbs