Topic 10- Fire

Historical Trends and Causes

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Fire impacts on the ecosystem

• Physical and Chemical properties on soil

• Changes in Nutrient availability and cycling

• Biomass accumulation

• Plant composition

• Wildlife habitat and population dynamics

• Forest Insects and microbial communities

• Impacts of smoke detections far from zone of life

Fire Regime

• Types

• Frequency

• Intensity

• Severity

• Size area affect

• Seasonality

Fire Regime Types

• Surface

-Burning of litter, woody debris, etc near the surface of the ground, mostly by flaming combustion

• Ground

-Burning mostly decaying roots below ground in the duff layer (compacted dead plant material)

• Crown

Burn forest canopy fuels. Ignited by surface fires.

-Passive- burning of individual trees or small group of trees (torching)

-Active- solid wall of flame from the surface through the canopy

Fire Regime Severity

• Non lethal understory fires

• Stand replacing fires

• Mixed severity fires

Outcomes dependent on Climate, fuel, flammable, soil water, topography

Ecological Strategies relating to fire

• Fire avoidant traits

-Thick Bark, Buried buds, Deep rooting, Self pruning ability, etc

• Fire Resilience

-Stem sprouting, rhizomes, basal sprouting, lignotubers, deep rooting

• Colonizing Post Fire

-Early flowering and seed dispersal, wind disbursed seeeds, no dormancy, on plant seed storage, heat induced germination, fire triggered seed release (Serotinous cones)

• Promoting Fire

-Flammable bark and foliage, retention of foliage near ground, short stature, retention of dead lower branches

Serotiny

• Cones are fused shut with resin and only open with high temps

• Cones can remain on the tree for decades and still be viable

• Can be a mix of serotinous cones and non on the same tree

• Rare in Appalachia but common in coastal plains

What are the direct effects of fire

• Release CO2, nitrogenous gases and ash to atmosphere

• Mineral ash deposit

• Increase in pH

• Reduction in infiltration

• Total N in environment decreases

• Mineral soil exposure (long lasting changes in soil temperature)

• Increase in run off due to changes in soil texture (More compact soil, and landslides often due to o.m. Being burned

Indirect effects of fire (Abiotic)

• Soil temp changes (Summer vs winter)

• Soil moisture

• Soil stability

• Soil function (porosity, infiltration, water holding capacity)

Indirect effects of fire (Biotic)

• Plant community impacts (Favored groups- serotinous, pioneers, high root/shoot allocation)

• Invertebrate communities (Fav groups- soil nesting limited groups- litter nesting)

Effects of fire on the microbial community

Temp of fire is important

-if community survives, rapid increase in abundance following a fire

-Fungal and bacteria ratio is likely to shift with high temps and change in pH

-Hot fires can cause reduction, sterilization, long lasting impact on the nurtrient cycling

Benefits of fire

• Controlled smaller scale burning can reduce many of the negative impacts of wildlife while promoting diversity

• In cold areas, the increase in soil temps can help hasten spring development

• Increase in water availability and wildlife habitat