Fire Ecology

What is Mesophication

A positive feedback cycle where fire suppression allows shade-tolerant, fire-sensitive tree species to replace fire-adapted species like oak and pine

What do grasslands rely on for fire

Rapid biomass accumulation to drive high-frequent surface fires

What are the catalyst for a grassland fire?

• Abundant fine fuels

• Continuous fuel bed

• Rapid drying after rain

• Frequent natural or human ignition

What is the fire return interval for grasslands?

1-3 years

Typically low severity surface fires

What is the Key Insight about identical weather in a prairie vs. a mountain forest?

Behavior differs greatly due to fuel continuity and structure

-The same weather gives vastly different behavior because of fuel continuity and structure.

Which two physical factors determine ecosystem distribution on Earth?

Temperature and Moisture

• Temperature and moisture determine ecosystem distribution and also drive fuel accumulation.

What is the primary limiting factor for fire in grasslands?

Fuel amount (biomass accumulation)

• Grasslands are highly flammable; fire is limited by how fast biomass grows to carry the next burn.

Which is NOT a condition required for grassland fires?

A dense closed canopy

• Grassland conditions: fine fuels, continuous fuel bed, rapid drying, frequent ignition.

What are the three primary North American prairie types

Tallgrass, mixed-grass, shortgrass

Which prairie type burns most frequently

Tallgrass

• Tallgrass prairies get more rain, are more productive, and burn more often than shortgrass.

What is the primary limiting factor in pine savannas?

Fuel moisture

• The open canopy lets sun and wind dry the grassy understory; without that drying, surface fire can't propagate.

What is the return interval and severity in pine savannas?

1-5 years

• Typically low intensity surface fires

What ignition source is key in pine savannas

Frequent lightning

How often did longleaf pine–wiregrass communities historically burn?

2-3 years burn interval

Which describes longleaf pine wiregrass communities?

Open canopy, little to no midstory, very high herbaceous plant diversity

• They are fire dependent

How often do pine-bluestem woodlands historically burn

About every 3 years

In pine bluestem, when does a shrubby understory component develop?

In areas that burn less frequently

How are oak woodlands different from oak forest structurally

Woodlands have open canopy

Forest have closed canopy

• Oak woodlands are open canopy (often lower productivity, south-facing slopes); oak forests are closed canopy.

What is the historical fire return interval of oak woodlands?

Historically burn every 3-15 years

What is the historical fire return interval of oak forest?

Historically burn every 3-15 year

Where do oak woodlands often occur

South-facing slope with lower productivity

What conditions favor fire in oak forests?

Leaf litter accumulation, seasonal drying, moderate fuel continuity

What are the limiting factors for fire in oak forests?

Increasing leaf moisture, seasonal humidity, and modern fire exclusion

• Leaf moisture, seasonal humidity and fire exclusion limit surface fire spread.

What is mesophication

Fire exclusion lets moisture-loving species establish and inhibit future flammability

• Mesophication is a self-reinforcing shift to moisture-loving species that reduces flammability.

In the historical vs. excluded oak regime table, the flammability trajectory under modern exclusion is:

Self-inhibiting / declining

• Historical = stable and cyclic; modern exclusion = self-inhibiting/declining.

What is the modern fire frequency of oak forest?

Flatline/zero

• Dominate leading factor is due to mesophication

What is the primary limiting factor under modern oak fire exclusion vs. historical?

Historical: seasonal humidity and leaf moisture; Modern: human exclusion

• Today human exclusion does

What is the dominant dynamic in historical oak forests?

Periodic surface fires

What is the dominant dynamic in modern oak forest

Mesophication

Montane forests are mostly composed of which plant group?

Gymnosperms (conifers)

What is the montane forest fire regime?

Surface fires every 3-15 years, with crown fires every few hundred years

What is the primary limiting factor in montane forest?

Fuel moisture and structure

• Ladder fuels and summer drought dictate crown fire transition.

What role do ladder fuels play in montane forest?

Carry surface fire up into the canopy.

• Dense ladder fuels transition surface fires into mixed-severity/crown fire.

What are the modern drivers of severe fire in western montane forest

Extended drought, low fuel moisture, decades of suppression, dense forest

• Drought, chronically low fuel moisture, suppression policies and unnaturally dense stands.

Why are lower-elevation montane forest more productive?

Longer growing seasons

• Lower elevations have longer growing seasons vs higher elevations

What is the main threat to lodgepole pine forest?

Bark beetles

• Bark beetles kill trees, increasing dead fuels and fire potential.

Why do crown fires spread efficiently in lodgepole forest?

Stands are naturally dense

• Naturally dense forests carry crown fire efficiently.

What are serotinious cones

Cones that release seeds after fire

Or cones that require heat to open

• Serotinous cones are sealed with resin and scatter seeds mostly after canopy fires.

What is the fire return interval for chaparral?

27-50+ years

• Burns infrequently

What is the primary limiting factor in chaparral?

Fuel accumulation (time for woody biomass to build)

• Decades are required to build dense woody fuel loads

Describe typical chaparral fire behavior?

High-intensity, crown-dominated fire that consumes vegetation

Why is chaparral so flammable?

Plants contain volatile extractives

• Volatile extractives, dense woody fuels, high loads and seasonal drought.

What are the typical fires in Boreal forest?

They are usually canopy fire; no ladder fuel required because the branches are in contact with the ground

Why don’t Tropical Rainforest burn

They are too west and stay moist

• Usually rains every day

Where are tropical pine forest located

In the Caribbean and Central America

What is the burn type of tropical pine forest?

They burn regularly

Fire exclusion leads to a change in species
composition: tolerant and intolerant

Fire exclusion leads to a change in species
composition: tolerant and intolerant:
• Eastern Red Cedar: very intolerant: thin bark and
does not sprout after a fire: prescribed fire kills it.
• Western Red Cedar is also very intolerant
• American Beech very intolerant: very thin bark and
does not sprout after a fire
• Cucumber tree sensitive to fire
• Umbrella magnolia may sprout after a fire but also
sensitive to fire.

What is top-kill

Occurs when aboveground stems die while root systems
remain alive.

What does regrowth after top-kill rely on?

Living meristems and subterranean bud banks

What fuels explosive post-fire shoot emergence?

Stored starch and carbohydrates in roots power new shoots.

What is the approximate lethal plant tissue temperature threshold?

60°C (140°F)

What dictates survival probability of buds during a fire?

Bud depth in bark or soil

How does soil moisture affect underground meristem protection?

Soil moisture buffers heat penetration; dry soil doesn't protect as well.

Where are ground-level meristems located?

Root crowns or basal crooks

What is the root crown?

The transition between the stem and the ground

Ground-level meristem examples, and when do they resprout?

Shortleaf pine and oaks; when the canopy is destroyed

Where does basal sprouting initiate?

Dormant meristems clustered at the root collar or stem base

What triggers basal sprouting?

Fire top-kills the main stem and removes apical dominance

• Stress which includes damage

• Loss of the main stem removes apical dominance, releasing basal buds.

What drives basal sprout growth?

Massive underground root energy reserves

How does basal sprouting change growth architecture?

Transforms single-stemmed trees into multi-stemmed shrubby clumps

What does basal sprouting allow juvenile plants to do?

Persist under frequent surface fire regimes

What does basal sprouting ensure?

Individual survival even when above-ground biomass is completely lost

In the stump sprout photos, where do the new stems arise?

The root collar

What happens to dormant buds on cut or burned stumps (coppice growth)?

They burst into multiple vigorous sprouts

• Dormant stump buds burst into many vigorous sprouts.

Why do coppice sprouts grow so fast?

High root-to-shoot ratio supplies abundant water and nutrients

• A large root system feeds a small shoot system.