Wildfire: The Good, The Bad, and The Necessary

Question 1

How much of the world is a fire-prone ecosystem?

Answer 1

40%

Question 2

What is a fire regime and what are they characterised by (x6)?

Answer 2

Patterns of fire occurrence: size and severity of impact in given area.

Intensity (how hot), spatial extent, type, season, frequency, fire return period.

Question 3

What three key factors influence the effect a fire has on an ecosystem?

What else needs to be considered?

Answer 3

1. Fire type (crown, surface, ground)
2. Intensity (rate of spread)
3. Frequency and Return Interval (controlled by rate of veg accumulation following fire; climate, moisture, lightning etc.)

Fuel type

Question 4

How can we learn what a fire regime is?

Answer 4

Construction of fire history: biotic changes in response to fire, changes over time.

Question 5

How is a feedback between vegetation regrowth and fire occurrence produced?

Answer 5

The difference between frequency and fire return interval.

Can determine the biome type/vegetation composition e.g. Boreal forest has 100 yr F, compared to 3 yrs for moist temperate.

Question 6

What two factors are important in leading to cell-tissue death? What is it?

Answer 6

Fire type and intensity: strong influence of temperature.

Cell death occurs at 40-50degC. Heating causes metabolic changes, protein denaturation and chemical decomposition.

Question 7

What is a crown kill ratio?

Answer 7

Crown:tree survival

A fire can kill part of the crown but not the whole tree through a process called SCORCHING i.e. if the top of the crown remains green, photosynthesis can still occur.

Question 8

What is cambial heating?

Answer 8

When fires heat up the cambium (holds water and nutrients, like the xylum) of a tree trunk to >55degC.

This means that, even if whole tree and crown not on fire, tree can still die.

Question 9

What are the three ways plants have adapted to survive fire?

Answer 9

Resist, persist, invade.

Question 10

How do plants RESIST fire? Give 4 adaptations.

Answer 10

Bark: insulates plant, protects cambium because wood a poor conductor. Thicker barks can withstand higher temps for longer e.g. conifers in fire-prone areas

Growth points: insulated by being wrapped up in needles; densely arranged leaves/needles at tops of stems where growth point is i.e. long-leaf pine.

Grow rate/height: the higher the crown, the less likely to catch fire; rapid rate of growth to get into canopy before fires occur e.g. long-leaf pine ‘grass stage’ then bolt upwards!

Self-pruning: shed all branches (no ladder fuels).

Question 11

How do plants PERSIST through fires? Give 6 adaptations.

Answer 11

Growth points: positioning i.e. in ground, covered, distributed across plant.

Resprouters: underground/epicormic buds - sacrificed leaves but can regrow after fire e.g. eucalyptus

Large seed stores: seeds waiting in ground insulated by soil; fires enrich soils with P and K -> rapid growth.

Cones: cones won’t open until fire passes, heat-triggered e.g. conifers

Smoke-induced germination: seeds germinate only after smoke e.g. Californian chaparral

Fire-stimulated flowering: only flower after a fire

Question 12

How do plant INVASION adaptations enable fire-survival? Give 3 examples of plants.

Answer 12

Grasses: wait until previous veg gone

Weedy flowering plants e.g. fireweed

Ferns: spores can lay dormant in soil for 100 years!

Question 13

What is key to note about plant adaptations to fire in relation to management?

Answer 13

The fuel type drives fires, and the fire has driven adaptations over time. The adaptations of plants affects the fuel type.

Some traits will be positive, as in, enable survival, and others negative. Knowing what traits are in an ecosystem can help management be more appropriate i.e. suppression vs. encouragement.

Question 14

What are four non-ecological effects of fire?

Answer 14

Erosion, emissions/soot/smoke, soil nutrients and temperature.

Question 15

How does wildfire result in erosion?

Answer 15

Fire removes vegetation so soil is less protected. If rainfall occurs it will be more direct i.e. no interception, infiltration capacity met much quicker, more run-off etc.

Also can make soil HYDROPHOBIC -> oily compounds from fires prevent infiltration.

Erosion, naturally, would occurr from the masses of surface water flow.

Question 16

Give an example of a major erosion event after a fire.

Answer 16

Schultz Wildfire, 2010 in Flagstaff Arizona.

Cause: abandoned campfire (anthropogenic)

Initial fire: 15k acres of Ponderosa pine, conifer, jupiter forest burned.

Secondary impact: water drained from steep mountain slopes, small rain event created temporary streams. Then a huge storm occurred on the area, creating mass flooding and debris flows reaching 4 miles from the fire location. Moved boulders, incision into landscape (rapid geology).

Question 17

How do wildfires affect global carbon emissions? Give some key figures.

Answer 17

The average amount of carbon released from wildfires per year is 2.0 giga tonnes.

About 23% of total fire emissions are net carbon emissions because they are not balanced by C sequestration in plants.

Grasslands and savannas are largest contributer; 44% of total. But often rebalanced by rapid regrowth!

Note the spatial variation i.e. per area burned, some biomes release more C (often anthropogenic burning) peat vs savanna.

Question 18

Give an example of a large release of C.

What year and where?

Why?

Impacts? i.e. how much land burned, C released…

Answer 18

1997 Asian peatland (Kalimantan Borneo i.e. the Indonesian part of the Borneo island)

Land was drained for oil palm plantations. The area was underlain by thick tropical peat, a longterm C store.

Fires occurred 1997-1998 from routine burning, and El Nino caused this to get out of control; resulting in 45,600km2 land burned, and 38 billion m3 of peat burned and consumed! Up to 2.57 GtC was released!! This is equivalent to 13–40% of the mean annual global carbon emissions from fossil fuels. (Page et al., 2002)

Question 19

How can smoke, soot and black carbon result from fires, and what effect does this have?

Answer 19

Southeast Asian Haze is a regular occurrence, but notably awful following 1997 fires.

Haze expanded 3M km2, concentratins over national air quality standards, 20-40x normal! Visability decreased from 15 to 0.5km. Carcinogens into air. 20M suffered respiratory problems; lung infections; hospital pressures. Major traffic disruption, air crash killing 234; impaired crop photosynthesis.
Costs of US$9Bn.

Fun fact: smouldering fires release more fine particulates than flaming.

Soot on ice and snow -> reduced albedo -> increased melt -> flooding

Question 20

How does wildfire alter soils?

Answer 20

Fire can alter the nutrient content of soils - particularly C, Ca, P and K.

Type of fire determines amount of charcoal or ash:
If combustion is complete = only ash. If incomplete = lots of charcoal, bit of ash.

Charcoal is pure carbon, which is v inert, forming a long-term C store.

Smouldering fires are incomplete combustion -> consumption of char -> more C released.

Charcoal balanced by veg regrowth and char burial -> ash is nutrient-rich. Terra preta full of char; high porosity = better nutrient absorption.

Question 21

How does wildfire affect temperature?

Answer 21

Radiative forcing - smoke can increase amount of sun’s energy and heat being absorbed and scattered

Soot on snow can reduce albedo.