Plant Adaptations to Fire

Question 1

Attributes of fire regimes

Answer 1

• temporal (seasonality, fire return interval)
• magnitude (intensity, severity, fire type)
• spatial (size/extent, spatial complexity)

Question 2

Impact of fire regime attributes on plant/animals

Answer 2

Influence how plants and animals survive/regenerate after fire because they occur over evolutionary time-scales

Question 3

Flammability

Answer 3

Capacity for plant biomass to burn/start and sustain a flame

Question 4

Mutch hypothesis

Answer 4

Fire dependent plant communities burn more readily than non-fire dependent communities because natural selection has favored characteristics that make them more flammable

If plants possess traits to persist in a fire-prone environment, then there may be selection for characteristics that enhance flammability

Question 5

Criticisms of Mutch hypothesis

Answer 5

• lack of empirical evidence
• side effect of evolutionary selection for other traits
• context dependence (flammability depends on moisture content, chemical composition, physiology)
• flammability is not a trait of individuals but an emergent property of populations
• recent work suggests flammability can result in increased fitness in different fire-prone areas, but the world is complicated (mixed-severity regimes are important for promoting plants with multiple flammability strategies)

Question 6

Modes of fire resistance in plants

Answer 6

1. Hot flammable evaders
2. Avoiders
3. Non-flammable resisters
4. Fast-flammable endurers

Question 7

Hot flammable evaders

Answer 7

Seed-banking species with long-lived/heat-released seeds

Question 8

Avoiders

Answer 8

Shade-tolerant species that slowly recolonize after fire by seed

Question 9

Non-flammable resisters

Answer 9

Species with insulative bark/tissues

Question 10

Fast-flammable endurers

Answer 10

Species that resprout after fire where above-ground tissues are killed but below-ground tissues survive so plants can resprout

Question 11

Adaptations of non-flammable, fire-enduring species

Answer 11

Allow plants to survive fires
- thick bark
- self-pruning
- deep rooting
- fire-resistant foliage

Question 12

Adaptations of fire avoiding, hot-flammable species

Answer 12

Allow plants to reproduce/reestablish following fire
- prolific and early seed production
- serotiny
- heat-induced germination
- sprouting

Question 13

Adaptations of fire enduring/fast-flammable species

Answer 13

• allow below-ground or meristematic tissues to survive fire when plant is top-killed
• species that resprout after fire

Question 14

Plant mortality

Answer 14

• amount of heat determines likelihood of plant tissue being killed
• effect = function of temp and duration of exposure (residence time)
• % of plant tissue damaged determines mortality
• timing (plants are more vulnerable when moisture content is high, seasonality)

Question 15

Reproductive pathways

Answer 15

• asexual (resprouters)
• sexual (obligate seeders, fire effects on seeds are most important for obligate seeders)
• both (facultative sprouters)

Question 16

Vegetation regeneration

Answer 16

Plants resprouting after fire from living buds
- many of these structures are also energy storage devices

Question 17

Effect of low-severity fire on sprouting

Answer 17

May kill some epicormic buds but not all, little effect on most buried plant parts

Question 18

Effect of moderate-severity fire on sprouting

Answer 18

• consumes buds in litter and upper duff layer
• may kill buds on portions of upright stems
• sprouting from buds in deeper duff/soil layers may occur

Question 19

Effect of high-severity fire on sprouting

Answer 19

Kills buds in duff and upper soil layers, sprouting can only occur from deeply buried plant parts

Question 20

Grasses

Answer 20

• meristems (equivalent to buds): origin of growth and resprouting
• rhizomes or stolons: lateral spread
• bunch grasses more likley to be killed when meristems are near surface

Question 21

Stem damage

Answer 21

• trees damaged by lethal heating of cambium (bark thickness protects cambium)
• withstand stem damage = fire scars (girdling is when entire cambium is killed, leads to tree death)

Question 22

Root damage

Answer 22

• tree mortality (mostly feeder roots)
• degree depends on distance from soil surface
• importance of heat and residence time
• roots in duff layers are more vulnerable than in mineral soil
• smoldering duff can be lethal

Question 23

Seed responses to fire

Answer 23

1. Seeds survive in soil
2. Seeds germinate or are released as a result of fire
3. Seeds dispersed from outside burned area

Question 24

Seed banks

Answer 24

• seeds in litter layer (short longevity or recent dispersal); annuals
• seeds in mineral soil; perennials
• seed bank composition can be very different than plant composition growing on site

Question 25

Fire-enhanced seedling reestablishment

Answer 25

• bare mineral soil
• blackened surface causes increased temp
• nutrients in ash
• less competition from sprouters after severe fire

Question 26

Fire-stimulated germination

Answer 26

• smoke, heat, and ash can stimulate germination of species specifically adapted to fire

Question 27

Serotinous cones

Answer 27

Canopy-stored seed
- ability to retain seeds in canopy fruits for several years
- seeds stored in closed cones that only open when heated

Question 28

Seed dispersal to burned areas

Answer 28

• windblown
• carried by animals

Question 29

Case study: Kirtland’s warbler & jack pine forest

Answer 29

• habitat maintained historically by fire
• jack pine is fire-adapted
• decreased habitat due to fire suppression
• Kirtland warbler is an endangered species because of this