Plant Adaptations to Fire Flashcards
Attributes of fire regimes
- temporal (seasonality, fire return interval)
- magnitude (intensity, severity, fire type)
- spatial (size/extent, spatial complexity)
Impact of fire regime attributes on plant/animals
Influence how plants and animals survive/regenerate after fire because they occur over evolutionary time-scales
Flammability
Capacity for plant biomass to burn/start and sustain a flame
Mutch hypothesis
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
Criticisms of Mutch hypothesis
- 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)
Modes of fire resistance in plants
- Hot flammable evaders
- Avoiders
- Non-flammable resisters
- Fast-flammable endurers
Hot flammable evaders
Seed-banking species with long-lived/heat-released seeds
Avoiders
Shade-tolerant species that slowly recolonize after fire by seed
Non-flammable resisters
Species with insulative bark/tissues
Fast-flammable endurers
Species that resprout after fire where above-ground tissues are killed but below-ground tissues survive so plants can resprout
Adaptations of non-flammable, fire-enduring species
Allow plants to survive fires
- thick bark
- self-pruning
- deep rooting
- fire-resistant foliage
Adaptations of fire avoiding, hot-flammable species
Allow plants to reproduce/reestablish following fire
- prolific and early seed production
- serotiny
- heat-induced germination
- sprouting
Adaptations of fire enduring/fast-flammable species
- allow below-ground or meristematic tissues to survive fire when plant is top-killed
- species that resprout after fire
Plant mortality
- 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)
Reproductive pathways
- asexual (resprouters)
- sexual (obligate seeders, fire effects on seeds are most important for obligate seeders)
- both (facultative sprouters)
Vegetation regeneration
Plants resprouting after fire from living buds
- many of these structures are also energy storage devices
Effect of low-severity fire on sprouting
May kill some epicormic buds but not all, little effect on most buried plant parts
Effect of moderate-severity fire on sprouting
- 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
Effect of high-severity fire on sprouting
Kills buds in duff and upper soil layers, sprouting can only occur from deeply buried plant parts
Grasses
- 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
Stem damage
- 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)
Root damage
- 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
Seed responses to fire
- Seeds survive in soil
- Seeds germinate or are released as a result of fire
- Seeds dispersed from outside burned area
Seed banks
- 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
Fire-enhanced seedling reestablishment
- bare mineral soil
- blackened surface causes increased temp
- nutrients in ash
- less competition from sprouters after severe fire
Fire-stimulated germination
- smoke, heat, and ash can stimulate germination of species specifically adapted to fire
Serotinous cones
Canopy-stored seed
- ability to retain seeds in canopy fruits for several years
- seeds stored in closed cones that only open when heated
Seed dispersal to burned areas
- windblown
- carried by animals
Case study: Kirtland’s warbler & jack pine forest
- 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
