Pyrophytes are plants which have adapted to tolerate fire.
Fire acts favourably for some species. "Passive pyrophytes" resist the effects of fire, particularly when it passes over quickly, and hence can out-compete less resistant plants, which are damaged. "Active pyrophytes" have a similar competing advantage to passive pyrophytes, but they also contain volatile oils and hence encourage the incidence of fires which are beneficial to them. "Pyrophile" plants are plants which require fire in order to complete their cycle of reproduction. Pyrophytes while often considered being adapted to fire in general, they are actually just adapted to the specific fire regimes in which they are found. Problems can arise if the fire regime of a pyrophyte is disrupted or changed.
Passive pyrophytes
These resist fire with adaptations including thick bark, tissue with high moisture content, or underground storage structures. Examples include:
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Longleaf pine ( Pinus palustris)
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Giant sequoia ( Sequoiadendron giganteum)
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Coast redwood ( Sequoia sempervirens)
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Quercus suber ( Quercus suber)
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Niaouli ( Melaleuca quinquenervia) which is extending in areas where bush fires are a mode of clearing (e.g. New Caledonia).
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Venus fly trap ( Dionaea muscipula) – this grows low to the ground in acid marshes in North Carolina, and resists fires passing over due to being close to the moist soil;
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Asphodelus albus ( Asphodelus albus)
For some species of pine, such as Aleppo pine ( Pinus halepensis), European black pine ( Pinus nigra) and lodgepole pine ( Pinus contorta), the effects of fire can be antagonistic: if moderate, it helps pine cone bursting, seed dispersion and the cleaning of the underwoods; if intense, it destroys these resinous trees.
Active pyrophytes
Some trees and shrubs such as the
Eucalyptus of Australia actually encourage the spread of fires by producing flammable oils, and are dependent on their resistance to the fire which keeps other species of tree from invading their habitat. Today, many non-pyrophyte invasive plant species are able to invade fire adapted ecosystems as humans disrupt local fire cycles, raising questions about sustainable paths forward to preserve these ecosystems, their native biodiversity, and human based landscapes.
Pyrophile plants
Other plants which need fire for their reproduction are called
pyrophilic. Longleaf pine (
Longleaf pine) is a pyrophile, depending on fire to clear the ground for seed germination.
The passage of fire, by increasing temperature and releasing smoke, is necessary to raise seeds dormancy of pyrophile plants such as Cistus and Byblis, an Australian passive carnivorous plant. The importance of smoke in germination has been directly linked to its production of trace gases, mainly Nitrogen Oxide(NO) and Nitrogen dioxide(NO2). These trace gases produced in wildfires share significant overlap with anthropogenic pollution, leading some to believe premature germination of pyrophiles through accidental human interference is possible.
Imperata cylindrica is a plant of Papua New Guinea. Evergreen, it ignites easily and causes fires on the hills.
Evolution
99 million-year-old
amber-preserved fossils of
Phylica piloburmensis, belonging to the modern pyrophytic genus
Phylica, show clear adaptations to fire including pubescent, needle-like leaves, further affirmed by the presence of burned plant remains from other
Burmese amber specimens. These indicate that frequent fires have exerted an evolutionary pressure on flowering plants ever since their origins in the
Cretaceous, and that adaptation to fire has been present in the family
Rhamnaceae for over 99 million years.
See also
