Fire regime

A fire regime is the pattern, frequency, and intensity of the bushfires and wildfires that prevail in an area over long periods of time. It is an integral part of fire ecology, and renewal for certain types of ecosystems. If fires are too frequent, plants may be killed before they have matured, or before they have set sufficient seed to ensure population recovery. If fires are too infrequent, plants may mature, senesce, and die without ever releasing their seed. Fire is a type of disturbance regime that can define an ecosystem. Disturbance regimes like fire can change soil erosion, soil formation, nutrient cycles, energy flow, and other ecosystem characteristics. Disruption of an ecosystem can allow changes in species dominance and mutations in individual species. Fire regimes can change with the spatial and temporal variations in topography, climate, and fuel.

Fire regimes are characterized based on their frequency, intensity, extent, type, and seasonality. Fire frequency is the average time a fire burns in a given area. Fire intensity is the amount of heat released over time. Fire extent is the size and spatial similarities of the burning. Fire types or fire spread include ground fire, surface fire, and crown fire. Ground fires use glowing combustion to burn organic matter in the soil. Surface fires burn leaf litter, fallen branches, and ground plants. Crown fires burn through to the top layer of tree foliage. Seasonality is the period of time during the year that the fuels of a specific ecosystem can ignite.

Biota that are able to survive and adapt to their particular fire regimes can receive significant benefits: the ability to regrow stronger, greater protection against fire and disease, or new space to grow in formerly occupied locations. As fire regimes change the area, both current and future species may begin to suffer. Decreasing fire intervals negatively affect the ability of fire-killed species to recover to pre-disturbance levels, leading to longer recovery times. Some species, such as resprouters, are better able to withstand changing fire regimes through increased resistance and resilience. However, many fire-killed species may be unable to recover if shortened fire intervals persist over time.

Bushfire is especially important in Australia, where much of the vegetation has evolved in the presence of regular fires caused by the Aboriginal practice of firestick farming. As result, components of the vegetation are adapted to and dependent upon a particular fire regime. Disruption of that fire regime can affect their survival. An example of fire regime dependent species is the Banksia species which is both fire-sensitive and serotinous. In Banksia species, fire also triggers the release of seed, ensuring population recovery. In an ideal fire regime, a plant would need to have sufficient time to mature and build an adequately large bank of seed before the next fire kills it and triggers seed release.

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