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. A fire regime describes the spatial and temporal patterns and ecosystem impacts of fire on the landscape, and provides an integrative approach to identifying the impacts of fire at an ecosystem or landscape level. 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. 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. A fire regime describes the spatial and temporal patterns and ecosystem impacts of fire on the landscape, and provides an integrative approach to identifying the impacts of fire at an ecosystem or landscape level. 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 regimes can change with the spatial and temporal variations in topography, climate, and fuel. Understanding the historic fire regime is important for understanding and predicting future fire regime changes and the interactions between fire and climates. Fire regimes are characterized by a variety of factors including vegetation composition, fuel structure, climate and weather patterns, and topography. Because fire regimes are highly dependent on the landscape and ecosystem in which they occur, there is no standard classification for fire regimes. However, characteristics such as those described below are commonly used to characterize fire regimes on a broad scale. Other factors such as post-disturbance successional stages and types of previous management on the landscape may also be used to describe a fire regime's characteristics. Climate directly impacts the frequency, size, and severity of fires, while also affecting the vegetation structure and composition. Fire regimes are also impacted by topography, slope exposure, landscape management, and ignition (which may be human or lightning-caused). Although characteristics of fire regimes can vary based on regional differences, at a minimum fire regimes are characterized based on an assessment of the impacts on the vegetation (severity) and when and how often fires occur in a given landscape (expressed as fire interval and fire rotation). Fire severity is the impact of fire on the ecosystem, which may include the degree of vegetative mortality, the depth of burn, or other factors which may be site specific. The fire interval is the number of years between fires and is highly dependent on spatial scales. Fire rotation is a measure of the amount of fire in a landscape (the amount of time required to burn an area the size of the study area). The fire rotation statistic is best used for large areas that have mapped historic fire events. Other fire regime classifications may incorporate fire type (such as ground fires, surface fires, and crown fires), fire size, fire intensity, seasonality, and degree of variability within fire regimes. 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. Fire-line intensity is the energy released per unit of measurement per unit of time and is usually a description of flaming combustion. Seasonality is the period of time during the year that the fuels of a specific ecosystem can ignite. Fire regimes can be characterized by a wide variety of spatial and temporal scales which may range from highly site-specific to regional scales and from a few years to thousands of years. Understanding the variability of the fire regime across these scales is crucial to understanding current and future fire regimes. Distinctions should be made between 'fire history' and 'historic fire regimes'. Fire history is a more general term that measures the frequency of fires in a landscape. It may not always be possible to describe the type or severity of these past fire events depending on data availability. Historic fire regimes describe the characteristics of fires across a landscape and the relationship and interactions between ecosystem structure and processes. Recent fire history can be recorded on fire maps and atlases, often using remote sensing. The Canadian National Fire Database is a record of large fire events since 1980, is the first nationwide database of its kind. It includes point locations of all fires larger than 200 ha from 1959–1999. The United States has the Monitoring Trends in Burn Severity (MTBS) Project which uses satellite data to map fires from 1984 onward. MTBS maps fire severity within the areas burned and provides a standard on fire perimeters and severity for all fires within the U.S. Applications for projects such as these are used in modeling interactions between fire climate and vegetation. The Landscape Fire and Resource Management Planning Tools (LANDFIRE) classification is another example of a mapping and modeling system used in the U.S. that collects and analyzes vegetative, fire, and fuel characteristics of fire regimes across a variety of landscapes. LANDFIRE is unique in that it uses both historic fire regimes and current fire regimes to analyze differences between past and present characteristics. It describes fire regimes based on their fire frequencies and severities which helps detect changes in fire regimes over time which is helpful in assessing fire climate effects at regional and landscape scales. Understanding historic fire regimes can be difficult, as fire history data is not always reliable or available. Past fire events can be identified using fire scar analysis on trees, age distributions of stands, charcoal samples, or vegetation changes seen over long periods of time. Examining past fire events and historic fire regimes provides a means of examining trends in vegetation and fire-climate interactions over a long time frame. The variability and fire-climate-vegetation interactions of fire regimes are able to be examined in greater detail and over much longer time periods (thousands of years) rather than just decades as provided by examining historical fire records. Studies have found strong correlations between past climate and fire frequency and extent using these historical fire aging methods.