Pyrogeography is the study of the past, present, and projected distribution of wildfire. Wildland fire occurs under certain conditions of climate, vegetation, topography, and sources of ignition, such that it has its own biogeography, or pattern in space and time. The earliest published evidence of the term appears to be in the mid-1990s, and the meaning was primarily related to mapping fires The current understanding of pyrogeography emerged in the 2000s as a combination of biogeography and fire ecology, facilitated by the availability of global-scale datasets of fire occurrence, vegetation cover, and climate. Pyrogeography has also been placed at the juncture of biology, the geophysical environment, and society and cultural influences on fire. Pyrogeography often uses a framework of ecological niche concepts to evaluate the environmental controls on fire. By examining how environmental factors interact to facilitate fire activity, pyrogeographers can predict expected fire behavior under new conditions. Pyrogeographic research contributes to and informs land management policy in various regions across the globe.
Concepts
The pyrogeography framework Under the framework used in pyrogeography, there are three basic categories that control fire regimes across the world: consumable resources, ignitions and atmospheric conditions. Each of the three factors varies across space and time, causing and creating different fire regime types. Fire is a result of the intersection of these three components.
Consumable resources - This term refers to the vegetation consumed as a fuel source in wildfires. Vegetation type can vary in productivity, structure, and flammability, and that variability will lead to different types of fire behavior or intensity. Ignitions - Fire is controlled in part by the availability of an ignition source. There are two primary sources of ignition for fire: natural and anthropogenic. The importance of these two sources varies according to region. Natural Ignition: the primary form of natural ignition is lightning, though some fires may begin through other sources of ignition (such as volcanic activity). Anthropogenic ignition: humans cause fires both intentionally and unintentionally. Atmospheric conditions - Weather conditions can determine whether an area is conducive to fire: hot, dry and/or windy weather may make fire more likely, while damp and cold conditions may decrease the probability of fire occurring. By examining and quantifying this framework across time and space, pyrogeographers can examine the difference between fire regimes in different regions or time periods.
Fire variables
Several variables must be met for fire to occur, all of which are influenced by both natural and human factors. Due to the spatial and temporal characteristics of each variable, global fire behavior is a complex and fluid system to model and cannot be predicted by climate or vegetation alone.
Wind speed Wind speed is the driving force behind rate of spread, or how quickly a fire moves through a landscape. It is influenced by the season, weather, topography, and land cover of a location. Wind speed is affected by human activity through anthropogenic climate change and land use change.
Fuel continuity Fuel continuity is the distribution of fuel particles in a fuel bed, and affects the fire's ability to sustain combustion and spread. It is influenced by the terrain type, presence of water bodies, seasonality, and vegetation type/age. Human influences on continuity include artificial fuel breaks (roads, fire suppression tactics), habitat fragmentation, species displacement, and land management methods (patch burning, "slash and burn", etc.).
Fuel loads Fuel load is the amount of available fuel per unit area. Can also be defined by amount of heat energy generated per unit area upon combustion. Natural influences include vegetation type/cover, presence of natural disturbances (such as insect outbreak, wind damage), herbivory, soil fertility, and seasonality. Human influences can involve grazing, logging, suppression tactics, fuel treatments (preventative measures), and land use change such as deforestation and agricultural development.
Fuel moisture Fuel moisture is the measure of amount of water within fuels, and is expressed as a percent of dry weight of that fuel. Fuel moisture is affected by wind activity, season, antecedent rainfall, relative humidity, air temperature, and soil moisture. Human influences include anthropogenic climate change and land management activity (logging, grazing, burning).
Ignitions Ignitions can be either natural or anthropogenic. Natural ignitions are generally limited to lightning strikes, but volcanism and other sources have been observed. Human-caused fire may be intentional (arson, fuel management methods) or unintentional. Natural factors affecting ignitions include lightning flashes, volcanoes, and seasonality. Human influences include population size, land management, road networks, and arson.
Methodology Pyrogeographers use many different methods to study the distribution of fire. To study fire across space, pyrogeographers use spatial data of fire activity, which may come in several forms including observations, satellite imagery, and historical evidence of fire. The emergence of pyrogeography as a field is closely linked to the availability of satellite imagery. Since the late 1970s when satellite data became widely-available, the seasonal and geographical patterns of fire activity have come under inquiry, leading to the development of the field.
Fire observation data The observation of fire occurrence is an important piece of data in pyrogeography. Information on the occurrence of fire can be obtained from a variety of sources: historical and present. Historic fire observation data frequently comes from dendrochronology (tree ring records of fire) or other written historical records. Modern fire observations are often made with satellites: using aerial imagery, scientists can examine fire activity and the size of an area burned. Both forms of fire observation data are important for studying the distribution of fire.
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