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Fire history, the ecological science of studying the history of wildfires, is a subdiscipline of fire ecology. Patterns of forest fires in historical and prehistorical times provide information relevant to the vegetation pattern in modern landscapes. It gives an estimate of a natural disturbance regime's historical range of variability and can be used to identify the processes affecting fire occurrence. Fire history reconstructions are achieved by compiling atlases of past fires, using the tree ring record from fire scars and tree ages and the charcoal record from soils and sediments.
Sustained wildfire can only exist once oxygen levels and fuel sources are present in sufficient quantities. Between 400 and 450 million years ago, fire became a landscape feature. [1] : 11–14 The presence of fusain (fossil charcoal), beginning in the early Carboniferous attests to this fire history and forms an important element of the Cretaceous–Paleogene boundary. [1] : 11–14 [2]
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The growth record of a tree in seasonal climates is preserved in the growth rings in the stem wood; the field of dendrochronology is the study of the record of climate and other events preserved in the growth record. Each growth ring represents one year of life. The thickness of each ring indicates the amount of wood produced during that growing season. Large cells can quickly divide rapidly at the beginning of the growing season, creating a light-colored wood. When growth slows down, generally in colder months, a darker wood is created from smaller cells, dividing more slowly. Thus, one year is represented by a light inner ring and a darker outer ring. [3]
Rings can be counted from dead trees and stumps left behind from logging. A sample can be collected from a living tree using tools like the increment borer. The increment borer is a hollow steel tube that extracts a core sample from a tree’s trunk. The growth rings in a core sample are counted to determine the age of that tree. The ages of stand-replacing fires may be determined by determining the cohort age of trees established after a fire. For example, tree-ring dating of large stands will show the age of the forest and may provide an estimate of when the last significant disturbance event occurred.
Sometimes, growth rings exhibit scars. A fire scar forms when heat kills the vascular cambium beneath the bark, which then heals over subsequent years as growth rings curl over the scarred area, thus protecting the tree from infection. [4] This method can be used to date the year a fire occurred. Observing the scars establishes the timeline of a forest fire and the time between fires at a site. Surveying many trees over a large sample area provides a view to individual fire events and the overall fire regime. Not all tree species scar and show evidence of fire. Most pine species in the subgenus Pinus readily produce scars protected by resin; scarring on other trees may result in death, leaving no fire record behind.
Before Euro-American settlement in western North America, fire histories from scars preserved in ponderosa pine forests often reveal a pattern of frequent fire (often with 5 to 20-year intervals in a single area), with a pattern in time and space strongly related to past variations in climate. [5] Fuel reduction from grazing and fire suppression significantly reduced the amount of fire in dry forests over the last 100 years.
A study by Arne Buechiling and William L. Baker in 2004 identified 41 fire events beginning in 1533 in a 9200-ha study area north of Estes Park, Colorado. They sampled 3461 tree cores and 212 fire scars. [6] Fire scar data provided greater insight into the fire event parameters. Of the 41 fires, 22 were high-severity crown fires, seven low-severity surface fires, and eight mixed-severity fires. Fires larger than 300 ha were few but composed a substantial proportion of the area burned since 1700. Drought periods produced larger fires.
There is little known about the history of fires in some places. Central Europe, for instance, lacks intact forests with old-growth trees or an abundance of dead or cut-down trees that can be used to reconstruct past fire regimes. The Bialowieza Primeval Forest in Poland is an exception to this condition. [7] A group of researchers were able to use a 350-year tree-ring fire record to reconstruct the fire history in precise detail. This is a shining example of how the method can be used in a place with a lost or no written history of a fire regime.
Chaparral is a shrubland plant community found primarily in California, in southern Oregon and in the northern portion of the Baja California Peninsula in Mexico. It is shaped by a Mediterranean climate and infrequent, high-intensity crown fires.
Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction products. At a certain point in the combustion reaction, called the ignition point, flames are produced. The flame is the visible portion of the fire. Flames consist primarily of carbon dioxide, water vapor, oxygen and nitrogen. If hot enough, the gases may become ionized to produce plasma. Depending on the substances alight, and any impurities outside, the color of the flame and the fire's intensity will be different.
A wildfire, forest fire, or a bushfire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identified as a bushfire, desert fire, grass fire, hill fire, peat fire, prairie fire, vegetation fire, or veld fire. Some natural forest ecosystems depend on wildfire. Wildfires are different from controlled or prescribed burning, which are carried out to provide a benefit for people. Modern forest management often engages in prescribed burns to mitigate fire risk and promote natural forest cycles. However, controlled burns can turn into wildfires by mistake.
A savanna or savannah is a mixed woodland-grassland biome and ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of grasses. Four savanna forms exist; savanna woodland where trees and shrubs form a light canopy, tree savanna with scattered trees and shrubs, shrub savanna with distributed shrubs, and grass savanna where trees and shrubs are mostly nonexistent.
Stephen J. Pyne (1949–present) is an emeritus professor at Arizona State University, specializing in environmental history, the history of exploration, and especially the history of fire.
A controlled or prescribed (Rx) burn is the practice of intentionally setting a fire to change the assemblage of vegetation and decaying material in a landscape. The purpose could be for forest management, ecological restoration, land clearing or wildfire fuel management. A controlled burn may also refer to the intentional burning of slash and fuels through burn piles. Controlled burns may also be referred to as hazard reduction burning, backfire, swailing or a burn-off. In industrialized countries, controlled burning regulations and permits are usually overseen by fire control authorities.
Fire ecology is a scientific discipline concerned with the effects of fire on natural ecosystems. Many ecosystems, particularly prairie, savanna, chaparral and coniferous forests, have evolved with fire as an essential contributor to habitat vitality and renewal. Many plant species in fire-affected environments use fire to germinate, establish, or to reproduce. Wildfire suppression not only endangers these species, but also the animals that depend upon them.
Wildfire suppression is a range of firefighting tactics used to suppress wildfires. Firefighting efforts depend on many factors such as the available fuel, the local atmospheric conditions, the features of the terrain, and the size of the wildfire. Because of this wildfire suppression in wild land areas usually requires different techniques, equipment, and training from the more familiar structure fire fighting found in populated areas. Working in conjunction with specially designed aerial firefighting aircraft, fire engines, tools, firefighting foams, fire retardants, and using various firefighting techniques, wildfire-trained crews work to suppress flames, construct fire lines, and extinguish flames and areas of heat in order to protect resources and natural wilderness. Wildfire suppression also addresses the issues of the wildland–urban interface, where populated areas border with wild land areas.
Thomas W. Swetnam is Regents' Professor Emeritus of Dendrochronology at the University of Arizona, studying disturbances of forest ecosystems across temporal and spatial scales. He served as the Director of the Laboratory of Tree-Ring Research from 2000 to 2015.
Wildfires consume live and dead fuels, destabilize physical and ecological landscapes, and impact human social and economic systems. Post-fire seeding was initially used to stabilize soils. More recently it is being used to recover post wildfire plant species, manage invasive non-native plant populations and establish valued vegetation compositions.
Prior to the European colonization of the Americas, indigenous peoples used fire to modify the landscape. This influence over the fire regime was part of the environmental cycles and maintenance of wildlife habitats that sustained the cultures and economies of the Indigenous peoples of the Americas. What was initially perceived by colonists as "untouched, pristine" wilderness in North America was the cumulative result of the indigenous use of fire, creating a mosaic of grasslands and forests across North America, sustained and managed by the peoples indigenous to the landscape.
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.
The fossil record of fire first appears with the establishment of a land-based flora in the Middle Ordovician period, 470 million years ago, permitting the accumulation of oxygen in the atmosphere as never before, as the new hordes of land plants pumped it out as a waste product. When this concentration rose above 13%, it permitted the possibility of wildfire. Wildfire is first recorded in the Late Silurian fossil record, 420 million years ago, by fossils of charcoalified plants. Apart from a controversial gap in the Late Devonian, charcoal is present ever since. The level of atmospheric oxygen is closely related to the prevalence of charcoal: clearly oxygen is the key factor in the abundance of wildfire. Fire also became more abundant when grasses radiated and became the dominant component of many ecosystems, around 6 to 7 million years ago; this kindling provided tinder which allowed for the more rapid spread of fire. These widespread fires may have initiated a positive feedback process, whereby they produced a warmer, drier climate more conducive to fire.
Wildfire suppression in the United States has had a long and varied history. For most of the 20th century, any form of wildland fire, whether it was naturally caused or otherwise, was quickly suppressed for fear of uncontrollable and destructive conflagrations such as the Peshtigo Fire in 1871 and the Great Fire of 1910. In the 1960s, policies governing wildfire suppression changed due to ecological studies that recognized fire as a natural process necessary for new growth. Today, policies advocating complete fire suppression have been exchanged for those who encourage wildland fire use, or the allowing of fire to act as a tool, such as the case with controlled burns.
The wildland–urban interface (WUI) is a zone of transition between wilderness and land developed by human activity – an area where a built environment meets or intermingles with a natural environment. Human settlements in the WUI are at a greater risk of catastrophic wildfire.
Wildfires can happen in many places in the United States, especially during droughts, but are most common in the Western United States and Florida. They may be triggered naturally, most commonly by lightning, or by human activity like unextinguished smoking materials, faulty electrical equipment, overheating automobiles, or arson.
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.
Fire adaptations are traits of plants and animals that help them survive wildfire or to use resources created by wildfire. These traits can help plants and animals increase their survival rates during a fire and/or reproduce offspring after a fire. Both plants and animals have multiple strategies for surviving and reproducing after fire. Plants in wildfire-prone ecosystems often survive through adaptations to their local fire regime. Such adaptations include physical protection against heat, increased growth after a fire event, and flammable materials that encourage fire and may eliminate competition.
Triodia scariosa, is more commonly known as porcupine grass or spinifex, and belongs to the endemic Australian grass genus Triodia. The species is perennial and evergreen and individuals grow in mounds, called hummocks, that reach up to ~1m in height. The leaves are ~30 cm long, 1mm in diameter, needlepointed and rigid, and its inflorescence is a narrow, loose panicle that forms a flowering stalk up to ~2m in height. The name is derived from Latin; Triodia refers to the three-toothed lobes of the lemma, and scariosa is in reference to the thin, dry glume. The species is common to Mallee (MVG14) and Hummock grassland (MVG20) communities, in arid and semi-arid regions of Australia.
Crystal A. Kolden is an Associate Professor of Forest, Rangeland, and Fire Sciences at the University of Idaho. She received her Ph.D. in Geography from Clark University. She is an expert in fire sciences. She started her career as a wildfire fighter, but has since become a professor specializing in wildfire behavior.