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Friday, July 7, 2023

Modern dance

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Modern_dance
 
Martha Graham in 1948

Modern dance is a broad genre of western concert or theatrical dance which included dance styles such as ballet, folk, ethnic, religious, and social dancing; and primarily arose out of Europe and the United States in the late 19th and early 20th centuries. It was considered to have been developed as a rejection of, or rebellion against, classical ballet, and also a way to express social concerns like socioeconomic and cultural factors.

In the late 19th century, modern dance artists such as Isadora Duncan, Maud Allan, and Loie Fuller were pioneering new forms and practices in what is now called aesthetic or free dance. These dancers disregarded ballet's strict movement vocabulary (the particular, limited set of movements that were considered proper to ballet) and stopped wearing corsets and pointe shoes in the search for greater freedom of movement.

Throughout the 20th century, sociopolitical concerns, major historical events, and the development of other art forms contributed to the continued development of modern dance in the United States and Europe. Moving into the 1960s, new ideas about dance began to emerge as a response to earlier dance forms and to social changes. Eventually, postmodern dance artists would reject the formalism of modern dance, and include elements such as performance art, contact improvisation, release technique, and improvisation.

American modern dance can be divided (roughly) into three periods or eras. In the Early Modern period (c. 1880–1923), characterized by the work of Isadora Duncan, Loie Fuller, Ruth St. Denis, Ted Shawn, and Eleanor King, artistic practice changed radically, but clearly distinct modern dance techniques had not yet emerged. In the Central Modern period (c. 1923–1946), choreographers Martha Graham, Doris Humphrey, Katherine Dunham, Charles Weidman, and Lester Horton sought to develop distinctively American movement styles and vocabularies, and developed clearly defined and recognizable dance training systems. In the Late Modern period (c. 1946–1957), José Limón, Pearl Primus, Merce Cunningham, Talley Beatty, Erick Hawkins, Anna Sokolow, Anna Halprin, and Paul Taylor introduced clear abstractionism and avant-garde movements, and paved the way for postmodern dance.

Modern dance has evolved with each subsequent generation of participating artists. Artistic content has morphed and shifted from one choreographer to another, as have styles and techniques. Artists such as Graham and Horton developed techniques in the Central Modern Period that are still taught worldwide and numerous other types of modern dance exist today.

Background

Modern dance is often considered to have emerged as a rejection of, or rebellion against, classical ballet, although historians have suggested that socioeconomic changes in both the United States and Europe helped to initiate shifts in the dance world. In America, increasing industrialization, the rise of a middle class (which had more disposable income and free time), and the decline of Victorian social strictures led to, among other changes, a new interest in health and physical fitness. "It was in this atmosphere that a 'new dance' was emerging as much from a rejection of social structures as from a dissatisfaction with ballet." During that same period, "the champions of physical education helped to prepare the way for modern dance, and gymnastic exercises served as technical starting points for young women who longed to dance." Women's colleges began offering "aesthetic dance" courses by the end of the 1880s. Emil Rath, who wrote at length about this emerging art form at the time stated,

"Music and rhythmic bodily movement are twin sisters of art, as they have come into existence simultaneously...today we see in the artistic work of Isadora Duncan, Maud Allan, and others the use of a form of dancing which strives to portray in movements what the music master expresses in his compositions—interpretative dancing."

Free dance

Isadora Duncan in 1903
 
Main article: Free dance
  • Isadora Duncan (born in 1877) was a predecessor of modern dance with her stress on the center or torso, bare feet, loose hair, free-flowing costumes, and incorporation of humor into emotional expression. She was inspired by classical Greek arts, folk dances, social dances, nature, natural forces, and new American athleticism such as skipping, running, jumping, leaping, and abrupt movements. She thought that ballet was ugly and meaningless gymnastics. Although she returned to the United States at various points in her life, her work was not well received there. She returned to Europe and died in Nice in 1927.
  • Loie Fuller (born in 1862) was a burlesque "skirt" dancer experimenting with the effect that gas lighting had on her silk costumes. Fuller developed a form of natural movement and improvisation techniques that were used in conjunction with her revolutionary lighting equipment and translucent silk costumes. She patented her apparatus and methods of stage lighting, that included the use of coloured gels and burning chemicals for luminescence, and her voluminous silk stage costumes.
  • Ruth St. Denis (born in 1879) influenced by the actress Sarah Bernhardt and Japanese dancer Sada Yacco, developed her translations of Indian culture and mythology. Her performances quickly became popular and she toured extensively while researching Asian culture and arts.

Expressionist and early modern dance in Europe

Dancer at the Laban school, Berlin 1929
 
See also: Expressionist dance and Ausdruckstanz

In Europe, Mary Wigman in Germany, Francois Delsarte, Émile Jaques-Dalcroze (Eurhythmics), and Rudolf Laban developed theories of human movement and expression, and methods of instruction that led to the development of European modern and Expressionist dance. Other pioneers included Kurt Jooss (Ausdruckstanz) and Harald Kreutzberg.

Radical dance

Disturbed by the Great Depression and the rising threat of fascism in Europe, the radical dancers tried to raise consciousness by dramatizing the economic, social, ethnic and political crises of their time.

  • Hanya Holm - A student of Mary Wigman and an instructor at the Wigman School in Dresden, founded the New York Wigman School of Dance in 1931 (which became the Hanya Holm Studio in 1936) introducing Wigman technique, Rudolf Laban's theories of spatial dynamics, and later her own dance techniques to American modern dance. An accomplished choreographer, she was a founding artist of the first American Dance Festival in Bennington (1934). Holm's dance work Metropolitan Daily was the first modern dance composition to be televised on NBC and her labanotation score for Kiss Me, Kate (1948) was the first choreography to be copyrighted in the United States. Holm choreographed extensively in the fields of concert dance and musical theater.
  • Anna Sokolow - A student of Martha Graham and Louis Horst, Sokolow created her own dance company (c. 1930). Presenting dramatic contemporary imagery, Sokolow's compositions were generally abstract, often revealing the full spectrum of human experience reflecting the tension and alienation of the time and the truth of human movement.
  • José Limón - In 1946, after studying and performing with Doris Humphrey and Charles Weidman, Limón established his own company with Humphrey as artistic director. It was under her mentorship that Limón created his signature dance The Moor's Pavane (1949). Limón's choreographic works and technique remain a strong influence on contemporary dance practice.
  • Merce Cunningham - A former ballet student and performer with Martha Graham, he presented his first New York solo concert with John Cage in 1944. Influenced by Cage and embracing modernist ideology using postmodern processes, Cunningham introduced chance procedures and pure movement to choreography and Cunningham technique to the cannon of 20th-century dance techniques. Cunningham set the seeds for postmodern dance with his non-linear, non-climactic, non-psychological abstract work. In these works each element is in and of itself expressive, and the observer (in large part) determines what it communicates.
  • Erick Hawkins - A student of George Balanchine, became a soloist and the first male dancer in Martha Graham's dance company. In 1951, Hawkins, interested in the new field of kinesiology, opened his own school and developed his own technique (Hawkins technique) a forerunner of most somatic dance techniques.
  • Paul Taylor - A student of the Juilliard School of Music and the Connecticut College School of Dance. In 1952 his performance at the American Dance Festival attracted the attention of several major choreographers. Performing in the companies of Merce Cunningham, Martha Graham, and George Balanchine (in that order), he founded the Paul Taylor Dance Company in 1954. The use of everyday gestures and modernist ideology is characteristic of his choreography. Former members of the Paul Taylor Dance Company included Twyla Tharp, Laura Dean, Dan Wagoner, and Senta Driver.
  • Alwin Nikolais - A student of Hanya Holm. Nikolais use of multimedia in works such as Masks, Props, and Mobiles (1953), Totem (1960), and Count Down (1979) was unmatched by other choreographers. Often presenting his dancers in constrictive spaces and costumes with complicated sound and sets, he focused their attention on the physical tasks of overcoming obstacles he placed in their way. Nikolais viewed the dancer not as an artist of self-expression, but as a talent who could investigate the properties of physical space and movement.

In the United States

Main article: Modern dance in the United States

Early modern dance

Martha Graham and Bertram Ross in 1961; photo by Carl van Vechten

In 1915, Ruth St. Denis founded the Denishawn school and dance company with her husband Ted Shawn. Martha Graham, Doris Humphrey, and Charles Weidman were pupils at the school and members of the dance company. Seeking a wider and more accepting audience for their work, Duncan, Fuller, and Ruth St. Denis toured Europe. Martha Graham is often regarded as the founding mother of modern 20th-century concert dance. Graham viewed ballet as too one-sided: European, imperialistic, and un-American. She became a student at the Denishawn school in 1916 and then moved to New York City in 1923, where she performed in musical comedies, music halls, and worked on her own choreography. Graham developed her own dance technique, Graham technique, that hinged on concepts of contraction and release. In Graham's teachings, she wanted her students to "Feel". To "Feel", means having a heightened sense of awareness of being grounded to the floor while, at the same time, feeling the energy throughout your entire body, extending it to the audience. Her principal contributions to dance are the focus of the 'center' of the body (as contrast to ballet's emphasis on limbs), coordination between breathing and movement, and a dancer's relationship with the floor.

Popularization

In 1927, newspapers regularly began assigning dance critics, such as Walter Terry, and Edwin Denby, who approached performances from the viewpoint of a movement specialist rather than as a reviewer of music or drama. Educators accepted modern dance into college and university curricula, first as a part of physical education, then as performing art. Many college teachers were trained at the Bennington Summer School of the Dance, established at Bennington College in 1934. Of the Bennington program, Agnes de Mille wrote, "...there was a fine commingling of all kinds of artists, musicians, and designers, and secondly, because all those responsible for booking the college concert series across the continent were assembled there. ... free from the limiting strictures of the three big monopolistic managements, who pressed for preference of their European clients. As a consequence, for the first time American dancers were hired to tour America nationwide, and this marked the beginning of their solvency."

African American

Alvin Ailey American Dance Theater perform "Revelations" in 2011.

African American dance blended modern dance with African and Caribbean movement (flexible torso and spine, articulated pelvis, isolation of the limbs, and polyrhythmic movement). Katherine Dunham trained in ballet, founded Ballet Negre in 1936 and then the Katherine Dunham Dance Company based in Chicago. In 1945, she opened a school in New York, teaching Katherine Dunham Technique, African and Caribbean movement integrated with ballet and modern dance. Taking inspiration from African-based dance where one part of the body plays against one another, she focused on articulating the torso in her choreography. Pearl Primus drew on African and Caribbean dances to create strong dramatic works characterized by large leaps. She often based her dances on the work of black writers and on racial issues, such as Langston Hughes's 1944 The Negro Speaks of Rivers, and Lewis Allan's 1945 Strange Fruit (1945). Her dance company developed into the Pearl Primus Dance Language Institute. Alvin Ailey studied under Lester Horton, Bella Lewitzky, and later Martha Graham. He spent several years working in both concert and theater dance. In 1958, Ailey and a group of young African-American dancers performed as the Alvin Ailey American Dance Theater in New York. He drew upon his "blood memories" of Texas, the blues, spirituals and gospel as inspiration. His most popular and critically acclaimed work is Revelations (1960).

Legacy of modern dance

The legacy of modern dance can be seen in lineage of 20th-century concert dance forms. Although often producing divergent dance forms, many seminal dance artists share a common heritage that can be traced back to free dance.

Postmodern dance

Main article: Postmodern dance

Postmodern dance developed in the 1960s in United States when society questioned truths and ideologies in politics and art. This period was marked by social and cultural experimentation in the arts. Choreographers no longer created specific 'schools' or 'styles'. The influences from different periods of dance became more vague and fragmented.

Contemporary dance

Main article: Contemporary dance

Contemporary dance emerged in the 1950s as the dance form that is combining the modern dance elements and the classical ballet elements. It can use elements from non-Western dance cultures, such as African dancing with bent knees as a characteristic trait, and Butoh, Japanese contemporary dancing that developed in the 1950s. It incorporates modern European influences, via the work of pioneers like Isadora Duncan.

According to Treva Bedinghaus, "Modern dancers use dancing to express their innermost emotions, often to get closer to their inner-selves. Before attempting to choreograph a routine, the modern dancer decides which emotions to try to convey to the audience. Many modern dancers choose a subject near and dear to their hearts, such as a lost love or a personal failure. The dancer will choose music that relates to the story they wish to tell, or choose to use no music at all, and then choose a costume to reflect their chosen emotions."

Teachers and their students

This list illustrates some important teacher-student relationships in modern dance.

Rudolf von Laban and pupils at his dance school, Berlin 1929
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Fire ecology

From Wikipedia, the free encyclopedia
 
The Old Fire burning in the San Bernardino Mountains (image taken from the International Space Station)

Fire ecology is a scientific discipline concerned with natural processes involving fire in an ecosystem and the ecological effects, the interactions between fire and the abiotic and biotic components of an ecosystem, and the role as an ecosystem process. 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 campaigns in the United States have historically molded public opinion to believe that wildfires are harmful to nature. Ecological research has shown, however, that fire is an integral component in the function and biodiversity of many natural habitats, and that the organisms within these communities have adapted to withstand, and even to exploit, natural wildfire. More generally, fire is now regarded as a 'natural disturbance', similar to flooding, windstorms, and landslides, that has driven the evolution of species and controls the characteristics of ecosystems.

Fire suppression, in combination with other human-caused environmental changes, may have resulted in unforeseen consequences for natural ecosystems. Some large wildfires in the United States have been blamed on years of fire suppression and the continuing expansion of people into fire-adapted ecosystems as well as climate change. Land managers are faced with tough questions regarding how to restore a natural fire regime, but allowing wildfires to burn is likely the least expensive and most effective method in many situations.

Panoramic photo series of succession in Florida pine woodland
A combination of photos taken at a photo point at Florida Panther NWR. The photos are panoramic and cover a 360 degree view from a monitoring point. These photos range from pre-burn to two years post burn.

Fire components

A fire regime describes the characteristics of fire and how it interacts with a particular ecosystem. Its "severity" is a term that ecologists use to refer to the impact that a fire has on an ecosystem. It is usually studied using tools such as remote sensing which can detect burned area estimates, severity and fire risk associated with an area. Ecologists can define this in many ways, but one way is through an estimate of plant mortality. Fire can burn at three levels. Ground fires will burn through soil that is rich in organic matter. Surface fires will burn through dead plant material that is lying on the ground. Crown fires will burn in the tops of shrubs and trees. Ecosystems generally experience a mix of all three.

Fires will often break out during a dry season, but in some areas wildfires may also commonly occur during a time of year when lightning is prevalent. The frequency over a span of years at which fire will occur at a particular location is a measure of how common wildfires are in a given ecosystem. It is either defined as the average interval between fires at a given site, or the average interval between fires in an equivalent specified area.

Defined as the energy released per unit length of fireline (kW m−1), wildfire intensity can be estimated either as

  • the product of
    • the linear spread rate (m s−1),
    • the low heat of combustion (kJ kg−1),
    • and the combusted fuel mass per unit area,
  • or it can be estimated from the flame length.
Radiata pine plantation burnt during the 2003 Eastern Victorian alpine bushfires, Australia

Abiotic responses

Fires can affect soils through heating and combustion processes. Depending on the temperatures of the soils caused by the combustion processes, different effects will happen- from evaporation of water at the lower temperature ranges, to the combustion of soil organic matter and formation of pyrogenic organic matter, otherwise known as charcoal.

Fires can cause changes in soil nutrients through a variety of mechanisms, which include oxidation, volatilization, erosion, and leaching by water, but the event must usually be of high temperatures for significant loss of nutrients to occur. However, quantity of nutrients available in soils are usually increased due to the ash that is generated, and this is made quickly available, as opposed to the slow release of nutrients by decomposition. Rock spalling (or thermal exfoliation) accelerates weathering of rock and potentially the release of some nutrients.

Increase in the pH of the soil following a fire is commonly observed, most likely due to the formation of calcium carbonate, and the subsequent decomposition of this calcium carbonate to calcium oxide when temperatures get even higher. It could also be due to the increased cation content in the soil due to the ash, which temporarily increases soil pH. Microbial activity in the soil might also increase due to the heating of soil and increased nutrient content in the soil, though studies have also found complete loss of microbes on the top layer of soil after a fire. Overall, soils become more basic (higher pH) following fires because of acid combustion. By driving novel chemical reactions at high temperatures, fire can even alter the texture and structure of soils by affecting the clay content and the soil's porosity.

Removal of vegetation following a fire can cause several effects on the soil, such as increasing the temperatures of the soil during the day due to increased solar radiation on the soil surface, and greater cooling due to loss of radiative heat at night. Fewer leaves to intercept rain will also cause more rain to reach the soil surface, and with fewer plants to absorb the water, the amount of water content in the soils might increase. However, it might be seen that ash can be water repellent when dry, and therefore water content and availability might not actually increase.

Biotic responses and adaptations

Two photographs of the same section of a pine forest; both show blackened bark at least halfway up the trees. The first picture is noticeably lacking in surface vegetation, while the second shows small, green grasses on the forest floor.
Ecological succession after a wildfire in a boreal pine forest next to Hara Bog, Lahemaa National Park, Estonia. The pictures were taken one and two years after the 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.

For example, plants of the genus Eucalyptus contain flammable oils that encourage fire and hard sclerophyll leaves to resist heat and drought, ensuring their dominance over less fire-tolerant species. Dense bark, shedding lower branches, and high water content in external structures may also protect trees from rising temperatures. Fire-resistant seeds and reserve shoots that sprout after a fire encourage species preservation, as embodied by pioneer species. Smoke, charred wood, and heat can stimulate the germination of seeds in a process called serotiny. Exposure to smoke from burning plants promotes germination in other types of plants by inducing the production of the orange butenolide.

Plants

Lodgepole pine cones

Plants have evolved many adaptations to cope with fire. Of these adaptations, one of the best-known is likely pyriscence, where maturation and release of seeds is triggered, in whole or in part, by fire or smoke; this behaviour is often erroneously called serotiny, although this term truly denotes the much broader category of seed release activated by any stimulus. All pyriscent plants are serotinous, but not all serotinous plants are pyriscent (some are necriscent, hygriscent, xeriscent, soliscent, or some combination thereof). On the other hand, germination of seed activated by trigger is not to be confused with pyriscence; it is known as physiological dormancy.

In chaparral communities in Southern California, for example, some plants have leaves coated in flammable oils that encourage an intense fire. This heat causes their fire-activated seeds to germinate (an example of dormancy) and the young plants can then capitalize on the lack of competition in a burnt landscape. Other plants have smoke-activated seeds, or fire-activated buds. The cones of the Lodgepole pine (Pinus contorta) are, conversely, pyriscent: they are sealed with a resin that a fire melts away, releasing the seeds. Many plant species, including the shade-intolerant giant sequoia (Sequoiadendron giganteum), require fire to make gaps in the vegetation canopy that will let in light, allowing their seedlings to compete with the more shade-tolerant seedlings of other species, and so establish themselves. Because their stationary nature precludes any fire avoidance, plant species may only be fire-intolerant, fire-tolerant or fire-resistant.

Fire intolerance

Fire-intolerant plant species tend to be highly flammable and are destroyed completely by fire. Some of these plants and their seeds may simply fade from the community after a fire and not return; others have adapted to ensure that their offspring survives into the next generation. "Obligate seeders" are plants with large, fire-activated seed banks that germinate, grow, and mature rapidly following a fire, in order to reproduce and renew the seed bank before the next fire. Seeds may contain the receptor protein KAI2, that is activated by the growth hormones karrikin released by the fire.

Fire tolerance. Typical regrowth after an Australian bushfire.

Fire tolerance

Fire-tolerant species are able to withstand a degree of burning and continue growing despite damage from fire. These plants are sometimes referred to as "resprouters". Ecologists have shown that some species of resprouters store extra energy in their roots to aid recovery and re-growth following a fire. For example, after an Australian bushfire, the Mountain Grey Gum tree (Eucalyptus cypellocarpa) starts producing a mass of shoots of leaves from the base of the tree all the way up the trunk towards the top, making it look like a black stick completely covered with young, green leaves.

Fire resistance

Fire-resistant plants suffer little damage during a characteristic fire regime. These include large trees whose flammable parts are high above surface fires. Mature ponderosa pine (Pinus ponderosa) is an example of a tree species that suffers little to no crown damage during a low severity fire because it sheds its lower, vulnerable branches as it matures.

Animals, birds and microbes

A mixed flock of hawks hunting in and around a bushfire

Like plants, animals display a range of abilities to cope with fire, but they differ from most plants in that they must avoid the actual fire to survive. Although birds may be vulnerable when nesting, they are generally able to escape a fire; indeed they often profit from being able to take prey fleeing from a fire and to recolonize burned areas quickly afterwards. In fact, many wildlife species globally are dependent on recurring fires in fire-dependent ecosystems to create and maintain habitat. Some anthropological and ethno-ornithological evidence suggests that certain species of fire-foraging raptors may engage in intentional fire propagation to flush out prey. Mammals are often capable of fleeing a fire, or seeking cover if they can burrow. Amphibians and reptiles may avoid flames by burrowing into the ground or using the burrows of other animals. Amphibians in particular are able to take refuge in water or very wet mud.

Some arthropods also take shelter during a fire, although the heat and smoke may actually attract some of them, to their peril. Microbial organisms in the soil vary in their heat tolerance but are more likely to be able to survive a fire the deeper they are in the soil. A low fire intensity, a quick passing of the flames and a dry soil will also help. An increase in available nutrients after the fire has passed may result in larger microbial communities than before the fire. The generally greater heat tolerance of bacteria relative to fungi makes it possible for soil microbial population diversity to change following a fire, depending on the severity of the fire, the depth of the microbes in the soil, and the presence of plant cover. Certain species of fungi, such as Cylindrocarpon destructans appear to be unaffected by combustion contaminants, which can inhibit re-population of burnt soil by other microorganisms, and therefore have a higher chance of surviving fire disturbance and then recolonizing and out-competing other fungal species afterwards.

Fire and ecological succession

Fire behavior is different in every ecosystem and the organisms in those ecosystems have adapted accordingly. One sweeping generality is that in all ecosystems, fire creates a mosaic of different habitat patches, with areas ranging from those having just been burned to those that have been untouched by fire for many years. This is a form of ecological succession in which a freshly burned site will progress through continuous and directional phases of colonization following the destruction caused by the fire. Ecologists usually characterize succession through the changes in vegetation that successively arise. After a fire, the first species to re-colonize will be those with seeds are already present in the soil, or those with seeds are able to travel into the burned area quickly. These are generally fast-growing herbaceous plants that require light and are intolerant of shading. As time passes, more slowly growing, shade-tolerant woody species will suppress some of the herbaceous plants. Conifers are often early successional species, while broad leaf trees frequently replace them in the absence of fire. Hence, many conifer forests are themselves dependent upon recurring fire. Both natural and human fires affect all ecosystems from peatlands to shrublands to forests and tropical landscapes. This impacts the way that the ecosystem is structured and functions. Though there have always been wildfires naturally, the frequency of wildfires has increased at a rapid rate in recent years. This is largely due to decreases in precipitation, increases in temperature, and increases in human ignitions.

Different species of plants, animals, and microbes specialize in exploiting different stages in this process of succession, and by creating these different types of patches, fire allows a greater number of species to exist within a landscape. Soil characteristics will be a factor in determining the specific nature of a fire-adapted ecosystem, as will climate and topography. Different frequencies of fire also result in different successional pathways; short intervals between fires often eliminate tree species due to the time required to rebuild a seed bank, resulting in replacement by lighter seeded species like grasses and forbs. 

https://www.ipcc.ch/report/ar6/wg3/

Examples of fire in different ecosystems

Forests

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Mild to moderate fires burn in the forest understory, removing small trees and herbaceous groundcover. High-severity fires will burn into the crowns of the trees and kill most of the dominant vegetation. Crown fires may require support from ground fuels to maintain the fire in the forest canopy (passive crown fires), or the fire may burn in the canopy independently of any ground fuel support (an active crown fire). High-severity fire creates complex early seral forest habitat, or snag forest with high levels of biodiversity. When a forest burns frequently and thus has less plant litter build-up, below-ground soil temperatures rise only slightly and will not be lethal to roots that lie deep in the soil. Although other characteristics of a forest will influence the impact of fire upon it, factors such as climate and topography play an important role in determining fire severity and fire extent. Fires spread most widely during drought years, are most severe on upper slopes and are influenced by the type of vegetation that is growing.

Forests in British Columbia

In Canada, forests cover about 10% of the land area and yet harbor 70% of the country’s bird and terrestrial mammal species. Natural fire regimes are important in maintaining a diverse assemblage of vertebrate species in up to twelve different forest types in British Columbia. Different species have adapted to exploit the different stages of succession, regrowth and habitat change that occurs following an episode of burning, such as downed trees and debris. The characteristics of the initial fire, such as its size and intensity, cause the habitat to evolve differentially afterwards and influence how vertebrate species are able to use the burned areas. The change in forest fire intensity over time has been studied for the period since 1600 in an area of central British Columbia and is consistent with fire suppression since regulation was introduced.

Shrublands

Lightning-sparked wildfires are frequent occurrences on shrublands and grasslands in Nevada.

Shrub fires typically concentrate in the canopy and spread continuously if the shrubs are close enough together. Shrublands are typically dry and are prone to accumulations of highly volatile fuels, especially on hillsides. Fires will follow the path of least moisture and the greatest amount of dead fuel material. Surface and below-ground soil temperatures during a burn are generally higher than those of forest fires because the centers of combustion lie closer to the ground, although this can vary greatly. Common plants in shrubland or chaparral include manzanita, chamise and coyote brush.

California shrublands

California shrubland, commonly known as chaparral, is a widespread plant community of low growing species, typically on arid sloping areas of the California Coast Ranges or western foothills of the Sierra Nevada. There are a number of common shrubs and tree shrub forms in this association, including salal, toyon, coffeeberry and Western poison oak. Regeneration following a fire is usually a major factor in the association of these species.

South African Fynbos shrublands

Fynbos shrublands occur in a small belt across South Africa. The plant species in this ecosystem are highly diverse, yet the majority of these species are obligate seeders, that is, a fire will cause germination of the seeds and the plants will begin a new life-cycle because of it. These plants may have coevolved into obligate seeders as a response to fire and nutrient-poor soils. Because fire is common in this ecosystem and the soil has limited nutrients, it is most efficient for plants to produce many seeds and then die in the next fire. Investing a lot of energy in roots to survive the next fire when those roots will be able to extract little extra benefit from the nutrient-poor soil would be less efficient. It is possible that the rapid generation time that these obligate seeders display has led to more rapid evolution and speciation in this ecosystem, resulting in its highly diverse plant community.

Grasslands

Grasslands burn more readily than forest and shrub ecosystems, with the fire moving through the stems and leaves of herbaceous plants and only lightly heating the underlying soil, even in cases of high intensity. In most grassland ecosystems, fire is the primary mode of decomposition, making it crucial in the recycling of nutrients. In some grassland systems, fire only became the primary mode of decomposition after the disappearance of large migratory herds of browsing or grazing megafauna driven by predator pressure. In the absence of functional communities of large migratory herds of herbivorous megafauna and attendant predators, overuse of fire to maintain grassland ecosystems may lead to excessive oxidation, loss of carbon, and desertification in susceptible climates. Some grassland ecosystems respond poorly to fire.

North American grasslands

In North America fire-adapted invasive grasses such as Bromus tectorum contribute to increased fire frequency which exerts selective pressure against native species. This is a concern for grasslands in the Western United States.

In less arid grassland presettlement fires worked in concert with grazing to create a healthy grassland ecosystem as indicated by the accumulation of soil organic matter significantly altered by fire. The tallgrass prairie ecosystem in the Flint Hills of eastern Kansas and Oklahoma is responding positively to the current use of fire in combination with grazing.

South African savanna

In the savanna of South Africa, recently burned areas have new growth that provides palatable and nutritious forage compared to older, tougher grasses. This new forage attracts large herbivores from areas of unburned and grazed grassland that has been kept short by constant grazing. On these unburned "lawns", only those plant species adapted to heavy grazing are able to persist; but the distraction provided by the newly burned areas allows grazing-intolerant grasses to grow back into the lawns that have been temporarily abandoned, so allowing these species to persist within that ecosystem.

Longleaf pine savannas

Yellow pitcher plant is dependent upon recurring fire in coastal plain savannas and flatwoods.

Much of the southeastern United States was once open longleaf pine forest with a rich understory of grasses, sedges, carnivorous plants and orchids. These ecosystems had the highest fire frequency of any habitat, once per decade or less. Without fire, deciduous forest trees invade, and their shade eliminates both the pines and the understory. Some of the typical plants associated with fire include yellow pitcher plant and rose pogonia. The abundance and diversity of such plants is closely related to fire frequency. Rare animals such as gopher tortoises and indigo snakes also depend upon these open grasslands and flatwoods. Hence, the restoration of fire is a priority to maintain species composition and biological diversity.

Fire in wetlands

Many kinds of wetlands are also influenced by fire. This usually occurs during periods of drought. In landscapes with peat soils, such as bogs, the peat substrate itself may burn, leaving holes that refill with water as new ponds. Fires that are less intense will remove accumulated litter and allow other wetland plants to regenerate from buried seeds, or from rhizomes. Wetlands that are influenced by fire include coastal marshes, wet prairies, peat bogs, floodplains, prairie marshes and flatwoods. Since wetlands can store large amounts of carbon in peat, the fire frequency of vast northern peatlands is linked to processes controlling the carbon dioxide levels of the atmosphere, and to the phenomenon of global warming. Dissolved organic carbon (DOC) is abundant in wetlands and plays a critical role in their ecology. In the Florida Everglades, a significant portion of the DOC is "dissolved charcoal" indicating that fire can play a critical role in wetland ecosystems.

Fire suppression

Main article: Wildfire suppression

Fire serves many important functions within fire-adapted ecosystems. Fire plays an important role in nutrient cycling, diversity maintenance and habitat structure. The suppression of fire can lead to unforeseen changes in ecosystems that often adversely affect the plants, animals and humans that depend upon that habitat. Wildfires that deviate from a historical fire regime because of fire suppression are called "uncharacteristic fires".

Chaparral communities

A fire engine approaching smoldering brush at the Tumbleweed Fire near Los Angeles in July 2021

In 2003, southern California witnessed powerful chaparral wildfires. Hundreds of homes and hundreds of thousands of acres of land went up in flames. Extreme fire weather (low humidity, low fuel moisture and high winds) and the accumulation of dead plant material from eight years of drought, contributed to a catastrophic outcome. Although some have maintained that fire suppression contributed to an unnatural buildup of fuel loads, a detailed analysis of historical fire data has showed that this may not have been the case. Fire suppression activities had failed to exclude fire from the southern California chaparral. Research showing differences in fire size and frequency between southern California and Baja has been used to imply that the larger fires north of the border are the result of fire suppression, but this opinion has been challenged by numerous investigators and ecologists.

One consequence of the fires in 2003 has been the increased density of invasive and non-native plant species that have quickly colonized burned areas, especially those that had already been burned in the previous 15 years. Because shrubs in these communities are adapted to a particular historical fire regime, altered fire regimes may change the selective pressures on plants and favor invasive and non-native species that are better able to exploit the novel post-fire conditions.

Fish impacts

The Boise National Forest is a US national forest located north and east of the city of Boise, Idaho. Following several uncharacteristically large wildfires, an immediately negative impact on fish populations was observed, posing particular danger to small and isolated fish populations. In the long term, however, fire appears to rejuvenate fish habitats by causing hydraulic changes that increase flooding and lead to silt removal and the deposition of a favorable habitat substrate. This leads to larger post-fire populations of the fish that are able to recolonize these improved areas.

Fire as a management tool

Prescribed Burn in Oak Savannah in Iowa

Restoration ecology is the name given to an attempt to reverse or mitigate some of the changes that humans have caused to an ecosystem. Controlled burning is one tool that is currently receiving considerable attention as a means of restoration and management. Applying fire to an ecosystem may create habitats for species that have been negatively impacted by fire suppression, or fire may be used as a way of controlling invasive species without resorting to herbicides or pesticides. However, there is debate as to what land managers should aim to restore their ecosystems to, especially as to whether it be pre-human or pre-European conditions. Native American use of fire, along with natural fire, historically maintained the diversity of the savannas of North America. When, how, and where managers should use fire as a management tool is a subject of debate.

The Great Plains shortgrass prairie

Further information: Shortgrass prairie

A combination of heavy livestock grazing and fire-suppression has drastically altered the structure, composition, and diversity of the shortgrass prairie ecosystem on the Great Plains, allowing woody species to dominate many areas and promoting fire-intolerant invasive species. In semi-arid ecosystems where the decomposition of woody material is slow, fire is crucial for returning nutrients to the soil and allowing the grasslands to maintain their high productivity.

Although fire can occur during the growing or the dormant seasons, managed fire during the dormant season is most effective at increasing the grass and forb cover, biodiversity and plant nutrient uptake in shortgrass prairies. Managers must also take into account, however, how invasive and non-native species respond to fire if they want to restore the integrity of a native ecosystem. For example, fire can only control the invasive spotted knapweed (Centaurea maculosa) on the Michigan tallgrass prairie in the summer, because this is the time in the knapweed's life cycle that is most important to its reproductive growth.

Mixed conifer forests in the US Sierra Nevada

Mixed conifer forests in the United States Sierra Nevada used to have fire return intervals that ranged from 5 years up to 300 years, depending on the locale. Lower elevations tended to have more frequent fire return intervals, whilst higher and wetter sites saw longer intervals between fires. Native Americans tended to set fires during fall and winter, and land at higher elevations was generally occupied by Native Americans only during the summer.

Finnish boreal forests

The decline of habitat area and quality has caused many species populations to be red-listed by the International Union for Conservation of Nature. According to a study on forest management of Finnish boreal forests, improving the habitat quality of areas outside reserves can help in conservation efforts of endangered deadwood-dependent beetles. These beetles and various types of fungi both need dead trees in order to survive. Old growth forests can provide this particular habitat. However, most Fennoscandian boreal forested areas are used for timber and therefore are unprotected. The use of controlled burning and tree retention of a forested area with deadwood was studied and its effect on the endangered beetles. The study found that after the first year of management the number of species increased in abundance and richness compared to pre-fire treatment. The abundance of beetles continued to increase the following year in sites where tree retention was high and deadwood was abundant. The correlation between forest fire management and increased beetle populations shows a key to conserving these red-listed species.

Australian eucalypt forests

Much of the old growth eucalypt forest in Australia is designated for conservation. Management of these forests is important because species like Eucalyptus grandis rely on fire to survive. There are a few eucalypt species that do not have a lignotuber, a root swelling structure that contains buds where new shoots can then sprout. During a fire a lignotuber is helpful in the reestablishment of the plant. Because some eucalypts do not have this particular mechanism, forest fire management can be helpful by creating rich soil, killing competitors, and allowing seeds to be released.

Management policies

United States

Fire policy in the United States involves the federal government, individual state governments, tribal governments, interest groups, and the general public. The new federal outlook on fire policy parallels advances in ecology and is moving towards the view that many ecosystems depend on disturbance for their diversity and for the proper maintenance of their natural processes. Although human safety is still the number one priority in fire management, new US government objectives include a long-term view of ecosystems. The newest policy allows managers to gauge the relative values of private property and resources in particular situations and to set their priorities accordingly.

One of the primary goals in fire management is to improve public education in order to suppress the "Smokey Bear" fire-suppression mentality and introduce the public to the benefits of regular natural fires.

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Period 7 element

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Period_7_element

A period 7 element is one of the chemical elements in the seventh row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behavior of the elements as their atomic number increases: a new row is begun when chemical behavior begins to repeat, meaning that elements with similar behavior fall into the same vertical columns. The seventh period contains 32 elements, tied for the most with period 6, beginning with francium and ending with oganesson, the heaviest element currently discovered. As a rule, period 7 elements fill their 7s shells first, then their 5f, 6d, and 7p shells in that order, but there are exceptions, such as uranium.

Properties

All elements of period 7 are radioactive. This period contains the actinides, which includes plutonium, the naturally occurring element with the heaviest nucleus; subsequent elements must be created artificially. While the first five of these synthetic elements (americium through einsteinium) are now available in macroscopic quantities, most are extremely rare, having only been prepared in microgram amounts or less. The later transactinide elements have only been identified in laboratories in batches of a few atoms at a time.

Becaus the rarity of many of these elements means that experimental results are not very extensive, their periodic and group trends are less well defined than other periods. Whilst francium and radium do show typical properties of their respective groups, actinides display a much greater variety of behavior and oxidation states than the lanthanides. These peculiarities are due to a variety of factors, including a large degree of spin–orbit coupling and relativistic effects, ultimately caused by the very high positive electrical charge from their massive atomic nuclei. Periodicity mostly holds throughout the 6d series, and is predicted also for moscovium and livermorium, but the other four 7p elements, nihonium, flerovium, tennessine, and oganesson, are predicted to have very different properties from those expected for their groups.

Elements

Chemical element Block Electron configuration Occurrence
 




87 Fr Francium s-block [Rn] 7s1 From decay
88 Ra Radium s-block [Rn] 7s2 From decay
89 Ac Actinium f-block [Rn] 6d1 7s2 (*) From decay
90 Th Thorium f-block [Rn] 6d2 7s2 (*) Primordial
91 Pa Protactinium f-block [Rn] 5f2 6d1 7s2 (*) From decay
92 U Uranium f-block [Rn] 5f3 6d1 7s2 (*) Primordial
93 Np Neptunium f-block [Rn] 5f4 6d1 7s2 (*) From decay
94 Pu Plutonium f-block [Rn] 5f6 7s2 From decay
95 Am Americium f-block [Rn] 5f7 7s2 Synthetic
96 Cm Curium f-block [Rn] 5f7 6d1 7s2 (*) Synthetic
97 Bk Berkelium f-block [Rn] 5f9 7s2 Synthetic
98 Cf Californium f-block [Rn] 5f10 7s2 Synthetic
99 Es Einsteinium f-block [Rn] 5f11 7s2 Synthetic
100 Fm Fermium f-block [Rn] 5f12 7s2 Synthetic
101 Md Mendelevium f-block [Rn] 5f13 7s2 Synthetic
102 No Nobelium f-block [Rn] 5f14 7s2 Synthetic
103 Lr Lawrencium d-block [Rn] 5f14 7s2 7p1 (*) Synthetic
104 Rf Rutherfordium d-block [Rn] 5f14 6d2 7s2 Synthetic
105 Db Dubnium d-block [Rn] 5f14 6d3 7s2 Synthetic
106 Sg Seaborgium d-block [Rn] 5f14 6d4 7s2 Synthetic
107 Bh Bohrium d-block [Rn] 5f14 6d5 7s2 Synthetic
108 Hs Hassium d-block [Rn] 5f14 6d6 7s2 Synthetic
109 Mt Meitnerium d-block [Rn] 5f14 6d7 7s2 (?) Synthetic
110 Ds Darmstadtium d-block [Rn] 5f14 6d8 7s2 (?) Synthetic
111 Rg Roentgenium d-block [Rn] 5f14 6d9 7s2 (?) Synthetic
112 Cn Copernicium d-block [Rn] 5f14 6d10 7s2 (?) Synthetic
113 Nh Nihonium p-block [Rn] 5f14 6d10 7s2 7p1 (?) Synthetic
114 Fl Flerovium p-block [Rn] 5f14 6d10 7s2 7p2 (?) Synthetic
115 Mc Moscovium p-block [Rn] 5f14 6d10 7s2 7p3 (?) Synthetic
116 Lv Livermorium p-block [Rn] 5f14 6d10 7s2 7p4 (?) Synthetic
117 Ts Tennessine p-block [Rn] 5f14 6d10 7s2 7p5 (?) Synthetic
118 Og Oganesson p-block [Rn] 5f14 6d10 7s2 7p6 (?) Synthetic

(?) Prediction

(*) Exception to the Madelung rule.

In many periodic tables, the f-block is erroneously shifted one element to the right, so that lanthanum and actinium become d-block elements, and Ce–Lu and Th–Lr form the f-block tearing the d-block into two very uneven portions. This is a holdover from early erroneous measurements of electron configurations. Lev Landau and Evgeny Lifshitz pointed out in 1948 that lutetium is not an f-block element, and since then physical, chemical, and electronic evidence has overwhelmingly supported that the f-block contains the elements La–Yb and Ac–No, as shown here and as supported by International Union of Pure and Applied Chemistry reports dating from 1988 and 2021.

Francium and radium

Main articles: Francium and Radium

Francium and radium make up the s-block elements of the 7th period.

Francium (Fr, and atomic number 87). It was formerly known as eka-caesium and actinium K. It is one of the two least electronegative elements, the other being caesium. Francium is a highly radioactive metal that decays into astatine, radium, and radon. As an alkali metal, it has one valence electron. Francium was discovered by Marguerite Perey in France (from which the element takes its name) in 1939. It was the last element discovered in nature, rather than by synthesis. Outside the laboratory, francium is extremely rare, with trace amounts found in uranium and thorium ores, where the isotope francium-223 continually forms and decays. As little as 20–30 g (one ounce) exists at any given time throughout Earth's crust; the other isotopes are entirely synthetic. The largest amount produced in the laboratory was a cluster of more than 300,000 atoms.

Radium (Ra, atomic number 88), is an almost pure-white alkaline earth metal, but it readily oxidizes, reacting with nitrogen (rather than oxygen) on exposure to air, becoming black in color. All isotopes of radium are highly radioactive; the most stable isotope is radium-226, which has a half-life of 1601 years and decays into radon gas. Because of such instability, radium is luminescent, glowing a faint blue. Radium, in the form of radium chloride, was discovered by Marie and Pierre Curie in 1898. They extracted the radium compound from uraninite and published the discovery at the French Academy of Sciences five days later. Radium was isolated in its metallic state by Marie Curie and André-Louis Debierne through the electrolysis of radium chloride in 1910. Since its discovery, it has given names such as radium A and radium C2 to several isotopes of other elements that are decay products of radium-226. In nature, radium is found in uranium ores in trace amounts as small as a seventh of a gram per ton of uraninite. Radium is not necessary for living organisms, and adverse health effects are likely when it is incorporated into biochemical processes because of its radioactivity and chemical reactivity.

Actinides

Main article: Actinide
 
The atomic bomb dropped on Nagasaki had a plutonium charge.

The actinide or actinoid (IUPAC nomenclature) series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.

The actinide series is named after its first element actinium. All but one of the actinides are f-block elements, corresponding to the filling of the 5f electron shell; lawrencium, a d-block element, is also generally considered an actinide. In comparison with the lanthanides, also mostly f-block elements, the actinides show much more variable valence.

Of the actinides, thorium and uranium occur naturally in substantial, primordial, quantities. Radioactive decay of uranium produces transient amounts of actinium, protactinium and plutonium, and atoms of neptunium are occasionally produced from transmutation reactions in uranium ores. The other actinides are purely synthetic elements, though the first six actinides after plutonium would have been produced at Oklo (and long since decayed away), and curium almost certainly previously existed in nature as an extinct radionuclide. Nuclear tests have released at least six actinides heavier than plutonium into the environment; analysis of debris from a 1952 hydrogen bomb explosion showed the presence of americium, curium, berkelium, californium, einsteinium and fermium.

All actinides are radioactive and release energy upon radioactive decay; naturally occurring uranium and thorium, and synthetically produced plutonium are the most abundant actinides on Earth. These are used in nuclear reactors and nuclear weapons. Uranium and thorium also have diverse current or historical uses, and americium is used in the ionization chambers of most modern smoke detectors.

In presentations of the periodic table, the lanthanides and the actinides are customarily shown as two additional rows below the main body of the table, with placeholders or else a selected single element of each series (either lanthanum or lutetium, and either actinium or lawrencium, respectively) shown in a single cell of the main table, between barium and hafnium, and radium and rutherfordium, respectively. This convention is entirely a matter of aesthetics and formatting practicality; a rarely used wide-formatted periodic table (32 columns) shows the lanthanide and actinide series in their proper columns, as parts of the table's sixth and seventh rows (periods).

Transactinides

Main article: Transactinide elements

Transactinide elements (also, transactinides, or super-heavy elements) are the chemical elements with atomic numbers greater than those of the actinides, the heaviest of which is lawrencium (103). All transactinides of period 7 have been discovered, up to oganesson (element 118).

Transactinide elements are also transuranic elements, that is, have an atomic number greater than that of uranium (92), an actinide. The further distinction of having an atomic number greater than the actinides is significant in several ways:

  • The transactinide elements all have electrons in the 6d subshell in their ground state (and thus are placed in the d-block).
  • Even the longest-lasting isotopes of many transactinide elements have extremely short half-lives, measured in seconds or smaller units.
  • The element naming controversy involved the first five or six transactinide elements. These elements thus used three-letter systematic names for many years after their discovery had been confirmed. (Usually, the three-letter symbols are replaced with two-letter symbols relatively shortly after a discovery has been confirmed.)

Transactinides are radioactive and have only been obtained synthetically in laboratories. None of these elements has ever been collected in a macroscopic sample. Transactinide elements are all named after nuclear physicists and chemists or important locations involved in the synthesis of the elements.

Chemistry Nobel Prize winner Glenn T. Seaborg, who first proposed the actinide concept which led to the acceptance of the actinide series, also proposed the existence of a transactinide series ranging from element 104 to 121 and a superactinide series approximately spanning elements 122 to 153. The transactinide seaborgium is named in his honor.

IUPAC defines an element to exist if its lifetime is longer than 10−14 seconds, the time needed for the nucleus to form an electronic cloud.

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