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Saturday, July 8, 2023

Rewilding (conservation biology)

From Wikipedia, the free encyclopedia

Rewilding is a form of ecological restoration aimed at increasing biodiversity and restoring natural processes. It differs from ecological restoration in that, while human intervention may be involved, rewilding aspires to reduce human influence on ecosystems. It is also distinct in that, while it places emphasis on recovering geographically specific sets of ecological interactions and functions that would have maintained ecosystems prior to human influence, rewilding is open to novel or emerging ecosystems which encompass new species and new interactions.

A key feature of rewilding is its focus on replacing human interventions with natural processes. The aim is to create resilient, self-regulating and self-sustaining ecosystems.

While rewilding initiatives can be controversial, the United Nations has listed rewilding as one of several methods needed to achieve massive scale restoration of natural ecosystems, which they say must be accomplished by 2030 as part of the 30x30 campaign.

Origin

The term rewilding was coined by members of the grassroots network Earth First!, first appearing in print in 1990. It was refined and grounded in a scientific context in a paper published in 1998 by conservation biologists Michael Soulé and Reed Noss. Soulé and Noss envisaged rewilding as a conservation method based on the concept of 'cores, corridors, and carnivores'. Cores, corridors and carnivores (or the '3Cs') was based on the theory that large predators play regulatory roles in ecosystems. 3Cs rewilding therefore relied on protecting 'core' areas of wild land, linked together by 'corridors' allowing passage for 'carnivores' to move around the landscape and perform their functional role. The concept was developed further in 1999 and Earth First co-founder, Dave Foreman, subsequently wrote a full-length book on rewilding as a conservation strategy.

History

Rewilding was developed as a method to preserve functional ecosystems and reduce biodiversity loss, incorporating research in island biogeography and the ecological role of large carnivores. In 1967, The Theory of Island Biogeography by Robert H. MacArthur and Edward O. Wilson established the importance of considering the size and fragmentation of wildlife conservation areas, stating that protected areas remained vulnerable to extinctions if small and isolated. In 1987, William D. Newmark's study of extinctions in national parks in North America added weight to the theory. The publications intensified debates on conservation approaches. With the creation of the Society for Conservation Biology in 1985, conservationists began to focus on reducing habitat loss and fragmentation.

Practice and interest in rewilding grew rapidly in the first two decades of the 21st century. An early and groundbreaking initiative was led in the United Kingdom by Neil A. Hill, an ecologist and early proponent of non-interventional land management. His published work on the Landscape Enhancement Initiative (LEI) went on to inform a number of European projects under the Interreg IIIb tier. He undertook later work with the Iberian lynx that led to large-scale rewilding initiatives in the Dehesa/Montado ecosystems of the Iberian Peninsula. An early conceptual framework was further provided by Frans Vera's wood-pasture hypothesis, which hypothesizes a primary role for herbivores in shaping prehistoric European landscapes.

Supporters of rewilding initiatives range from individuals, small land owners, local non-governmental organizations and authorities, to national governments and international non-governmental organizations such as the International Union for Conservation of Nature. While small-scale efforts are generally well regarded the increased popularity of rewilding has generated controversy, especially regarding large-scale projects. These have sometimes attracted criticism from academics and practicing conservationists, as well as government officials and business people. In a June 2021 report for the launch of the UN Decade on Ecosystem Restoration, the United Nations listed rewilding as one of several restoration methods which they state should be used for ecosystem restoration of over 1 billion hectares (a total area bigger than China).

Guiding principles

Since its origin, the term rewilding has been used as a signifier of particular forms of ecological restoration projects (or advocacy thereof) that have ranged widely in scope and geographic application. In 2021 the journal Conservation Biology published a paper by 33 coauthors from around the world. Titled, 'Guiding Principles for Rewilding'. Researchers and project leaders from North America (Canada, Mexico and the United States) joined with counterparts in Europe (Denmark, France, Hungary, The Netherlands, Switzerland, and the UK), China, and South America (Chile and Colombia) to produce a unifying description, along with a set of ten guiding principles.

The group wrote, 'Commonalities in the concept of rewilding lie in its aims, whereas differences lie in the methods used, which include land protection, connectivity conservation, removing human infrastructure, and species reintroduction or taxon replacement.' Referring to the span of project types they stated, 'Rewilding now incorporates a variety of concepts, including Pleistocene megafauna replacement, taxon replacement, species reintroductions, retrobreeding, release of captive-bred animals, land abandonment, and spontaneous rewilding.' 

Empowered by a directive from the International Union for the Conservation of Nature to produce a document on rewilding that reflected a global scale inventory of underlying goals as well as practices, the group sought a 'unifying definition', producing the following:

'Rewilding is the process of rebuilding, following major human disturbance, a natural ecosystem by restoring natural processes and the complete or near complete food web at all trophic levels as a self-sustaining and resilient ecosystem with biota that would have been present had the disturbance not occurred. This will involve a paradigm shift in the relationship between humans and nature. The ultimate goal of rewilding is the restoration of functioning native ecosystems containing the full range of species at all trophic levels while reducing human control and pressures. Rewilded ecosystems should—where possible—be self-sustaining. That is, they require no or minimal management (i.e., natura naturans [nature doing what nature does]), and it is recognized that ecosystems are dynamic.'

Ten principles were developed by the group:

1. Rewilding utilizes wildlife to restore trophic interactions.
2. Rewilding employs landscape-scale planning that considers core areas, connectivity, and co-existence.
3. Rewilding focuses on the recovery of ecological processes, interactions, and conditions based on reference ecosystems.
4. Rewilding recognizes that ecosystems are dynamic and constantly changing.
5. Rewilding should anticipate the effects of climate change and where possible act as a tool to mitigate impacts.
6. Rewilding requires local engagement and support.
7. Rewilding is informed by science, traditional ecological knowledge, and other local knowledge.
8. Rewilding is adaptive and dependent on monitoring and feedback.
9. Rewilding recognizes the intrinsic value of all species and ecosystems.
10. Rewilding requires a paradigm shift in the coexistence of humans and nature.

Rewilding and climate change

Rewilding can mitigate global climate change. An example of this would be rewilding pasture land, thereby reducing the number of cows and sheep and increasing the number of trees.

Also, restoring megafauna may have a positive impact on biodiversity, and may also increase public enthusiasm for biodiversity. One rewilding effort specifically focused on mitigating global climate change is restoring Pleistocene megafauna. By restoring large herbivores, greenhouse gas levels may be lowered. Grazers may also reduce fire frequency by eating flammable brush, which would, in turn, lower greenhouse gas emissions, lower aerosol levels in the atmosphere, and alter the planet's albedo. Browsing and grazing also accelerates nutrient cycling, which may increase local plant productivity, and maintain ecosystem productivity specifically in grassy biomes. Megafauna also aid with carbon storage. In fact, the loss of megafauna that eat fruits may be responsible for up to 10% of lost carbon storage in forests.

Types of rewilding

Passive rewilding

Passive rewilding (also referred to as ecological rewilding) aims to restore natural ecosystem processes via withdrawal of or minimal direct human management of the landscape.

Active rewilding

Active rewilding is an umbrella term used to describe a range of rewilding approaches all of which involve human intervention. These might include species reintroductions or translocations and/or habitat engineering and the removal of man-made structures.

Trophic rewilding

Trophic rewilding is an ecological restoration strategy focussed on restoring trophic interactions (specifically top-down and associated trophic cascades where a top consumer/predator controls the primary consumer population) through species introductions, in order to promote self-regulating biodviserse ecosystems.

Pleistocene rewilding

Pleistocene rewilding is the advocacy of the reintroduction of extant Pleistocene megafauna, or the close ecological equivalents of extinct megafauna, to restore ecosystem function.

In 1988, researcher Sergey A. Zimov established Pleistocene Park in northeastern Siberia to test the possibility of restoring a full range of grazers and predators, with the aim of recreating an ecosystem similar to the one in which mammoths lived. Yakutian horses, reindeer, European bison, plains bison, Domestic yak, moose, and Bactrian camels were reintroduced, and reintroduction is also planned for saigas, wood bison, and Siberian tigers.This project remains controversial — a letter published in Conservation Biology accused the Pleistocene camp of promoting "Frankenstein ecosystems", stating that 'the biggest problem is not the possibility of failing to restore lost interactions, but rather the risk of getting new, unwanted interactions instead.'

Saiga antelope are one of the animals which are proposed to be reintroduced in Pleistocene Park, a massive proposal of Pleistocene rewilding in Siberia. Once possessing a natural range from Alaska to France, Saigas are now extinct in Europe and North America, as well as a critically endangered species.

Pleistocene rewilding of parts of Brazil and other parts of the Americas was proposed by Brazilian ecologist Mauro Galetti in 2004. He suggested the introduction of elephants (and other analogues for extinct megafauna) to private lands in the Brazilian Cerrado and other parts of the Americas. Paul S. Martin made a similar argument in favour of taxon reaplacement, suggesting that the megafauna of North America which becaume extinct after the arrival of humans (e.g., mastodons, mammoths, ground sloths, and smilodons) could be replaced with species which have similar ecological roles.

A controversial 2005 editorial in Nature, signed by a number of conservation biologists, took up the argument, urging that elephants, lions, and cheetahs could be reintroduced in protected areas in the Great Plains. The Bolson tortoise, discovered in 1959 in Durango, Mexico, was the first species proposed for this restoration effort, and in 2006 the species was reintroduced to two ranches in New Mexico owned by media mogul Ted Turner. Other proposed species include various camelids such as the Wild Bactrian camel, and various equids such as the Prezwalski's horse.

Rewilding plants

In 1982 Daniel Janzen and Paul S. Martin originated the concept of evolutionary anachronism in a Science article titled, "Neotropical Anachronisms: The Fruits the Gomphotheres Ate". Eighteen years later Connie Barlow, in her book The Ghosts of Evolution: Nonsensical Fruit, Missing Partners, and Other Ecological Anachronisms (2000), explored the specifics of temperate North American plants whose fruits displayed the characteristics of megafauna dispersal syndrome. Barlow noted that a consequence for such native fruits following the loss of their megafaunal seed dispersal partners was range constriction during the Holocene, made increasingly severe since the mid-20th century by rapid human-driven climate change. Additional details of range contraction were incorporated in Barlow's 2001 article, "Anachronistic Fruits and the Ghosts Who Haunt Them".

Torreya taxifolia is an ancient conifer whose seeds entail some anachronistic features.

A plant species beset with anachronistic features whose range had already become so restricted that it warranted endangered species classification was the glacial relict Torreya taxifolia. For this species, Barlow and Martin advocated assisted migration poleward in an article published in Wild Earth in 2004, titled "Bring Torreya taxifolia North Now". In 2005 Barlow and Lee Barnes (co-founders of Torreya Guardians) began obtaining seeds from mature horticultural plantings in states northward of Florida and Georgia for distribution to volunteer planters whose lands contained forested habitats potentially suitable for this native of Florida. Documentation of seed distribution and ongoing results, state by state, are publicly available on the Torreya Guardians website.) Articles published in Scientific American in 2009 and in Landscape Architecture Magazine in 2014 referred to the actions of Torreya Guardians as an example of "rewilding". Connie Barlow expressly referred to such efforts as "rewilding" in the 2020 book by Zach St. George, The Journeys of Trees. Her earliest use of the term "rewilding" was in her 1999 essay, "Rewilding for Evolution", in Wild Earth.

Because part of Barlow's activities occurred on public and private lands for which she did not expressly obtain planting permission, this form of rewilding action could be referred to as guerrilla rewilding, which is an adaptation of the established term guerrilla gardening. One example of guerrilla rewilding was reported in 2022. Himantoglossum robertianum is a tall orchid native to the Mediterranean Basin, but it is documented growing wild in Great Britain. As reported in The Guardian, "It is not believed these plants arrived naturally, but rather by someone scattering seeds about 15 years ago."

Wild-planting of pawpaw, Asimina triloba, is occurring in Pittsburgh as a way to recover a native butterfly whose caterpillars eat only the leaves of the pawpaw tree.

Within range, or slightly poleward of range, wild plantings are underway for a common subcanopy tree of the eastern United States. Pawpaw, Asimina triloba, is the northernmost species of an otherwise tropical fruit family, Annonaceae. Citizens in three states independently stepped forward to begin this rewilding effort in their home regions within Massachusetts, Pennsylvania, and Michigan. Because the fruit of pawpaw is regarded as an evolutionary anachronism, extinction of its coevolved seed dispersers (notably, mastodons) severely reduced its ability to obtain long-distance seed dispersal from any animals other than humans. Archeological evidence points to indigenous peoples of North America as fulfilling this function. That pawpaw planting sites chosen by citizens center on damaged riverine forests of old industrial sites in Pittsburgh, Pennsylvania, and Ypsilanti, Michigan, may account for the lack of controversy regarding their actions.

While the intrinsic value of plants is an ethical foundation for many forms of plant conservation, the Pittsburgh wild-planting of pawpaw also entails an animal conservation ethic. Gabrielle Marsden is recruiting volunteers for the project she calls "Pittsburgh Pawpaw Pathways for Zebra Swallowtail Trails". Because the larval stage of the zebra swallowtail butterfly feeds only on pawpaw leaves, and because the butterfly is not a long-distance traveller, planting pawpaws within recovering forests on slopes of the Allegheny River is supported primarily as a way of expanding the population of the butterfly.

Elements

Rewilding aims to restore three key ecological processes: trophic complexity, dispersal, and stochastic disturbances.

Keystone species

Keystone species are animals which interact strongly with the environment.

Ecosystem engineers

One example of ecosystem engineers are ground disrupting powerful animals that push over trees, trample shrubs and dig holes. These ensure that trees in grasslands do not become dominant. Some of these species currently being used in rewilding efforts include beaver, elephants, bison, elk, cattle (as analogues for the extinct aurochs). These species also disperse seeds in their dung. Pig species, originally wild boar, dig creating soil where new plants can grow. Beavers are another important example of ecosystem engineers. The dams they build create micro ecosystems that can be used as spawning beds for salmon and collect invertebrates for the salmon fry to feed on. The dams also create wetlands for plant, insect, and bird life. Specific trees, such as alder, birch, cottonwood, and willow, are important to beaver's diets and should be encouraged to grow in areas near beavers.

Predators

Predators may be required to ensure that browsing and grazing animals are kept from over-breeding/over-feeding, destroying vegetation complexity, as may be concluded from mass-starvations which happened in Oostvaardersplassen. Some examples of these predators are Eurasian lynx and wolves. However, although it is generally undebated that predators occupy an important role in ecosystems, there is no general agreement about whether wild predators keep herbivore populations in check, or whether their influence is of more subtle nature (see Ecology of fear). By analogy, wildebeest populations in the Serengeti are primarily controlled by food constraints despite the presence of many predators. The consequence is natural mass-starvation.

Criticism

Compatibility with economic activity

A view expressed by some national governments and officials within multilateral agencies such as the United Nations, is that excessive rewilding, such as large rigorously enforced protected areas where no extraction activities are allowed, can be too restrictive on people's ability to earn sustainable livelihoods. The alternative view is that increasing ecotourism can provide employment.

Farming

Some farmers have been critical of rewilding for 'abandoning productive farmland when the world's population is growing'. Farmers have also attacked plans to reintroduce the lynx in the United Kingdom because of fears that reintroduction will lead to an increase in sheep predation.

Conflicts with animal rights and welfare

Rewilding has been criticized by animal rights scholars, such as Dale Jamieson, who argues that 'most cases of rewilding or reintroducing are likely to involve conflicts between the satisfaction of human preferences and the welfare of nonhuman animals.' Erica von Essen and Michael Allen, using Donaldson and Kymlicka's political animal categories framework, assert that wildness standards imposed on animals are arbitrary and inconsistent with the premise that wild animals should be granted sovereignty over the territories that they inhabit and the right to make decisions about their own lives. To resolve this, Essen and Allen contend that rewilding needs to shift towards full alignment with mainstream conservation and welcome full sovereignty, or instead take full responsibility for the care of animals who have been reintroduced. Ole Martin Moen argues that rewilding projects should be brought to an end because they unnecessarily increase wild animal suffering and are expensive, and the funds could be better spent elsewhere.

Erasure of environmental history

The environmental historian Dolly Jørgensen argues that rewilding, as it currently exists, 'seeks to erase human history and involvement with the land and flora and fauna. Such an attempted split between nature and culture may prove unproductive and even harmful.' She calls for rewilding to be more inclusive to combat this. Jonathan Prior and Kim J. Ward challenge Jørgensen's criticism and provide existing examples of rewilding programs which 'have been developed and governed within the understanding that human and non-human world are inextricably entangled'.

Harm to conservation

Some conservationists have expressed concern that rewilding 'could replace the traditional protection of rare species on small nature reserves', which could potentially lead to an increase in habitat fragmentation and species loss. David Nogués-Bravo and Carsten Rahbek assert that the benefits of rewilding lack evidence and that such programs may inadvertently lead to 'de-wilding', through the extinction of local and global species. They also contend that rewilding programs may draw funding away from 'more scientifically supported conservation projects'.

Rewilding in different locations

Both grassroots groups and major international conservation organizations have incorporated rewilding into projects to protect and restore large-scale core wilderness areas, corridors (or connectivity) between them, and apex predators, carnivores, or keystone species (species which interact strongly with the environment, such as elephant and beaver). Projects include the Yellowstone to Yukon Conservation Initiative in North America (also known as Y2Y) and the European Green Belt, built along the former Iron Curtain, transboundary projects, including those in southern Africa funded by the Peace Parks Foundation, community-conservation projects, such as the wildlife conservancies of Namibia and Kenya, and projects organized around ecological restoration, including Gondwana Link, regrowing native bush in a hotspot of endemism in southwest Australia, and the Area de Conservacion Guanacaste, restoring dry tropical forest and rainforest in Costa Rica.

North America

A wildlife crossing structure on the Trans-Canada Highway in Banff National Park, Canada. Wildlife-friendly overpasses and underpasses have helped restore connectivity in the landscape for wolves, bears, elk, and other species.

In North America, a major project aims to restore the prairie grasslands of the Great Plains. The American Prairie is reintroducing bison on private land in the Missouri Breaks region of north-central Montana, with the goal of creating a prairie preserve larger than Yellowstone National Park.

Dam removal has led to the restoration of many river systems in the Pacific Northwest. This has been done in an effort to restore salmon populations specifically but with other species in mind. As stated in an article on environmental law, 'These dam removals provide perhaps the best example of large-scale environmental remediation in the twenty-first century. This restoration, however, has occurred on a case-by-case basis, without a comprehensive plan. The result has been to put into motion ongoing rehabilitation efforts in four distinct river basins: the Elwha and White Salmon in Washington and the Sandy and Rogue in Oregon.'

South America

Argentina

In 1997, Douglas and Kristine Tompkins created 'The Conservation Land Trust Argentina', a team of conservationists and scientists with the goal of transforming the Iberá Wetlands. Thanks to them, and to a donation of 195,094 ha made by Kristine, in 2018 an area was converted into a National Park, and the jaguar was reintroduced into it, a species that had been extinct in the region for seven decades. They also introduced anteaters and giant otters. Currently, the Rewilding Argentina Foundation is an organization that is dedicated, in addition to Iberá National Park, to the restoration of El Impenetrable National Park, in Chaco, Patagonia Park, in Santa Cruz, and the Patagonian coastal area in the province of Chubut.

Brazil

In Tijuca National Park (Rio de Janeiro state, Brazil), two important seed dispersers, the red-humped agouti and the brown howler monkey, were reintroduced between years 2010 and 2017. The goal of the reintroductions was to restore seed dispersal interactions between seed dispersing animals and fleshy-fruited trees. The agoutis and howler monkeys interacted with several plant and dung beetle species. Before reintroductions, the national park did not have large or intermediate -sized seed dispersers, meaning that the increased dispersal of tree seeds following the reintroductions can have a large effect on forest regeneration in the national park. The Tijuca National Park is part of heavily fragmented Atlantic Forest, where there is potential to restore many more seed dispersal interactions if seed dispersing mammals and birds are reintroduced to forest patches where the tree species diversity remains high.

Australia

Rewilding is newer in Australia than in Europe and North America, but there are many projects under way across the country as of 2023. Colonisation has had a huge impact on the native flora and fauna, and the introduction of red foxes and cats has devastated many of the smaller ground-dwelling mammals. The island state of Tasmania has become an important location for rewilding efforts because, as an island, it is easier to remove feral cat populations and manage other invasive species. The reintroduction and management of the Tasmanian devil in this state, and dingoes on the mainland, is being trialled in an effort to contain introduced predators, as well as over-populations of kangaroos.

WWF-Australia has a program called 'Rewilding Australia' which aims to 'test strategies to increase resilience and adaptability to these current and future threats'. Its projects include the platypus in the Royal National Park, south of Sydney, eastern quolls in the Booderee National Park in Jervis Bay and at Silver Plains in Tasmania, and brush-tailed bettongs in the Marna Banggara project on the Yorke Peninsula in South Australia. Other projects around the country include:

Europe

In 2011, the 'Rewilding Europe' initiative was established with the aim of rewilding one million hectares of land in ten areas including the western Iberian Peninsula, Velebit, the Carpathians and the Danube delta by 2020, mostly abandoned farmland among other identified candidate sites. The present project considers only species that are still present in Europe, such as the Iberian lynx, Eurasian lynx, grey wolf, European jackal, brown bear, chamois, Iberian ibex, European bison, red deer, griffon vulture, cinereous vulture, Egyptian vulture, great white pelican and horned viper, along with a few primitive breeds of domestic horse/Przewalski's horse and cattle as proxies for the extinct tarpan and aurochs. Since 2012, Rewilding Europe has been heavily involved in the Tauros Programme, which seeks to create a breed of cattle that resembles the aurochs, the wild ancestors of domestic cattle, by selectively breeding existing breeds of cattle. Many projects also employ domestic water buffalo as a grazing analogue for the extinct European water buffalo.

Areas of rewilding include the Côa River, a Natura 2000 area. European Wildlife, established in 2008, advocates the establishment of a European Centre of Biodiversity at the German–Austrian–Czech borders.

Austria

De Biosphärenpark Wienerwald was created in Austria in 2003. Within this area 37 kernzonen (core zones) covering 5,400 ha in total were designated areas free from human interference.

Britain

Rewilding Britain, a charity founded in 2015, aims to promote rewilding in Britain and is a leading advocate of rewilding. Rewilding Britain has laid down 'five principles of rewilding' which it expects to be followed by affiliated rewilding projects. These are: 1. Support people and nature together, 2. Let nature lead, 3. Create resilient local economies, 4. Work at nature’s scale, 5. Secure benefits for the long-term. In practice rewilding as effected by private landowners and managers takes many different forms, with emphases placed on varying aspects.

Celtic Reptile & Amphibian is a limited company established in 2020, with the aim of reintroducing extinct species of reptile and amphibian (such as the European pond turtle, moor frog, agile frog, common tree frog and pool frog) to Britain, as part of rewilding schemes. Success has already been achieved with the captive breeding of the moor frog.

In 2020, nature writer Melissa Harrison reported a significant increase in attitudes supportive of rewilding among the British public, with plans recently approved for the release of European bison, Eurasian elk, and great bustard in England, along with calls to rewild as much as 20% of the land in East Anglia, and even return apex predators such as the Eurasian lynx, brown bear, and grey wolf. More recently, academic work on rewilding in England has highlighted that support for rewilding is by no means universal. As in other countries, rewilding in England remains controversial to the extent that some of its more ambitious aims are being 'domesticated' both in a proactive attempt to make it less controversial and in reactive response to previous controversy. Projects may also refer to their activity using terminology other than 'rewilding', possibly for political and diplomatic reasons, taking account of local sentiment or possible opposition. Examples include 'Sanctuary Nature Recovery Programme' (at Broughton) and 'nature restoration project', the preferred term used by the Cambrian Wildwood project, an area aspiring to encompass 7,000 acres in Wales.

Notable rewilding sites ' include:

  • Knepp Castle. The 3,500 acre (1,400 hectare) Knepp Castle estate in West Sussex was the first major pioneer of rewilding in England, and started that land-management policy there in 2001 on land formerly used as dairy farmland. (See Knepp Wildland). Rare species including common nightingale, turtle doves, peregrine falcons and purple emperor butterflies are now breeding at Knepp and populations of more common species are increasing. In 2019 a pair of white storks built a nest in an oak tree at Knepp, part of a group imported from Poland, the result of a programme to re-introduce that species to England run by the Roy Dennis Wildlife Foundation, which has overseen reintroductions of other extinct bird species to the UK.
  • Broughton Hall Estate, Yorkshire. In 2021 about 1,100 acres (a third of the estate) have been devoted to rewilding, with advice from Prof. Alastair Driver of Rewilding Britain.
  • Mapperton Estate,n Dorset, largely inspired by the work at Knepp. At Mapperton one of the five farms comprising the estate entered the process of re-wilding in 2021, accounting for 200 acres.

The Netherlands

Konik ponies in the Oostvaardersplassen reserve

In the 1980s, the Dutch government began introducing analogue species in the Oostvaardersplassen nature reserve, an area covering over 56 square kilometres (22 sq mi), in order to recreate a grassland ecology. This happened in line with Vera's proposal that grazing animals played a significant role in the shaping of European landscapes before the Neolithic - the wood-pasture hypothesis. Though not explicitly referred to as rewilding many of the goals and intentions of the project were in line with those of rewilding. The reserve is considered somewhat controversial due to the lack of predators and other native megafauna such as wolves, bears, lynx, elk, boar, and wisent. Konik ponies were reintroduced together with Heck cattle and red deer to keep the landscape open by natural grazing. This provided habitat for geese who are key species in the wetlands of the area. The grazing of geese made it possible for reedbeds to remain and therefore conserved many protected birds species. This is a prime example how water and land ecosystems are connected and how reintroducing keystone species can conserve other protected species.

Compact star

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

In astronomy, the term compact star (or compact object) refers collectively to white dwarfs, neutron stars, and black holes. It would grow to include exotic stars if such hypothetical, dense bodies are confirmed to exist. All compact objects have a high mass relative to their radius, giving them a very high density, compared to ordinary atomic matter.

Compact stars are often the endpoints of stellar evolution and, in this respect, are also called stellar remnants. The state and type of a stellar remnant depends primarily on the mass of the star that it formed from. The ambiguous term compact star is often used when the exact nature of the star is not known, but evidence suggests that it has a very small radius compared to ordinary stars. A compact star that is not a black hole may be called a degenerate star.

In June 2020, astronomers reported narrowing down the source of Fast Radio Bursts (FRBs), which may now plausibly include "compact-object mergers and magnetars arising from normal core collapse supernovae".

Formation

The usual endpoint of stellar evolution is the formation of a compact star.

All active stars will eventually come to a point in their evolution when the outward radiation pressure from the nuclear fusions in its interior can no longer resist the ever-present gravitational forces. When this happens, the star collapses under its own weight and undergoes the process of stellar death. For most stars, this will result in the formation of a very dense and compact stellar remnant, also known as a compact star.

Compact stars have no internal energy production, but will—with the exception of black holes—usually radiate for millions of years with excess heat left from the collapse itself.

According to the most recent understanding, compact stars could also form during the phase separations of the early Universe following the Big Bang. Primordial origins of known compact objects have not been determined with certainty.

Lifetime

Although compact stars may radiate, and thus cool off and lose energy, they do not depend on high temperatures to maintain their structure, as ordinary stars do. Barring external disturbances and proton decay, they can persist virtually forever. Black holes are however generally believed to finally evaporate from Hawking radiation after trillions of years. According to our current standard models of physical cosmology, all stars will eventually evolve into cool and dark compact stars, by the time the Universe enters the so-called degenerate era in a very distant future.

The somewhat wider definition of compact objects often includes smaller solid objects such as planets, asteroids, and comets. There are a remarkable variety of stars and other clumps of hot matter, but all matter in the Universe must eventually end as some form of compact stellar or substellar object, according to current theoretical interpretations of thermodynamics.

White dwarfs

The Eskimo Nebula is illuminated by a white dwarf at its center.

The stars called white or degenerate dwarfs are made up mainly of degenerate matter; typically carbon and oxygen nuclei in a sea of degenerate electrons. White dwarfs arise from the cores of main-sequence stars and are therefore very hot when they are formed. As they cool they will redden and dim until they eventually become dark black dwarfs. White dwarfs were observed in the 19th century, but the extremely high densities and pressures they contain were not explained until the 1920s.

The equation of state for degenerate matter is "soft", meaning that adding more mass will result in a smaller object. Continuing to add mass to what begins as a white dwarf, the object shrinks and the central density becomes even greater, with higher degenerate-electron energies. After the degenerate star's mass has grown sufficiently that its radius has shrunk to only a few thousand kilometers, the mass will be approaching the Chandrasekhar limit – the theoretical upper limit of the mass of a white dwarf, about 1.4 times the mass of the Sun (M).

If matter were removed from the center of a white dwarf and slowly compressed, electrons would first be forced to combine with nuclei, changing their protons to neutrons by inverse beta decay. The equilibrium would shift towards heavier, neutron-richer nuclei that are not stable at everyday densities. As the density increases, these nuclei become still larger and less well-bound. At a critical density of about 4×1014 kg/m3 – called the “neutron drip line” – the atomic nucleus would tend to dissolve into unbound protons and neutrons. If further compressed, eventually it would reach a point where the matter is on the order of the density of an atomic nucleus – about 2×1017 kg/m3. At that density the matter would be chiefly free neutrons, with a light scattering of protons and electrons.

Neutron stars

In certain binary stars containing a white dwarf, mass is transferred from the companion star onto the white dwarf, eventually pushing it over the Chandrasekhar limit. Electrons react with protons to form neutrons and thus no longer supply the necessary pressure to resist gravity, causing the star to collapse. If the center of the star is composed mostly of carbon and oxygen then such a gravitational collapse will ignite runaway fusion of the carbon and oxygen, resulting in a Type Ia supernova that entirely blows apart the star before the collapse can become irreversible. If the center is composed mostly of magnesium or heavier elements, the collapse continues. As the density further increases, the remaining electrons react with the protons to form more neutrons. The collapse continues until (at higher density) the neutrons become degenerate. A new equilibrium is possible after the star shrinks by three orders of magnitude, to a radius between 10 and 20 km. This is a neutron star.

Although the first neutron star was not observed until 1967 when the first radio pulsar was discovered, neutron stars were proposed by Baade and Zwicky in 1933, only one year after the neutron was discovered in 1932. They realized that because neutron stars are so dense, the collapse of an ordinary star to a neutron star would liberate a large amount of gravitational potential energy, providing a possible explanation for supernovae. This is the explanation for supernovae of types Ib, Ic, and II. Such supernovae occur when the iron core of a massive star exceeds the Chandrasekhar limit and collapses to a neutron star.

Like electrons, neutrons are fermions. They therefore provide neutron degeneracy pressure to support a neutron star against collapse. In addition, repulsive neutron-neutron interactions provide additional pressure. Like the Chandrasekhar limit for white dwarfs, there is a limiting mass for neutron stars: the Tolman–Oppenheimer–Volkoff limit, where these forces are no longer sufficient to hold up the star. As the forces in dense hadronic matter are not well understood, this limit is not known exactly but is thought to be between 2 and 3 M. If more mass accretes onto a neutron star, eventually this mass limit will be reached. What happens next is not completely clear.

Black holes

A simulated black hole of ten solar masses, at a distance of 600 km

As more mass is accumulated, equilibrium against gravitational collapse exceeds its breaking point. Once the star's pressure is insufficient to counterbalance gravity, a catastrophic gravitational collapse occurs within milliseconds. The escape velocity at the surface, already at least 13 light speed, quickly reaches the velocity of light. At that point no energy or matter can escape and a black hole has formed. Because all light and matter is trapped within an event horizon, a black hole appears truly black, except for the possibility of very faint Hawking radiation. It is presumed that the collapse will continue inside the event horizon.

In the classical theory of general relativity, a gravitational singularity occupying no more than a point will form. There may be a new halt of the catastrophic gravitational collapse at a size comparable to the Planck length, but at these lengths there is no known theory of gravity to predict what will happen. Adding any extra mass to the black hole will cause the radius of the event horizon to increase linearly with the mass of the central singularity. This will induce certain changes in the properties of the black hole, such as reducing the tidal stress near the event horizon, and reducing the gravitational field strength at the horizon. However, there will not be any further qualitative changes in the structure associated with any mass increase.

Alternative black hole models

Exotic stars

An exotic star is a hypothetical compact star composed of something other than electrons, protons, and neutrons balanced against gravitational collapse by degeneracy pressure or other quantum properties. These include strange stars (composed of strange matter) and the more speculative preon stars (composed of preons).

Exotic stars are hypothetical, but observations released by the Chandra X-Ray Observatory on April 10, 2002 detected two candidate strange stars, designated RX J1856.5-3754 and 3C58, which had previously been thought to be neutron stars. Based on the known laws of physics, the former appeared much smaller and the latter much colder than they should, suggesting that they are composed of material denser than neutronium. However, these observations are met with skepticism by researchers who say the results were not conclusive.

Quark stars and strange stars

If neutrons are squeezed enough at a high temperature, they will decompose into their component quarks, forming what is known as a quark matter. In this case, the star will shrink further and become denser, but instead of a total collapse into a black hole, it is possible that the star may stabilize itself and survive in this state indefinitely, so long as no more mass is added. It has, to an extent, become a very large nucleon. A star in this hypothetical state is called a "quark star" or more specifically a "strange star". The pulsar 3C58 has been suggested as a possible quark star. Most neutron stars are thought to hold a core of quark matter but this has proven difficult to determine observationally.

Preon stars

A preon star is a proposed type of compact star made of preons, a group of hypothetical subatomic particles. Preon stars would be expected to have huge densities, exceeding 1023 kilogram per cubic meter – intermediate between quark stars and black holes. Preon stars could originate from supernova explosions or the Big Bang; however, current observations from particle accelerators speak against the existence of preons.

Q stars

Q stars are hypothetical compact, heavier neutron stars with an exotic state of matter where particle numbers are preserved with radii less than 1.5 times the corresponding Schwarzschild radius. Q stars are also called "gray holes".

Electroweak stars

An electroweak star is a theoretical type of exotic star, whereby the gravitational collapse of the star is prevented by radiation pressure resulting from electroweak burning, that is, the energy released by conversion of quarks to leptons through the electroweak force. This process occurs in a volume at the star's core approximately the size of an apple, containing about two Earth masses.

Boson star

A boson star is a hypothetical astronomical object that is formed out of particles called bosons (conventional stars are formed out of fermions). For this type of star to exist, there must be a stable type of boson with repulsive self-interaction. As of 2016 there is no significant evidence that such a star exists. However, it may become possible to detect them by the gravitational radiation emitted by a pair of co-orbiting boson stars.

Compact relativistic objects and the generalized uncertainty principle

Based on the generalized uncertainty principle (GUP), proposed by some approaches to quantum gravity such as string theory and doubly special relativity, the effect of GUP on the thermodynamic properties of compact stars with two different components has been studied recently. Tawfik et al. noted that the existence of quantum gravity correction tends to resist the collapse of stars if the GUP parameter is taking values between Planck scale and electroweak scale. Comparing with other approaches, it was found that the radii of compact stars should be smaller and increasing energy decreases the radii of the compact stars.

Neutronium

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

Neutronium (sometimes shortened to neutrium, also referred to as neutrite) is a hypothetical substance composed purely of neutrons. The word was coined by scientist Andreas von Antropoff in 1926 (before the 1932 discovery of the neutron) for the hypothetical "element of atomic number zero" (with zero protons in its nucleus) that he placed at the head of the periodic table (denoted by -, or Nu). However, the meaning of the term has changed over time, and from the last half of the 20th century onward it has been also used to refer to extremely dense substances resembling the neutron-degenerate matter theorized to exist in the cores of neutron stars; hereinafter "degenerate neutronium" will refer to this.

In neutron stars

Neutronium is used in popular physics literature to refer to the material present in the cores of neutron stars (stars which are too massive to be supported by electron degeneracy pressure and which collapse into a denser phase of matter). This term is very rarely used in scientific literature, for three reasons: there are multiple definitions for the term "neutronium"; there is considerable uncertainty over the composition of the material in the cores of neutron stars (it could be neutron-degenerate matter, strange matter, quark matter, or a variant or combination of the above); the properties of neutron star material should depend on depth due to changing pressure (see below), and no sharp boundary between the crust (consisting primarily of atomic nuclei) and almost protonless inner layer is expected to exist.

When neutron star core material is presumed to consist mostly of free neutrons, it is typically referred to as neutron-degenerate matter in scientific literature.

In the periodic table

The term "neutronium" was coined in 1926 by Andreas von Antropoff for a conjectured form of matter made up of neutrons with no protons or electrons, which he placed as the chemical element of atomic number zero at the head of his new version of the periodic table. It was subsequently placed in the middle of several spiral representations of the periodic system for classifying the chemical elements, such as those of Charles Janet (1928), E. I. Emerson (1944), and John D. Clark (1950).

Although the term is not used in the scientific literature either for a condensed form of matter, or as an element, there have been reports that, besides the free neutron, there may exist two bound forms of neutrons without protons. If neutronium were considered to be an element, then these neutron clusters could be considered to be the isotopes of that element. However, these reports have not been further substantiated.

  • Mononeutron: An isolated neutron undergoes beta decay with a mean lifetime of approximately 15 minutes (half-life of approximately 10 minutes), becoming a proton (the nucleus of hydrogen), an electron, and an antineutrino.
  • Dineutron: The dineutron, containing two neutrons, was unambiguously observed in 2012 in the decay of beryllium-16. It is not a bound particle, but had been proposed as an extremely short-lived resonance state produced by nuclear reactions involving tritium. It has been suggested to have a transitory existence in nuclear reactions produced by helions (completely ionized helium-3 nuclei) that result in the formation of a proton and a nucleus having the same atomic number as the target nucleus but a mass number two units greater. The dineutron hypothesis had been used in nuclear reactions with exotic nuclei for a long time. Several applications of the dineutron in nuclear reactions can be found in review papers. Its existence has been proven to be relevant for nuclear structure of exotic nuclei. A system made up of only two neutrons is not bound, though the attraction between them is very nearly enough to make them so. This has some consequences on nucleosynthesis and the abundance of the chemical elements.
  • Trineutron: A trineutron state consisting of three bound neutrons has not been detected, and is not expected to exist even for a short time.
  • Tetraneutron: A tetraneutron is a hypothetical particle consisting of four bound neutrons. Reports of its existence have not been replicated.
  • Pentaneutron: Calculations indicate that the hypothetical pentaneutron state, consisting of a cluster of five neutrons, would not be bound.

Although not called "neutronium", the National Nuclear Data Center's Nuclear Wallet Cards lists as its first "isotope" an "element" with the symbol n and atomic number Z = 0 and mass number A = 1. This "isotope" is described as decaying to hydrogen-1 with a half life of 10.24±0.2 min.

Properties

Neutron matter is equivalent to a chemical element with atomic number 0, which is to say that it is equivalent to a species of atoms having no protons in their atomic nuclei. It is extremely radioactive; its only legitimate equivalent isotope, the free neutron, has a half-life of 10 minutes, which is approximately half that of the most stable known isotope of francium. Neutron matter decays quickly into hydrogen. Neutron matter has no electronic structure on account of its total lack of electrons.

While this lifetime is long enough to permit the study of neutronium's chemical properties, there are serious practical problems. Having no charge or electrons, neutronium would not interact strongly with ordinary low-energy photons (visible light) and would feel no electrostatic forces, so it would diffuse into the walls of most containers made of ordinary matter. Certain materials are able to resist diffusion or absorption of ultracold neutrons due to nuclear-quantum effects, specifically reflection caused by the strong interaction. At ambient temperature and in the presence of other elements, thermal neutrons readily undergo neutron capture to form heavier (and often radioactive) isotopes of that element.

Neutron matter at standard pressure and temperature is predicted by the ideal gas law to be less dense than even hydrogen, with a density of only 0.045 kg/m3 (roughly 27 times less dense than air and half as dense as hydrogen gas). Neutron matter is expected to remain gaseous down to absolute zero at normal pressures, as the zero-point energy of the system is too high to allow condensation. However, neutron matter should in theory form a degenerate gaseous superfluid at these temperatures, composed of transient neutron-pairs called dineutrons. Under extremely low pressure, this low temperature, gaseous superfluid should exhibit quantum coherence producing a Bose–Einstein condensate. At higher temperatures, neutron matter will only condense with sufficient pressure, and solidify with even greater pressure. Such pressures exist in neutron stars, where the extreme pressure causes the neutron matter to become degenerate. However, in the presence of atomic matter compressed to the state of electron degeneracy, β decay may be inhibited due to the Pauli exclusion principle, thus making free neutrons stable. Also, elevated pressures should make neutrons degenerate themselves.

Compared to ordinary elements, neutronium should be more compressible due to the absence of electrically charged protons and electrons. This makes neutronium more energetically favorable than (positive-Z) atomic nuclei and leads to their conversion to (degenerate) neutronium through electron capture, a process that is believed to occur in stellar cores in the final seconds of the lifetime of massive stars, where it is facilitated by cooling via
ν
e
emission. As a result, degenerate neutronium can have a density of 4×1017 kg/m3, roughly 14 orders of magnitude denser than the densest known ordinary substances. It was theorized that extreme pressures of order 100 MeV/fm3 (1.6×1034 Pa) might deform the neutrons into a cubic symmetry, allowing tighter packing of neutrons, or cause a strange matter formation.

Lie group

From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Lie_group In mathematics , a Lie gro...