Temperate rainforests are coniferous or broadleaf forests that occur in the temperate zone and receive heavy rainfall. Temperate rain forests occur in oceanic moist regions around the world: the Pacific temperate rain forests of North American Pacific Northwest as well as the Mid-Atlantic region of the US; the moist conditions of temperate rain forests support an understory of mosses and some shrubs. Temperate rain forests can be temperate broadleaf and mixed forests. For temperate rain forests of North America, Alaback's definition is recognized: Annual precipitation over 140 cm Mean annual temperature is between 4 and 12 °C. However, required annual precipitation depends on factors such as distribution of rainfall over the year, temperatures over the year and fog presence, definitions in other regions of the world differ considerably. For example, Australian definitions are ecological-structural rather than climatic: Closed canopy of trees excludes at least 70% of the sky. Forest is composed of tree species which do not require fire for regeneration, but with seedlings able to regenerate under shade and in natural openings.
The latter would, for example, exclude a part of the temperate rain forests of western North America, as Coast Douglas-fir, one of its dominant tree species, requires stand-destroying disturbance to initiate a new cohort of seedlings. The North American definition would in turn exclude a part of temperate rain forests under definitions used elsewhere. For forests, canopy refers to the upper layer or habitat zone, formed by mature tree crowns and including other biological organisms; the canopy level is the third level of the temperate rainforest. The trees forming the canopy, can stand as tall as 100 meters or more. A variety of species survive in the canopy; the tops of these trees collect most of the rain and photosynthesis that the rainforest takes in. They form a canopy over the forest; the canopy’s coverage affects the shade tolerance levels of forest floor plants. When the canopy is in full bloom, covering about 95% of the floor, plant survival decreases; some plant species have become shade tolerant in order to survive.
The treetops keep the lower levels of the forest damp. The canopy survives through photosynthesis; the leaves provide energy and nutrients for the trees. Through satellite data, the radiation use efficiency calculates the annual amount of photosynthesis that occurs in temperate rainforests. A diverse amount of photosynthesis occurs based on the location and microclimates of the forest. Temperate forests cover a large part of the Earth, but temperate rainforests only occur in a few regions around the world. Most of these occur in oceanic moist climates: the Pacific temperate rain forests in Western North America, the Valdivian and Magellanic temperate rainforests of southwestern South America, pockets of rain forest in Northwestern Europe, temperate rainforests of southeastern Australia and the New Zealand temperate rainforests. Others occur in subtropical moist climates. Additionally pockets of temperate rainforest occur in dreary climates that are not categorized by just annual precipitation but number of cloudy days as well as number of days of measurable precipitation in the form of rain or snow.
In Western North America outside the Pacific Northwest, the Columbia Mountains of British Columbia, northern Idaho and northwestern Montana, have more of a continental climate and have pockets of temperate coniferous rainforest. In Eastern North America, there are scattered pockets of temperate rainforest along the Allegheny Plateau and adjacent parts of the Appalachian Mountains from West Virginia to New England; these areas include sections of West Virginia, Western Pennsylvania, as well as Western Upstate New York and the Adirondack Mountains. A good example of these forests are found in Zoar Valley in Western New York, Cook Forest State Park within the Allegheny National Forest, Cathedral State Park in West Virginia. In Eastern Asia, there are scattered pockets of temperate rainforest in what is known as the Russian Far East in Asia where the climate is continental in nature, but get enough precipitation and cloud cover to harbor significant pockets of temperate rainforest. Like Eastern North America, much precipitation is in the form of snow.
The mountainous coniferous forests of the Changbai Mountains bordering China and North Korea are a good example, containing some of the r
Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is flora. Flora and other forms of life such as fungi are collectively referred to as biota. Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess Shale fauna". Paleontologists sometimes refer to a sequence of faunal stages, a series of rocks all containing similar fossils; the study of animals of a particular region is called faunistics. Fauna comes from the name Fauna, a Roman goddess of earth and fertility, the Roman god Faunus, the related forest spirits called Fauns. All three words are cognates of the name of the Greek god Pan, panis is the Greek equivalent of fauna. Fauna is the word for a book that catalogues the animals in such a manner; the term was first used by Carl Linnaeus from Sweden in the title of his 1745 work Fauna Suecica. Cryofauna refers to the animals that live in, or close to, cold areas.
Cryptofauna are the fauna. Infauna are benthic organisms that live within the bottom substratum of a water body within the bottom-most oceanic sediments, rather than on its surface. Bacteria and microalgae may live in the interstices of bottom sediments. In general, infaunal animals become progressively smaller and less abundant with increasing water depth and distance from shore, whereas bacteria show more constancy in abundance, tending toward one million cells per milliliter of interstitial seawater. Epifauna called epibenthos, are aquatic animals that live on the bottom substratum as opposed to within it, that is, the benthic fauna that live on top of the sediment surface at the seafloor. Macrofauna are soil organisms which are retained on a 0.5 mm sieve. Studies in the deep sea define macrofauna as animals retained on a 0.3 mm sieve to account for the small size of many of the taxa. Megafauna are large animals of any particular time. For example, Australian megafauna. Meiofauna are small benthic invertebrates that live in both freshwater environments.
The term meiofauna loosely defines a group of organisms by their size, larger than microfauna but smaller than macrofauna, rather than a taxonomic grouping. One environment for meiofauna is between grains of damp sand. In practice these are metazoan animals that can pass unharmed through a 0.5 – 1 mm mesh but will be retained by a 30–45 μm mesh, but the exact dimensions will vary from researcher to researcher. Whether an organism passes through a 1 mm mesh depends upon whether it is alive or dead at the time of sorting. Mesofauna are macroscopic soil animals such as nematodes. Mesofauna are diverse. Microfauna are microscopic or small animals. Other terms include avifauna, which means "bird fauna" and piscifauna, which means "fish fauna". Linnaeus, Carolus. Fauna Suecica. 1746 "Biodiversity of Collembola and their functional role in the ecosystem"
Coarse woody debris
Coarse woody debris or coarse woody habitat refers to fallen dead trees and the remains of large branches on the ground in forests and in rivers or wetlands. A dead standing tree - known as a snag - provides many of the same functions as coarse woody debris; the minimum size required for woody debris to be defined as "coarse" varies by author, ranging from 2.5–20 cm in diameter. Since the 1970s, forest managers worldwide have been encouraged to allow dead trees and woody debris to remain in woodlands, recycling nutrients trapped in the wood and providing food and habitat for a wide range of organisms, thereby improving biodiversity; the amount of coarse woody debris is considered an important criterion for the evaluation and restoration of temperate deciduous forest. Coarse woody debris is important in wetlands in deltas where woody debris accumulates. Coarse woody debris comes from natural tree mortality and insects, as well as catastrophic events such as fires and floods. Ancient, or old growth, with its dead trees and woody remains lying where they fell to feed new vegetation, constitutes the ideal woodland in terms of recycling and regeneration.
In healthy temperate forests, dead wood comprises up to thirty per cent of all woody biomass. In recent British studies, woods managed for timber had between a third and a seventh less fallen debris than unmanaged woods, left undisturbed for many years, while in coppiced woods the amount of CWD was zero. In old growth Douglas fir forests of the Pacific Northwest of North America, CWD concentrations were found to be from 72 metric tons/hectare in drier sites to 174 t/ha in moister sites. Australian native forests have mean CWD concentrations ranging from 19 t/ha to 134 t/ha, depending on forest type. Coarse woody debris and its subsequent decomposition recycles nutrients that are essential for living organisms, such as carbon, nitrogen and phosphorus. Saprotrophic fungi and detritivores such as bacteria and insects directly consume dead wood, releasing nutrients by converting them into other forms of organic matter which may be consumed by other organisms; however CWD itself is scarce in physiologically important nutrients.
To fulfill nutritional requirements of consumers, CWD must be first nutritionally enriched by transport of nutrients from outside of CWD. Thus CWD is important actor contributing to soil nutrients cycles. CWD, while itself not rich in nitrogen, contributes nitrogen to the ecosystem by acting as a host for nonsymbiotic free-living nitrogen-fixing bacteria. Scientific studies show that coarse woody debris can be a significant contributor to biological carbon sequestration. Trees store atmospheric carbon in their wood using photosynthesis. Once the trees die and other saprotrophs transfer some of that carbon from CWD into the soil; this sequestration can continue in old-growth forests for hundreds of years. By providing both food and microhabitats for many species, coarse woody debris helps to maintain the biodiversity of forest ecosystems. Up to forty percent of all forest fauna is dependent on CWD. Studies in western North America showed that only five per cent of living trees consisted of living cells by volume, whereas in dead wood it was as high as forty percent by volume fungi and bacteria.
Colonizing organisms that live on the remains of cambium and sapwood of dead trees aid decomposition and attract predators that prey on them and so continue the chain of metabolizing the biomass. The list of organisms dependent on CWD for habitat or as a food source includes bacteria, lichens and other plants, in the animal kingdom, invertebrates such as termites, ants and snails, amphibians such as salamanders, reptiles such as the slow-worm, as well as birds and small mammals. One third of all woodland birds live in the cavities of dead tree trunks. Woodpeckers, tits and owls all live in dead trees, grouse shelter behind woody debris; some plants use coarse woody debris as habitat. Mosses and lichens may cover logs, while trees may regenerate on the top of logs. Large fragments of CWD that provide such habitat for herbs and trees are called nurse logs. CWD can protect young plants from herbivory damage by acting as barriers to browsing animals; the persistence of coarse woody debris can shelter organisms during a large disturbance to the ecosystem such as wildfire or logging.
Fallen debris and trees in streams provide shelter for fish and mammals by modifying the flow of water and sediment. Turtles of many species may use coarse woody debris for basking. Musk turtles may lay their eggs under logs near wetlands. Coarse woody debris on slopes, stabilizes soils by slowing downslope movement of organic matter and mineral soil. Leaves and other debris collect behind CWD. Infiltration of precipitation is improved as well. During dry weather, CWD slows evaporation of soil moisture and provides damp microhabitats for moisture-sensitive organisms. In fire-prone forests, coarse woody debris can be a significant fuel during a wildfire. High amounts of fuels can lead to size. CWD may be managed to reduce fuel levels in forests where fire exclusion has resulted in the buildup of fuels. Reductions in CWD for fire safety should be balanced with the retention of CWD for habitat and other benefits. CWD is classified as 1000-hour fuel by fire managers, referring to the amount of time needed for the moisture level in the wood to react to the surrounding environment.
In Glen Affric, the Trees for Life group found the black tinder fungus beetl
Belgium the Kingdom of Belgium, is a country in Western Europe. It is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeast, France to the southwest, the North Sea to the northwest, it has a population of more than 11.4 million. The capital and largest city is Brussels; the sovereign state is a federal constitutional monarchy with a parliamentary system. Its institutional organisation is structured on both regional and linguistic grounds, it is divided into three autonomous regions: Flanders in the north, Wallonia in the south, the Brussels-Capital Region. Brussels is the smallest and most densely populated region, as well as the richest region in terms of GDP per capita. Belgium is home to two main linguistic groups or Communities: the Dutch-speaking Flemish Community, which constitutes about 59 percent of the population, the French-speaking Community, which comprises about 40 percent of all Belgians. A small German-speaking Community, numbering around one percent, exists in the East Cantons.
The Brussels-Capital Region is bilingual, although French is the dominant language. Belgium's linguistic diversity and related political conflicts are reflected in its political history and complex system of governance, made up of six different governments. Belgium was part of an area known as the Low Countries, a somewhat larger region than the current Benelux group of states that included parts of northern France and western Germany, its name is derived after the Roman province of Gallia Belgica. From the end of the Middle Ages until the 17th century, the area of Belgium was a prosperous and cosmopolitan centre of commerce and culture. Between the 16th and early 19th centuries, Belgium served as the battleground between many European powers, earning the moniker the "Battlefield of Europe", a reputation strengthened by both world wars; the country emerged in 1830 following the Belgian Revolution. Belgium participated in the Industrial Revolution and, during the course of the 20th century, possessed a number of colonies in Africa.
The second half of the 20th century was marked by rising tensions between the Dutch-speaking and the French-speaking citizens fueled by differences in language and culture and the unequal economic development of Flanders and Wallonia. This continuing antagonism has led to several far-reaching reforms, resulting in a transition from a unitary to a federal arrangement during the period from 1970 to 1993. Despite the reforms, tensions between the groups have remained, if not increased. Unemployment in Wallonia is more than double that of Flanders. Belgium is one of the six founding countries of the European Union and hosts the official seats of the European Commission, the Council of the European Union, the European Council, as well as a seat of the European Parliament in the country's capital, Brussels. Belgium is a founding member of the Eurozone, NATO, OECD, WTO, a part of the trilateral Benelux Union and the Schengen Area. Brussels hosts several of the EU's official seats as well as the headquarters of many major international organizations such as NATO.
Belgium is a developed country, with an advanced high-income economy. It has high standards of living, quality of life, education, is categorized as "very high" in the Human Development Index, it ranks as one of the safest or most peaceful countries in the world. The name "Belgium" is derived from Gallia Belgica, a Roman province in the northernmost part of Gaul that before Roman invasion in 100 BC, was inhabited by the Belgae, a mix of Celtic and Germanic peoples. A gradual immigration by Germanic Frankish tribes during the 5th century brought the area under the rule of the Merovingian kings. A gradual shift of power during the 8th century led the kingdom of the Franks to evolve into the Carolingian Empire; the Treaty of Verdun in 843 divided the region into Middle and West Francia and therefore into a set of more or less independent fiefdoms which, during the Middle Ages, were vassals either of the King of France or of the Holy Roman Emperor. Many of these fiefdoms were united in the Burgundian Netherlands of the 15th centuries.
Emperor Charles V extended the personal union of the Seventeen Provinces in the 1540s, making it far more than a personal union by the Pragmatic Sanction of 1549 and increased his influence over the Prince-Bishopric of Liège. The Eighty Years' War divided the Low Countries into the northern United Provinces and the Southern Netherlands; the latter were ruled successively by the Spanish and the Austrian Habsburgs and comprised most of modern Belgium. This was the theatre of most Franco-Spanish and Franco-Austrian wars during the 17th and 18th centuries. Following the campaigns of 1794 in the French Revolutionary Wars, the Low Countries—including territories that were never nominally under Habsburg rule, such as the Prince-Bishopric of Liège—were annexed by the French First Republic, ending Austrian rule in the region; the reunification of the Low Countries as the United Kingdom of the Netherlands occurred at the dissolution of the First French Empire in 1815, after the defeat of Napo
An old-growth forest — termed primary forest or late seral forest — is a forest that has attained great age without significant disturbance and thereby exhibits unique ecological features and might be classified as a climax community. Old-growth features include diverse tree-related structures that provide diverse wildlife habitat that increases the biodiversity of the forested ecosystem; the concept of diverse tree structure includes multi-layered canopies and canopy gaps varying tree heights and diameters, diverse tree species and classes and sizes of woody debris. Old-growth forests are valuable for economic reasons and for the ecosystem services they provide; this can be a point of contention when some in the logging industry may desire to cut down the forests to obtain valuable timber, while environmentalists seek to preserve the forests for benefits such as maintenance of biodiversity, water regulation, nutrient cycling. Old-growth forests tend to have large trees and standing dead trees, multilayered canopies with gaps that result from the deaths of individual trees, coarse woody debris on the forest floor.
Forest regenerated after a severe disturbance, such as wildfire, insect infestation, or harvesting, is called second-growth or'regeneration' until enough time passes for the effects of the disturbance to be no longer evident. Depending on the forest, this may take from a century to several millennia. Hardwood forests of the eastern United States can develop old-growth characteristics in 150–500 years. In British Columbia, old growth is defined as 120 to 140 years of age in the interior of the province where fire is a frequent and natural occurrence. In British Columbia’s coastal rainforests, old growth is defined as trees more than 250 years, with some trees reaching more than 1,000 years of age. In Australia, eucalypt trees exceed 350 years of age due to frequent fire disturbance. Forest types have different development patterns, natural disturbances and appearances. A Douglas-fir stand may grow for centuries without disturbance while an old-growth ponderosa pine forest requires frequent surface fires to reduce the shade-tolerant species and regenerate the canopy species.
In the Boreal-West Forest Region, catastrophic disturbances like wildfires minimize opportunities for major accumulations of dead and downed woody material and other structural legacies associated with old growth conditions. Typical characteristics of old-growth forest include presence of older trees, minimal signs of human disturbance, mixed-age stands, presence of canopy openings due to tree falls, pit-and-mound topography, down wood in various stages of decay, standing snags, multilayered canopies, intact soils, a healthy fungal ecosystem, presence of indicator species. Old-growth forests are biologically diverse, home to many rare species, threatened species, endangered species of plants and animals, such as the northern spotted owl, marbled murrelet and fisher, making them ecologically significant. Levels of biodiversity may be higher or lower in old-growth forests compared to that in second-growth forests, depending on specific circumstances, environmental variables, geographic variables.
Logging in old-growth forests is a contentious issue in many parts of the world. Excessive logging reduces biodiversity, affecting not only the old-growth forest itself, but indigenous species that rely upon old-growth forest habitat. A forest in old-growth stage has a mix of tree ages, due to a distinct regeneration pattern for this stage. New trees regenerate at different times from each other, because each one of them has different spatial location relative to the main canopy, hence each one receives a different amount of light; the mixed age of the forest is an important criterion in ensuring that the forest is a stable ecosystem in the long term. A climax stand, uniformly aged becomes senescent and degrades within a short time to result in a new cycle of forest succession. Thus, uniformly aged stands are less stable ecosystems. Forest canopy gaps are essential in maintaining mixed-age stands; some herbaceous plants only become established in canopy openings, but persist beneath an understory.
Openings are a result of tree death due to small impact disturbances such as wind, low-intensity fires, tree diseases. Old-growth forests are unique having multiple horizontal layers of vegetation representing a variety of tree species, age classes, sizes, as well as "pit and mound" soil shape with well-established fungal nets; because old-growth forest is structurally diverse, it provides higher-diversity habitat than forests in other stages. Thus, sometimes higher biological diversity can be sustained in old-growth forest, or at least a biodiversity, different from other forest stages; the characteristic topography of much old-growth forest consists of mounds. Mounds are caused by decaying fallen trees, pits by the roots pulled out of the ground when trees fall due to natural causes, including being pushed over by animals. Pits expose humus-poor, mineral-rich soil and collect moisture and fallen leaves, forming a thick organic layer, able to nurture certain types of organisms. Mounds provide a place free of leaf inundation and saturation, where other types of organisms thrive.
Standing snags provide food sources and habitat for many types of organisms. In particular, many species of dead-wood predators such as woodpeckers must have standing snags available for feeding. In North America, the spotted owl is well known for needing standing snags for nesting habitat. Fallen timber, or coarse woody debris, contributes carbon-rich organic matter directly to the soil, providing a substrate for mosses and seedlings, cr
An earthworm is a tube-shaped, segmented worm found in the phylum Annelida. They have a world-wide distribution and are found living in soil, feeding on live and dead organic matter. An earthworm's digestive system runs through the length of its body, it conducts respiration through its skin. It has a double transport system composed of coelomic fluid that moves within the fluid-filled coelom and a simple, closed blood circulatory system, it has a peripheral nervous system. The central nervous system consists of two ganglia above the mouth, one on either side, connected to a nerve cord running back along its length to motor neurons and sensory cells in each segment. Large numbers of chemoreceptors are concentrated near its mouth. Circumferential and longitudinal muscles on the periphery of each segment enable the worm to move. Similar sets of muscles line the gut, their actions move the digesting food toward the worm's anus. Earthworms are hermaphrodites: each individual carries both male and female sex organs.
As invertebrates, they lack either an internal skeleton or exoskeleton, but maintain their structure with fluid-filled coelom chambers that function as a hydrostatic skeleton. "Earthworm" is the common name for the largest members of Oligochaeta. In classical systems, they were placed in the order Opisthopora, on the basis of the male pores opening posterior to the female pores, though the internal male segments are anterior to the female. Theoretical cladistic studies have placed them, instead, in the suborder Lumbricina of the order Haplotaxida, but this may again soon change. Folk names for the earthworm include "dew-worm", "rainworm", "night crawler", "angleworm". Larger terrestrial earthworms are called megadriles, as opposed to the microdriles in the semiaquatic families Tubificidae and Enchytraeidae, among others; the megadriles are characterized by having a distinct clitellum and a vascular system with true capillaries. Depending on the species, an adult earthworm can be from 10 mm long and 1 mm wide to 3 m long and over 25 mm wide, but the typical Lumbricus terrestris grows to about 360 mm long.
The longest worm on confirmed records is Amynthas mekongianus that extends up to 3 m in the mud along the banks of the 4,350 km Mekong River in Southeast Asia. From front to back, the basic shape of the earthworm is a cylindrical tube, divided into a series of segments that compartmentalize the body. Furrows are externally visible on the body demarking the segments. Except for the mouth and anal segments, each segment carries bristle-like hairs called lateral setae used to anchor parts of the body during movement. Special ventral setae are used to anchor mating earthworms by their penetration into the bodies of their mates. Within a species, the number of segments found is consistent across specimens, individuals are born with the number of segments they will have throughout their lives; the first body segment features both the earthworm's mouth and, overhanging the mouth, a fleshy lobe called the prostomium, which seals the entrance when the worm is at rest, but is used to feel and chemically sense the worm's surroundings.
Some species of earthworm can use the prehensile prostomium to grab and drag items such as grasses and leaves into their burrow. An adult earthworm develops a belt-like glandular swelling, called the clitellum, which covers several segments toward the front part of the animal; this produces egg capsules. The posterior is most cylindrical like the rest of the body, but depending on the species, may be quadrangular, trapezoidal, or flattened; the last segment is called the periproct. The exterior of an individual segment is a thin cuticle over skin pigmented red to brown, which has specialized cells that secrete mucus over the cuticle to keep the body moist and ease movement through soil. Under the skin is a layer of nerve tissue, two layers of muscles—a thin outer layer of circular muscle, a much thicker inner layer of longitudinal muscle. Interior to the muscle layer is a fluid-filled chamber called a coelom that by its pressurization provides structure to the worm's boneless body; the segments are separated from each other by septa which are perforated transverse walls, allowing the coelomic fluid to pass between segments.
A pair of structures called. This tubule leads to the main body fluid filtering organ, the nephridium or metanephridium, which removes metabolic waste from the coelomic fluid and expels it through pores called nephridiopores on the worm's sides. At the center of a worm is the digestive tract, which runs straight through from mouth to anus without coiling, is flanked above and below by blood vessels and the ventral nerve cord, is surrounded in each segment by a pair of pallial blood vessels that connect the dorsal to th
International Standard Serial Number
An International Standard Serial Number is an eight-digit serial number used to uniquely identify a serial publication, such as a magazine. The ISSN is helpful in distinguishing between serials with the same title. ISSN are used in ordering, interlibrary loans, other practices in connection with serial literature; the ISSN system was first drafted as an International Organization for Standardization international standard in 1971 and published as ISO 3297 in 1975. ISO subcommittee TC 46/SC 9 is responsible for maintaining the standard; when a serial with the same content is published in more than one media type, a different ISSN is assigned to each media type. For example, many serials are published both in electronic media; the ISSN system refers to these types as electronic ISSN, respectively. Conversely, as defined in ISO 3297:2007, every serial in the ISSN system is assigned a linking ISSN the same as the ISSN assigned to the serial in its first published medium, which links together all ISSNs assigned to the serial in every medium.
The format of the ISSN is an eight digit code, divided by a hyphen into two four-digit numbers. As an integer number, it can be represented by the first seven digits; the last code digit, which may be 0-9 or an X, is a check digit. Formally, the general form of the ISSN code can be expressed as follows: NNNN-NNNC where N is in the set, a digit character, C is in; the ISSN of the journal Hearing Research, for example, is 0378-5955, where the final 5 is the check digit, C=5. To calculate the check digit, the following algorithm may be used: Calculate the sum of the first seven digits of the ISSN multiplied by its position in the number, counting from the right—that is, 8, 7, 6, 5, 4, 3, 2, respectively: 0 ⋅ 8 + 3 ⋅ 7 + 7 ⋅ 6 + 8 ⋅ 5 + 5 ⋅ 4 + 9 ⋅ 3 + 5 ⋅ 2 = 0 + 21 + 42 + 40 + 20 + 27 + 10 = 160 The modulus 11 of this sum is calculated. For calculations, an upper case X in the check digit position indicates a check digit of 10. To confirm the check digit, calculate the sum of all eight digits of the ISSN multiplied by its position in the number, counting from the right.
The modulus 11 of the sum must be 0. There is an online ISSN checker. ISSN codes are assigned by a network of ISSN National Centres located at national libraries and coordinated by the ISSN International Centre based in Paris; the International Centre is an intergovernmental organization created in 1974 through an agreement between UNESCO and the French government. The International Centre maintains a database of all ISSNs assigned worldwide, the ISDS Register otherwise known as the ISSN Register. At the end of 2016, the ISSN Register contained records for 1,943,572 items. ISSN and ISBN codes are similar in concept. An ISBN might be assigned for particular issues of a serial, in addition to the ISSN code for the serial as a whole. An ISSN, unlike the ISBN code, is an anonymous identifier associated with a serial title, containing no information as to the publisher or its location. For this reason a new ISSN is assigned to a serial each time it undergoes a major title change. Since the ISSN applies to an entire serial a new identifier, the Serial Item and Contribution Identifier, was built on top of it to allow references to specific volumes, articles, or other identifiable components.
Separate ISSNs are needed for serials in different media. Thus, the print and electronic media versions of a serial need separate ISSNs. A CD-ROM version and a web version of a serial require different ISSNs since two different media are involved. However, the same ISSN can be used for different file formats of the same online serial; this "media-oriented identification" of serials made sense in the 1970s. In the 1990s and onward, with personal computers, better screens, the Web, it makes sense to consider only content, independent of media; this "content-oriented identification" of serials was a repressed demand during a decade, but no ISSN update or initiative occurred. A natural extension for ISSN, the unique-identification of the articles in the serials, was the main demand application. An alternative serials' contents model arrived with the indecs Content Model and its application, the digital object identifier, as ISSN-independent initiative, consolidated in the 2000s. Only in 2007, ISSN-L was defined in the