Pinus contorta, with the common names lodgepole pine and shore pine, known as twisted pine, contorta pine, is a common tree in western North America. It is common near the ocean shore and in dry montane forests to the subalpine, but is rare in lowland rain forests. Like all pines, it is an evergreen conifer. There are four subspecies of Pinus contorta, one of them is sometimes considered to have two varieties; the subspecies are sometimes treated at the rank of variety. Pinus contorta subsp. Bolanderi: Bolander's beach pine, Bolander pine. Contorta: shore pine. Pinus contorta subsp. Murrayana: tamarack pine, or Sierra lodgepole pine. Pinus contorta subsp. Latifolia: lodgepole pine. Depending on subspecies, Pinus contorta grows as tree; the shrub form is krummholz and is 1 to 3 m high. The thin and narrow-crowned tree is 40 to 50 m high and can achieve up to 2 m in diameter at chest height; the murrayana subspecies is the tallest. The crown is rounded and the top of the tree is flattened. In dense forests, the tree has a conical crown.
The formation of twin trees is common in some populations in British Columbia. The elastic branches are difficult to break; the branches are covered with short shoots. The species name is contorta because of the twisted, bent pines found at coastal areas and the tree's twisted needles. Pinus contorta is known under several English names: black pine, scrub pine, coast pine. P. contorta subsp. Latifolia will hybridise with the related jack pine; the egg-shaped growth buds are between 20 and 30 mm long. They are short pointed rotated, resinous. Spring growth starts in beginning of April and the annual growth is completed by early July; the dark and shiny needles are pointed and 4 to 8 cm long and 0.9 to 2 mm wide. The needle edge is weak to serrated; the needles rotated about the shoots' longitudinal axes. In Alberta above 2,000 m, 1 to 5 needles occur per short shoot. A population with a high proportion of three-needled short shoots occurs in the Yukon. Needles live an average of four to six years, with a maximum of 13 years.
The cones are 3–7 centimetres long. The cones have prickles on the scales. Many populations of the Rocky Mountain subspecies, P. contorta subsp. Latifolia, have serotinous cones; this means that the cones are closed and must be exposed to high temperatures, such as from forest fires, in order to open and release their seeds. The variation in their serotiny has been correlated with mountain pine beetle attacks; the cones of the coastal Pacific subspecies, P. contorta subsp. Contorta, are non-serotinous, those of the inland Pacific subspecies, P. contorta subsp. Murrayana, are non-serotinous. Pinus contorta is a fire-dependent species, requiring wildfires to maintain healthy populations of diverse ages; the bark of the lodgepole pine is thin, minimizing the tree's defense to fire. This allows the species to maintain its place in the forest habitat. One plant community in which Pinus contorta is found is the closed-cone pine forest of coastal California. Excessive wildfire prevention disrupts the fire ecology.
The stands are so densely populated that the trees self-thin, or out-compete each other, leaving dead trees standing. These become a dry ladder fuel; when the fire reaches the crowns of the trees, it can jump from tree to tree and becomes unstoppable. The natural fire regime for this species is driven by climate; the fires occur most after years of drought. Pinus contorta occurs from the upper montane to the subalpine region; these types of forests experience a lot of moisture in the form of snow in the winter due to their altitude. The density of the tree stand prohibits the establishment of an understory. With all of that being said, the likelihood of a surface fire occurring is rare. Thus, infrequent but severe fires dominate this species. An example of the climate that plays a huge role in the fire regime of Pinus contorta is quite complex. There are three different oscillations; these are Atlantic Multi-decadal Oscillation and El Nino. A combination of these oscillations being in effect or not in effect have a global effect on the water available to these forests.
So when the AMO +, ENSO – and PDO –, there is going to be a drought and a severe subalpine fire. Suillus tomentosus, a fungus, produces specialized structures called tuberculate ectomycorrhizae with the roots of lodgepole pine; these structures have been shown to be the location of concentrations of nitrogen-fixing bacteria which contribute a significant amount of nitrogen to tree growth and allow the pines to colonize nutrient-poor sites. This species is attacked by blue stain fungus, distributed
Anacortes is a city in Skagit County, United States. The name "Anacortes" is an adaptation of the name of Anne Curtis Bowman, the wife of early Fidalgo Island settler Amos Bowman. Anacortes' population was 15,778 at the time of the 2010 census, it is one of two principal cities of and included in the Mount Vernon-Anacortes Metropolitan Statistical Area. Anacortes is known for the Washington State Ferries dock and terminal serving Lopez Island, Shaw Island, Orcas Island, San Juan Island, as well as Victoria, British Columbia on Vancouver Island. There is a Skagit County-operated ferry that serves Guemes Island, a residential island located across Guemes Channel, north of Anacortes. Anacortes was incorporated on May 19, 1891. In 1877, railroad surveyor and town founder Amos Bowman moved his family to the northern tip of Fidalgo Island. Bowman began promoting the area as an obvious terminus for the Northern Pacific Railway as it was built through the north Cascades to the Pacific. Bowman established the town's first newspaper, The Northwest Enterprise, to promote his vision of the New York of the West.
Seattle and Northern Company began building a rail line from the town in 1888. Real estate and development boomed from 1888 to 1890 as a result of the railroad rumors, the Oregon Improvement Company posted $15 million in bonds to develop the town. In 1891, the real estate bubble burst. Speculators lost money and the Oregon Improvement Company could no longer afford to complete tracks over the Cascades; the town failed to become. After the bust, the town became prominent for its fishing tradition, thriving canning industry, timber mills. Anacortes is on Fidalgo Island. According to the United States Census Bureau, the city has a total area of 15.53 square miles, of which 11.75 square miles is land and 3.78 square miles is water. According to the Köppen climate classification system, Anacortes has a warm-summer Mediterranean climate; as of the census of 2010, there were 15,778 people, 6,980 households, 4,461 families residing in the city. The population density was 1,342.8 inhabitants per square mile.
There were 7,680 housing units at an average density of 653.6 per square mile. The racial makeup of the city was 91.5% White, 0.7% African American, 1.0% Native American, 1.9% Asian, 0.1% Pacific Islander, 1.6% from other races, 3.3% from two or more races. Hispanic or Latino of any race were 5.0% of the population. There were 6,980 households of which 24.3% had children under the age of 18 living with them, 51.5% were married couples living together, 9.0% had a female householder with no husband present, 3.5% had a male householder with no wife present, 36.1% were non-families. 29.5% of all households were made up of individuals and 14.3% had someone living alone, 65 years of age or older. The average household size was 2.25 and the average family size was 2.75. The median age in the city was 47.2 years. 19.6% of residents were under the age of 18. The gender makeup of the city was 47.9% male and 52.1% female. Anacortes is on Fidalgo Island. Rosario Strait and the San Juan Islands are to the West while to the South, Deception Pass separates Fidalgo and Whidbey Islands.
To the East, the Swinomish Channel separates Fidalgo Island from the mainland. The weather is milder than other areas of the Pacific Northwest, because it lies within the Olympic Mountain rain shadow. Fidalgo Island gets 21 inches of rain per year, only half as much as Seattle. First known as Ship Harbor, Anacortes was established with a name and a post office in 1879 in the vain hope that it would be selected as the western terminus of the transcontinental railroad; the town was incorporated in 1891 shortly after the railroad bust, became a lumber and fishing center. In the 1950s oil companies built big refineries near Anacortes. Two of the five refineries operating in Washington are located near the town. One is owned and operated by Marathon Petroleum, the Marathon Anacortes Refinery, the other is owned and operated by Shell Puget Sound Refinery Company. Refining remains the area's largest industry, but the economic base now includes yacht construction/shipbuilding and residential services for the nearby Whidbey Island Naval Air Station.
Anacortes is governed via the mayor-council system. The mayor is elected directly; the city council consists of seven members. The remaining four are elected at-large. Anacortes is a popular destination for those traveling on to the San Juan Islands; the city maintains a 220-acre city park on the northwestern end of Fidalgo Island named "Washington Park". This park features camping, boat launching, majestic views of the San Juan Islands; the most prominent view is of Cypress Island. As a result of Anacortes' proximity to the Strait of Juan de Fuca, the area provides opportunities for whale-watching; the waters off of Anacortes and Fidalgo Island offer numerous varieties of marine-life, including three resident Orca pods. Anacortes Community Forest Lands, 2,800 acres with 50 miles of mountain biking and hiking trails, are a rare amenity in a city the size of Anacortes. In adjacent Mount Erie Park, a number of rock climbing routes are popular on the cliffs of the south and west faces of Mount Erie.
Mount Erie offers scenic vistas from its 1273-foot peak. Anacortes hosts many long-distance cyclists, as it is t
Little Cranberry Lake, Washington
Little Cranberry Lake is located within Anacortes Community Forest Lands on Fidalgo Island in the northwestern corner of the U. S. state of Washington. The lake is deepened by a dam on the northern end, constructed in the 1930s; the previous dam had broken in 1921 releasing a large amount of water which crashed down the hills to the beach. The lake basin is part of a 10-mile long, north-south wilderness corridor that follows an ancient moraine, which snakes its way down the middle of the island; this moraine is a major source of gravel for the region which adjoins Washington. The trails in this corridor are of variable quality. All are ideal for mountain biking, in particular. Little Cranberry Lake is a popular swimming location for visitors to the annual summer music celebration, What the Heck Fest. Wildlife is diverse. Coyotes, beaver, pelicans, bald eagles, Canada geese and many different varieties of reptiles and insects are plentiful in the Little Cranberry basin. Hunting is not allowed. To the south of the lake are swamplands whose size and depth has been increasing since 1985, when the beavers moved in.
Several varieties of orchids exist in this area. The area around the lake was clearcut between 1890 and 1920 but some of the basin's less accessible trees, such as those on the southern end of the lake, are old growth; until the 1950s locals say, morel mushrooms were plentiful. As of 2005, morels are impossible to find
Arbutus menziesii, the Pacific madrone or madrona, is a species of tree in the family Ericaceae, native to the western coastal areas of North America, from British Columbia to California. It is known as the madroa, madroño, madroña, or bearberry; the name "strawberry tree" may be found in relation to A. menziesii. According to the Sunset Western Garden Book, in the United States, the name "madrone" is more common south of the Siskiyou Mountains of southern Oregon and Northern California and the name "madrona" is more common north of the Siskiyous; the Concow tribe calls the tree dis-tā' - kou-wät ′ - chu. In British Columbia it is referred to as arbutus, its species name was given it in honour of the Scottish naturalist Archibald Menzies, who noted it during George Vancouver's voyage of exploration. Arbutus menziesii is an evergreen tree with rich orange-red bark that when mature peels away in thin sheets, leaving a greenish, silvery appearance that has a satin sheen and smoothness. In spring, it bears sprays of small bell-like flowers, in autumn, red berries.
The berries have hooked barbs that latch onto larger animals for migration. It is common to see madronas of about 10 to 25 metres in height, but with the right conditions trees may reach up to 30 metres. In ideal conditions madronas can reach a thickness of 5 to 8 feet at the trunk, much like an oak tree. Leaves are thick with a waxy texture, oval, 7 to 15 centimetres long and 4 to 8 centimetres broad, arranged spirally; the leaves are evergreen, lasting a few years before detaching, but in the north of its range, wet winters promote a brown to black leaf discoloration due to fungal infections. The stain lasts until the leaves detach at the end of their lifespan. Madrones are native to the western coast of North America, from British Columbia to California, they are found in Puget Sound, the Oregon Coast Range, California Coast Ranges. They are rare south of Santa Barbara County, with isolated stands south to Palomar Mountain in California. One author lists their southern range as extending as far as Baja California in Mexico, but others point out that there are no recorded specimens collected that far south, the trees are absent from modern surveys of native trees there.
However other Arbutus species are endemic to the area. The trees are difficult to transplant and a seedling should be set in its permanent spot while still small. Transplant mortality becomes significant; the site should be sunny, well drained, lime-free. In its native range, a tree needs no food once it has become established. Water and nitrogen fertilizer will boost its growth, but at the cost of making it more susceptible to disease; this plant has gained the Royal Horticultural Society's Award of Garden Merit. Native Americans ate the berries, but because the berries have a high tannin content and are thus astringent, they more chewed them or made them into a cider, they used the berries to make necklaces and other decorations, as bait for fishing. Bark and leaves were used to treat stomach aches, skin ailments, sore throats; the bark was made into a tea to be drunk for these medicinal purposes. Many mammal and bird species feed off the berries, including American robins, cedar waxwings, band-tailed pigeons, varied thrushes, mule deer, ring-tailed cats, bears.
Mule deer will eat the young shoots when the trees are regenerating after fire. It is important as a nest site for many birds, in mixed woodland it seems to be chosen for nestbuilding disproportionately to its numbers; the wood is durable and has a warm color after finishing, so it has become more popular as a flooring material in the Pacific Northwest. An attractive veneer can be made from the wood. However, because large pieces of madrona lumber warp and unpredictably during the drying process, they are not used much. Madrone is burned for firewood, since it is a hard and dense wood that burns long and hot, surpassing oak in this regard. Although drought tolerant and fast growing, Arbutus menziesii is declining throughout most of its range. One cause is fire control. Mature trees survive fire, can regenerate more after fire than the Douglas firs with which they are associated, they produce large numbers of seeds, which sprout following fire. Increasing development pressures in its native habitat have contributed to a decline in the number of mature specimens.
This tree is sensitive to alteration of the grade or drainage near the root crown. Until about 1970, this phenomenon was not recognized on the west coast; the species is affected to a small extent by sudden oak death, a disease caused by the water-mold Phytophthora ramorum. During the Soberanes Fire in the summer of 2016, the largest known specimen of madrone was burned and killed; the tree, 125 feet tall and more th
Geographic coordinate system
A geographic coordinate system is a coordinate system that enables every location on Earth to be specified by a set of numbers, letters or symbols. The coordinates are chosen such that one of the numbers represents a vertical position and two or three of the numbers represent a horizontal position. A common choice of coordinates is latitude and elevation. To specify a location on a plane requires a map projection; the invention of a geographic coordinate system is credited to Eratosthenes of Cyrene, who composed his now-lost Geography at the Library of Alexandria in the 3rd century BC. A century Hipparchus of Nicaea improved on this system by determining latitude from stellar measurements rather than solar altitude and determining longitude by timings of lunar eclipses, rather than dead reckoning. In the 1st or 2nd century, Marinus of Tyre compiled an extensive gazetteer and mathematically-plotted world map using coordinates measured east from a prime meridian at the westernmost known land, designated the Fortunate Isles, off the coast of western Africa around the Canary or Cape Verde Islands, measured north or south of the island of Rhodes off Asia Minor.
Ptolemy credited him with the full adoption of longitude and latitude, rather than measuring latitude in terms of the length of the midsummer day. Ptolemy's 2nd-century Geography used the same prime meridian but measured latitude from the Equator instead. After their work was translated into Arabic in the 9th century, Al-Khwārizmī's Book of the Description of the Earth corrected Marinus' and Ptolemy's errors regarding the length of the Mediterranean Sea, causing medieval Arabic cartography to use a prime meridian around 10° east of Ptolemy's line. Mathematical cartography resumed in Europe following Maximus Planudes' recovery of Ptolemy's text a little before 1300. In 1884, the United States hosted the International Meridian Conference, attended by representatives from twenty-five nations. Twenty-two of them agreed to adopt the longitude of the Royal Observatory in Greenwich, England as the zero-reference line; the Dominican Republic voted against the motion, while Brazil abstained. France adopted Greenwich Mean Time in place of local determinations by the Paris Observatory in 1911.
In order to be unambiguous about the direction of "vertical" and the "horizontal" surface above which they are measuring, map-makers choose a reference ellipsoid with a given origin and orientation that best fits their need for the area they are mapping. They choose the most appropriate mapping of the spherical coordinate system onto that ellipsoid, called a terrestrial reference system or geodetic datum. Datums may be global, meaning that they represent the whole Earth, or they may be local, meaning that they represent an ellipsoid best-fit to only a portion of the Earth. Points on the Earth's surface move relative to each other due to continental plate motion and diurnal Earth tidal movement caused by the Moon and the Sun; this daily movement can be as much as a metre. Continental movement can be up to 10 m in a century. A weather system high-pressure area can cause a sinking of 5 mm. Scandinavia is rising by 1 cm a year as a result of the melting of the ice sheets of the last ice age, but neighbouring Scotland is rising by only 0.2 cm.
These changes are insignificant if a local datum is used, but are statistically significant if a global datum is used. Examples of global datums include World Geodetic System, the default datum used for the Global Positioning System, the International Terrestrial Reference Frame, used for estimating continental drift and crustal deformation; the distance to Earth's center can be used both for deep positions and for positions in space. Local datums chosen by a national cartographical organisation include the North American Datum, the European ED50, the British OSGB36. Given a location, the datum provides the latitude ϕ and longitude λ. In the United Kingdom there are three common latitude and height systems in use. WGS 84 differs at Greenwich from the one used on published maps OSGB36 by 112 m; the military system ED50, used by NATO, differs from about 120 m to 180 m. The latitude and longitude on a map made against a local datum may not be the same as one obtained from a GPS receiver. Coordinates from the mapping system can sometimes be changed into another datum using a simple translation.
For example, to convert from ETRF89 to the Irish Grid add 49 metres to the east, subtract 23.4 metres from the north. More one datum is changed into any other datum using a process called Helmert transformations; this involves converting the spherical coordinates into Cartesian coordinates and applying a seven parameter transformation, converting back. In popular GIS software, data projected in latitude/longitude is represented as a Geographic Coordinate System. For example, data in latitude/longitude if the datum is the North American Datum of 1983 is denoted by'GCS North American 1983'; the "latitude" of a point on Earth's surface is the angle between the equatorial plane and the straight line that passes through that point and through the center of the Earth. Lines joining points of the same latitude trace circles on the surface of Earth called parallels, as they are parallel to the Equator and to each other; the North Pole is 90° N. The 0° parallel of latitude is designated the Equator, the fun
The United States of America known as the United States or America, is a country composed of 50 states, a federal district, five major self-governing territories, various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U. S. is the third most populous country. The capital is Washington, D. C. and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico; the State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean; the U. S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The diverse geography and wildlife of the United States make it one of the world's 17 megadiverse countries.
Paleo-Indians migrated from Siberia to the North American mainland at least 12,000 years ago. European colonization began in the 16th century; the United States emerged from the thirteen British colonies established along the East Coast. Numerous disputes between Great Britain and the colonies following the French and Indian War led to the American Revolution, which began in 1775, the subsequent Declaration of Independence in 1776; the war ended in 1783 with the United States becoming the first country to gain independence from a European power. The current constitution was adopted in 1788, with the first ten amendments, collectively named the Bill of Rights, being ratified in 1791 to guarantee many fundamental civil liberties; the United States embarked on a vigorous expansion across North America throughout the 19th century, acquiring new territories, displacing Native American tribes, admitting new states until it spanned the continent by 1848. During the second half of the 19th century, the Civil War led to the abolition of slavery.
By the end of the century, the United States had extended into the Pacific Ocean, its economy, driven in large part by the Industrial Revolution, began to soar. The Spanish–American War and World War I confirmed the country's status as a global military power; the United States emerged from World War II as a global superpower, the first country to develop nuclear weapons, the only country to use them in warfare, a permanent member of the United Nations Security Council. Sweeping civil rights legislation, notably the Civil Rights Act of 1964, the Voting Rights Act of 1965 and the Fair Housing Act of 1968, outlawed discrimination based on race or color. During the Cold War, the United States and the Soviet Union competed in the Space Race, culminating with the 1969 U. S. Moon landing; the end of the Cold War and the collapse of the Soviet Union in 1991 left the United States as the world's sole superpower. The United States is the world's oldest surviving federation, it is a representative democracy.
The United States is a founding member of the United Nations, World Bank, International Monetary Fund, Organization of American States, other international organizations. The United States is a developed country, with the world's largest economy by nominal GDP and second-largest economy by PPP, accounting for a quarter of global GDP; the U. S. economy is post-industrial, characterized by the dominance of services and knowledge-based activities, although the manufacturing sector remains the second-largest in the world. The United States is the world's largest importer and the second largest exporter of goods, by value. Although its population is only 4.3% of the world total, the U. S. holds 31% of the total wealth in the world, the largest share of global wealth concentrated in a single country. Despite wide income and wealth disparities, the United States continues to rank high in measures of socioeconomic performance, including average wage, human development, per capita GDP, worker productivity.
The United States is the foremost military power in the world, making up a third of global military spending, is a leading political and scientific force internationally. In 1507, the German cartographer Martin Waldseemüller produced a world map on which he named the lands of the Western Hemisphere America in honor of the Italian explorer and cartographer Amerigo Vespucci; the first documentary evidence of the phrase "United States of America" is from a letter dated January 2, 1776, written by Stephen Moylan, Esq. to George Washington's aide-de-camp and Muster-Master General of the Continental Army, Lt. Col. Joseph Reed. Moylan expressed his wish to go "with full and ample powers from the United States of America to Spain" to seek assistance in the revolutionary war effort; the first known publication of the phrase "United States of America" was in an anonymous essay in The Virginia Gazette newspaper in Williamsburg, Virginia, on April 6, 1776. The second draft of the Articles of Confederation, prepared by John Dickinson and completed by June 17, 1776, at the latest, declared "The name of this Confederation shall be the'United States of America'".
The final version of the Articles sent to the states for ratification in late 1777 contains the sentence "The Stile of this Confederacy shall be'The United States of America'". In June 1776, Thomas Jefferson wrote the phrase "UNITED STATES OF AMERICA" in all capitalized letters in the headline of his "original Rough draught" of the Declaration of Independence; this draft of the document did not surface unti
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