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95-465: The forest was named in honor of General John Forbes . It includes 20 separate tracts of land and covers over 50,000 acres (20,230 ha) that stretch across Fayette , Somerset , and Westmoreland Counties. The designated forest tracts generally follow one of the area's dominant terrain features, Laurel Ridge, part of the Laurel Highlands . Forbes State Forest was formed as a direct result of

190-558: A Latinate word denoting a woodland, may be admitted; in a specific technical sense it is restricted to denoting the species of trees that comprise the woodlands of a region, as in its sense in the subject of silviculture . The resorting to sylva in English indicates more precisely the denotation that the use of forest intends. The first known forests on Earth arose in the Middle Devonian (approximately 390 million years ago ), with

285-469: A 0.075 mm (No. 200) sieve or 3 percent or more pass through a 0.02 mm (No. 635) sieve. Chamberlain reported other, more direct methods for measuring frost susceptibility. Based on such research, standard tests exist to determine the relative frost and thaw weakening susceptibility of soils used in pavement systems by comparing the heave rate and thawed bearing ratio with values in an established classification system for soils where frost-susceptibility

380-464: A combination of measures aimed at increasing forest carbon stocks, andsustainable timber offtake will generate the largest carbon sequestration benefit. The term forest-dependent people is used to describe any of a wide variety of livelihoods that are dependent on access to forests, products harvested from forests, or ecosystem services provided by forests, including those of Indigenous peoples dependent on forests. In India , approximately 22 percent of

475-405: A different classification of forest vegetation is often used: tree, shrub, herb, and moss layers (see stratification (vegetation) ). Forests are classified differently and to different degrees of specificity. One such classification is in terms of the biomes in which they exist, combined with leaf longevity of the dominant species (whether they are evergreen or deciduous ). Another distinction

570-437: A few main pathways, including increase in commercial tree plantations, adoption of agroforestry techniques by small farmers, or spontaneous regeneration when former agricultural land is abandoned. It can be motivated by the economic benefits of forests, the ecosystem services forests provide, or cultural changes where people increasingly appreciate forests for their spiritual, aesthetic, or otherwise intrinsic value. According to

665-409: A forest may be of a great variety of species (as in tropical rainforests and temperate deciduous forests ), or relatively few species over large areas (e.g., taiga and arid montane coniferous forests). The biodiversity of forests also encompasses shrubs , herbaceous plants, mosses , ferns , lichens , fungi , and a variety of animals . Trees rising up to 35 meters (115 ft) in height add

760-542: A forested area by cutting or burning, either to harvest timber or to make way for farming. Most deforestation today occurs in tropical forests. The vast majority of this deforestation is because of the production of four commodities: wood , beef , soy , and palm oil . Over the past 2,000 years, the area of land covered by forest in Europe has been reduced from 80% to 34%. Large areas of forest have also been cleared in China and in

855-495: A groundwater source that is lower in the soil and below the freezing line in the soil. The presence of frost-susceptible soil with a pore structure that allows capillary flow is essential to supplying water to the ice lenses as they form. Owing to the Gibbs–Thomson effect of the confinement of liquids in pores, water in soil can remain liquid at a temperature that is below the bulk freezing point of water. Very fine pores have

950-448: A legal term, as seen in Latin texts such as Magna Carta , to denote uncultivated land that was legally designated for hunting by feudal nobility (see royal forest ). These hunting forests did not necessarily contain any trees. Because that often included significant areas of woodland, "forest" eventually came to connote woodland in general, regardless of tree density. By the beginning of

1045-403: A locale with more open space between trees, and distinguish kinds of woodlands as open forests and closed forests , premised on their crown covers . Finally, sylva (plural sylvae or, less classically, sylvas ) is a peculiar English spelling of the Latin silva , denoting a "woodland", and has precedent in English, including its plural forms. While its use as a synonym of forest , and as

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1140-476: A number of important natural features and points of interest: Roaring Run Natural Area , at 3,070 acres (1,242 ha), was acquired by the State of Pennsylvania in 1975. After previous development and logging, this portion of the west slope of Laurel Ridge is currently undergoing reforestation . It is compromised largely of second and third growth mixed mesophytic forest. Roaring Run feeds into Indian Creek , which

1235-579: A region, releasing water from their leaves in anticipation of seasonal rains to trigger the wet season early. Because of this, seasonal rainfall in the Amazon begins two to three months earlier than the climate would otherwise allow. Deforestation in the Amazon and anthropogenic climate change hold the potential to interfere with this process, causing the forest to pass a threshold where it transitions into savanna. Deforestation threatens many forest ecosystems. Deforestation occurs when humans remove trees from

1330-713: A thermal gradient of as low as 1 °C m . As ice lenses grow, they lift the soil above, and segregate soil particles below, while drawing water to the freezing face of the ice lens via capillary action. Frost heaving requires a frost-susceptible soil, a continual supply of water below (a water table ) and freezing temperatures, penetrating into the soil. Frost-susceptible soils are those with pore sizes between particles and particle surface area that promote capillary flow . Silty and loamy soil types , which contain fine particles, are examples of frost-susceptible soils. Many agencies classify materials as being frost susceptible if 10 percent or more constituent particles pass through

1425-722: A vertical dimension to the area of land that can support plant and animal species, opening up numerous ecological niches for arboreal animal species, epiphytes , and various species that thrive under the regulated microclimate created under the canopy. Forests have intricate three-dimensional structures that increase in complexity with lower levels of disturbance and greater variety of tree species. The biodiversity of forests varies considerably according to factors such as forest type, geography, climate, and soils – in addition to human use. Most forest habitats in temperate regions support relatively few animal and plant species, and species that tend to have large geographical distributions, while

1520-413: A very high curvature , and this results in the liquid phase being thermodynamically stable in such media at temperatures sometimes several tens of degrees below the bulk freezing point of the liquid. This effect allows water to percolate through the soil towards the ice lens, allowing the lens to grow. Another water-transport effect is the preservation of a few molecular layers of liquid water on

1615-412: A wide range of characteristics. Generally, richer households derive more cash value from forest resources, whereas among poorer households, forest resources are more important for home consumption and increase community resilience. Forests are fundamental to the culture and livelihood of indigenous people groups that live in and depend on forests, many of which have been removed from and denied access to

1710-774: Is a tributary of the Youghiogheny River . The state forest also includes Quebec Run Wild Area . Mount Davis is the highest point in Pennsylvania and is found within the state forest. The high point is protected within Mount Davis Natural Area . The area eventually drains into the Casselman River , a part of the Mississippi River watershed (via the Youghiogheny , Monongahela , and Ohio Rivers). One of

1805-491: Is a continuous replenishment of water flowing from the warm side to the cold side of the particle, and continuous melting to re-establish the thicker film on the warm side. The particle migrates downwards toward the warmer soil in a process that Faraday called "thermal regelation." This effect purifies the ice lenses as they form by repelling fine soil particles. Thus a 10- nanometer film of unfrozen water around each micrometer -sized soil particle can move it 10 micrometers/day in

1900-401: Is based on tree densities measured on over 400,000 plots. It remains subject to a wide margin of error, not least because the samples are mainly from Europe and North America. Forests can also be classified according to the amount of human alteration. Old-growth forest contains mainly natural patterns of biodiversity in established seral patterns, and they contain mainly species native to

1995-630: Is high compared to other vegetation communities. Much of this biomass occurs below ground in the root systems and as partially decomposed plant detritus . The woody component of a forest contains lignin , which is relatively slow to decompose compared with other organic materials such as cellulose or carbohydrate. The world's forests contain about 606 gigatonnes of living biomass (above- and below-ground) and 59 gigatonnes of dead wood. The total biomass has decreased slightly since 1990, but biomass per unit area has increased. Forest ecosystems broadly differ based on climate ; latitudes 10° north and south of

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2090-460: Is legally protected from resource development. Much more forest land—about 40 percent of the total forest land base—is subject to varying degrees of protection through processes such as integrated land use planning or defined management areas, such as certified forests. Frost heaving Frost heaving (or a frost heave ) is an upwards swelling of soil during freezing conditions caused by an increasing presence of ice as it grows towards

2185-531: Is not on track to meet the target of the United Nations Strategic Plan for Forests to increase forest area by 3 percent by 2030. While deforestation is taking place in some areas, new forests are being established through natural expansion or deliberate efforts in other areas. As a result, the net loss of forest area is less than the rate of deforestation; and it, too, is decreasing: from 7.8 million hectares (19 million acres) per year in

2280-579: Is now designated as part of the Forbes State Forest had previously been either developed or commercially exploited through logging through the early-to-mid-20th century. These areas have been allowed, and sometimes encouraged, to return to their natural state. The U.S. states of Maryland and West Virginia are to the south and west, respectively Forbes State Forest lies within the Appalachian mixed mesophytic forests ecoregion . It also includes

2375-423: Is predominantly under agricultural or urban use." Using this definition, Global Forest Resources Assessment 2020 found that forests covered 4.06 billion hectares (10.0 billion acres; 40.6 million square kilometres; 15.7 million square miles), or approximately 31 percent of the world's land area in 2020. Forests are the largest terrestrial ecosystems of Earth by area, and are found around

2470-428: Is that forests can turn from a carbon sink to a carbon source if plant diversity, density or forest area decreases, as has been observed in different tropical forests The typical tropical forest may become a carbon source by the 2060s. An assessment of European forests found early signs of carbon sink saturation, after decades of increasing strength. The Intergovernmental Panel on Climate Change (IPCC) concluded that

2565-690: Is uncertain. Non-frost-susceptible soils may be too dense to promote water flow (low hydraulic conductivity) or too open in porosity to promote capillary flow. Examples include dense clays with a small pore size and therefore a low hydraulic conductivity and clean sands and gravels , which contain small amounts of fine particles and whose pore sizes are too open to promote capillary flow. Frost heaving creates raised-soil landforms in various geometries, including circles, polygons and stripes, which may be described as palsas in soils that are rich in organic matter, such as peat, or lithalsa in more mineral-rich soils. The stony lithalsa (heaved mounds) found on

2660-416: Is whether the forests are composed predominantly of broadleaf trees, coniferous (needle-leaved) trees, or mixed. The number of trees in the world, according to a 2015 estimate, is 3 trillion, of which 1.4 trillion are in the tropics or sub-tropics, 0.6 trillion in the temperate zones, and 0.7 trillion in the coniferous boreal forests. The 2015 estimate is about eight times higher than previous estimates, and

2755-593: The Equator , and temperate forests at the middle latitudes . Forests form in areas of the Earth with high rainfall, while drier conditions produce a transition to savanna . However, in areas with intermediate rainfall levels, forest transitions to savanna rapidly when the percentage of land that is covered by trees drops below 40 to 45 percent. Research conducted in the Amazon rainforest shows that trees can alter rainfall rates across

2850-703: The Mars Global Surveyor and the HiRISE camera on the Mars Reconnaissance Orbiter . In May 2008 the Mars Phoenix lander touched down on such a polygonal frost-heave landscape and quickly discovered ice a few centimetres below the surface. Cold-storage buildings and ice rinks that are maintained at sub-freezing temperatures may freeze the soil below their foundations to a depth of tens of meters. Seasonally frozen buildings, e.g. some ice rinks, may allow

2945-630: The Medieval Latin foresta , denoting "open wood", Carolingian scribes first used foresta in the capitularies of Charlemagne , specifically to denote the royal hunting grounds of the king. The word was not endemic to the Romance languages , e.g., native words for forest in the Romance languages derived from the Latin silva , which denoted "forest" and " wood(land) " ( cf. the English sylva and sylvan ;

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3040-488: The Pittsburgh, Westmoreland and Somerset Railroad ignited wildfires that prevented the formation of second growth forests . The conservationists feared that the forest would never regrow if there was not a change in the philosophy of forest management. They called for the state to purchase land from the lumber and iron companies and the lumber and iron companies were more than willing to sell their land since that had depleted

3135-571: The Proto-Germanic * furhísa- , * furhíþija- , denoting "a fir-wood , coniferous forest", from the Proto-Indo-European * perk u- , denoting "a coniferous or mountain forest , wooded height" all attest to the Frankish * forhist . Uses of forest in English to denote any uninhabited and unenclosed area are presently considered archaic. The Norman rulers of England introduced the word as

3230-537: The Special Report on Global Warming of 1.5 °C of the Intergovernmental Panel on Climate Change , to avoid temperature rise by more than 1.5 degrees above pre-industrial levels, there will need to be an increase in global forest cover equal to the land area of Canada (10 million square kilometres (3.9 million square miles)) by 2050. China instituted a ban on logging, beginning in 1998, due to

3325-581: The World Resources Institute recorded that only 20% of the world's original forests remained in large intact tracts of undisturbed forest. More than 75% of these intact forests lie in three countries: the boreal forests of Russia and Canada, and the rainforest of Brazil. According to Food and Agriculture Organization 's (FAO) Global Forest Resources Assessment 2020 , an estimated 420 million hectares (1.0 billion acres) of forest have been lost worldwide through deforestation since 1990, but

3420-418: The boreal region and in the seasonally dry tropics. At high latitudes, north of the main zone of boreal forestland, growing conditions are not adequate to maintain a continuously closed forest cover , so tree cover is both sparse and discontinuous. This vegetation is variously called open taiga , open lichen woodland, and forest tundra. A savanna is a mixed woodland – grassland ecosystem characterized by

3515-407: The equator are mostly covered in tropical rainforest , and the latitudes between 53°N and 67°N have boreal forest . As a general rule, forests dominated by angiosperms ( broadleaf forests ) are more species-rich than those dominated by gymnosperms ( conifer , montane , or needleleaf forests ), although exceptions exist. The trees that form the principal structural and defining component of

3610-408: The slash and burn practices of swidden agriculture or shifting cultivation . The loss and re-growth of forests lead to a distinction between two broad types of forest: primary or old-growth forest and secondary forest . There are also many natural factors that can cause changes in forests over time, including forest fires , insects , diseases , weather, competition between species, etc. In 1997,

3705-429: The 1990s to 4.7 million hectares (12 million acres) per year during 2010–2020. In absolute terms, the global forest area decreased by 178 million hectares (440 million acres; 1,780,000 square kilometres; 690,000 square miles) between 1990 and 2020, which is an area about the size of Libya. Forests provide a diversity of ecosystem services including: The main ecosystem services can be summarized in

3800-514: The 1990s. In 2015, a study for Nature Climate Change showed that the trend has recently been reversed, leading to an "overall gain" in global biomass and forests. This gain is due especially to reforestation in China and Russia. New forests are not equivalent to old growth forests in terms of species diversity, resilience, and carbon capture. On 7 September 2015, the FAO released a new study stating that over

3895-699: The Italian, Spanish, and Portuguese selva ; the Romanian silvă ; the Old French selve ). Cognates of forest in Romance languages—e.g., the Italian foresta , Spanish and Portuguese floresta , etc.—are all ultimately derivations of the French word. The precise origin of Medieval Latin foresta is obscure. Some authorities claim the word derives from the Late Latin phrase forestam silvam , denoting "the outer wood"; others claim

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3990-452: The U.S. state of Wisconsin , forests managed by indigenous people have more plant diversity, fewer invasive species, higher tree regeneration rates, and higher volume of trees. Forest management has changed considerably over the last few centuries, with rapid changes from the 1980s onward, culminating in a practice now referred to as sustainable forest management . Forest ecologists concentrate on forest patterns and processes, usually with

4085-460: The aim of elucidating cause-and-effect relationships. Foresters who practice sustainable forest management focus on the integration of ecological, social, and economic values, often in consultation with local communities and other stakeholders . Humans have generally decreased the amount of forest worldwide. Anthropogenic factors that can affect forests include logging, urban sprawl , human-caused forest fires , acid rain , invasive species , and

4180-399: The archipelago of Svalbard are an example. Frost heaves occur in alpine regions, even near the equator , as illustrated by palsas on Mount Kenya . In Arctic permafrost regions, a related type of ground heaving over hundreds of years can create structures, as high as 60 metres, known as pingos , which are fed by an upwelling of ground water, instead of the capillary action that feeds

4275-482: The base. Spruce Flats Wildlife Management Area covers 305 acres (123 ha), with a focal point on the 28 acres (11 ha) of the Spruce Flats Bog which formed in a natural depression atop Laurel Ridge. The area had previously passed through the successional sequence from open water to (eventually) forest. This process was actually reversed in the early part of the 20th century by a combination of clear-cutting

4370-420: The basis of the variation of physiognomy corresponding to changes in altitude. Tropical dry forests are characteristic of areas in the tropics affected by seasonal drought. The seasonality of rainfall is usually reflected in the deciduousness of the forest canopy, with most trees being leafless for several months of the year. Under some conditions, such as less fertile soils or less predictable drought regimes,

4465-575: The canopy; but other taxa are also important. In the Southern Hemisphere , most coniferous trees (members of Araucariaceae and Podocarpaceae ) occur mixed with broadleaf species, and are classed as broadleaf-and-mixed forests. Temperate broadleaf and mixed forests include a substantial component of trees of the Anthophyta group. They are generally characteristic of the warmer temperate latitudes, but extend to cool temperate ones, particularly in

4560-423: The children live. Canada has about 4 million square kilometres (1.5 million square miles) of forest land. More than 90% of forest land is publicly owned and about 50% of the total forest area is allocated for harvesting. These allocated areas are managed using the principles of sustainable forest management, which include extensive consultation with local stakeholders. About eight percent of Canada's forest

4655-517: The cutoff points are between a forest, woodland , and savanna . Under some definitions, to be considered a forest requires very high levels of tree canopy cover, from 60% to 100%, which excludes woodlands and savannas, which have a lower canopy cover . Other definitions consider savannas to be a type of forest, and include all areas with tree canopies over 10%. Some areas covered with trees are legally defined as agricultural areas, for example Norway spruce plantations, under Austrian forest law, when

4750-418: The density of trees, area of tree canopy cover, or area of the land occupied by the cross-section of tree trunks ( basal area ) meeting a particular threshold. This type of definition depends upon the presence of trees sufficient to meet the threshold, or at least of immature trees that are expected to meet the threshold once they mature. Under land-cover definitions, there is considerable variation on where

4845-451: The depletion of the forests of Pennsylvania that took place during the mid-to-late 19th century. Conservationists like Dr. Joseph Rothrock became concerned that the forests would not regrow if they were not managed properly. Lumber and iron companies had harvested the old-growth forests for various reasons. They clear cut the forests and left behind nothing but dried tree tops and rotting stumps. The sparks of passing steam locomotives of

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4940-416: The development of ice lenses inside columns of soil that were frozen by cooling the upper surface only, thereby establishing a temperature gradient . The dominant cause of soil displacement in frost heaving is the development of ice lenses . During frost heave, one or more soil-free ice lenses grow, and their growth displaces the soil above them. These lenses grow by the continual addition of water from

5035-411: The eastern United States , in which only 0.1% of land was left undisturbed. Almost half of Earth's forest area (49 percent) is relatively intact, while 9 percent is found in fragments with little or no connectivity. Tropical rainforests and boreal coniferous forests are the least fragmented, whereas subtropical dry forests and temperate oceanic forests are among the most fragmented. Roughly 80 percent of

5130-578: The erosion and flooding that it caused. In addition, ambitious tree-planting programmes in countries such as China, India, the United States, and Vietnam – combined with natural expansion of forests in some regions – have added more than 7 million hectares (17 million acres) of new forests annually. As a result, the net loss of forest area was reduced to 5.2 million hectares (13 million acres) per year between 2000 and 2010, down from 8.3 million hectares (21 million acres) annually in

5225-458: The evolution of cladoxylopsid plants like Calamophyton . Appeared in the Late Devonian , Archaeopteris was both tree-like and fern -like plant, growing to 20 metres (66 ft) in height or more. It quickly spread throughout the world, from the equator to subpolar latitudes. It is the first species known to cast shade due to its fronds and forming soil from its roots. Archaeopteris

5320-417: The forest ecosystem. Since 2002, the amount of land that is legally owned by or designated for indigenous peoples has broadly increased, but land acquisition in lower-income countries by multinational corporations, often with little or no consultation of indigenous peoples, has also increased. Research in the Amazon rainforest suggests that indigenous methods of agroforestry form reservoirs of biodiversity. In

5415-467: The forest, and fires which burned away much of the forest floor. This resulted in a return to the swamp or bog stage of development, and the area is now slowly proceeding back into the forest stage. The bog currently hosts a large community of cranberry , pitcher plant , sundew , and cotton grass . Forest A forest is an ecosystem characterized by a dense community of trees . Hundreds of definitions of forest are used throughout

5510-415: The fourteenth century, English texts used the word in all three of its senses: common, legal, and archaic. Other English words used to denote "an area with a high density of trees" are firth , frith , holt , weald , wold , wood , and woodland . Unlike forest , these are all derived from Old English and were not borrowed from another language. Some present classifications reserve woodland for denoting

5605-756: The globe. 45 percent of forest land is in the tropical latitudes . The next largest share of forests are found in subarctic climates , followed by temperate , and subtropical zones. Forests account for 75% of the gross primary production of the Earth's biosphere , and contain 80% of the Earth's plant biomass . Net primary production is estimated at 21.9 gigatonnes of biomass per year for tropical forests , 8.1 for temperate forests , and 2.6 for boreal forests . Forests form distinctly different biomes at different latitudes and elevations, and with different precipitation and evapotranspiration rates. These biomes include boreal forests in subarctic climates, tropical moist forests and tropical dry forests around

5700-659: The growth of frost heaves. Cryogenic earth hummocks are a small formation resulting from granular convection that appear in seasonally frozen ground and have many different names; in North America they are earth hummocks; thúfur in Greenland and Iceland ; and pounus in Fennoscandia . Polygonal forms apparently caused by frost heave have been observed in near-polar regions of Mars by the Mars Orbiter Camera (MOC) aboard

5795-524: The higher latitudes of the Northern Hemisphere , as well as some warm temperate areas, especially on nutrient-poor or otherwise unfavourable soils. These forests are composed entirely, or nearly so, of coniferous species ( Coniferophyta ). In the Northern Hemisphere, pines Pinus , spruces Picea , larches Larix , firs Abies , Douglas firs Pseudotsuga , and hemlocks Tsuga make up

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5890-469: The lands on which they lived as part of global colonialism . Indigenous lands contain 36% or more of intact forest worldwide, host more biodiversity, and experience less deforestation. Indigenous activists have argued that degradation of forests and indigenous peoples' marginalization and land dispossession are interconnected. Other concerns among indigenous peoples include lack of Indigenous involvement in forest management and loss of knowledge related for

5985-493: The last 25 years the global deforestation rate has decreased by 50% due to improved management of forests and greater government protection. There is an estimated 726 million hectares (1.79 billion acres) of forest in protected areas worldwide. Of the six major world regions, South America has the highest share of forests in protected areas, at 31 percent. The area of such areas globally has increased by 191 million hectares (470 million acres) since 1990, but

6080-575: The migration of water within the soil. Since the molar volume of water expands by about 9% as it changes phase from water to ice at its bulk freezing point , 9% would be the maximum expansion possible owing to molar volume expansion, and even then only if the ice were rigidly constrained laterally in the soil so that the entire volume expansion had to occur vertically. Ice is unusual among compounds because it increases in molar volume from its liquid state, water . Most compounds decrease in volume when changing phase from liquid to solid. Taber showed that

6175-986: The montane forests of Africa, South America, Southeast Asia, and lowland forests of Australia, coastal Brazil, the Caribbean islands, Central America, and insular Southeast Asia have many species with small geographical distributions. Areas with dense human populations and intense agricultural land use, such as Europe, parts of Bangladesh, China, India, and North America, are less intact in terms of their biodiversity. Northern Africa, southern Australia, coastal Brazil, Madagascar, and South Africa are also identified as areas with striking losses in biodiversity intactness. A forest consists of many components that can be broadly divided into two categories: biotic (living) and abiotic (non-living). The living parts include trees , shrubs , vines , grasses and other herbaceous (non-woody) plants, mosses , algae , fungi , insects , mammals , birds , reptiles , amphibians , and microorganisms living on

6270-413: The natural attractions of the area is the presence of small concentric stone rings which result from frost heaving in small patches of earth which are softer than the ground surrounding them. Frost causing the patches to be pushed up higher than their surroundings is followed by the effects of natural erosion which results in stones sliding to the bottom of the protrusion and forming ring-like patterns at

6365-496: The natural resources of the forests. The changes began to take place in 1895 when Dr. Rothrock was appointed the first commissioner of the Pennsylvania Department of Forests and Waters, the forerunner of today's Pennsylvania Department of Conservation and Natural Resources . The Pennsylvania General Assembly passed a piece of legislation in 1897 that authorized the purchase of "unseated lands for forest reservations." This

6460-530: The next table: Some researchers state that forests do not only provide benefits, but can in certain cases also incur costs to humans. Forests may impose an economic burden, diminish the enjoyment of natural areas, reduce the food-producing capacity of grazing land and cultivated land, reduce biodiversity, reduce available water for humans and wildlife, harbour dangerous or destructive wildlife, and act as reservoirs of human and livestock disease. An important consideration regarding carbon sequestration

6555-411: The plants and animals and in the soil, connected by mycorrhizal networks . The main layers of all forest types are the forest floor , the understory, and the canopy. The emergent layer, above the canopy, exists in tropical rainforests. Each layer has a different set of plants and animals, depending upon the availability of sunlight, moisture, and food. In botany and countries like Germany and Poland,

6650-512: The population belongs to forest-dependent communities, which live in close proximity to forests and practice agroforestry as a principal part of their livelihood. People of Ghana who rely on timber and bushmeat harvested from forests and Indigenous peoples of the Amazon rainforest are also examples of forest-dependent people. Though forest-dependence by more common definitions is statistically associated with poverty and rural livelihoods, elements of forest-dependence exist in communities with

6745-615: The proportion of evergreen species increases and the forests are characterised as " sclerophyllous ". Thorn forest , a dense forest of low stature with a high frequency of thorny or spiny species, is found where drought is prolonged, and especially where grazing animals are plentiful. On very poor soils, and especially where fire or herbivory are recurrent phenomena, savannas develop. Sparse trees and savanna are forests with sparse tree- canopy cover. They occur principally in areas of transition from forested to non-forested landscapes. The two major zones in which these ecosystems occur are in

6840-428: The rate of forest loss has declined substantially. In the most recent five-year period (2015–2020), the annual rate of deforestation was estimated at 10 million hectares (25 million acres), down from 12 million hectares (30 million acres) annually in 2010–2015. The transition of a region from forest loss to net gain in forested land is referred to as the forest transition. This change occurs through

6935-465: The rate of annual increase slowed in 2010–2020. Smaller areas of woodland in cities may be managed as urban forestry , sometimes within public parks. These are often created for human benefits; Attention Restoration Theory argues that spending time in nature reduces stress and improves health, while forest schools and kindergartens help young people to develop social as well as scientific skills in forests. These typically need to be close to where

7030-460: The region and habitat. In contrast, secondary forest is forest regrowing following timber harvest and may contain species originally from other regions or habitats. Different global forest classification systems have been proposed, but none has gained universal acceptance. UNEP - WCMC 's forest category classification system is a simplification of other, more complex systems (e.g. UNESCO 's forest and woodland 'subformations'). This system divides

7125-425: The rising water at the freezing front. Differential frost heaving can crack road surfaces —contributing to springtime pothole formation—and damage building foundations . Frost heaves may occur in mechanically refrigerated cold-storage buildings and ice rinks . Needle ice is essentially frost heaving that occurs at the beginning of the freezing season, before the freezing front has penetrated very far into

7220-550: The soil and there is no soil overburden to lift as a frost heave. Urban Hjärne described frost effects in soil in 1694. By 1930, Stephen Taber, head of the Department of Geology at the University of South Carolina , had disproved the hypothesis that frost heaving results from molar volume expansion with freezing of water already present in the soil prior to the onset of subzero temperatures, i.e. with little contribution from

7315-414: The soil particle will be displaced downward towards the warm direction within the thermal gradient due to melting and refreezing of the thin film of water that surrounds the particle. The thickness of such a film is temperature dependent and is thinner on the colder side of the particle. Water has a lower thermodynamic free energy when in bulk ice than when in the supercooled liquid state. Therefore, there

7410-472: The soil to thaw and recover when the building interior is warmed. If a refrigerated building's foundation is placed on frost-susceptible soils with a water table within reach of the freezing front, then the floors of such structures may heave, due to the same mechanisms found in nature. Such structures may be designed to avoid such problems by employing several strategies, separately or in tandem. The strategies include placement of non-frost-susceptible soil beneath

7505-412: The soil. Yet the force of one or more growing ice lenses is sufficient to lift a layer of soil, as much as 1 foot (0.30 metres) or more. The soil through which water passes to feed the formation of ice lenses must be sufficiently porous to allow capillary action, yet not so porous as to break capillary continuity. Such soil is referred to as "frost susceptible". The growth of ice lenses continually consumes

7600-609: The southern hemisphere. They include such forest types as the mixed deciduous forests of the United States and their counterparts in China and Japan; the broadleaf evergreen rainforests of Japan, Chile , and Tasmania ; the sclerophyllous forests of Australia, central Chile, the Mediterranean , and California; and the southern beech Nothofagus forests of Chile and New Zealand. There are many different types of tropical moist forests , with lowland evergreen broad-leaf tropical rainforests : for example várzea and igapó forests and

7695-419: The surface of the ice lens, and between ice and soil particles. Faraday reported in 1860 on the unfrozen layer of premelted water. Ice premelts against its own vapor , and in contact with silica . The same intermolecular forces that cause premelting at surfaces contribute to frost heaving at the particle scale on the bottom side of the forming ice lens. When ice surrounds a fine soil particle as it premelts,

7790-400: The surface, upwards from the depth in the soil where freezing temperatures have penetrated into the soil (the freezing front or freezing boundary). Ice growth requires a water supply that delivers water to the freezing front via capillary action in certain soils. The weight of overlying soil restrains vertical growth of the ice and can promote the formation of lens-shaped areas of ice within

7885-674: The terra firme forests of the Amazon Basin ; the peat swamp forests ; dipterocarp forests of Southeast Asia ; and the high forests of the Congo Basin . Seasonal tropical forests , perhaps the best description for the colloquial term " jungle ", typically range from the rainforest zone 10 degrees north or south of the equator , to the Tropic of Cancer and Tropic of Capricorn . Forests located on mountains are also included in this category, divided largely into upper and lower montane formations, on

7980-470: The trees are being grown as Christmas trees and are below a certain height. The word forest derives from the Old French forest (also forès ), denoting "forest, vast expanse covered by trees"; forest was first introduced into English as the word denoting wild land set aside for hunting without necessarily having trees on the land. Possibly a borrowing, probably via Frankish or Old High German , of

8075-425: The trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer that consists primarily of grasses. Savannas maintain an open canopy despite a high tree density. Forest plantations are generally intended for the production of timber and pulpwood . Commonly mono-specific, planted with even spacing between

8170-403: The trees, and intensively managed, these forests are generally important as habitat for native biodiversity . Some are managed in ways that enhance their biodiversity protection functions and can provide ecosystem services such as nutrient capital maintenance, watershed and soil structure protection and carbon storage. The annual net loss of forest area has decreased since 1990, but the world

8265-505: The type of vegetation that grows upon the land; an area can be legally designated "forest" even if no trees grow on it. Land-use definitions are based on the primary purpose the land is used for. Under a land-use definition, any area used primarily for harvesting timber, including areas that have been cleared by harvesting, disease, fire, or for the construction of roads and infrastructure, are still defined as forests, even if they contain no trees. Land-cover definitions define forests based upon

8360-459: The vertical displacement of soil in frost heaving could be significantly greater than that due to molar volume expansion. Taber demonstrated that liquid water migrates towards the freeze line within soil. He showed that other liquids, such as benzene , which contracts when it freezes, also produce frost heave. This excluded molar volume changes as the dominant mechanism for vertical displacement of freezing soil. His experiments further demonstrated

8455-626: The word forest is commonly used, there is no universally recognised precise definition, with more than 800 definitions of forest used around the world. Although a forest is usually defined by the presence of trees, under many definitions an area completely lacking trees may still be considered a forest if it grew trees in the past, will grow trees in the future, or was legally designated as a forest regardless of vegetation type. There are three broad categories of definitions of forest in use: administrative, land use , and land cover . Administrative definitions are legal designations, and may not reflect

8550-461: The word is a Latinisation of the Frankish * forhist , denoting "forest, wooded country", and was assimilated to forestam silvam , pursuant to the common practice of Frankish scribes. The Old High German forst denoting "forest"; Middle Low German vorst denoting "forest"; Old English fyrhþ denoting "forest, woodland, game preserve, hunting ground" (English frith ); and Old Norse fýri , denoting " coniferous forest "; all of which derive from

8645-579: The world's forest area is found in patches larger than 1 million hectares (2.5 million acres). The remaining 20 percent is located in more than 34 million patches around the world – the vast majority less than 1,000 hectares (2,500 acres) in size. Human society and forests can affect one another positively or negatively. Forests provide ecosystem services to humans and serve as tourist attractions. Forests can also affect people's health. Human activities, including unsustainable use of forest resources, can negatively affect forest ecosystems. Although

8740-416: The world's forests into 26 major types, which reflect climatic zones as well as the principal types of trees. These 26 major types can be reclassified into 6 broader categories: temperate needleleaf, temperate broadleaf and mixed, tropical moist, tropical dry, sparse trees and parkland, and forest plantations. Each category is described in a separate section below. Temperate needleleaf forests mostly occupy

8835-403: The world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' Food and Agriculture Organization (FAO) defines a forest as, "Land spanning more than 0.5 hectares with trees higher than 5 meters and a canopy cover of more than 10 percent, or trees able to reach these thresholds in situ . It does not include land that

8930-436: Was deciduous , dropping its fronds onto the forest floor, the shade, soil, and forest duff from the dropped fronds creating the early forest. The shed organic matter altered the freshwater environment, slowing its flow and providing food. This promoted freshwater fish. Forests account for 75% of the gross primary productivity of the Earth's biosphere , and contain 80% of the Earth's plant biomass. Biomass per unit area

9025-537: Was the beginning of the State Forest system. In order to accommodate visitors, the state has allowed the development of 9 areas within Forbes. This includes 6 State Parks and 3 State Forest Picnic Areas. The remainder of the area is undeveloped except for hiking trails maintained by the state. These are generally closed to vehicles but open to hiking , cross-country skiing , hunting , and fishing . Several portions of what

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