It depends on the tree's species and age, but a mature, healthy tree can have 200,000 leaves. During 60 years of life, such a MORE
Deciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe. In a more general sense, deciduous means the dropping of a part that is no longer needed, or falling away after its purpose is finished. In plants it is the result of natural processes. Deciduous has a similar meaning when referring to animal parts, such as deciduous antlers in deer, or deciduous teeth, also known as baby teeth, in some mammals (including humans).
In botany and horticulture, deciduous plants, including trees, shrubs and herbaceous perennials, are those that lose all of their leaves for part of the year. This process is called abscission. In some cases leaf loss coincides with winter — namely in temperate or polar climates. In other parts of the world, including tropical, subtropical, and arid regions, plants lose their leaves during the dry season or other seasons, depending on variations in rainfall.
The converse of deciduous is evergreen, where green foliage is persistent year round. Plants that are intermediate may be called semi-deciduous; they lose old foliage as new growth begins. Other plants are semi-evergreen and lose their leaves before the next growing season, retaining some during winter or dry periods. Some trees, including a few species of oak, have desiccated leaves that remain on the tree through winter; these dry persistent leaves are called marcescent leaves and are dropped in the spring as new growth begins.
Many deciduous plants flower during the period when they are leafless, as this increases the effectiveness of pollination. The absence of leaves improves wind transmission of pollen for wind-pollinated plants and increases the visibility of the flowers to insects in insect-pollinated plants. This strategy is not without risks, as the flowers can be damaged by frost or, in dry season regions, result in water stress on the plant. Nevertheless, there is much less branch and trunk breakage from glaze ice storms when leafless, and plants can reduce water loss due to the reduction in availability of liquid water during cold winter days.
Leaf drop or abscission involves complex physiological signals and changes within plants. The process of photosynthesis steadily degrades the supply of chlorophylls in foliage; plants normally replenish chlorophylls during the summer months. When autumn arrives and the days are shorter or when plants are drought-stressed, deciduous trees decrease chlorophyll pigment production, allowing other pigments present in the leaf to become apparent, resulting in non-green colored foliage. The brightest leaf colors are produced when days grow short and nights are cool, but remain above freezing. These other pigments include carotenoids that are yellow, brown, and orange. Anthocyanin pigments produce red and purple colors, though they are not always present in the leaves. Rather, they are produced in the foliage in late summer, when sugars are trapped in the leaves after the process of abscission begins. Parts of the world that have showy displays of bright autumn colors are limited to locations where days become short and nights are cool. In other parts of the world, the leaves of deciduous trees simply fall off without turning the bright colors produced from the accumulation of anthocyanin pigments.
The beginnings of leaf drop starts when an abscission layer is formed between the leaf petiole and the stem. This layer is formed in the spring during active new growth of the leaf; it consists of layers of cells that can separate from each other. The cells are sensitive to a plant hormone called auxin that is produced by the leaf and other parts of the plant. When auxin coming from the leaf is produced at a rate consistent with that from the body of the plant, the cells of the abscission layer remain connected; in autumn, or when under stress, the auxin flow from the leaf decreases or stops, triggering cellular elongation within the abscission layer. The elongation of these cells break the connection between the different cell layers, allowing the leaf to break away from the plant. It also forms a layer that seals the break, so the plant does not lose sap.
A number of deciduous plants remove nitrogen and carbon from the foliage before they are shed and store them in the form of proteins in the vacuoles of parenchyma cells in the roots and the inner bark. In the spring, these proteins are used as a nitrogen source during the growth of new leaves or flowers.
Plants with deciduous foliage have both advantages and disadvantages compared to plants with evergreen foliage. Since deciduous plants lose their leaves to conserve water or to better survive winter weather conditions, they must regrow new foliage during the next suitable growing season; this uses resources which evergreens do not need to expend. Evergreens suffer greater water loss during the winter and they also can experience greater predation pressure, especially when small. Losing leaves in winter may reduce damage from insects; repairing leaves and keeping them functional may be more costly than just losing and regrowing them. Removing leaves also reduces cavitation which can damage xylem vessels in plants. This then allows deciduous plants to have xylem vessels with larger diameters and therefore a greater rate of transpiration (and hence CO2 uptake as this occurs when stomata are open) during the summer growth period.
The deciduous characteristic has developed repeatedly among woody plants. Trees include Maple, many Oaks, Elm, Aspen, and Birch, among others, as well as a number of coniferous genera, such as Larch and Metasequoia. Deciduous shrubs include honeysuckle, viburnum, and many others. Most temperate woody vines are also deciduous, including grapes, poison ivy, virginia creeper, wisteria, etc. The characteristic is useful in plant identification; for instance in parts of Southern California and the American Southeast, deciduous and evergreen oak species may grow side by side.
Periods of leaf fall often coincide with seasons: winter in the case of cool-climate plants or the dry-season in the case of tropical plants, however there are no deciduous species among tree-like monocotyledonous plants, e.g. palms, yuccas, and Dracaenas.
Forests where a majority of the trees lose their foliage at the end of the typical growing season are called deciduous forests. These forests are found in many areas worldwide and have distinctive ecosystems, understory growth, and soil dynamics.
Two distinctive types of deciduous forest are found growing around the world.
Temperate deciduous forest biomes are plant communities distributed in North and South America, Asia, Southern slopes of the Himalayas, Europe and for cultivation purposes in Oceania. They have formed under climatic conditions which have great seasonable temperature variability with growth occurring during warm summers and leaf drop in autumn and dormancy during cold winters. These seasonally distinctive communities have diverse life forms that are impacted greatly by the seasonality of their climate, mainly temperature and precipitation rates. These varying and regionally different ecological conditions produce distinctive forest plant communities in different regions.
Tropical and subtropical deciduous forest biomes have developed in response not to seasonal temperature variations but to seasonal rainfall patterns. During prolonged dry periods the foliage is dropped to conserve water and prevent death from drought. Leaf drop is not seasonally dependent as it is in temperate climates, and can occur any time of year and varies by region of the world. Even within a small local area there can be variations in the timing and duration of leaf drop; different sides of the same mountain and areas that have high water tables or areas along streams and rivers can produce a patchwork of leafy and leafless trees.
In botany, a tree is a plant with an elongated stem, or trunk, supporting leaves or branches.
In some usages, the definition of a tree may be narrower, including only woody plants, only plants that are usable as lumber, only plants above a specified height or only perennial species. At its broadest, trees include the taller palms, the tree ferns, bananas and bamboo.
A tree typically has many secondary branches supported clear of the ground by the trunk. This trunk typically contains woody tissue for strength, and vascular tissue to carry materials from one part of the tree to another. For most trees it is surrounded by a layer of bark which serves as a protective barrier. Below the ground, the roots branch and spread out widely; they serve to anchor the tree and extract moisture and nutrients from the soil. Above ground, the branches divide into smaller branches and shoots. The shoots typically bear leaves, which capture light energy and convert it into chemical energy by photosynthesis, providing the food needed by the tree for its growth and development.
Flowers and fruit may also be present, but some trees such as conifers instead have pollen cones and seed cones, and others such as tree ferns produce spores instead.
Trees tend to be long-lived, some reaching several thousand years old. The tallest known specimen on Earth is 115.6 m (379 ft) and they have a theoretical maximum height of 130 m (426 ft). Trees have been in existence on the Earth for 370 million years. Trees are not a taxonomic group but are a number of plant species that have independently evolved a woody trunk and branches as a way to tower above other plants and make full use of the sunlight.
Trees play a significant role in reducing erosion and moderating the climate. They remove carbon dioxide from the atmosphere and store large quantities of carbon in their tissues. Trees and forests provide a habitat for many species of animals and plants. Tropical rainforests are one of the most biodiverse habitats in the world. Trees provide shade and shelter, timber for construction, fuel for cooking and heating, and fruit for food as well as having many other uses. In parts of the world, forests are shrinking as trees are cleared to increase the amount of land available for agriculture. Because of their longevity and usefulness, trees have always been revered and they play a role in many of the world's mythologies.
Although "tree" is a term of common parlance, there is no universally recognised precise definition what a tree is, neither botanically nor in common language.
In its broadest sense, a tree is any plant with the general form of an elongated stem, or trunk, which supports the photosynthetic leaves or branches at some distance above the ground. Trees are also typically defined by height, with smaller plants being classified as shrubs, however the minimum height which defines a tree varies widely, from 10 m to 0.5 m. By these broadest definitions, large herbaceous plants such as papaya and bananas are trees, despite not being considered as trees under more rigorous definitions.
Another criterion often added to the definition of a tree is that it has a woody trunk. Such a definition excludes herbaceous trees such as bananas and papayas. Monocots such as bamboo and palms may be considered trees under such a definition. Despite being herbaceous and not undergoing secondary growth and never producing wood, palms and bamboo may produce "pseudo-wood" by lignifying cells produced through primary growth.
Aside from structural definitions, trees are commonly defined by use. Trees may be defined as plants from which lumber can be produced.
Trees are an evolutionary adaptation to competition for space. By growing taller trees are able to compete better for sunlight. They have modified structures that allow them to grow much taller and spread out their foliage, such as thicker stems that are composed of specialized cells that add structural strength and durability. They are long-lived perennial plants that can increase their size each year by producing woody stems. They differ from shrubs, which are also woody plants, by usually growing larger and having a single main stem; but the distinction between a small tree and a large shrub is not always clear, made more confusing by the fact that trees may be reduced in size under harsher environmental conditions such as on mountains and subarctic areas. The tree form has evolved separately in unrelated classes of plants in response to similar environmental challenges, making it a classic example of parallel evolution. With an estimated 100,000 species, the number of trees worldwide might total twenty-five percent of all living plant species. Their greatest number grow in tropical regions and many of these areas have not yet been fully surveyed by botanists, making tree diversity and ranges poorly known.
Trees exist in two different groups of vascular or higher plants, the gymnosperms and the angiosperms][. Both groups are seed plants. The gymnosperm trees include conifers, cycads, ginkgophytes and gnetales. Angiosperm trees are also known as broad-leaved trees. Most angiosperm trees are eudicots, the "true dicotyledons", so named because the seeds contain two cotyledons or seed leaves. A relatively smaller number of other angiosperm trees are paleodicots; these include Amborella, Magnolia, nutmeg, avocado, and others.
Wood gives structural strength to a tree stem which is used to support the plant as it grows larger. The vascular system of trees allows water, nutrients and other chemicals to be distributed around the plant, and without it trees would not be able to grow as large as they do. The three main parts of trees include the root, stem, and leaves; they are integral parts of the vascular system which interconnects all the living cells. In trees and other plants that develop wood, the vascular cambium allows the expansion of vascular tissue that produces woody growth. Because this growth ruptures the epidermis of the stem, woody plants also have a cork cambium that develops among the phloem. The cork cambium gives rise to thickened cork cells to protect the surface of the plant and reduce water loss. Both the production of wood and the production of cork are forms of secondary growth.
Trees are either evergreen, having foliage that persists and remains green throughout the year, or deciduous, shedding their leaves at the end of the growing season and then having a dormant period without foliage. Most conifers are evergreens but larches (Larix and Pseudolarix) are deciduous, dropping their needles each autumn, and some species of cypress (Glyptostrobus, Metasequoia and Taxodium) shed small leafy shoots annually in a process known as cladoptosis. The crown is a name for the upper part][ of a tree including the branches and leaves and the uppermost layer in a forest, formed by the crowns of the trees, is known as the canopy. A sapling is a young tree.
Tree-like plants include some palms which are not trees but herbaceous monocots that do not undergo secondary growth and never produce wood, and hence do not meet the definition of tree used in this article. In many tree-like palms, the terminal bud on the main stem is the only one to develop so they have tall, unbranched trunks with spirally arranged large leaves. Some of the tree ferns, order Cyatheales, have tree-like growth forms, growing up to 20 metres (66 ft) but they are structurally very different from other trees: their trunks are composed of rhizomes which grow vertically and which are covered by numerous adventitious roots.
In places where the climate is suitable, trees are the climax vegetation][. In some of the cool temperate regions, conifers tend to predominate, but in much of the southern hemisphere, the tropics, or in warm-temperate climates, broad-leaved trees are more common. Shade tolerance in young trees varies between species, and may determine the pattern of forest succession.
More than half the species of terrestrial plants and animals on the Earth are thought to live in tropical rainforests even though these occupy just five percent of the land area. In tropical regions with a monsoon climate, where a drier part of the year alternates with a wet period, different species of broad-leaved trees dominate the forest, some of them being deciduous.
Tropical regions with a drier savanna climate have insufficient rainfall to support dense forests][; the canopy is not closed and plenty of sunshine reaches the ground which is covered with grass and scrub. Acacia and baobab are well adapted to living in such areas.
In cool temperate parts of the world, particularly in the northern hemisphere, deciduous broad-leaved trees tend to be replaced by conifers. The long cold winter is unsuitable for plant growth and trees must grow rapidly in the short summer season when the temperature rises and the days are long. Light is very limited under their dense cover and there may be little plant life on the forest floor although fungi may abound. Similar woodland is found on mountains where the altitude causes the average temperature to be lower thus reducing the length of the growing season.
The roots of a tree serve to anchor it to the ground and gather water and nutrients to transfer to all parts of the tree, and for reproduction defense, survival, energy storage and many, many other purposes. The first root produced by a newly germinated seedling is a taproot which goes straight downwards. Within a few weeks lateral roots branch out of the side of this and grow horizontally through the upper layers of the soil. In most trees, the tap root eventually withers away and the wide-spreading laterals remain. Near the tip of the finer roots are single cell root hairs. These are in immediate contact with the soil particles and can absorb water and nutrients such as potassium in solution. The roots require oxygen to respire and only a few species such as the mangrove and the pond cypress (Taxodium ascendens) can live in permanently waterlogged soil.
In the soil, the roots encounter the hyphae of fungi. Many of these are known as mycorrhiza and form a mutualistic relationship with the tree roots. Some are specific to a single tree species, which will not flourish in the absence of its mycorrhizal associate. Others are generalists and associate with many species. The tree acquires minerals such as phosphorus from the fungus while it obtains the carbohydrate products of photosynthesis from the tree. The hyphae of the fungus can link different trees and a network is formed, transferring nutrients from one place to another. The fungus promotes growth of the roots and helps protect the trees against predators and pathogens. It can also limit damage done to a tree by pollution as the fungus accumulate heavy metals within its tissues. Fossil evidence shows that roots have been associated with mycorrhizal fungi since the early Paleozoic, four hundred million years ago, when the first vascular plants colonised dry land.
Some trees such as the alders (Alnus spp.) have a symbiotic relationship with Frankia sp,, a filamentous bacterium that can fix nitrogen from the air, converting it into ammonia. They have actinorhizal root nodules on their roots in which the bacteria live. This process enables the tree to live in low nitrogen habitats where they would otherwise be unable to thrive. Researchers have discovered that certain plant hormones called cytokinins initiate root nodule formation and that this process is closely related to the mechanisms involved in mycorrhizal association.
It has been demonstrated that some trees are interconnected through their root system, forming a colony. The interconnections are made by the inosculation process, a kind of natural grafting or welding of vegetal tissues. The tests to demonstrate this networking are performed injecting chemicals, sometimes radioactive, in a tree, and then checking for its presence in neighbor trees.
The roots are, generally, a subterranean part of the tree, but some tree species have evolved roots that are aerial. The common purposes for aerial roots may be of two kinds, to contribute to the mechanical stability of the tree, and to obtain oxygen from air. An instances of mechanical stability enhancement is the red mangrove that develops prop roots that loop out of the trunk and branches and descend vertically into the mud. A similar structure is developed by the Indian banyan. Many large trees have buttress roots which flare out from the lower part of the trunk. These brace the tree rather like angle brackets and provide stability, reducing sway in high winds. They are particularly prevalent in tropical rainforests where the soil is poor and the roots are close to the surface.
Some tree species have developed root extensions that pop out of soil, in order to get oxygen, when it is not available in the soil because of excess water. These root extensions are called pneumatophores, and are present, among other, in black mangrove and pond cypress.
The main purpose of the trunk is to raise the leaves above the ground in order to overtop other plants and shading them out. It also performs the task of transporting water and nutrients from the roots to the aerial parts of the tree and to distribute the food produced by the leaves to all other parts including the roots.
In the case of Angiosperms and Gymnosperms, the outermost layer of the trunk is the bark and is mostly composed of dead cells. It provides a thick, waterproof covering to the living inner tissue. It protects the trunk against the elements, disease, animal attack and fire. It is perforated by a large number of fine breathing pores called lenticels through which oxygen diffuses. Bark is continually replaced by a living layer of cells called the cork cambium. The London plane (Platanus × acerifolia) periodically sheds its bark in large flakes. Similarly, the bark of the silver birch (Betula pendula) peels off in strips. As the tree's girth expands, newer layers of bark are larger in circumference, and the older layers develop fissures in many species. In some trees such as the pine (Pinus spp.,) the bark exudes sticky resin which deters attackers whereas in rubber trees (Hevea brasiliensis) it is a milky latex that oozes out. The quinine bark tree (Cinchona officinalis) contains bitter substances to make the bark unpalatable. Tree-like plants][ in the Pteridophyta, Arecales, Cycadophyta and Poales such as the tree ferns, palms, cycads and bamboos have no true bark but all have an outer protective covering of some form.
Although the bark functions as a protective barrier, it is itself attacked by boring insects such as beetles. These lay their eggs in crevices and the larvae chew their way through the cellulose tissues leaving a gallery of tunnels. This may allow fungal spores to gain admittance and attack the tree. Dutch elm disease is caused by a fungus (Ophiostoma sp.) carried from one elm tree to another by various beetles. The tree reacts to the growth of the fungus by blocking off the xylem tissue carrying sap upwards and the branch above, and eventually the whole tree, is deprived of nourishment and dies. In Britain in the 1990s, 25 million elm trees were killed by this disease.
The innermost layer of bark is known as the phloem and this is involved in the transport of the sap containing the sugars made by photosynthesis to other parts of the tree. It is a soft spongy layer of living cells, some of which are arranged end to end to form tubes. These are supported by parenchyma cells which provide padding and include fibres for strengthening the tissue. Inside the phloem is a layer of undifferentiated cells one cell thick called the vascular cambium layer. The cells are continually dividing, creating phloem cells on the outside and wood cells known as xylem on the inside.
The newly created xylem is the sapwood. It is composed of water-conducting cells and associated cells which are often living, and is usually pale in colour. It transports water and minerals from the roots to the upper parts of the tree. The oldest, inner part of the sapwood is progressively converted into heartwood as new sapwood is formed at the cambium. The conductive cells of the heartwood are blocked in some species, and the surrounding cells are more often dead. Heartwood is usually darker in colour than the sapwood. It is the dense central core of the trunk giving it rigidity. Three quarters of the dry mass of the xylem is cellulose, a polysaccharide, and most of the remainder is lignin, a complex polymer. A transverse section through a tree trunk or a horizontal core will show concentric circles or lighter or darker wood - tree rings. These rings are the annual growth rings There may also be rays running at right angles to growth rings. These are vascular rays which are thin sheets of living tissue permeating the wood. Many older trees may become hollow but may still stand upright for many years.
Trees do not usually grow continuously throughout the year but mostly have spurts of active expansion followed by periods of rest. This pattern of growth is related to the climatic conditions, growth normally ceasing when conditions are either too cold or too dry. In readiness for the inactive period, trees form buds to protect the meristem, the zone of active growth. Before the period of dormancy, the last few leaves produced at the tip of a twig form scales. These are thick, small and closely wrapped and enclose the growing point in a waterproof sheath. Inside this bud there is a rudimentary stalk and neatly folded miniature leaves, ready to expand when the next growing season arrives. Buds also form in the axils of the leaves ready to produce new side shoots. A few trees, such as the eucalyptus, have "naked buds" with no protective scales and some conifers, such as the Lawson's cypress, have no buds but instead have little pockets of meristem concealed among the scale-like leaves.
When growing conditions improve, such as the arrival of warmer weather and the longer days associated with spring in temperate regions, growth starts again. The expanding shoot pushes its way out, shedding the scales in the process. These leave behind scars on the surface of the twig. The whole year's growth may take place in just a few weeks. The new stem is unlignified at first and may be green and downy. Palm trees][ have their leaves spirally arranged on an unbranched trunk. In some tree species in temperate climates, a second spurt of growth, a Lammas growth may occur which is believed to be a strategy to compensate for loss of early foliage to insect predators.
Primary growth is the elongation of the stems and roots. Secondary growth consists of a progressive thickening and strengthening of the tissues as the outer layer of the epidermis is converted into bark and the cambium layer creates new phloem and xylem cells. The bark is inelastic. Sooner or later][ the growth of a tree slows down and stops and it gets no taller. As long as the crown remains in balance with the roots][ the tree should remain healthy but its ability to defend itself against fungal attack is diminished. If damage occurs the tree may in time become hollow.
Trees are much taller than herbaceous or shrubby plants][and ensuring the upper-most leaves are supplied with water originating in the root system requires that water is drawn up through the xylem from the roots by the suction produced as it evaporates from the leaves.][ If insufficient water is available the leaves will die.
The leaves of trees come in a wide range of shapes and sizes which have evolved in response to environmental pressures including climate and predation. They can be broad or needle-like, simple or compound, lobed or entire, smooth or hairy, delicate or tough, deciduous or evergreen. The needles of coniferous trees are compact but are structurally similar to those of broad-leaved trees. They are adapted for life in environments where resources are low or water is scarce. Frozen ground may limit water availability and conifers are often found in colder places at higher altitudes and higher latitudes than broad leaved trees. In many cases, their branches hang down at an angle to the trunk which decreases the likelihood of them breaking when weighed down by snow.][ Broad leaved trees in temperate regions have a different][ strategy for dealing with winter weather. When the days get shorter and the temperature begins to decrease, the leaves no longer makes new chlorophyll and the red and yellow pigments already present in the blades become apparent. Synthesis in the leaf of a plant hormone called auxin also ceases. This causes the cells at the junction of the petiole and the twig to weaken and sooner or later the joint breaks and the leaf floats to the ground. In tropical and subtropical regions, many trees keep their leaves all year round. Individual leaves may fall intermittently and be replaced by new growth but most leaves remain intact for some time. Other tropical species and those in arid regions may shed all their leaves annually at a particular time of year.][ Often this will coincide with the onset of the dry season or some other climatic event.][ Many deciduous trees flower before the new leaves emerge.
Tree forms are found in a wide range of plants and their reproductive strategies are substantially the same as shrub or herbaceous plant forms.
Many trees are wind pollinated which may be an evolutionary adaptation to take advantage of increased wind speeds high above the ground, particularly in the case of those that produce pollen before the leaves emerge. A vast quantity of pollen is produced because of the low likelihood of any particular grain landing on an appropriate female flower. Wind-pollinated flowers of broad-leaved trees are characterised by a lack of showy parts, no scent and a copious production of pollen, often with separate male and female flowers, or separate male and female trees. The male flowers may be high up in the tree, often in the form of dangling catkins. The female flowers may be lower down the tree. The pollen of pine trees contains air sacs which give it buoyancy and it has been known to travel as far as 800 kilometres (500 mi). Tree pollen can cause allergies. A prime example would be hay fever, which can be caused by pollen.
Seeds are the primary way that trees reproduce and their seeds vary greatly in size and shape. Some of the largest seeds come from trees, but the largest tree, Sequoiadendron giganteum, produces one of the smallest tree seeds. The great diversity in tree fruits and seeds reflects the many different ways that tree species have evolved to disperse their offspring.
The single extant species of Ginkgophyta (Ginkgo biloba) has fleshy seeds produced at the ends of short branches on female trees, and Gnetum, a tropical and subtropical group of gymnosperms produce seeds at the tip of a shoot axis. The seeds of conifers, the largest group of Gymnosperms, are enclosed in a cone and most species have seeds that are light and papery that can be blown considerable distances once free from the cone. Sometimes the seed remains in the cone for years waiting for a trigger event to liberate it. Fire stimulates release and germination of seeds of the jack pine, and also enriches the forest floor with wood ash and removes competing vegetation. Similarly, a number of Angiosperms including Acacia cyclops and Acacia mangium have seeds that germinate better after exposure to high temperatures.
Angiosperm tree produce seeds in a wide variety of fruits, some of them include acorn, nut, berrie, pome, drupe, samaras, hesperdium, capsule and legume.
For a tree seeding to grow into an adult tree it needs light and space, if seeds only fell straight to the ground, competition among the concentrated saplings and the shade of the parent would likely prevent it from flourishing. Many seeds such as birch are small and have papery wings to aid dispersal by the wind. Ash trees and maples have larger seeds with blade shaped wings which spiral down to the ground when released. The kapok tree has cottony threads to catch the breeze. The flame tree does not rely on fire but shoots its seeds through the air when the two sides of its long pods crack apart explosively on drying. The miniature cone-like catkins of Alder trees produce seeds that contain small droplets of oil that help disperse the seeds on the surface of water. Mangroves often grow in water and some species have propagules, which are buoyant fruits with seeds that start germinating before becoming detached from the parent tree. These float on the water and may become lodged on emerging mudbanks and successfully take root. Other seeds, such as apple pips and plum stones, have fleshy receptacles and smaller fruits like hawthorns have seeds enclosed in edible tissue; birds and animals][ eat the fruits and the seeds are either discarded or are consumed and pass through the gut to be deposited in the animal's droppings well away from the parent tree. In some cases, germination is improved by being processed in this way. Nuts and other large seeds are gathered by animals that hide in caches][ any not immediately consumed. Many of these caches are never revisited, the nut-casing softens with rain and frost and the seed germinates in the spring. Pine cones may be hoarded in a similar way by red squirrels, and grizzly bears raiding the caches may also help to disperse the seed.
The earliest tree-like organisms were tree ferns, horsetails and lycophytes, which grew in forests in the Carboniferous period. The first tree may have been Wattieza, fossils of which have been found in New York State in 2007 dating back to the Middle Devonian (about 385 million years ago). Prior to this discovery, Archaeopteris was the earliest known tree. Both of these reproduced by spores rather than seeds and are considered to be links between ferns and the gymnosperms which evolved in the Triassic period. The gymnosperms include conifers, cycads, gnetales and ginkgos and these may have appeared as a result of a whole genome duplication event which took place about 319 million years ago. Ginkgophyta was once a widespread diverse group of which the only survivor is the maidenhair tree Ginkgo biloba. This is considered to be a living fossil because it is virtually unchanged from the fossilised specimens found in Triassic deposits.
During the Mesozoic (245 to 65 million years ago) the conifers flourished and became adapted to live in all the major terrestrial habitats. Subsequently the tree forms of flowering plants evolved during the Cretaceous period. These began to dominate the conifers during the Tertiary era (65 to 2 million years ago) when forests covered the globe. When the climate cooled 1.5 million years ago and the first of four ice ages occurred, the forests retreated as the ice advanced. In the interglacials, trees recolonised the land][ only to be driven back again at the start of the next ice age.
Trees are an important part of the terrestrial ecosystem, providing essential habitat for a community of organisms. Epiphytic plants such as ferns, some mosses, liverworts, orchids and some species of parasitic plants (e.g., mistletoe) hang from branches; these along with arboreal lichens, algae, and fungi provide micro-habitats for themselves and for other organisms, including animals. Leaves, flowers and fruits are seasonally available. On the ground underneath trees there is shade, and often there is undergrowth, leaf litter, fallen branches and/or decaying wood that provide other habitat. Trees stabilise the soil, prevent rapid run-off of rain water, help prevent desertification, have a role in climate control and help in the maintenance of biodiversity and ecosystem balance.
Many species of tree support their own specialised invertebrates. In their natural habitats, 284 different species of insect have been found on the English oak (Quercus robur) and 306 species of invertebrate on the Tasmanian oak (Eucalyptus obliqua). Non-native tree species provide a less biodiverse community, for example in the United Kingdom the sycamore (Acer pseudoplatanus), which originates from southern Europe, has few associated invertebrate species, though its base rich bark][ does support a wide range of lichens, bryophytes and epiphytes.
Trees can play a role in the development of an ecosystem,][ for example in mangrove swamps the roots of the mangrove trees reduce the speed of flow of tidal currents and hence trap water-borne sediment, leading over time to a reduction in water depth and the creation of suitable conditions for further mangrove colonisation. Thus mangrove swamps tend to extend seawards in suitable locations. Mangrove swamps also provide an effective buffer against the more damaging effects of cyclones and tsunamis.
Silviculture is the practice of controlling the establishment, growth, composition, health, and quality of forests, which are areas that have a high density of trees. Cultivated trees are planted and tended by humans, usually because they provide food (fruits or nuts), ornamental beauty, or some type of wood product that benefits people. A small wooded area, usually with no undergrowth, is called a grove and a small wood or thicket of trees and bushes is called a coppice or copse. A large area of land covered with trees and undergrowth is called woodland or forest. An area of woodland composed primarily of trees established by planting or artificial seeding is known as a plantation and an area of land planted with fruit or nut trees is an orchard. Several biotopes are defined largely by the trees that inhabit them, examples being rainforest and taiga. A landscape of trees scattered or spaced across grassland is called a savanna. A forest of great age is called ancient woodland][ and a forest in its natural state, before being explored or exploited by man is a virgin forest.][ Trees have conservation value and add interest to the landscape. They can be planted as isolated specimens in hedgerows or as shelter belts. They provide shade for people and animals. They can be planted in grand avenues in parkland or alongside roads in town and country.
Trees are the source of many of the world's best known fleshy fruits. Apples, pears, plums, cherries and citrus are all grown commercially in temperate climates and a wide range of edible fruits are found in the tropics. Other commercially important fruit include dates, coconuts and other nuts, figs and olives. Palm oil is obtained from the fruits of the oil palm (Elaeis guineensis). The fruits of the cocoa tree (Theobroma cacao) are used to make cocoa and chocolate and the berries of coffee trees, (Coffea arabica) and (Coffea canephora), are processed to extract the coffee beans. In many rural areas of the world, fruit is gathered from forest trees for consumption.
Many trees have flowers rich in nectar which are attractive to bees. The production of forest honey is an important industry in rural areas of the developing world where it is undertaken by small-scale beekeepers using traditional methods. The flowers of the elder (Sambucus) are used to make elderflower cordial and petals of the plum (Prunus spp.) can be candied.
The leaves of trees are widely gathered as fodder for livestock and some can be eaten by humans but they tend to be high in tannins which makes them bitter. Leaves of the curry tree (Murraya koenigii) are eaten, those of kaffir lime Citrus × hystrix (e.g., Thai food) Ailanthus (e.g., in Korean dishes such as bugak) and those of the European bay tree (Laurus nobilis) and the California bay tree (Umbellularia californica) are used for flavouring food. Camellia sinensis, the source of tea, is a small tree but seldom reaches its full height, being heavily pruned to make picking the leaves easier.
In temperate climates there is a sudden movement of sap at the end of the winter as trees prepare to burst into growth. In North America, the sap of the sugar maple (Acer saccharum) is most often used in the production of a sweet liquid, maple syrup. About 90% of the sap is water, the remaining 10% being a mixture of various sugars and certain minerals. The sap is harvested by drilling holes in the trunks of the trees and collecting the liquid that flows out of the inserted spigots. It is piped to a sugarhouse where it is heated to concentrate it and improve its flavour. One litre of maple syrup is obtained from every forty litres of sap and has a sugar content of exactly 66%. A similar process happens in northern Europe when the spring rise in the sap of the silver birch (Betula pendula) is tapped and collected. This is either drunk fresh or is fermented into an alcoholic drink. In Alaska, the sap of the sweet birch (Betula lenta) is similarly collected and converted into birch syrup with a sugar content of 67%. Sweet birch sap is more dilute than maple sap and one hundred litres are required to make one litre of birch syrup.
Various parts of trees are used as spices. These include cinnamon, made from the bark of the cinnamon tree (Cinnamomum zeylanicum) and allspice, the dried small fruits of the pimento tree (Pimenta dioica). Nutmeg is a seed found in the fleshy fruit of the nutmeg tree (Myristica fragrans) and cloves are the unopened flower buds of the clove tree (Syzygium aromaticum). Sassafras oil is an important flavouring obtained from distilling bark from the roots of (Sassafras albidum).
Wood has traditionally been used for fuel, especially in rural areas. In less developed nations it may be the only fuel available and collecting firewood is often a time consuming task as it becomes necessary to travel further and further afield in the search for fuel. It is often burned inefficiently on an open fire. In more developed countries other fuels are available and burning wood is a choice rather than a necessity. Modern wood-burning stoves are very fuel efficient and new products such as wood pellets are available to burn.
Charcoal can be made by slow pyrolysis of wood by heating it in the absence of air in a kiln. The carefully stacked branches, often oak, are burned with a very limited amount of air. The process of converting them into charcoal takes about fifteen hours. Charcoal is used as a fuel in barbecues and by blacksmiths and has many industrial and other uses.
Wood smoke can be used to preserve food. In the hot smoking process the food is exposed to smoke and heat in a controlled environment. The food is ready to eat when the process is complete, having been tenderised and flavoured by the smoke it has absorbed. In the cold process, the temperature is not allowed to rise above . The flavour of the food is enhanced but raw food requires further cooking. If it is to be preserved, meat should be cured before cold smoking.
Wood has been an important, easily available material for construction since humans started building shelters. Engineered wood products are available which bind the particles, fibres or veneers of wood together with adhesives to form composite materials. Plastics have taken over from wood for some traditional uses.
Wood is used in the construction of buildings, bridges, trackways, piles, poles for power lines, masts for boats, pit props, railway sleepers, fencing, hurdles, shuttering for concrete, pipes, scaffolding and pallets. In housebuilding it is used in joinery, for making joists, roof trusses, roofing shingles, thatching, staircases, doors, window frames, floor boards, parquet flooring, panelling and cladding.
Wood is used to construct carts, farm implements, boats, dugout canoes and in shipbuilding. It is used for making furniture, tool handles, boxes, ladders, musical instruments, bows, weapons, matches, clothes pegs, brooms, shoes, baskets, turnery, carving, toys, pencils, rollers, cogs, wooden screws, barrels, coffins, skittles, veneers, artificial limbs, oars, skis, wooden spoons, sports equipment and wooden balls.
Wood is pulped for paper and used in the manufacture of cardboard and made into engineered wood products for use in construction such as fibreboard, hardboard, chipboard and plywood. The wood of conifers is known as softwood while that of broad-leaved trees is hardwood.
Cork is produced from the thick bark of the cork oak (Quercus suber). It is harvested from the living trees about once every ten years in an environmentally sustainable industry. More than half the world's cork comes from Portugal and is largely used to make stoppers for wine bottles. Other uses include floor tiles, bulletin boards, balls, footwear, cigarette tips, packaging, insulation and joints in woodwind instruments.
The bark of other varieties of oak has traditionally been used in Europe for the tanning of hides though bark from other species of tree has been used elsewhere. The active ingredient, tannin, is extracted and after various preliminary treatments, the skins are immersed in a series of vats containing solutions in increasing concentrations. The tannin causes the hide to become supple, less affected by water and more resistant to bacterial attack.
The commonly used spice Cinnamon is obtained from the bark from a number of species of the genus Cinnamomum
At least one hundred and twenty drugs come from plant sources, many of them from the bark of trees. Quinine originates from the cinchona tree (Cinchona) and was for a long time the remedy of choice for the treatment of malaria. Aspirin was synthesized to replace the sodium salicylate derived from the bark of willow trees (Salix) which had unpleasant side effects. The anti-cancer drug Paclitaxel is derived from taxol, a substance found in the bark of the Pacific yew (Taxus brevifolia). Other tree based drugs come from the paw-paw (Carica papaya), the cassia (Cassia spp.), the cocoa tree (Theobroma cacao), the tree of life (Camptotheca acuminata) and the downy birch (Betula pubescens).
The papery bark of the white birch tree (Betula papyrifera) was used extensively by Native Americans. Wigwams were covered by it and canoes were constructed from it. Other uses included food containers, hunting and fishing equipment, musical instruments, toys and sledges. Nowadays, bark chips, a by-product of the timber industry, are used as a mulch and as a growing medium for epiphytic plants that need a soil-free compost.
Latex is a sticky defensive secretion that protects plants against herbivores. Many trees produce it when injured but the main source of the latex used to make natural rubber is the Pará rubber tree (Hevea brasiliensis). Originally used to create bouncy balls and for the waterproofing of cloth, natural rubber is now mainly used in tyres for which synthetic materials have proved less durable. The latex exuded by the balatá tree (Manilkara bidentata) is used to make golf balls and is similar to gutta-percha, made from the latex of the "getah perca" tree Palaquium. This is also used as an insulator, particularly of undersea cables, and in dentistry, walking sticks and gun butts. It has now largely been replaced by synthetic materials.
Resin is another plant exudate that may have a defensive purpose. It is a viscous liquid composed mainly of volatile terpenes and is produced mostly by coniferous trees. It is used in varnishes, for making small castings and in ten-pin bowling balls. When heated, the terpenes are driven off and the remaining product is called "rosin" and is used by stringed instrumentalists on their bows. Some resins contain essential oils and are used in incense and aromatherapy. Fossilized resin is known as amber and was mostly formed in the Cretaceous (145 to 65 million years ago) or more recently. The resin that oozed out of trees sometimes trapped insects or spiders and these are still visible in the interior of the amber.
The camphor tree (Cinnamomum camphora) produces an essential oil and the eucalyptus tree (Eucalyptus globulus) is the main source of eucalyptus oil which is used in medicine, as a fragrance and in industry.
Dead trees pose a safety risk, especially during high winds and severe storms, and removing dead trees involves a financial burden, whereas the presence of healthy trees can clean the air, increase property values, and reduce the temperature of the built environment and thereby reduce building cooling costs. During times of drought, trees can fall into water stress, which may cause a tree to become more susceptible to disease and insect problems, and ultimately may lead to a tree's death. Irrigating trees during dry periods can reduce the risk of water stress and death. Irrigation can be accomplished by use of a garden hose, soaker hose, sprinkler, or modified five-gallon bucket.
Trees have been venerated since time immemorial. To the ancient Celts, certain trees held special significance as providing fuel, building materials, ornamental objects and weaponry. Other cultures have similarly revered trees, often linking the lives and fortunes of individuals to them or using them as oracles. In Greek mythology, dryads were believed to be shy nymphs who inhabited trees. The Tree of Life or World Tree linked the dead with the living and was associated with the Earth Goddess who brought fertility.
The Oubangui people of west Africa plant a tree when a child is born. As the tree flourishes, so does the child but if the tree fails to thrive, the health of the child is considered at risk. When it flowers it is time for marriage. Gifts are left at the tree periodically and when the individual dies, their spirit lives on in the tree.
Trees have their roots in the ground and their trunk and branches extended towards the sky. This concept is found in many of the world's religions as a tree which links the underworld and the earth and holds up the heavens. The best known example from European mythology is the ancient Norse Yggdrasil. In India, Kalpavriksha is a wish-fulfilling tree that was one of nine jewels that emerged from the primitive ocean. Icons are placed beneath it to be worshipped, tree nymphs inhabit the branches and it grants favours to the devout who tie threads round the trunk. Democracy started in North America when the Great Peacemaker formed the Iroquois Confederacy, inspiring the warriors of the original five American nations to bury their weapons under the Tree of Peace, an eastern white pine (Pinus strobus). In the creation story in the Bible, the tree of life and the knowledge of good and evil was planted by God in the Garden of Eden.
Sacred groves exist in China, India, Africa and elsewhere. They are places where the deities live and where all the living things are either sacred or are companions of the gods. Folklore lays down the supernatural penalties that will result if desecration takes place for example by the felling of trees. Because of their protected status, sacred groves may be the only relicts of ancient forest and have a biodiversity much greater than the surrounding area. Some Ancient Indian tree deities, such as Puliyidaivalaiyamman, the Tamil deity of the tamarind tree, or Kadambariyamman, associated with the kadamba tree were seen as manifestations of a goddess who offers her blessings by giving fruits in abundance.
The tallest living tree is believed to be a coast redwood (Sequoia sempervirens) at Redwood National Park, California. It has been named Hyperion and is 115.66 metres (379.5 ft) tall. The tallest known broad-leaved tree is a mountain ash (Eucalyptus regnans) growing in Tasmania with a height of 97 metres (318 ft). The largest tree by volume is believed to be a giant sequoia (Sequoiadendron giganteum) known as the General Sherman Tree in the Sequoia National Park in Tulare County, California. Only the trunk is used in the calculation and the volume is estimated to be 1,487 m³ (52,508 cu ft). Also in California is the oldest living tree with a verified age. It is a Great Basin bristlecone pine (Pinus longaeva) called Methuselah growing in the White Mountains. It has been dated by drilling a core sample and counting the annual rings and was considered to be 4,844 years old in 2012. It is thought likely that other bristlecone pines exceed 5,000 years of age. A little further south, at Santa Maria del Tule, Oaxaca, Mexico, is the tree with the broadest trunk. It is a Montezuma cypress (Taxodium mucronatum) known as Árbol del Tule and its diameter at breast height is 11.62 m (38.1 ft) giving it a girth of 36.2 m (119 ft). The tree's trunk is far from round and the exact dimensions may be misleading as the circumference includes much empty space between the large buttress roots.
Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines, and shrubs. Bark refers to all the tissues outside of the vascular cambium and is a nontechnical term. It overlays the wood and consists of the inner bark and the outer bark. The inner bark, which in older stems is living tissue, includes the innermost area of the periderm. The outer bark in older stems includes the dead tissue on the surface of the stems, along with parts of the innermost periderm and all the tissues on the outer side of the periderm. The outer bark on trees is also called the rhytidome.
Products used by people that are derived from bark include: bark shingle siding and wall coverings, spices and other flavorings, tanbark for tannin, resin, latex, medicines, poisons, various hallucinatory chemicals and cork. Bark has been used to make cloth, canoes, and ropes and used as a surface for paintings and map making. A number of plants are also grown for their attractive or interesting bark colorations and surface textures or their bark is used as landscape mulch.
What is commonly called bark includes a number of different tissues. Cork is an external, secondary tissue that is impermeable to water and gases, and is also called the phellem. The cork is produced by the cork cambium which is a layer of meristematically active cells which serve as a lateral meristem for the periderm. The cork cambium, which is also called the phellogen, is normally only one cell layer thick and it divides periclinally to the outside producing cork. The phelloderm, which is not always present in all barks, is a layer of cells formed by and interior to the cork cambium. Together, the phellem (cork), phellogen (cork cambium) and phelloderm constitute the periderm.
Cork cell walls contain suberin, a waxy substance which protects the stem against water loss, the invasion of insects into the stem, and prevents infections by bacteria and fungal spores. The cambium tissues, i.e., the cork cambium and the vascular cambium, are the only parts of a woody stem where cell division occurs; undifferentiated cells in the vascular cambium divide rapidly to produce secondary xylem to the inside and secondary phloem to the outside. Phloem is a nutrient-conducting tissue composed of sieve tubes or sieve cells mixed with parenchyma and fibers. The Cortex is the primary tissue of stems and roots. In stems the cortex is between the epidermis layer and the phloem, in roots the inner layer is not phloem but the pericycle.
From the outside to the inside of a mature woody stem, the layers include:
The bark includes (1) through (5), and is composed of periderm and phloem and the cells that produce these tissues. The periderms includes (1), (2) and (3).
In young stems, which lack what is commonly called bark, the tissues are from the outside to the inside: epidermis, periderm, cortex, primary phloem, secondary phloem, vascular cambium, secondary xylem, and primary xylem. As the stem ages and grows, changes occur that transform the surface of the stem into the bark. The epidermis, which is a layer of cells that cover the plant body, including the stems, leaves, flowers and fruits, that protects the plant from the outside world. In old stems the epidermal layer, cortex, and primary phloem become separated from the inner tissues by thicker formations of cork. Due to the thickening cork layer these cells die because they do not receive water and nutrients. This dead layer is the rough corky bark that forms around tree trunks and other stems.
Often a secondary covering called the periderm forms on small woody stems and many non woody plants, which is composed of cork (phellem), the cork cambium (phellogen), and the phelloderm. The periderm forms from the phellogen which serves as a lateral meristem. The periderm replaces the epidermis, and acts as a protective covering like the epidermis. Mature phellem cells have suberin in their walls to protect the stem from desiccation and pathogen attack. Older phellem cells are dead, as is the case with woody stems. The skin on the potato tuber (which is an underground stem) constitutes the cork of the periderm.
In woody plants the epidermis of newly grown stems is replaced by the periderm later in the year. As the stems grow a layer of cells form under the epidermis, called the cork cambium, these cells produce cork cells that turn into cork. A limited number of cell layers may form interior to the cork cambium, called the phelloderm. As the stem grows, the cork cambium produces new layers of cork which are impermeable to gases and water and the cells outside of the periderm, namely the epidermis, cortex and older secondary phloem die.
Within the periderm are lenticels, which form during the production of the first periderm layer. Since there are living cells within the cambium layers that need to exchange gases during metabolism, these lenticels, because they have numerous intercellular spaces, allow gaseous exchange with the outside atmosphere. As the bark develops, new lenticels are formed within the cracks of the cork layers.
The rhytidome is the most familiar part of bark, it is the outer layer that covers the trunks of trees. It is composed mostly of dead cells and is produced by the formation of multiple layers of suberized periderm, cortical and phloem tissue. It is generally thickest and most distinctive at the trunk or bole (The area from the ground to where the main branching starts) of the tree.
Cork, sometimes confused with bark in colloquial speech, is the outermost layer of a woody stem, derived from the cork cambium. It serves as protection against damage from parasites, herbivorous animals and diseases, as well as dehydration and fire. Cork can contain antiseptics like tannins, that protect against fungal and bacterial attacks that would cause decay.
In some plants, the bark is substantially thicker, providing further protection and giving the bark a characteristically distinctive structure with deep ridges. In the cork oak (Quercus suber) the bark is thick enough to be harvested as a cork product without killing the tree; in this species the bark may get very thick (e.g. more than 20 cm has been reported ). Some barks can be removed in long sheets; the smooth surfaced bark of birch trees has been used as a covering in the making of canoes, as the drainage layer in roofs, for shoes, backpacks etc. The most famous example of using birch bark for canoes is the birch canoes of North America.
The inne bark (phloem) of some trees is edible; in Scandinavia, bark bread is made from rye to which the toasted and ground innermost layer of bark of scots pine or birch is added, the Sami people of far northern Europe used large sheets of Pinus sylvestris bark that were removed in the spring, prepared and stored for use as a staple food resource and the inner bark was eaten fresh, dried or roasted.
Bark contains strong fibres known as bast, and there is a long tradition in northern Europe of using bark from coppiced young branches of the small-leaved lime (Tilia cordata) to produce cordage and rope, used for example in the rigging of Viking age longships.
Among the commercial products made from bark are cork, cinnamon, quinine (from the bark of Cinchona) and aspirin (from the bark of willow trees). The bark of some trees notably oak (Quercus robur) is a source of tannic acid, which is used in tanning. Bark chips generated as a by-product of lumber production, are often used in bark mulch in western North America. Bark is important to the horticultural industry since in shredded form it is used for plants that do not thrive in ordinary soil, such as epiphytes.
Cut logs used for the production of lumber or even log cabins generally have the bark removed, either just before cutting or for curing. Such logs and even trunks and branches found in their natural state of decay in forests, where the bark has fallen off, are said to be decorticated.
A number of living organisms live in or on bark, including insects, fungi and other plants like mosses, algae and other vascular plants. Many of these organisms are pathogens or parasites but some also have symbiotic relationships.
The degree to which trees are able to repair gross physical damage to their bark is very variable. Some are able to produce a callus growth which heals over the wound rapidly, but leaves a clear scar, whilst others such as oaks do not produce an extensive callus repair.
Frost crack and sun scald are examples of damage found on tree bark which trees can repair to a degree, depending on the severity.
Extensive callus growth on a young Ash tree with Frost crack
Beech bark with callus growth following fire (heat) damage
Holly Oak Damaged
A samara is a type of fruit in which a flattened wing of fibrous, papery tissue develops from the ovary wall. A samara is a simple dry fruit and indehiscent (not opening along a seam). It is a winged achene. The shape of a samara enables the wind to carry the seed farther away than regular seeds from the parent tree:
A samara is sometimes called a key and is often referred to as a whirlybird, helicopter, whirligig, polynose, or, in the north of England, a spinning jenny. During the autumn months, they are a popular source of amusement for children who enjoy tossing them in the air and watching them spin to the ground.
Some species that normally produce double samaras, such as Acer pseudoplatanus, can also produce a few multi-lobed samaras with 3 or 4 seeds.
An unusual triple samara of sycamore maple (Acer pseudoplatanus, normally paired)
Seeds of the tropical ash (Fraxinus uhdei)
The hoptree (Ptelea trifoliata)
The Siberian elm (Ulmus pumila)
Diameter at breast height, or DBH, is a standard method of expressing the diameter of the trunk or bole of a standing tree. DBH is one of the most common dendrometric measurements.
Tree trunks are measured at the height of an adult's breast, which is defined differently in different countries and situations. In continental Europe, Australia, the UK, and Canada the diameter is measured at 1.3 metres above ground. In The US, New Zealand, Burma, India, Malaysia, and South Africa, breast height diameter is measured at a height of 1.4 metres. Previously 4.5 ft (1.37 m) was used. In many cases the height makes little difference to the measured diameter. Ornamental trees are usually measured at 1.5 metres above ground.
However, some authors correctly maintain that the term DBH should be abolished precisely because the heights at which the diameter is measured are so variable and because it may strongly influence forestry calculations such as biomass. Instead Dx was proposed whereby the x denotes the exact height above the floor (and along the stem) at which the diameter is measured. For instance D130 denotes a diameter measured at 130 cm above the floor and along the stem.
On sloping ground, the "above ground" reference point is usually taken as the highest point on the ground touching the trunk, but some use the average between the highest and lowest points of ground. If the DBH point falls on a swelling in the trunk it is customary to measure the girth below the swelling at the point where the diameter is smallest. Other ambiguous settings for determining the exact place where to measure the diameter is given in Dahdouh-Guebas & Koedam (2006).
The two most common instruments used to measure DBH are a girthing (or diameter) tape and calipers.
A girthing tape actually measures the girth (circumference) of the tree; the girthing tape is calibrated in divisions of π centimetres (3.14159 cm), thus giving a directly converted reading of the diameter. This assumes the trunk has a circular cross-section, which is typically accurate for most plantation trees.
Calipers consist of two parallel arms one of which is fixed and the other able to slide along a scale. Calipers are held at right-angles to the trunk with the arms on either side of the trunk. Precision can be improved on non-circular stems by averaging two caliper measurements taken at right-angles. Electronic calipers are also available enabling highly accurate measurements to be taken and stored for further analysis.
DBH is used in estimating the amount of timber volume in a single tree or stand of trees utilising the allometric correlation between stem diameter, tree height and timber volume, (Mackie, 2006). It can also be used in the estimation of the age of veteran trees, given that diameter increment is the only, "constant non-reversible feature of tree growth", (White, 1998).
See speciesQuercusList of
An oak is a tree or shrub in the genus Quercus (; Latin "oak tree"), having approximately 600 extant species. The common name "Oak" may also appear in the names of species in related genera, notably Lithocarpus. The genus is native to the Northern Hemisphere, and includes deciduous and evergreen species extending from cool temperate to tropical latitudes in Asia and the Americas. The center of endemism is regarded as North America, particularly Mexico.
Oaks have spirally arranged leaves, with lobed margins in many species; some have serrated leaves or entire leaves with smooth margins. Many deciduous species are marcescent, not dropping dead leaves until spring. The flowers are catkins, produced in spring. The fruit is a nut called an acorn, borne in a cup-like structure known as a cupule; each acorn contains one seed (rarely two or three) and takes 6–18 months to mature, depending on species. The live oaks are distinguished for being evergreen, but are not actually a distinct group and instead are dispersed across the genus.
Oak trees are a flowering plant. Oaks may be considered divided into two genera (sometimes referred to as subgenera) and a number of sections:
The genus Quercus is divided into the following sections:
Rare species of oak trees include scarlet oak (Quercus coccinea), chinkapin oak (Quercus muehlenbergii), and post oak (Quercus stellata).
Interspecific hybridization is quite common among oaks but usually between species within the same section only and most common in the white oak group (subgenus Quercus, section Quercus; see speciesQuercusList of ). Inter-section hybrids, except between species of sections Quercus and Mesobalanus, are unknown. Recent systematic studies appear to confirm a high tendency of Quercus species to hybridize because of a combination of factors. White oaks are unable to discriminate against pollination by other species in the same section. Because they are wind pollinated and they have weak internal barriers to hybridization, hybridization produces functional seeds and fertile hybrid offspring. Ecological stresses, especially near habitat margins, can also cause a breakdown of mate recognition as well as a reduction of male function (pollen quantity and quality) in one parent species.
Frequent hybridization among oaks has consequences for oak populations around the world; most notably, hybridization has produced large populations of hybrids with copious amounts of introgression, and the evolution of new species. Frequent hybridization and high levels of introgression have caused different species in the same populations to share up to 50% of their genetic information. Having high rates of hybridization and introgression produces genetic data that often does not differentiate between two clearly morphologically distinct species, but instead differentiates populations. Numerous hypotheses have been proposed to explain how oak species are able to remain morphologically and ecologically distinct with such high levels of gene flow, but the phenomenon is still largely a mystery to botanists.
The Fagaceae, or oak family, is a very slow evolving clade compared to other angiosperms, and the patterns of hybridization and introgression in Quercus pose a great challenge to the concept of a species since a species is often defined as a group of “actually or potentially interbreeding populations which are reproductively isolated from other such groups.” By this definition, many species of Quercus would be lumped together according to their geographic and ecological habitat, despite clear distinctions in morphology and, to a large extent, genetic data.
Oak wood has a density of about 0.75 g/cm3, great strength and hardness, and is very resistant to insect and fungal attack because of its high tannin content. It also has very appealing grain markings, particularly when quartersawn. Oak planking was common on high status Viking longships in the 9th and 10th centuries. The wood was hewn from green logs, by axe and wedge, to produce radial planks, similar to quarter-sawn timber. Wide, quarter-sawn boards of oak have been prized since the Middle Ages for use in interior paneling of prestigious buildings such as the debating chamber of the House of Commons in London, and in the construction of fine furniture. Oak wood, from Quercus robur and Quercus petraea, was used in Europe for the construction of ships, especially naval men of war, until the 19th century, and was the principal timber used in the construction of European timber-framed buildings. Today oak wood is still commonly used for furniture making and flooring, timber frame buildings, and for veneer production. Barrels in which wines, sherry, and spirits such as brandy, Scotch whisky and Bourbon whiskey are aged are made from European and American oak. The use of oak in wine can add many different dimensions to wine based on the type and style of the oak. Oak barrels, which may be charred before use, contribute to the colour, taste, and aroma of the contents, imparting a desirable oaky vanillin flavour to these drinks. The great dilemma for wine producers is to choose between French and American oakwoods. French oaks (Quercus robur, Q. petraea) give the wine greater refinement and are chosen for the best wines since they increase the price compared to those aged in American oak wood. American oak contributes greater texture and resistance to ageing, but produces more violent wine bouquets. Oak wood chips are used for smoking fish, meat, cheeses and other foods.
Japanese oak is used in the making of professional drums from manufacturer Yamaha Drums. The higher density of oak gives the drum a brighter and louder tone compared to traditional drum materials such as maple and birch. In hill states of India, besides fuelwood and timber, the local people use oak wood for making agricultural implements. The leaves are used as fodder during lean period and bedding for livestock.
The bark of the cork oak is used to produce wine stoppers (corks). This species grows in the Mediterranean Sea region, with Portugal, Spain, Algeria and Morocco producing most of the world's supply. Of the North American oaks, the Northern red oak is the most prized of the red oak group for lumber, all of which is marketed as red oak regardless of the species of origin. It is not good for outdoor use due to its open capillaries. One can blow air through an end grain piece 10 inches long to make bubbles come out in a glass of water. These openings give fungus easy access when the finish deteriorates. The standard for the lumber of the white oak group – all of which is marketed as white oak – is the White Oak. White Oak is often used to make wine barrels. The wood of the deciduous Pedunculate Oak and Sessile Oak accounts for most of the European oak production, but evergreen species, such as Holm oak and Cork oak also produce valuable timber.
The bark of the White Oak is dried and used in medical preparations. Oak bark is also rich in tannin, and is used by tanners for tanning leather. Acorns are used for making flour or roasted for acorn coffee.
Oak galls were used for centuries as the main ingredient in manuscript ink, harvested at a specific time of year.][ In Korea, oak bark is used to make shingles for traditional roof construction.
Oaks are keystone species in a wide range of habitats from Mediterranean semi-desert to subtropical rainforest. For example, oak trees are important components of hardwood forests, and certain species are particularly known to grow in associations with members of the Ericaceae in oak-heath forests. A number of kinds of truffles, including the two well known varieties, the black Périgord truffle and the white Piedmont truffle, have symbiotic relationships with oak trees. The European pied flycatcher is an example of an animal species that often depends upon oak trees.
Many species of oaks are under threat of extinction in the wild, largely due to land use changes, livestock grazing and unsustainable harvesting. For example, over the past 200 years, large areas of oak forest in the highlands of Mexico, Central America and the northern Andes have been cleared for coffee plantations and cattle ranching. There is a continuing threat to these forests from exploitation for timber, fuelwood and charcoal. In the USA, entire oak ecosystems have declined due to a combination of factors still imperfectly known, but thought to include fire suppression, increased consumption of acorns by growing mammal populations, herbivory of seedlings, and introduced pests. In a recent survey, 78 wild oak species have been identified as being in danger of extinction, from a global total of over 500 species. The proportion under threat may be much higher in reality, as there is insufficient information about over 300 species, making it near impossible to form any judgement of their status.
In the Himalayan region of India, oak forests are being invaded by pine forests due to the increase in temperature. The associated species of pine forest may cross frontiers and become new elements of the oak forests.
Sudden Oak Death (Phytophthora ramorum) is a water mould that can kill oaks within just a few weeks. Oak Wilt, caused by the fungus Ceratocystis fagacearum (a fungus closely related to Dutch Elm Disease), is also a lethal disease of some oaks, particularly the red oaks (the white oaks can be infected but generally live longer). Other dangers include wood-boring beetles, as well as root rot in older trees which may not be apparent on the outside, often being discovered only when the trees come down in a strong gale. Oak apples are galls on oaks made by the gall wasp. The female kermes scale causes galls to grow on kermes oak. Oaks are used as food plants by the larvae of Lepidoptera (butterfly and moth) species such as the Gypsy Moth, Lymantria dispar, which can defoliate oak and other broadleaved tree species in North America.
A considerable number of galls are found on oak leaves, buds, flowers, roots, etc. Examples are Oak artichoke gall, Oak Marble gall, Oak apple gall, Knopper gall, and Spangle gall.
A number of species of fungus cause powdery mildew on oak species. In Europe the species Erysiphe alphitoides is the most common cause.
A new and as yet little understood disease of mature oaks, Acute oak decline, has been reported in parts of the UK since 2009.
Additionally, the Oak Processionary Moth (Thaumetopoea processionea) has become a serious threat in the UK since 2006. It defoliates the trees, and is hazardous to human health.
In recent years, a new infestation of a hazardous moth has effected the population of oak trees in London. The oak processionary moth has been discovered but the caterpillars of this moth are especially harmful to oak trees because they eat the leaves leaving it vulnerable to other types of diseases.
The leaves and acorns of the oak tree are poisonous to cattle, horses, sheep, and goats in large amounts due to the toxin tannic acid, and cause kidney damage and gastroenteritis. Additionally, once livestock have a taste for the leaves and acorns, they may seek them out. Symptoms of poisoning include lack of appetite, depression, constipation, diarrhea (which may contain blood), blood in urine, and colic. The exception to livestock and oak toxicity is the domestic pig, which may be fed entirely on acorns in the right conditions, and has traditionally been pastured in oak woodlands (such as the Spanish dehesa and the English system of pannage) for hundreds of years. Acorns are also edible to humans in processed form, after leaching of the tannins. They are a staple part of the forage consumed by wildlife, including squirrels.
The oak is a common symbol of strength and endurance and has been chosen as the national tree of many countries. Already an ancient Germanic symbol (in the form of the Donar Oak, for instance), certainly since the early nineteenth century, it stands for the nation of Germany and oak branches are thus displayed on some German coins, both of the former Deutsche Mark and the current Euro currency. In 2004 the Arbor Day Foundation held a vote for the official National Tree of the United States of America. In November 2004, Congress passed legislation designating the oak as America's National Tree.
Other countries have also designated the oak as their national tree including England, Estonia, France, Germany, Moldova, Romania, Latvia, Lithuania, Poland, the United States, Wales, Galicia, Bulgaria, and Serbia.
The oak is the emblem of County Londonderry in Northern Ireland, as a vast amount of the county was covered in forests of the tree until relatively recently. The name of the county comes from the city of Derry, which originally in Irish was known as Doire meaning oak.
The Irish County Kildare derives its name from the town of Kildare which originally in Irish was Cill Dara meaning the Church of the Oak or Oak Church.
Iowa designated the oak as its official state tree in 1961; and the White Oak is the state tree of Connecticut, Illinois and Maryland. The Northern Red Oak is the provincial tree of Prince Edward Island, as well as the state tree of New Jersey. The Live Oak is the state tree of Georgia, USA.
The oak is a national symbol from the Basque Country, specially in the province of Biscay.
The coat-of-arms of Vest-Agder, Norway, features an oak tree.
Oak leaves are traditionally an important part of German Army regalia.][ They also symbolize rank in the United States Armed Forces. A gold oak leaf indicates an O-4 (Major or Lt. Commander), whereas a silver oak leaf indicates an O-5 (Lt. Colonel or Commander). Arrangements of oak leaves, acorns and sprigs indicate different branches of the United States Navy Staff corps officers. Oak leaves are embroidered onto the covers (hats) worn by field grade officers and flag officers in the United States armed services.
If a member of the United States Army or Air Force earns multiple awards of the same medal, then instead of wearing a ribbon or medal for each award, he or she wears one metal representation of an "oak leaf cluster" attached to the appropriate ribbon for each subsequent award.][
The oak tree is used as a symbol by a number of political parties. It is the symbol of the Conservative Party in the United Kingdom, and formerly of the Progressive Democrats in Ireland. In the cultural arena, the oakleaf is the symbol of the National Trust (UK) and The Royal Oak Foundation.
In Greek mythology, the oak is the tree sacred to Zeus, king of the gods. In Zeus's oracle in Dodona, Epirus, the sacred oak was the centerpiece of the precinct, and the priests would divine the pronouncements of the god by interpreting the rustling of the oak's leaves.
In Baltic mythology, the oak is the sacred tree of Latvian Pērkons, Lithuanian Perkūnas and Prussian Perkūns.][ Pērkons is the god of thunder and one of the most important deities in the Baltic pantheon.
In Celtic polytheism, the name of the oak tree was part of the Proto-Celtic word for 'druid': *derwo-weyd- > *druwid- ; however, Proto-Celtic *derwo- (and *dru-) can also be adjectives for 'strong' and 'firm', so Ranko Matasovic interprets that *druwid- may mean 'strong knowledge'. As in other Indo-European faiths, Taranus, being a Thunder God, was associated with the oak tree. The Indo-Europeans worshiped the oak and connected it with a thunder or lightning god; "tree" and drus may also be cognate with "Druid," the Celtic priest to whom the oak was sacred. There has even been a study that shows that oaks are more likely to be struck by lightning than any other tree of the same height.
In Norse mythology, the oak was sacred to the thunder god, Thor. Thor's Oak was a sacred tree of the Germanic Chatti tribe. According to legend, the Christianisation of the heathen tribes by Saint Boniface was marked by the oak's being replaced by the fir (whose triangular shape symbolizes the Trinity) as a "sacred" tree.
In the Bible, the oak tree at Shechem is the site where Jacob buries the foreign gods of his people (Gen. 35:4) . In addition, Joshua erects a stone under an oak tree as the first covenant of the Lord (Josh. 24.25–7). In Isaiah 61, the prophet refers to the Israelites as "Oaks of Righteousness".
In Slavic mythology, the oak was the most important tree of the god Perun.
Several singular oak trees, such as the Royal Oak in Britain and the Charter Oak in the United States, are of great historical or cultural importance; for a list of important oaks, see Individual oak trees.
"The Proscribed Royalist, 1651", a famous painting by John Everett Millais, depicted a Royalist fleeing from Cromwell's forces and hidden in an oak. Millais painted the picture in Hayes, Kent, from a local oak tree that became known as the Millais Oak.
Approximately 50 km west of Toronto, Canada is the town of Oakville, ON, famous for its history as a shipbuilding port on Lake Ontario.
The city of Raleigh, N.C., is known as "The City of Oaks."
The Jurupa Oak tree – a clonal colony of Quercus palmeria or Palmer’s Oak found in Riverside County, California – is believed to be the world's oldest organism at 13,000 years.
Large groups of very old oak trees are rare. One of the oldest groups of oak trees, found in Poland, is about 480 years old, which was assessed by dendrochronological methods.
In Republican Rome a crown of oak leaves was given to those who had saved a life of a citizen in battle; it was called the "civic oak"
Linnaeus described only five species of oak from eastern North America, based on general leaf form. These were White oak, Quercus alba; Chestnut oak, Q. montana; Red oak, Q. rubra; Willow oak Q. phellos; and Water oak, Q. nigra. Because he was dealing with confusing leaf forms, the Q. prinus and Q. rubra specimens actually included mixed foliage of more than one species.
The crown of a plant refers to the totality of the plant's aboveground parts, including stems, leaves, and reproductive structures. A plant canopy consists of one or more plant crowns growing in a given area.
The crown of a woody plant (tree, shrub, liana) is the branches, leaves, and reproductive structures extending from the trunk or main stems.
Shapes of crowns are highly variable. The major types for trees are the excurrent branching habit resulting in conoid shapes and decurrent (deliquescent) branching habit, resulting in round shapes. Crowns are also characterized by their width, depth, surface area, volume, and density. Measurements of crowns are important in quantifying and qualifying plant health, growth stage, and efficiency.
Major functions of the crown include light energy assimilation, carbon dioxide absorption and release of oxygen via photosynthesis, energy release by respiration, and movement of water to the atmosphere by transpiration. These functions are performed by the leaves. Branches of the crown provide mechanical support to distribute the leaves efficiently and serve as conduits for resources (water, nutrients, photosynthates) to perform these functions.
Plant morphology or phytomorphology is the study of the physical form and external structure of plants. This is usually considered distinct from plant anatomy, which is the study of the internal structure of plants, especially at the microscopic level. Plant morphology is useful in the visual identification of plants.
Plant morphology "represents a study of the development, form, and structure of plants, and, by implication, an attempt to interpret these on the basis of similarity of plan and origin." There are four major areas of investigation in plant morphology, and each overlaps with another field of the biological sciences. Plants
Plant pathology (also phytopathology) is the scientific study of plant diseases caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants. Not included are ectoparasites like insects, mites, vertebrate, or other pests that affect plant health by consumption of plant tissues. Plant pathology also involves the study of pathogen identification, disease etiology, disease cycles, economic impact, plant disease epidemiology, plant disease resistance, how plant diseases affect humans and animals, pathosystem genetics, and management of plant diseases.
The majority of phytopathogenic fungi belong to the Ascomycetes and the Basidiomycetes.
Oak wilt is a fungal disease that can quickly kill an oak tree. It is caused by the fungus Ceratocystis fagacearum. Symptoms vary by tree species but generally consist of leaf discoloration, wilt, defoliation, and death. The fungus is spread from diseased to healthy trees by insect vectors or via connections between tree roots. Management of the disease consists mainly of preventing infection by avoiding tree wounds, removing diseased trees and digging trenches that disrupt root connections. Chemical treatments are available and are mostly preventive as well. Oak wilt is an important disease of oak for timber production and of oak trees in urban areas.
Oak wilt affects all oak species, but affects different groups differently. Oaks in the red oak group (black]disambiguation needed[, northern red, northern pin and others with pointed leaf edges) are particularly susceptible and, when infected, generally die over the course of a single summer. Infected red oak wilt from the top of the tree down as leaves become a bronze color and fall off the tree. Another symptom is discoloration of the vascular tissues. Brown streaks or spots can be seen under the bark in the sapwood.
Bonsai aesthetics are the aesthetic goals and characteristics of the Japanese tradition in the art of growing a miniature tree in a container. Many Japanese cultural characteristics, particularly the influence of Zen Buddhism and the expression of sabi or wabi, inform the bonsai tradition in that culture. As well, a lengthy catalog of conventional tree shapes and styles helps provide cohesion to the Japanese styling tradition. A number of other cultures around the globe have adopted the Japanese approach to bonsai, and while some variations have begun to appear, most hew closely to the rules and design philosophies of the Japanese tradition.
The aesthetics of penjing, a Chinese form of container-grown tree, are distinct from those of bonsai and are discussed elsewhere. The aesthetics of saikei, Japanese multi-tree landscapes in a container, are also distinct and are not described in this article. Botany