When the days get shorter and the temperature begins to decrease, the leaves no longer make new chlorophyll and the red and yellow pigments already present in the blades become apparent. This causes the cells at the junction of the petiole and the twig to weaken until 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, such as at the start of the dry season. Trees can be pollinated either by wind or by animals, mostly insects. Many angiosperm trees are insect pollinated. Wind pollination may take advantage of increased wind speeds high above the ground. Some rely on wind, with winged or plumed seeds. Others rely on animals, for example with edible fruits. Others again eject their seeds ballistic dispersal , or use gravity so that seeds fall and sometimes roll.
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. For a tree seedling to grow into an adult tree it needs light. 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 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. Fire stimulates release and germination of seeds of the jack pine , and also enriches the forest floor with wood ash and removes competing vegetation.
The flame tree Delonix regia 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.
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. Other seeds, such as apple pips and plum stones, have fleshy receptacles and smaller fruits like hawthorns have seeds enclosed in edible tissue; animals including mammals and birds eat the fruits and either discard the seeds, or swallow them so they pass through the gut to be deposited in the animal's droppings well away from the parent tree.
The germination of some seeds is improved when they are processed in this way. 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 earliest trees 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 dating back to the Middle Devonian about million years ago. Prior to this discovery, Archaeopteris was the earliest known tree. 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 million years ago.
This is considered to be a living fossil because it is virtually unchanged from the fossilised specimens found in Triassic deposits. During the Mesozoic to 66 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 displace the conifers during the Tertiary era 66 to 2 million years ago when forests covered the globe. In the interglacials , trees recolonised the land that had been covered by ice, only to be driven back again in the next ice age.
Trees are an important part of the terrestrial ecosystem ,  providing essential habitats including many kinds of forest for communities of organisms. Epiphytic plants such as ferns , some mosses, liverworts, orchids and some species of parasitic plants e. Leaves, flowers and fruits are seasonally available. On the ground underneath trees there is shade, and often there is undergrowth, leaf litter, and decaying wood that provide other habitat.
Many species of tree support their own specialised invertebrates. In their natural habitats, different species of insect have been found on the English oak Quercus robur  and species of invertebrate on the Tasmanian oak Eucalyptus obliqua. In ecosystems such as mangrove swamps, trees play a role in developing the habitat, since the roots of the mangrove trees reduce the speed of flow of tidal currents and trap water-borne sediment, reducing the water depth and creating suitable conditions for further mangrove colonisation. Thus mangrove swamps tend to extend seawards in suitable locations.
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.
An area of land planted with fruit or nut trees is an orchard. 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, 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. These include coconuts Cocos nucifera , Brazil nuts Bertholletia excelsa , pecans Carya illinoinensis , hazel nuts Corylus , almonds Prunus dulcis , walnuts Juglans regia , pistachios Pistacia vera and many others. They are high in nutritive value and contain high-quality protein, vitamins and minerals as well as dietary fibre.
Walnuts are particularly beneficial to health and contain a higher level of antioxidants than do other nuts. 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. It is piped to a sugarhouse where it is heated to concentrate it and improve its flavour. Sweet birch sap is more dilute than maple sap; a 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.
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 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. 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.
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. 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.
Timber, "trees that are grown in order to produce wood"  is cut into lumber sawn wood for use in construction. 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. Besides inspiring artists down the centuries, trees have been used to create art. Living trees have been used in bonsai and in tree shaping , and both living and dead specimens have been sculpted into sometimes fantastic shapes.
The word bonsai is often used in English as an umbrella term for all miniature trees in containers or pots. The purposes of bonsai are primarily contemplation for the viewer and the pleasant exercise of effort and ingenuity for the grower. Bonsai can be created from nearly any perennial woody-stemmed tree or shrub species  that produces true branches and can be cultivated to remain small through pot confinement with crown and root pruning. Some species are popular as bonsai material because they have characteristics, such as small leaves or needles, that make them appropriate for the compact visual scope of bonsai and a miniature deciduous forest can even be created using such species as Japanese maple , Japanese zelkova or hornbeam.
Tree shaping is the practice of changing living trees and other woody plants into man made shapes for art and useful structures. There are a few different methods  of shaping a tree. There is a gradual method and there is an instant method. Tree shaping has been practised for at least several hundred years, the oldest known examples being the living root bridges built and maintained by the Khasi people of Meghalaya , India using the roots of the rubber tree Ficus elastica.
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. 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. At least drugs come from plant sources , many of them from the bark of trees. 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. Trees create a visual impact in the same way as do other landscape features and give a sense of maturity and permanence to park and garden. They are grown for the beauty of their forms, their foliage, flowers, fruit and bark and their siting is of major importance in creating a landscape. They can be grouped informally, often surrounded by plantings of bulbs, laid out in stately avenues or used as specimen trees. As living things, their appearance changes with the season and from year to year.
Trees are often planted in town environments where they are known as street trees or amenity trees. They can provide shade and cooling through evapotranspiration , absorb greenhouse gases and pollutants, intercept rainfall, and reduce the risk of flooding. It has been shown that they are beneficial to humans in creating a sense of well-being and reducing stress.
Many towns have initiated tree-planting programmes. Latex is a sticky defensive secretion that protects plants against herbivores.
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. 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. Fossilised resin is known as amber and was mostly formed in the Cretaceous to 66 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. The roots of the tree often reflect a similar spread and growth below ground as the tree does above ground, creating a reflection.
As above, so below. I learned a few years ago that there are such thing as male and female trees. I guess that makes sense. There is also a myth about ancient guardian trees, that protect the trees in the forest, who some say can actually move across the ground as if they have feet. One day, I had a particularly hard healing session; I had brought in a lot of energy over a very short period of time, and my body ached in discomfort.
The person recovered immediately from what appeared to be radiation poisoning. And when I left from the client, I went outside, trying to rebalance my energy.
The number of trees in the world, according to a estimate, is 3. Newton Ask a Scientist. For other uses, see Tree disambiguation. Because this growth ruptures the epidermis of the stem, woody plants also have a cork cambium that develops among the phloem. Connect with Black Inc.
I walked up to a beautiful old Cherry Tree. And as I stood, leaning against the tree, my head and arms resting on the branches in the tree, I felt as if the tree was trying to hug me. I opened my eyes, because I thought I was imagining things. But I continued to feel a strong supporting connection from the tree. Within moments, I felt balanced, and at peace again.
And while I may not be a tree hugger, I have definitely been hugged by trees. I believe there is a lot more to things in nature than we recognize, because of our busy lives. I believe that all things are made of energy. He used the tree as an example to illustrate his point: If we perceive the tree in this way, rather than as a bunch of dead particles into which the property of life has somehow infused when the seed is planted, then its aliveness ceases to be such a mystery.
Trees possess consciousness and intelligence, as do all living things in varying measures: It is only human ignorance and arrogance that asserts otherwise. Trees and plants possess awareness , sensitivity , memory , and a capacity to feel — all of which attributes have been established scientifically and are sufficiently well documented.
Yet they remain virtually unknown, due to the limited and limiting doctrine of materialism which currently pervades virtually all of our academic, scientific as well as educational, establishments — seriously limiting the possibilities of more advanced knowledge. Kirlian 'electrophotograph' of a leaf - photo by Thorius.
They may be blind, deaf and dumb in the human sense, but there is no doubt in my mind that they are extremely sensitive … They radiate energy, forces that are beneficial to man. One can feel these forces!