Atreeis a tallplantwith a trunk and branches made ofwood. It can live for many years. The four main parts of a tree are theroots, thetrunk, thebranches, and theleaves.The roots of a tree are usually under the ground. One case for which this is not true are the roots of themangrovetree.[1]A single tree has many roots. The roots carry food andwaterfrom the ground through the trunk and branches to the leaves of the tree. They can also breathe in air.[1]Sometimes, roots are specialized intoaerial roots, which can also provide support, as is the case with theBanyantree.The trunk is the main body of the tree. The trunk is covered withbarkwhich protects it from damage. Branches grow from the trunk. They spread out so that the leaves can get more sunlight.The leaves of a tree are green most of the time, but they can come in many colours, shapes and sizes. The leaves take in sunlight and use water and food from the roots to make the tree grow, and to reproduce.Trees andshrubstake inwaterandcarbon dioxideand give outoxygenwith sunlight to formsugars. This is the opposite of what animals do in respiration. Plants also do some respiration using oxygen the way animals do. They need oxygen as well as carbon dioxide to live.Contents[hide] 1Parts of trees 1.1Growth of the trunk 1.2Roots 1.3Exceptions 2Classification 3Records 3.1Height 3.2Stoutest trees 3.3Age of trees 4Tree value estimation 5Tree climbing 6Damage 7Trees in culture 7.1Wishing trees 7.2Tree worship 7.2.1World tree 7.3In literature 8List of trees 9Related pages 10References 11Other websitesParts of trees[change|change source]

Beechleaves.

Treerootsanchor the structure and providewaterandnutrients. The ground haserodedaway around the roots of this youngpinetree.

The dark lines between the centre and the bark aremedullary rays, which allow nutrients to flow across the tree trunk.The parts of a tree are theroots,trunk(s),branches,twigsandleaves. Tree stems are mainly made of support and transport tissues (xylemandphloem).Woodconsists ofxylemcells, andbarkis made ofphloemand other tissues external to the vascular cambium.Growth of the trunk[change|change source]As a tree grows, it may producegrowth ringsas new wood is laid down around the old wood.It may live to be a thousand years old. In areas with seasonal climate, wood produced at different times of the year may alternate light and dark rings. In temperate climates, and tropical climates with a single wet-dry season alternation, the growth rings are annual, each pair of light and dark rings being one year of growth. In areas with two wet and dry seasons each year, there may be two pairs of light and dark rings each year; and in some (mainly semi-desert regions with irregular rainfall), there may be a new growth ring with eachrainfall.[2]In tropicalrainforestregions, with constant year-round climate, growth is continuous. Growth rings are not visible and there is no change in the wood texture. Inspecieswith annual rings, these rings can be counted to find the age of the tree. This way, wood taken from trees in the past can be dated, because the patterns of ring thickness are very distinctive. This isdendrochronology. Very few tropical trees can be accurately dated in this manner.Roots[change|change source]Therootsof a tree are generally down in earth, providinganchoragefor the parts above ground, and taking inwaterandnutrientsfrom thesoil. Most trees need help from a fungus for better uptake of nutriens: this ismycorrhiza. Most of a tree'sbiomasscomes from carbon dioxide absorbed from the atmosphere (seephotosynthesis). Above ground, the trunk gives height to the leaf-bearing branches, competing with other plant species forsunlight. In many trees, the order of the branches makes exposure of the leaves to sunlight better.Exceptions[change|change source]Not all trees have all the organs or parts as mentioned above. For example, most palm trees are not branched, thesaguaro cactusof North America has no functional leaves,tree fernsdo not produce bark, etc. Based on their general shape and size, all of these are nonetheless generally regarded as trees. Trees can vary very much. A plant form that is similar to a tree, but generally having smaller, multiple trunks and/or branches that arise near the ground, is called ashrub(or a bush). Even though that is true, no precise differentiation between shrubs and trees is possible. Given their small size,bonsaiplants would not technically be 'trees', but one should not confuse reference to the form of a species with the size or shape of individual specimens. A spruce seedling does not fit the definition of a tree, but all spruces are trees.Classification[change|change source]

ASweet Chestnuttree inTicino,SwitzerlandA tree is a plant form that can be found in many differentordersandfamiliesof plants. Trees show manygrowth forms, leaf type and shape, bark traits andorgans.The tree form has changed separately in classes of plants that are not related, in response to similar problems (for the tree). With about 100,000typesof trees, the number of tree types in the whole world might be onefourthof all livingplanttypes.[3]Most tree species grow intropicalparts of the world and many of these areas have not been surveyed yet bybotanists(they study plants), making species difference and ranges not well understood.[4]The earliest trees weretree ferns,horsetailsandlycophytes, which grew inforestsin theCarboniferousperiod; tree ferns still survive, but the only surviving horsetails and lycophytes are not of tree form. Later, in theTriassicPeriod,conifers,ginkgos,cycadsand othergymnospermsappeared, and subsequentlyflowering plantsin theCretaceousperiod. Most species of trees today are flowering plants (Angiosperms) andconifers.A small group of trees growing together is called agroveorcopse, and a landscape covered by a dense growth of trees is called aforest. Severalbiotopesare defined largely by the trees that inhabit them; examples arerainforestandtaiga(seeecozones). A landscape of trees scattered or spaced across grassland (usually grazed or burned over periodically) is called asavanna. A forest of great age is calledold growth forestorancient woodland(in the UK). A very young tree is called a sapling.