Girdling, also calledring-barking, is the circumferential removal or injury of thebark (consisting ofcork cambium or "phellogen",phloem,cambium and sometimes also thexylem) of abranch ortrunk of awoody plant. Girdling prevents the tree from sending nutrients from its foliage to its roots, resulting in thedeath of the tree over time, and it can also prevent flow of nutrients in the other direction depending on how much of the xylem is removed. A branch completely girdled will fail; and, when the main trunk of a tree is girdled, the entire tree will die if it cannot regrow from above to bridge the wound. Human practices of girdling includeforestry,horticulture, andvandalism.Foresters use the practice of girdling to thinforests. Extensivecankers caused by certainfungi,bacteria orviruses can girdle a trunk or limb. Animals such as rodents will girdle trees by feeding on outer bark, often during winter under snow. Girdling can also be caused by herbivorous mammals feeding on plant bark and by birds and insects, both of which can effectively girdle a tree by boring rows of adjacent holes.
Orchardists use girdling as a cultural technique to yield larger fruit or to set fruit.[1] Inviticulture (grape cultivation), the technique is also called "cincturing".
Like all vascular plants, trees use twovascular tissues for transportation ofwater and nutrients: thexylem (also known as thewood) and thephloem (the innermost layer of thebark). Girdling results in the removal of thephloem, and death occurs from the inability of theleaves to transportsugars (primarilysucrose) to theroots. In this process, thexylem is left untouched, and the tree can usually still temporarily transportwater and minerals from the roots to the leaves. Trees normally sprout shoots below the wound; if not, the roots die. Death occurs when the roots can no longer produceATP and transport nutrients upwards through thexylem. The formation of new shoots below the wound can be prevented by painting the wound with herbicide.[2]
Girdling is a slow process compared tofelling and is often used only when necessary, such as in the removal of an individual tree from an ecologically protected area without damaging surrounding growth.[citation needed] An example is the girdling of selectedDouglas-fir trees in some NorthernCalifornia oak woodlands, such asAnnadel State Park, in order to prevent that Douglas-fir from massive invasion of the mixed oak woodland.[3] Girdling can be used to create standing dead wood, orsnags. This can provide a valuable habitat for a variety of wildlife, including insects and nesting birds.[citation needed]
Accidental girdling is also possible and some activities must be performed with care. Saplings which are tied to a supporting stake may unintentionally be girdled as they grow, due to friction caused by contact with the tie. If ropes are tied frequently to a tree (e.g. to tether an animal or moor a boat), the friction of the rope can also lead to the removal of bark.[citation needed]
Girdling is also used as a technique to force afruit-bearing plant to bear larger fruit. A farmer would place a girdle (bark removal) at base of a large branch or at the trunk. Thus, all sugars manufactured by the leaves have no sinks but the fruit, which grows to above the normal size. Forgrapes girdling orcincturing is used to make the grapes large and sweeter on thegrape canopy and are sold asgirdled grapes.Flowering and fruit setting is a problem on some trees; girdling may improve yield in the same way. The "damage" done by girdling restricts the movement ofnutrients to theroots, thus thecarbohydrates produced in the leaves do not go to the roots for storage. Girdling temporarily stops tree growth and thus can serve as a form of pruning.[4] Rootpruning, an ancient Asian practice, and other controlled damaging, such as driving nails into the trunk or beating the branches and trunk, produce results that are similar to girdling. Girdling is commonly used on grape,avocado,apple,litchi,mango,citrus and other trees. Girdling is normally only done to healthy trees that did not yield well the previous year. Care must be used not to damagesapwood that may kill the tree orvine. Trees normally heal in four to five weeks after cincturing. Painting the cut can protect againstfungus andpests.[5][6][7][8]
Various animals can girdle trees through their feeding or others activities.
In North America, trees are prone to damage byvoles in particular girdling both their roots and trunk.[9] Among North American birds, thesapsuckers are the most common girdlers of trees. While sapsuckers will bore holes in tree trunks to feed upon insects, they also make parallel rings of holes in order to eat sap that collects in the openings or to feed it to their young. They most frequently attack pine, birch, maple, spruce and fruit trees and do the most damage during breeding season and territory establishment between February and June.[10]
Beavers girdle the bases of stems 3-6 inches in diameter, and girdle the roots of larger trees. This often weakens or kills trees.[11]
In the United Kingdom and other parts of Europe, theeastern grey squirrel is also known to girdle or entirely strip bark from trees.
Bucks (maledeer) inadvertently girdle trees by rubbing their antlers on trees of various ages.[12]
Agrilus biguttatus can girdle trees through their feeding behavior and create zigzag galleries that measure up to 1.5 meters in length.[13]
One of several waysrabbits damage the environment in Australia is by girdling.[14]
Trees can be girdled by climbing, twining, and ground-creeping (rampant) vines. There are several invasive species that harm trees in this way and cause significant damage to forest canopy and the health of ecosystems dependent on it. Oriental Bittersweet, Oriental Wisteria, and English Ivy all can damage and kill trees by girdling.[citation needed]
