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Tree topping is the practice of removing whole tops of
tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...
s or large branches and/or trunks from the tops of trees, leaving stubs or lateral branches that are too small to assume the role of a terminal leader. Other common names for the practice include hat-racking, heading, rounding over, and tipping. Some species of trees are more likely to recover from topping than others. There are alternatives to topping that can help to achieve the same goals without damaging trees.


Purpose

Hundreds of large trees are topped each year, which causes significant stress and future safety issues. It has been shown through survey that the average person's knowledge on tree care is limited. Another popular misconception is that a topped tree will benefit from increased light penetration. The removal of a large portion of a tree's canopy can have detrimental effects. When a tree is topped, newly formed bark may be susceptible to
sun scald Sun scald is the freezing of bark following high temperatures in the winter season, resulting in permanent visible damage to bark. Fruits may also be damaged. In the northern hemisphere, it is also called southwest injury. Causes The reason the ...
. Prolonged exposure can severely damage the bark, thus creating an attractive home for decay-causing organisms. Evidence of decay may be the presence of conks (fungal fruiting structures) on the outer tree bark. The loss of leaves reduces a tree's ability to
photosynthesize Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
and produce food. If a large tree is unable to produce enough sugars to feed the roots, it will slowly die from starvation. Some people have been known to top trees in order to stimulate new growth. When a tree is topped, many adventitious shoots, known as suckers begin to grow from the wound. This is the tree's response to the sudden loss of leaves. Although the tree is able to produce an abundance of suckers, they are susceptible to numerous problems. Firstly, this adventitious growth is succulent and susceptible to attacks by insects such as aphids and caterpillars, and pathogens like fire blight (Rosaceae). Secondly, the branch-stubs that the suckers emerge from are rarely able to form a complete
callus A callus is an area of thickened and sometimes hardened skin that forms as a response to repeated friction, pressure, or other irritation. Since repeated contact is required, calluses are most often found on the feet and hands, but they may o ...
. This means that any pathogen that attacks a sucker may enter the tree directly through the open wound. If wood begins to rot it could create a weak branch connection between the developing suckers and the main tree leading to a possible branch failure. If a tree is unable to compartmentalize the fungi, it may reach the trunk and ultimately kill the tree. Aesthetics is another reason why people hire arborists to top their trees. A tree may be blocking the mountain view, shading the garden, or interfering with solar energy collection. As a result, the tree never fully returns to its initial natural form.


Topping precautions

Large pruning wounds, such as those left behind in trees after topping, may become entry points for
pathogens In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a ger ...
and may result in extensive decay. Decay undermines, to greater or lesser extent, the long-term health and physical stability of trees; most notably in those species which compartmentalize decay less effectively. Should a tree survive topping, tissue regrowth at the site of the original topping wound(s) is generally profuse. These new multiple leaders are less well-attached than was the original treetop, partly due to the effect of advancing decay at the wound site. As these weakly attached trunks increase in size, they become more prone to fall from the tree.
Wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ho ...
can increase this potential. Previously topped trees can present significant hazards and should be inspected by a qualified
arborist An arborist, tree surgeon, or (less commonly) arboriculturist, is a professional in the practice of arboriculture, which is the cultivation, management, and study of individual trees, shrubs, vines, and other perennial woody plants in dend ...
, who can recommend possible solutions, such as removal, cabling, bracing, or ongoing inspection. Aesthetic appeal is also compromised by topping, as the natural shapes of trees are lost.


Alternatives

Alternatives based on scientific research are replacing tree topping. For example, size reduction can maintain the aesthetics and structural integrity of a tree without damage. Spiral thinning and other forms of canopy thinning can decrease wind resistance and allow wind to pass through trees, reducing the potential for branch failure due to wind-throw. Thinning also allows more light penetration and air circulation, both important to tree health. Other cultural practices include choosing plant material that will fit in the desired location at its mature size.


Species indications


More effective compartmentalization of decay

* '' Ulmus parvifolia'' – Chinese Elm


Less effective compartmentalization of decay


See also

*
Arboriculture Arboriculture () is the cultivation, management, and study of individual trees, shrubs, vines, and other perennial woody plants. The science of arboriculture studies how these plants grow and respond to cultural practices and to their environme ...
*
Coppicing Coppicing is a traditional method of woodland management which exploits the capacity of many species of trees to put out new shoots from their stump or roots if cut down. In a coppiced wood, which is called a copse, young tree stems are repeate ...
*
Pollarding Pollarding is a pruning system involving the removal of the upper branches of a tree, which promotes the growth of a dense head of foliage and branches. In ancient Rome, Propertius mentioned pollarding during the 1st century BCE. The practice o ...
* Plant Amnesty * Topping (agriculture)


References

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External links


International Society of Arboriculture
Horticulture Trees