A branch collar is the "
shoulder
The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder mak ...
" between the branch and trunk of
woody plant
A woody plant is a plant that produces wood as its structural tissue and thus has a hard stem. In cold climates, woody plants further survive winter or dry season above ground, as opposite to herbaceous plants that die back to the ground until sp ...
s; the inflammation formed at the base of the branch is caused by annually overlapping
trunk tissue.
The shape of the branch collar is due to two separate growth patterns, initially the branch grows basipetally, followed by seasonal trunk growth which envelops the branch.
Branch collars serve as a strong foundation to the branch, and its orientation and internal characteristics allow the branch to withstand stress from numerous directions.
Functionally the branch collars also influence the
conductivity
Conductivity may refer to:
*Electrical conductivity, a measure of a material's ability to conduct an electric current
**Conductivity (electrolytic), the electrical conductivity of an electrolyte in solution
**Ionic conductivity (solid state), elec ...
of nutrients and growth patterns.
The branch collar which provides a protective barrier to prevent infection and decay, can also be useful in diagnosing bacterial diseases.
Proper
pruning
Pruning is a horticultural, arboricultural, and silvicultural practice involving the selective removal of certain parts of a plant, such as branches, buds, or roots.
The practice entails the ''targeted'' removal of diseased, damaged, dead, ...
techniques should accommodate for the branch collar structure, as by damaging the tree it is likely to decay or become diseased.
Definition
In
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 environmen ...
, the "shoulder" junction structure between the branch and the trunk is known as the branch collar.
This structure can be identified as a raised ring of tissue around the base of the branch The branch collar and trunk collar are collectively called the branch collar.
Morphology
Growth stages
![Branch collar on Qrob 02](https://upload.wikimedia.org/wikipedia/commons/5/5f/Branch_collar_on_Qrob_02.JPG)
Tree branches are attached to the trunk with a series of trunk collars that annually envelope the branch collar.
The branch tissues develop a basal collar first in spring, then trunk tissue envelops the collar later during seasons of growth.
This rhythm of growth results in a tissue arrangement that wraps around the branch, creating the branch collar.
This processes where the branch tissue develops basipetally and the trunk tissue develops perpendicular to the branch, results in the
cambium cells of the upper segments of the branch collar to develop in a right-angle formation.
The expanding cambium of the trunk, over time, slowly overtakes the newly forming branch tissue, which causes the branch collar to swallow up more of the branch as the tree grows.
The development of
xylem tissue within the tight pocket above the branch collar known as the "crotch", causes the cells to be compacted to form the hard zone of connective tissue between the branch and the trunk.
The formation of narrow channels and loops within the branch collar tissue are the pathways left behind by the flowing of large volumes of
hormonal signals.
Function
Structural integrity
The branch collar forms a sturdy foundation structure, the enveloping of branch tissue by trunk tissue gives the branch unique properties of strength.
The branch collar junction due to various regions of differing elasticity allows the branch collar to withstand mechanical loads by distributing stress within tissue regions of varying strengths.
Additionally, the orientation of
fibres
Fiber or fibre (from la, fibra, links=no) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate ...
within critical regions of the branch collar can change their physical orientation to withstand and match stress from various directions.
Furthermore,
microfibril A microfibril is a very fine fibril, or fiber-like strand, consisting of glycoproteins and cellulose. It is usually, but not always, used as a general term in describing the structure of protein fiber, e.g. hair and sperm tail. Its most frequently ...
angles and density are adapted locally within the branch and branch collar, to develop patterns within the branch collar that best protect the plant from stress damage caused by loads on the branch and tension from branch growth. The points on the branch closest to the branch collar structure can take the most duress, similarly the branch collar provides the length of the branch with a strong foundation.
Low Conductivity
The presence of visible branch collars is a good indicator of low branch junction conductivity, this is because branch collars with perpendicular branches have significantly lower hydraulic conductivities than more upright branches.
Within the branch collar there are water flow restriction zones, which are the combination of narrow
vascular
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away f ...
elements and non-functional circular vessels these structures help enhance the segmentation of the plant and promotes the movement of water and sap up the central xylem.
Influence on growth patterns
The circular tissues within the branch junctions directly influence the growth and dimensions of the tree, by affecting the shedding of branches and by attenuating their ability to withstand mechanical load, and indirectly, by affecting the movement of growth regulators and ascent of sap, which influence the development of branches especially the dominance of the leader branch.
Trees can also self-prune by the bark building a ring notch at the branch collar which becomes a weak point so that at some stage the branch will be knocked off. Then the bark then grows over the wound and seals the tree.
This function allows plants such as the crack willow (
Salix Fragilis) to perform
vegetative propagation
Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is any form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or speci ...
where the shed branch will then root itself and grow.
Ecology and disease
Compartmentalising disease
The branch collar inhibits infection by acting as a protective barrier.
Trees compartmentalize their injury by producing
antimicrobial
An antimicrobial is an agent that kills microorganisms or stops their growth. Antimicrobial medicines can be grouped according to the microorganisms they act primarily against. For example, antibiotics are used against bacteria, and antifungals ar ...
substances then growing over the area.
Events such as storms or incorrect pruning activity can cause damage to the branch collar When the trunk collar is injured, the trunk xylem below it is rapidly infected and decays.
Within the branch collar there is a narrow cone of cells known as the branch defence zone, these cells activate the development of wood wound which is a callus tissue that grows when the branch is broken off.
Suberization followed by
periderm
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 the vascular cambium and is a nontechnical term. It overlays the wood and consist ...
formation may provide a barrier to further mycelial advance, and the abundant production of resin may constitute further protection.
However periderm barriers can be penetrated by
hypha
A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium.
Structure
A hypha consists of one or ...
e, especially in weather favouring the rapid extension of canker, and it is common to find a succession of such barriers which have been crossed by
fungus
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...
.
Epidemiology using the branch collar
The branch collar can be used to diagnose dying trees, Liberibacter asiaticus bacteria was found in higher concentration in the branch collar than the
pith
Pith, or medulla, is a tissue in the stem
Stem or STEM may refer to:
Plant structures
* Plant stem, a plant's aboveground axis, made of vascular tissue, off which leaves and flowers hang
* Stipe (botany), a stalk to support some other ...
.
Branch collar cortical tissue is soft compared to other tissues used for bacterial measure like the pith, making the tissue of the branch collar easier and more efficient in the
epidemiological
Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population.
It is a cornerstone of public health, and shapes policy decisions and evidenc ...
diagnosis of infected trees.
Furthermore, the ability to conduct an epidemiological study using branch collar is useful as it can be used instead of leaves, which allows for the diagnosing of trees without any leaves.
Canker diseases
While most infections occur commonly at the main branch crotches,
canker
A plant canker is a small area of dead tissue, which grows slowly, often over years. Some cankers are of only minor consequence, but others are ultimately lethal and therefore can have major economic implications for agriculture and horticultur ...
s start at the branch collar.
For young trees branches crotch and collar could confine the infection within itself, in older trees (older than 4 years of age) there were more stem cankers which frequently originated on pruning scars.
Wounds infection of the stem also originated in wounds caused by large wildlife.
Proper pruning techniques of the branches can prevent the development of cankers.
Pruning
Guidelines
![Branch_Collar_Pruned](https://upload.wikimedia.org/wikipedia/commons/c/c8/Branch_Collar_Pruned.jpg)
The generally accepted guideline for urban pruning has been a technique commonly referred to as "natural target pruning". Natural target pruning aims to retain the branch collar on the primary trunk while removing the rest of the branch, thereby promoting the development of the wood wound
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 ...
tissue free of defects and therefore possessing greater wood strength. Furthermore, Natural target pruning recommended guidelines aiming to retain the integrity of the branch collar has been shown to facilitate effective wound closure. The traditional method of pruning branches was to make an even level cut against the tree trunk, but this technique is currently avoided as evidence has shown that flush cuts increase the wound size and encourage the invasion of the wound by microorganisms and decay. Therefore, the current recommendation encourages that branches should be removed outside the branch collar as this technique facilitates a circular closure around the wound, while flush cuts often result in a distorted closure that exposes the wood to discolouration and decay.
Optimal pruning summary
Pruning according to the branch collar is integral in maintaining the health of woody plants. When pruning injures or removes the branch collar, the trunk xylem above and below the cut is rapidly infected by the microorganisms inhabiting the wood and decay of the plant occurs.
Optimal pruning is carried out by cutting with respect to the perimeter of the branch collar and cutting adjacent to it.
When cutting it is important to use sharp equipment, as any crushing will damage the branch collar.
[Mckenna, Jim & Woeste, Keith. (2020). Fertilizing, Pruning, and Thinning Hardwood Plantations]
Young trees should be pruned enough to control the direction of the plants growth and to correct any form of weakness along the branch.
The tree should be pruned at its desired height.
When pruning choose roughly five to seven main branches and prune the rest.
Older trees need to be pruned more delicately – they are more susceptible to infections.
When pruning older trees, prune out dead, weak, diseased and
insect-infested branches and also remove low, broken and crossing branches.
The quality of pruning has significant effect on the infection by fungal pathogens, which can consequently cause stem disease.
Remove damaged, weak diseased, or insect infested growth or small unwanted branches anytime.
It is most beneficial to prune prior to the annual period of most rapid growth, which is usually spring.
Conversely, pruning when growth is nearly complete for the season tends to retard and stunt growth. The period of growth tends to vary for different trees, but generally;
Deciduous
In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, aft ...
trees should be pruned when dormant.
Evergreen
In botany, an evergreen is a plant which has foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, which ...
trees should be pruned before growth in spring.
Spring flowering trees should be pruned towards the end of late spring as this tends to be their period of new growth, this can be indicated by the fading of flowers.
Summer trees should be pruned before growth in late winter or spring.
Pruning methodology
The stages in pruning living branches with respect to branch collar
1. Decide where the branch collar begins and ends
2. Identify the
branch bark ridge (raised strip of bark at the top of the branch union or crotch that sits above the branch itself connecting to the trunk of the plant.
3. Mark a point outside both the branch bark ridge and the branch collar, mark a line angling down away following the angle of the branch collar.
4. Ternary Method; the first cut should be down from the underside of the branch around 6 to 12 inches away from the branch's union to the trunk. This cut is done to prevent the falling weight of the branch from tearing the stem tissue as it pulls away from the tree, which can cause damage and infection.
5. The second cut; called the top cut is made above and is further along the branch than the undercut. As beforementioned it is important to prevent any ripping while cutting and manipulating the branch.
6. Once both these cuts have been completed the branch should fall and be removed.
7. Make a third and final cut outside the previously marked point, at a 45 to 60 degree angle to the branch ridge, while cutting do so in a precise manner as to maintain the structurally integrity of the branch collar (in step 3).
Consequences of Optimal Pruning
Proper pruning techniques are integral in keeping the tree healthy.
The branch collar has a variety of functions one of which is a natural defence system from disease and infection.
Therefore, proper pruning techniques by maintaining the structurally integrity of the branch collar, allows for the branch collar to develop callus tissue which seals of the wound minimizing disease and infection.
Application of Optimal Pruning Techniques
Studies testing
Kuala Lumpur City Hall
The Kuala Lumpur City Hall ( ms, Dewan Bandaraya Kuala Lumpur, abbreviated DBKL) is the city council which administers the city of Kuala Lumpur in Malaysia. This council was established after the city was officially granted city status on 1 Feb ...
(DBKL) tree maintenance workers on correct pruning techniques and conditions illustrated a need for improved education of optimal pruning practices.
This would be beneficial as a clear understanding of optimal pruning techniques would improve the quality of their roadside tree pruning and consequently the health of the trees and the individuals living in communities with trees situated nearby.
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 environmen ...
*
Branch attachment
*
Plant morphology
Phytomorphology is the study of the morphology (biology), physical form and external structure of plants.Raven, P. H., R. F. Evert, & S. E. Eichhorn. ''Biology of Plants'', 7th ed., page 9. (New York: W. H. Freeman, 2005). . This is usually cons ...
*
Tree fork A tree fork is a bifurcation in the trunk of a tree giving rise to two roughly equal diameter branches. These forks are a common feature of tree crowns. The wood grain orientation at the top of a tree fork is such that the wood's grain pattern mos ...
References
{{reflist
Trees
Plant morphology
Plant anatomy
Biomechanics
Horticulture