A branch attachment is where a
branch
A branch, sometimes called a ramus in botany, is a woody structural member connected to the central trunk (botany), trunk of a tree (or sometimes a shrub). Large branches are known as boughs and small branches are known as twigs. The term '' ...
is attached to the
trunk of a
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 ...
. Three types of branch attachment are recognized due to differences in the anatomical position of buds that form them. Two key components contribute to the mechanical
strength
Strength may refer to:
Physical strength
*Physical strength, as in people or animals
* Hysterical strength, extreme strength occurring when people are in life-and-death situations
*Superhuman strength, great physical strength far above human c ...
and
toughness
In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing.[knot
A knot is an intentional complication in cordage which may be practical or decorative, or both. Practical knots are classified by function, including hitches, bends, loop knots, and splices: a ''hitch'' fastens a rope to another object; a ' ...]
that often lies within the attachment. A common malformation of a branch attachment is the inclusion of bark within the join, which can weaken the attachment.
Anatomy in trees
![Branch attachment model (Slater et al](https://upload.wikimedia.org/wikipedia/commons/c/c7/Branch_attachment_model_%28Slater_et_al.%2C_2014%29.png)
Initially
branch
A branch, sometimes called a ramus in botany, is a woody structural member connected to the central trunk (botany), trunk of a tree (or sometimes a shrub). Large branches are known as boughs and small branches are known as twigs. The term '' ...
es are mechanically attached to the
trunks of trees by forming interlocking wood grain patterns at the top of the joint, within what is known as 'axillary wood' (Fig. 1).
[Slater, D. and Ennos, A. R. (2015) Interlocking wood grain patterns provide improved wood strength in forks of hazel (''Corylus avellana'' L.), ''Arboricultural Journal'' 37 (1) 1-12] The axillary wood (or xylem) formed in this location is denser than in surrounding tissues of the tree's stem or
branch
A branch, sometimes called a ramus in botany, is a woody structural member connected to the central trunk (botany), trunk of a tree (or sometimes a shrub). Large branches are known as boughs and small branches are known as twigs. The term '' ...
, the wood grain pattern formed is tortuous and in these tissues there is typically a reduction in vessel length, diameter and frequency of occurrence (i.e. more of the xylem consists of fibre cells). This specialized xylem tissue (axillary wood), formed under the branch bark ridge, provides unique mechanical properties to the union of the branch to the trunk, requiring that wood fibres are stretched along their length (the axial strength of the wood) in order to rupture the attachment apart.
[
As the typical lateral branch of a ]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 ...
and its trunk expand in diameter at different rates, the base of the smaller branch becomes occluded in the larger trunk of the 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 ...
which is producing a larger increment of growth, and this occluded part of the branch
A branch, sometimes called a ramus in botany, is a woody structural member connected to the central trunk (botany), trunk of a tree (or sometimes a shrub). Large branches are known as boughs and small branches are known as twigs. The term '' ...
forms a knot
A knot is an intentional complication in cordage which may be practical or decorative, or both. Practical knots are classified by function, including hitches, bends, loop knots, and splices: a ''hitch'' fastens a rope to another object; a ' ...
that provides substantial additional mechanical support to the attachment as it develops (Fig. 2). This is not the case in tree forks 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 ...
, where the growth rate of both branches is approximately equal, and no occluded knot is formed.
The combination of the interlocking axillary wood patterns at the junction apex and the occluded knot embedded into the tree's trunk make mature branch attachments in trees very strong components of a tree's crown. From static testing, branch attachments have been found to be far stronger than attachments made at forks in trees.
Types
Botanists commonly differentiate between branches that originate from the initial extension growth and those that have developed epicormically from the growth of latent bud
In botany, a bud is an undeveloped or embryonic shoot and normally occurs in the axil of a leaf or at the tip of a stem. Once formed, a bud may remain for some time in a dormant condition, or it may form a shoot immediately. Buds may be spec ...
s or adventitious Important structures in plant development are buds, shoots, roots, leaves, and flowers; plants produce these tissues and structures throughout their life from meristems located at the tips of organs, or between mature tissues. Thus, a living plant a ...
bud
In botany, a bud is an undeveloped or embryonic shoot and normally occurs in the axil of a leaf or at the tip of a stem. Once formed, a bud may remain for some time in a dormant condition, or it may form a shoot immediately. Buds may be spec ...
s that developed later on the tree's trunk surface. A clear anatomical difference can be found on dissection between these branch attachments, in that the former has an initial knot
A knot is an intentional complication in cordage which may be practical or decorative, or both. Practical knots are classified by function, including hitches, bends, loop knots, and splices: a ''hitch'' fastens a rope to another object; a ' ...
that originates near to the stem's 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 ...
, those developing from latent buds will have a bud trace that originates near the stem's 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 ...
, and adventitious epicormic branches will exhibit neither of these internal features.
Malformations
A common malformation of a branch attachment in a tree is the inclusion of bark within the join, commonly referred to as a 'bark inclusion' or 'included bark'. This malformation is known to weaken the connection of the branch
A branch, sometimes called a ramus in botany, is a woody structural member connected to the central trunk (botany), trunk of a tree (or sometimes a shrub). Large branches are known as boughs and small branches are known as twigs. The term '' ...
to the rest of the tree's structure, as it acts to block the formation of the axillary wood at the branch attachment's apex.
Bark included branch junctions are commonly found in a wide range of tree species, and are primarily caused by the effects of natural bracing within the crowns of the trees. In amenity trees, it is common practice for arborists to prune out young branches with such malformed attachments, subordinate the branch by reducing its length or brace the weakened branch to the rest of the tree, ideally using a flexible brace.
Previous anatomical models
In 1985, the researcher Dr. Alex Shigo
Alex L. Shigo (May 8, 1930 – October 6, 2006) was a biologist, plant pathologist with the United States Forest Service whose studies of tree decay resulted in many improvements to standard arboricultural practices. He travelled and lect ...
published an anatomical model of branch attachment[ based on analysis of extensive tree cross-sections and which came to be widely utilised in the arboricultural industry. Unfortunately, this model of branch attachment is illogical and anatomically incorrect.][Slater, D. and Harbinson, C. J. (2010) Towards a new model for branch attachment; ''Arboricultural Journal'' 33 (2) 95-105]
The basis of Shigo's model was that the branch base grew first, then the branch's base was overlapped by the growth of the trunk, and the further development of overlapping layers of these two distinct xylem tissues resulted in the development of a strong connection (Fig. 3). However, this model does not take into account the anatomy of tree forks 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 ...
, nor when tree growth is continuous (such as in tropical trees) and it requires contortions of the vascular cambium
The vascular cambium is the main growth tissue in the stems and roots of many plants, specifically in dicots such as buttercups and oak trees, gymnosperms such as pine trees, as well as in certain other vascular plants. It produces secondary xyle ...
that are infeasible.[
Prior to the development of Shigo's model of branch attachment, it was commonly thought that wood grain traversed directly from the top of the branch into the trunk of the tree, ascending to the tree's crown. Such a wood grain arrangement would result in sap travelling from the foliage at the end of the branch to other foliage in the tree's crown, which is contrary to the 'source-to-sink' model widely accepted for sap distribution in all woody plants,][Kramer P. J. & Kozlowski T. T. (1979) ''Physiology of Woody Plants''; New York: Academic Press, Inc] and can clearly be seen not to be the case by dissections of junctions formed in trees.
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
A branch, sometimes called a ramus in botany, is a woody structural member connected to the central trunk (botany), trunk of a tree (or sometimes a shrub). Large branches are known as boughs and small branches are known as twigs. The term '' ...
* Branch collar
A branch collar is the "shoulder" between the branch and trunk of woody plants; 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 patter ...
* Leaf gap
A leaf gap is a space in the stem of a plant through which the leaf grows. The leaf is connected to the stem by the leaf trace, which grows through the leaf gap.
The leaf gap is a break in the vascular tissue of a plant stem, stem above the po ...
* Node (botany)
* 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 ...
* 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 ...
* Vascular cylinder
* Xylem development
Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...
* ''''
References
{{Reflist
External links
Arboricultural Association
Arboricultural Journal
International Society of Arboriculture
Trees
Forest management
Plant morphology
Plant anatomy