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Branch attachment

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This is an old revision of this page, as edited by Anarchyte (talk | contribs) at 07:21, 25 June 2015 (Undid revision 668583387 by Anarchyte (talk)). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

  • Comment: One other comment: you need a lede -- a sentence or two that summarizes the topic, e.g. "A branch attachment is the point where a branch is mechanically attached to the trunk of a tree. There are n types of branch attachments: x, y, z." You should also provide a lede for your other articles. The reason for this is that systems that pull in info from WP articles for display usually pull just the lede because it is a summary and is short. So every article should have a lede that would give someone outside of WP an idea of the topic of the article. You can do this after moving to main space. LaMona (talk) 16:17, 24 June 2015 (UTC)
  • Comment: Just one question: did you personally re-draw the diagrams? If they were copied (e.g. scanned digitally) from the texts, then they cannot be used in WP. I'm not absolutely sure that a re-drawing avoids copyright violation, so I'll try to research that. LaMona (talk) 16:05, 24 June 2015 (UTC)

Branch Attachment

Anatomy of branch attachment in trees

Branch attachment in common ash Fraxinus excelsior L.
Figure 1: Anatomical drawing of the wood grain of a branch attachment in a tree

Initially branches are mechanically attached to the trunks of trees by forming interlocking wood grain patterns at the top of the join (Fig. 1)..[1]. The xylem tissues in this location are denser than in surrounding tissues of the tree's stem or branch, the wood grain pattern formed is tortuous and in these tissues there is typically a reduction in vessel length, diameter and frequency[2]. This specialized xylem tissue, 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.[1]

As the typical lateral branch of a tree and its trunk expand in diameter at different rates, the base of the smaller branch becomes occluded in the larger trunk of the tree which is producing a larger increment of growth, and this occluded part of the branch forms a knot that provides substantial additional mechanical support to the attachment as it develops (Fig. 2). This is not the case in tree forks, where the growth rate of both branches is approximately equal, and no occluded knot is formed.

The combination of the interlocking wood grain at the apex of the branch 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[3].

Figure 2: Anatomical drawing of the attachment of a branch to the trunk of a tree, illustrating the formation of a knot inside the tree's trunk

Types of branch attachment

Botanists commonly differentiate between branches that originate from the initial extension growth and those that have developed epicormically from the growth of latent buds or adventitious buds that developed later on the tree's trunk surface[4]. A clear anatomical difference can be found on dissection between these branch attachments, in that the former has an initial knot that originates near to the stem's pith, those developing from latent buds will have a bud trace that originates near the stem's pith, and adventitious epicormic branches will exhibit neither of these internal features.

Malformations of branch attachments

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 to the rest of the tree's structure, as it acts to block the formation of the interlocking wood grain pattern at the branch attachment's apex[5][6][7]

Bark included branch junctions are commonly found in a wide range of tree species, and are considered to occur due to genetic traits in individual trees (e.g. fastigiated), tightly-angled joins and branches competing for light (phototropism). 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.[8]

Previous anatomical models of branch attachment

Figure 3: A visual representation of the branch attachment model of Dr. Alex L. Shigo based on overlapping growth, published in 1985[9]

In 1985, the researcher Dr. Alex Shigo published an anatomical model of branch attachment[9] which came to be widely utilised in the arboricultural industry. This previous model of branch attachment has been found to be illogical and anatomically incorrect. [10]

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 (which are teleologically equivalent to branch attachments), nor when tree growth is continuous (such as in tropical trees) and it requires contortions of the vascular cambium that are infeasible.[10]

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[11], and can clearly be seen not to be the case by dissections of junctions formed in trees.

See also

References

  1. ^ a b 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
  2. ^ Slater, D. Bradley, R, Withers, P. and Ennos, A. R. (2014) The anatomy and grain pattern in forks of hazel (Corylus avellana L.) and other tree species, Trees 28 (5) 1437-1448
  3. ^ Kane B., Farrell R., Zedaker S. M., Loferski J. R. and Smith D. W. (2008) Failure mode and prediction of the strength of branch attachments; Arboriculture & Urban Forestry 34, 308-316
  4. ^ Harris R. W., Clark J. R. & Matheny N. P. (1999) Arboriculture: Integrated Management of Landscape Trees, Shrubs and Vines; 3rd Edition; Prentice Hall: New Jersey
  5. ^ Lonsdale, D. (1999) Principles of Tree Hazard Assessment and Management, TSO: London
  6. ^ Smiley, E. T. (2003) Does included bark reduce the strength of co-dominant stems? Journal of Arboriculture 29 (2): 104-106
  7. ^ Slater, D. and Ennos, A. R. (2015) The level of occlusion of included bark affects the strength of bifurcations in hazel (Corylus avellana L.) Journal of Arboriculture and Urban Forestry 41 (4): 194-207
  8. ^ Gilman E. F. (2012) Illustrated guide to pruning; third edition; Delmar publishers, Albany, NY.
  9. ^ a b Shigo A. L. (1985) How tree branches are attached to trunks; Canadian Journal of Botany 63 (8) 1391-1401 [1]
  10. ^ a b Slater, D. and Harbinson, C. J. (2010) Towards a new model for branch attachment; Arboricultural Journal 33 (2) 95-105
  11. ^ Kramer P. J. & Kozlowski T. T. (1979) Physiology of Woody Plants; New York: Academic Press, Inc


Category:Botany Category:Trees Category:Forest management Category:Plant morphology Category:Plant anatomy

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