page_title: Branch attachment
section_title: Previous anatomical models
hierarchical_section_title: Branch attachment / Previous anatomical models
caption_attribution_description: English: This is a drawing which re-presents the branch attachment model of Dr. Alex L. Shigo, published in 1985
context_page_description: A branch attachment is where a branch is attached to the trunk of a tree. 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 and toughness of the attachment: interlocking wood grain at the top of the attachment and an embedded knot 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.
context_section_description: In 1985, the researcher Dr. Alex Shigo 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.
  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, nor when tree growth is continuous (such as in tropical trees) and it requires contortions of the vascular cambium 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, and can clearly be seen not to be the case by dissections of junctions formed in trees.
caption: Figure 3: A visual representation of the branch attachment model of Dr. Alex L. Shigo based on overlapping growth, published in 1985[9]
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