The association between natural braces and the development of bark-included junctions in trees

Abstract

Bark-included junctions are a malformation that occur in a wide range of tree species. Although the formation of an acute internal angle at a branch junction has been suggested as the primary cause of bark-included junctions in trees, it is logical to assume that a weak structure of this kind may develop under a much lower loading regime than that of a normally formed junction. One factor that would affect the mechanical loading of a junction is the presence of crossing or touching limbs that are situated above such a junction and that act as a ‘natural brace’ that straddles the join, thus restricting the natural movement of the junction and its associated limbs. Survey and analysis of data from a cohort of broadleaved trees identified a very strong association (93.9%) between bark-included junctions that exhibited no discernible bulging (n = 99) and the presence of one or more natural brace above those junctions. Additionally, the bark-included junctions that exhibited a major bulge (n = 30) were significantly associated with the absence of natural braces (93.3%). This finding has several important ramifications for professional tree surgery operations and tree surveying techniques, which will be the subject of a companion paper.

Keywords:

• Bark inclusion
• branch junction
• natural bracing
• tree fork
• tree surgery

Acknowledgments

The author gives thanks to the many people who, after being trained by the author in 2016 to look for natural braces in trees with bark-included junctions, have kindly made contact to confirm they also find a strong association between these two tree defects in their own tree surveys. The author would also like to acknowledge the considerable support and help of the Arboricultural Association in delivering this industry training to over 400 delegates in 2016 – it could not have been done without the AA team’s commitment to the dissemination of this finding.