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.