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The level of occlusion of included bark affects the strength of bifurcations in hazel (Corylus avellana L.)

Ennos, Roland; Slater, Daniel; Ennos, A R


Roland Ennos

Daniel Slater

A R Ennos


Bark-included junctions in trees are considered a defect as the bark weakens the union between the branches. To more accurately assess this weakening effect, 241 bifurcations from young specimens of hazel (Corylus avellana L.), of which 106 had bark inclusions, were harvested and subjected to rupture tests. Three-point bending of the smaller branches acted as a benchmark for the relative strength of the bifurcations. Bifurcations with included bark failed at higher displacements, and their modulus of rupture was 24% lower than normally formed bifurcations, while stepwise regression showed that the best predictors of strength in these bark-included bifurcations were the diameter ratio and width of the bark inclusion, which explained 16.6% and 8.1% of the variability, respectively. Cup-shaped, bark-included bifurcations where included bark was partially occluded by xylem were found, on average, to be 36% stronger than those, where included bark was situated at the bifurcation apex. These findings show that there are significant gradations in the strength of bark-included bifurcations in juvenile hazel trees that relate directly to the level of occlusion of the bark into the bifurcation. It therefore may be possible to assess the extent of the defect that a bark-included bifurcation represents in a tree by assessing the relative level of occlusion of the included bark.


Slater, D., Ennos, R., Slater, D., & Ennos, A. R. (2015). The level of occlusion of included bark affects the strength of bifurcations in hazel (Corylus avellana L.). Arboriculture & urban forestry, 41(4), 194-207

Journal Article Type Article
Acceptance Date Jul 28, 2015
Publication Date 2015-07
Deposit Date Feb 23, 2016
Publicly Available Date Feb 23, 2016
Journal Arboriculture and Urban Forestry
Print ISSN 1935-5297
Electronic ISSN 1935-5297
Peer Reviewed Peer Reviewed
Volume 41
Issue 4
Pages 194-207
Keywords Bifurcation, Corylus avellana, Hazel, Included bark, Rupture tests, Three-point bending
Public URL
Publisher URL
Additional Information Author's accepted manuscript of article published in: Arboriculture & urban forestry, 2015, v.41, issue 4.


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