Interlocking wood grain patterns provide improved wood strength properties in forks of hazel (Corylus avellana L.)

Abstract

Xylem found in the stems of woody plants has contrasting strength in different planes due to its anisotropy. At the apex of the junctions of woody plant branches, sufficient wood strength is needed to prevent the arising branches splitting apart. The main aim of this research was to address an issue so far overlooked, which is the contribution of wood grain orientation and patterns at this location (the apex of such junctions) to supplying the required strength. In this study, the wood grain patterns of xylem produced at the apex of junctions of hazel (Corylus avellana L.) were investigated. The mechanical properties were determined using compression and tensile tests of excised wood samples with an Instron^® Universal Testing Machine. Sample strength was contrasted with the strength of xylem produced at the side of the junctions and in the adjacent lower stems. Wood formed at the top of junctions in the hazel exhibited more tortuous wood grain patterns and had twice the radial and tangential tensile strength when compared with adjacent wood formed in the stem. It also had significantly higher radial and tangential compression strength. Density of xylem at the apex of hazel junctions was 13.4% greater than in the adjacent stem. The authors conclude that tortuous wood grain patterns supply additional strength to junctions in hazel trees. This mechanical arrangement should inform anatomical studies of junctions and may inform the design of manufactured Y-shaped components made from fibrous composite materials.

Keywords::

• bifurcation
• compression tests
• Corylus avellana
• hazel
• tensile tests
• tree fork
• whorled grain
• wood strength

Acknowledgements

This research work was supported by technical staff at the University of Manchester, England. For the provision of the hazel fork specimens used in this experiment, we thank Mike Carswell. Assistance in the production of figures was kindly given by Mike Heys of Myerscough College.

Additional information

Funding

This research work was sponsored by Myerscough College, Lancashire.

Notes on contributors

Duncan Slater

Duncan Slater is a senior lecturer in arboriculture at Myerscough College, Lancashire and a chartered forester. He holds a Bachelor of Science in Forestry, a Bachelor of Arts Honours in Philosophy and Masters in Resource Management (Arboriculture and Urban Forestry). He is currently in the fifth year of a part-time Ph.D. in Plant Sciences at the University of Manchester, England. His research interests are in the areas of tree biomechanics, tree pathology, nursery practices, urban tree establishment and tree selection.

Roland Ennos

Roland Ennos is Professor of Biological Sciences at the University of Hull, England. He studied Natural Sciences at Cambridge University, and holds a Ph.D. in Biomechanics from the University of Exeter. He has published many papers that relate to the biology and biomechanics of animals and plants, and has recently supervised a series of experiments relating to the performance and contribution of trees to the urban environment.