Diameter Ratio A lower diameter ratio results in higher stresses at the apex of the fork when pulled apart Stronger Weaker
Slimming down A rapid slimming down of the parent stem after the attachment results in higher stresses too Stronger Weaker
The ‘Fillet’ The geometry of the top of the fork is very important in determining the stresses at the apex Stronger Weaker
Fork Geometry The fork is weakened if it has: An open-topped bark inclusion A poor fillet shape A low (near 1:1) diameter ratio A slimming profile after the attachment CAUTION! THE TREE CAN REMODEL ITS JUNCTIONS
Bark Inclusions – Why? Better at conductance of sap (Wolf Trees) Probably caused by phototropism (Being drawn to the light) Never felt much tension (Won’t reinforce junction) Not wasteful of resources (Clever old trees! )
Bark Inclusions – How? We can cause bark inclusions to become a problem! Growing trees very close together in sheltered locations will give rise to many bark inclusions; even more so if we breed them to be fastigiate, upright cultivars. Then we complain when the junction snaps a few years later, after we thin or move it (Poor old trees! )
My Best Guidance on Forks The fork is adapted for the location in which it has developed. If it has been sheltered for many years, avoid suddenly exposing it to far windier conditions Forks with bark inclusions, a poor fillet shape, a low diameter ratio and that slim down rapidly after their point of attachment are not safe, where found in exposed situations and/or connected to an elongate limb
Acknowledgments Dr. Roland Ennos Dr. Robert Bradley at HMXIF Phil Benn & Mike Carswell David Elwell & Mike Heys Myerscough College BSc. (Hons) students Joe Barnes, Claire Harbinson & Ian Williams Thank You!