Differences in natural bracing between early mature street trees of Norway maple (Acer platanoides L.) and small-leaved lime (Tilia cordata Mill. “Rancho”)

ABSTRACT

Included bark is considered a significant structural flaw in the crown of an amenity tree. However, recent research identifies natural bracing within the crowns of trees is associated with the formation of bark-included junctions lower down. To advance this research, differences in natural bracing between species and cultivars should be assessed. A survey of thirty early mature specimens of both Acer platanoides L. and Tilia cordata Mill. ‘Rancho’ was completed in 2017. These two tree types have similar rates of formation of bark-included junctions but reputably have differing failure rates. In these sixty trees, all major branch junctions from ground level to three metres were inspected and any associated natural braces categorised. Bark inclusions in the Norway maples were associated with fewer natural braces (44.4% association) and the trees contained a higher proportion of cup unions. In comparison, bark inclusions in the thirty lime cultivars were associated with more natural braces (78.3% association) and the trees contained a higher proportion of wide-mouthed bark inclusions. The differing forms and levels of self-shading in these two tree types are considered the key factors that explain the differences found in the survey. This finding informs better tree assessment and formative pruning programmes.

KEYWORDS:

• Bark inclusion
• branch junction
• natural bracing
• tree forks
• tree risk management

Acknowledgments

We would like to thank Julie Smith and Richard Collins of Myerscough College for their support and encouragement in the completion of this research project.

Many thanks also go to Maxine Knagg and Neil Morris of Lancaster City Council for their assistance in providing information on the Norway maples surveyed in Morecambe, Lancashire.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Ruth M. Tothill

Ruth M. Tothill is a recent graduate of the BSc (Hons) Arboriculture and Urban Forestry course run at Myerscough College, Lancashire and currently works as a self-employed arborist and freelance arboricultural consultant in the UK. Ruth intends to continue studying arboriculture at a higher academic level and possibly teach on this topic in the future.

Duncan Slater is a senior lecturer in arboriculture at Myerscough College and a current candidate for an MEd at the University of Central Lancashire.