I’ve noticed that many practitioners in Sweden often overlook the significance of ”ribs” (ås or barkås in Swedish) on tree stems and branches. This is surprising, as the presence and interpretation of ribs was well-presented as far back as 1995 by Claus Matteck in his book ‘The Body Language of Trees’, available in both German and English.

A few species do sometimes build ribs as part of their typical growth, for example Hornbeam (Carpinus betulus). However, a rib usually indicates that something with the tree has deviated from what might be considered ”normal”. The building of a rib is often the tree’s response to something new in its mechanical world – for example a crack, internal decay,  exposure to new wind conditions due to removal of surrounding trees or buildings.

Assessors of trees should always consider the presence of ribs. Why has the tree built this rib?

The shape of the rib is also important – smoothly rounded is considered to be (generally) a good thing. However, this is not always the case. The presence of ”lips” (as described by Matteck) is considered to suggest that although the tree is building new woody tissues to compensate for a (often new) structural problem, the movement associated with the problem means that the cambium cannot completely form new bark over the rib. Or that movement is even causing the rib to open slightly. The presence of lips on ribs that are forming below included bark unions is common.

Case study

A recent inspection of a Horse Chestnut (Aesculus hippocastanum) revealed the presence of these ribs on the stem.

Horse Chestnut with two ribs on the stem

Why were the ribs present? Aural inspection (with a Thorex nylon mallet) suggested an extensive cavity at the base of the tree. A tomograph with the Arbotom confirmed this.

A tomograph indicates extensive decay.

Due to its location in a pre-school playground, the tree was felled.

The cut section reveals how small the amount of sound wood holding up the tree is. Dysfunction is even progressing out into the two ribs.

Practitioners should note that the defect (ribs) on this tree had been missed by a previous assessor, and the tree had been previously classified as ”low” risk.


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