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Carbon Brief technologies. The attributes significantly affecting visual stem
classification included the height of the first dead or living
branch, maximum branch diameter, and crookedness. They also
suggested introducing the number of branches, slenderness

(ratio of tree height to diameter), and branch insertion angle.
Furthermore, specifically designed for hardwoods are
the log grading guidelines developed in the United States.
These can and are also applied to standing trees, detailing
and data. Regarding standing trees and visual characteristics, characteristics for grouping logs into three quality classes.
Bosela et al. conducted a survey among 28 European countries Attributes considered include tree size, defects (knots/branches
to investigate the quality assessment in their NFIs and to and fractures), roundwood shape (sweep and crook), and
discuss potential harmonisation. They referred to the concept decay presence.
of “stem quality” as more suitable for the only visual (external) Similar attributes are included in the tree grading rules

parameters recorded in the field, distinguishing it from the for Southern pines.
more complex definition of wood quality. Finally, Canadian rules for hardwood standing trees primarily
Factors influencing stem quality were identified, considering consider dimensions, stem form, and tree vigour, with some
the possibility of using them to estimate the assortments also accounting for visible defects like biological damage.
obtainable from the harvest. These factors relate to stem form The attributes mentioned and assessed in the literature
and size, the height of the crown and fork, the presence of above were categorised into four general types and detailed
abiotic or mechanical damages, and branch characteristics at two levels. This schematic subdivision will be maintained

(size, height, number, and artificial pruning). throughout the paper during the review and discussion of the
Bosela et al. observed significant variability among national relevant scientific literature.
inventories, with the obvious exception of tree dimensional Regarding size, it is intuitive to assume that larger sizes
data (diameter and tree height) recorded by all of them. lead to greater yields and profits. Quality rules indeed prescribe
However, the feasibility of future harmonisation was highlighted, larger dimensions in the highest quality classes.
possibly by identifying a smaller number of attributes but It has been calculated that larger logs generally entail
highly descriptive ones. lower processing costs, potentially resulting in greater earnings
The same was not true for the assortment estimation, per cubic meter. However, larger dimensions do not always
which greatly depends on the different definitions of assortment guarantee better material quality.

present at the national or even local level. In this sense, the The height from the crown or the first branch provides
suggestion was to collect the quantitative and qualitative an indication of the length of the sawlog free from knots, at
data necessary for the estimate, enabling the assortment least externally.
generation afterwards. Additionally, slenderness, defined as the ratio of height
Recently, Ruano et al. developed a protocol to assess to diameter, has been found to be positively correlated with
stem quality for inclusion in the NFIs, which could serve as the mechanical properties of sawn timber obtained from
the basis for European-level harmonisation. They similarly measured trees.

proposed the surveying of visual characteristics, considered Regarding size, it is intuitive to assume that larger sizes
easier to detect extensively, particularly with the aid of new lead to greater yields and profits. Quality rules indeed prescribe