Classification of trees into Fractometer categories (100 Fractometer units = 26 MPa max. bending stress in the core)
| Species | Fracture moment in Fractometer units | ||
|---|---|---|---|
| Green | Yellow | Red | |
| Hardwoods | |||
| ash | 80-59 | 58-38 | 37-18 |
| birch | 40-30 | 29-20 | 19-10 |
| black alder, sweet chestnut | 50-38 | 37-25 | 24-12 |
| black locust, beech, hornbeam, maple, oak, plane | 120-89 | 88-58 | 57-27 |
| poplar, willow | 20-15 | 14-10 | 9-5 |
| elm | 110-82 | 81-54 | 53-26 |
| horsechestnut | 70-52 | 51-34 | 33-16 |
| lime | 60-46 | 45-30 | 29-14 |
| Softwoods | |||
| Douglas fir | 7-6 | 5-4 | 3-2 |
| fir, larch, pine | 15-12 | 11-8 | 7-4 |
| spruce | 20-15 | 14-10 | 9-5 |
| yew | 90-67 | 66-44 | 43-21 |
If any decay is present, the values for the surrounding healthy wood need to be within the green range.
The same applies to wood in leaning trees.
In heavily pruned trees, values in the yellow range may be acceptable. Wood with values in the red range is weak and should be regarded as unable to support the tree safely, so that severe crown reduction or felling may be needed. However, a fixed use of the table is dangerous. It is important to look at the tree as a system and not at the increment borer core only (e.g. a black poplar with 80 Fractometer units was felled because the tree had clear signs of local failure (fibre buckling) and was slanting heavily). For the fracture angles see ref. [9].