| Microsite Quality Class | Predicted height increment (cm) | Relative frequency |
| M1 | >32 | 0.33 |
| M2 | 29 - 32 | 0.09 |
| M3 | 9 - 29 | 0.48 |
| M4 | 0 - 9 | 0.07 |
| M5 | <0 | 0.03 |