| Degree of infection |
Needle length (cm) |
Length of needle-bearing twigs (cm) |
Total leaf surface (cm2) |
Needles per tree (thousands) |
|
|---|---|---|---|---|---|
| None | 13.7 (38) | 25.9 (37) | 6,555 (3) | 539 (3) | |
| Light | 11.4 (15) | 21.1 (15) | - | - | |
| Medium | 10.7 (18) | 14.7 (15) | - | - | |
| Heavy | 9.9 (32) | 12.2 (30) | 1,361 (2) | 83 (2) | |
| Source: Adapted from Korstian and Long (1922). Number of trees in parentheses. | |||||