A comparison of various potential decline indicator variables for 120 bur oak trees in Winnipeg, Manitoba, Canada, visually rated as healthy (n = 68) or declined (n = 52) based on crown dieback levelsz.
| Tree type | |||
|---|---|---|---|
| Decline indicator | Healthy | Declined | Total |
| Age (years since breast height)y | 94.6 ± 30.9 a | 112.1 ±29.4 b | 102.3 ±31.4 |
| Wounding (visual rating based on trunk circumference wounding)x | 0 = 32%, | 0 = 44%, | 0 = 38%, |
| 1 = 53%, | 1 = 31%, | 1 = 43%, | |
| 2 = 15% a | 2 = 25% b | 2 = 19% | |
| Total tree competition (cm2 competing tree trunk basal area/m2 growing area) | 19.2 ± 12.2 a | 27.4 ± 14.7 b | 22.7 ± 13.9 |
| Total competition from oaks (cm2 competing tree trunk basal area/m2 growing area) | 9.9 ± 9.9 a | 19.8 ± 15.6 b | 14.2 ± 13.6 |
↵zValues for variables with no letters in common were statistically different (P < 0.05), according to Student’s t-test, unless otherwise noted.
↵ySample numbers lower as a result of several hollow trees: healthy n = 63, declined n = 49.
↵xComparison made with χ2 analysis test of independence. Visual wound ratings correspond to the percentage of the trunk circumference visibly affected by wounds or scars: 0 = <5%, 1 = 5-10%, 2 = 10-25%.