| Winnipeg is the only city in western Canada with a large, indigenous population of bur oak (Quercus macrocarpa Michx.). In the 1980s, many of the city's bur oaks were showing signs of decline, a disease caused by a complex of abiotic and secondary biotic stressing agents. Potential causal factors were investigated by comparing various aspects of 180 bur oaks visually rated as healthy, medium, or declined, based on crown dieback levels. Selected trees were located away from roads where harmful deicing salt is applied in the winter. The results indicated that many selected bur oak trees predated their surrounding urban development. Declined trees were significantly older and had more severe stem wounds and competition from surrounding trees than healthy specimens. Medium trees were generally intermediate between healthy and declined trees. (Abstract shortened by UMI.)... |
