Climate and site factors affecting survival and yield of Douglas-fir in the Cedar-Hemlock ecosystem of the southern interior of British Columbia

摘要

Extended tree lifespans require investments against decay, herbivory, wind and fire. The commercially important conifer Douglas-fir [Pseudotsuga menziesii var. glauca (Beissn.) Franco] was studied to identify conditions affecting its survival and growth in nine planted and four natural study sites in British Columbia. Planted Douglas-fir ranged from 20 to 40 years in age, and natural stands from 63 to 110 years in age. Average survival for all tree species in planted stands was 86% after 30 years and for Douglas-fir in natural stands survival was 60% after 90 years. Armillaria root disease was the principal cause of Douglas-fir mortality in all sites. Mortality in planted stands increased with stand age but slowed by age 35. Planted tree mortality was reduced with greater accumulation of cold temperatures which is thought to affect inoculum potential or contact between inoculum and the host. In older and younger stands, site index was positively related to mortality, probably a direct result of the greater contact with fungal inoculum associated with the larger diameter trees. In older natural stands, mortality increased with stand age and was also positively related to the summer heat moisture (SHM) index thought to be through lower summer rainfall. Mortality impacted negatively on basal area yield, meaning that growth of living trees could not compensate for basal area lost to dead trees.