A method to calculate the losses caused by western spruce budworm in uneven-aged Douglas fir forests of British Columbia

Abstract

A system was designed for projecting the growth of uneven-aged stands of interior Douglas fir ( Pseudotsuga menziesii var. glauca (Beissn.) Franco) of the Kamloops Region of British Columbia after defoliation by the western spruce budworm ( Choristoneura occidentalis (Freeman)). The system reads forest inventory files and simulates infestations of varying severity and duration. The system produces the losses in total stand volume (all trees with a diameter larger than 2.5 cm) and in volume of the harvestable trees (all trees with a diameter larger than 30 cm) for every 10 year interval. In a trial consisting of a 20 year projection on 32 stands, assuming a 7 year infestation in the first decade, the system calculated that at the end of the projection, losses in total volume per hectare averaged 6.2%, 23.3% and 32.8% of the total stand volume, for light, moderate and severe infestations, respectively. Reduction in the 20 year periodic annual increment of the total volume averaged 7.1, 39.3 and 51.6%, for light, moderate, and severe infestations. Losses resulting from infestations lasting 1–9 years are also reported.