Productivity analysis of silvicultural treatments in cedar and hemlock stands on northern Vancouver Island

Due to many favourable characteristics such as a moist and mild climate year round, the absence of fire or a major insect infestation and disease, the coastal coniferous forests of northern Vancouver Island are among the most productive forests in British Columbia. However, the productivity rates can vary in a mosaic pattern of two very distinctive forest types: low-productivity “CH” and medium-productivity “HA”. In 1987-88 a trial was established to analyse growth effects of fertilization on western red cedar (Thuja plicata Donn ex D. Don) and western hemlock (Tsuga heterophylla (Raf.) Sarg.) at these two different sites. Previous projects measured the height and the DBH after 10 and 15 growing seasons, and have been recently re-measured again after 22 years since establishment. Fertilizer was applied three times after planting; stand density was established at: 500, 1500 and 2500 stems/ha. Fertilization significantly increased the height and volume of both species at all treatment. Depending on the site fertility and treatment used, the stand volume of fertilized red cedar increased from 123% to 351% and fertilized hemlock volume increased from 106% to 2190% compared to the non-fertilized counterparts. In most cases, higher densities had much greater volume per hectare than lower density stands; however, density caused a significant decrease in the average height of both species at CH sites. Biomass and carbon content were also estimated in this study. Results indicated a positive growth response of total biomass generated by fertilization. CH sites have shown the best increment response to fertilization; however, averages were still low if compared to HA sites. Overall, the best treatments were found to be high density fertilized hemlock stands on HA sites. This treatment not only had the greatest height, volume and biomass, but was also the most efficient for C capture. After 22 growing seasons, the results of this research reinforces the idea that fertilization is a reliable and effective tool to increase nutrient availability and productivity of these forests; it suggests that the focus of silvicultural treatments such as fertilization and increased stand density should be directed mostly towards the more productive HA sites.Forestry, Faculty ofGraduat