Increases in tree growth and nutrient supply still apparent 10 to 13 years following fertilization and vegetation control of salal-dominated cedar–hemlock stands on Vancouver Island
Cedar–hemlock forests on Vancouver Island are primarily nitrogen limited and characterized by an under story dominated by the ericaceous shrub salal (Gaultheria shallon Pursh.). In 1984, an experiment was established on regenerating cedar–hemlock forests to determine the effects of nitrogen and phosphorus (N + P) fertilization and vegetation control on conifer growth. It was hypothesized that these treatments would not only stimulate tree growth, but also improve nutrient supply, stand productivity, and site quality. To test this hypothesis, tree height growth, canopy closure, salal biomass, foliar and forest floor N and P concentrations, and seedling growth on forest floor were measured 10–13 years after treatment. Both salal control and fertilization increased tree growth and canopy cover, and reduced salal biomass. However, only fertilized plots showed changes in site quality measurable 10–13 years following N + P application. Hemlock foliar P concentrations, forest floor total N and P levels, and hemlock height increments were higher in these plots. Forest floors from the fertilized plots also supported greater growth of conifer seedlings. These results suggest that sustained changes to site quality may be achieved with N + P fertilization of cedar–hemlock forests.