Growth, camphor concentration, and nitrogen responses of white spruce (Picea glauca) leaves to browsing and fertilization

Abstract

We tested some responses of white spruce (Picea glauca) to fertilization, browsing, size of tree, and the season in which browsing took place. We collected leaf samples from trees that had been more or less fertilized and more or less browsed by snowshoe hares, for 9 y. We also used 3 levels of simulated browsing that removed approximately 10%, 30%, and 85% of all green biomass. We measured growth rate, camphor, and nitrogen concentrations in leaves, sampling monthly for 15 months. Camphor was induced by both natural browsing and clipping, and the response was influenced by plant resource status; camphor concentration increased with browsing pressure. At high browsing levels, both camphor concentration and growth rate declined. Seasonal camphor concentrations were highest in small trees that have a high risk of attack and during the winter, when trees are both slow growing and more heavily browsed.