Decrease in Sapling Nutrient Concentrations for Six Northern Rocky Mountain Coniferous Species

Abstract

In the west, fire exclusion, timber harvest, and last century’s climate led to copious regeneration on millions of ha that now need tending. Without treatment, overcrowding increases competition, snow and ice damage potential, and ladder fuels. Limited funding prevents treating all of the affected ha, but by selling small trees for wood pellets, biofuel, or methanol, costs would decrease and more ha could be cleaned. In the northern Rocky Mountains, 8 –10 tree species can occur in young forests, and until this study, information on foliage nutrient concentrations and leaching from saplings for all of these species was limited. We use a mixed-model analysis to examine the change in nutrient concentrations (calcium, magnesium, potassium, carbon, and nitrogen) remaining in saplings for 6 tree species (western white pine, ponderosa pine, western hemlock, western redcedar, Douglas-fir, and grand fir) over a 12-month period. Nutrient concentrations and the pattern of nutrient leaching did vary among the species, but we found that nutrient concentrations did not diminish in the first 200 days and western hemlock was the only species for which nutrient concentrations leached substantially in the 12-month period. Results suggest managers may need to use biomass utilization thresholds to ensure sufficient biomass is left on site to maintain soil productivity.