Nutrient pools in Sitka spruce and lodgepole pine forest biomass

Biomass harvesting may affect the nutrient pools of forests and impact negatively on forest ecosystems in the long-term. Appropriate knowledge regarding nutrient pools and potential nutrient removal is required for a good forest management to attain sustainable productivity. The main aims of this work were to give information of nutrient status (nitrogen N, phosphorus P, potassium K, calcium Ca, and magnesium Mg) of forests by studying a chronosequence Sitka spruce (Picea sitchensis (Bong.) Carr) and several mature Sitka spruce and lodgepole pine (Pinus contorta Dougl. var. latifolia) stands, and to determinate the potential nutrient removal in a site applying different harvest scenarios: stem-only harvest, stem-and-branch harvest and whole-tree harvest. The database of this study comes from selected and sampled forest harvest residue in brash bundles and from standing trees, which were divided in six components (needles, branches, deadwood, roots, stembark and stemwood). Nutrient concentrations of these samples were analysed. Both tree species showed that needles was the component with higher nutrient concentration, and stemwood that with the lowest. In general, nutrient concentration in a tree for both species was identified from large to lesser concentration: N > Ca > K > Mg > P. Nitrogen pool generally increased over time. Sitka spruce stands had larger nutrient pools than lodgepole pine stands. WTH system potentially removed approximately double the amount of nutrients than SOH system. Several investigators had suggested different percentages of harvest residues to be retained on site in order to manage the forest sustainably. More research will be needed to verify what amount of harvest residue and what type of it must be left on site.