Belowground biomass and nutrient content in a 47-year-old Douglas-fir plantation

Biomass and nutrient content of the root system of a Douglas-fir stand were calculated using the regression technique. Nine trees, evenly distributed in the girth classes of the stand, were felled for measurements and sampling. Results were compared to published data. Statistically significant relationships between tree circumference at 1.30 m and root biomass or nutrient content were observed. The root biomass was 58 t of dry matter, which was 18% of the total stand biomass. A linear model characterized the relationships between aerial and belowground biomass of 38 Douglas-fir stands previously described in the literature. This simple relationship is very useful when using estimates of the aerial biomass of a stand to calculate the carbon storage in the belowground compartment. Nutrient concentration in the belowground compartment was lower than in the aerial biomass. However, very fine roots and mycorrhizae were not considered. Contrary to aerial biomass, very few published data were found for belowground biomass, hindering any generalization for the nutrient content of the belowground compartment.