Fig. 6

Annual N₂O fluxes in tree stems and forest floor. The fluxes are expressed per stem or soil surface area unit (a) and scaled up to unit ground area of boreal forest (b). The fluxes are expressed as medians (solid line) and means (broken line) of measurements at both wet and moderately wet plots together, as the N₂O fluxes did not vary significantly between those plots at the annual scale. The dry plot was not included into this comparison of annual fluxes because only pine trees were available at this plot. The stem fluxes were measured from six trees per species (n = 6), the forest floor fluxes were determined at six positions (n = 6). The box boundaries mark the 25th and 75th percentiles. Statistically significant differences in annual fluxes among birch, spruce and pine at p < 0.05 are indicated by different letters above the bars. The contributions of stem fluxes to forest floor N₂O fluxes (equal to 100%) are expressed as percentages of the forest floor flux