Decomposing forest carbon density: Stem number vs. tree size

Forests consist of trees, as the FAO defines: “Land spanning more than 0.5 hectares with trees higher than 5 meters and a canopy cover of more than 10 percent, or trees able to reach these thresholds in situ. It does not include land that is predominantly under agricultural or urban land use”. The carbon density of forest vegetation varies by two orders of magnitude spatially between regions. It is important to analyze spatial and temporal trends in carbon density to assess the global or regional rates of change of the carbon sink of forested vegetation.

Here we show, how the number of tree stems and the size of an average tree have changed in Finland since the 1920´s. It turns out that the number of both small and large trees has increased in nearly all sub-regions in Finland. The change has been most pronounced for largest trees in southern boreal forests.

We discuss ecological and management changes driving the number vs. the average size of trees, asking whether a change of tree size is likely to sustain longer than change in the number of tree stems.