The major part of the energy in forests is stockpiled in organic molecules and woody biomass in particular. The carbon stock of the world’s forests is estimated as 861 +/- 66 Pg C (tropical forests represent 55 % of this carbon, while the boreal belt holds 32 % and the temperate forests 14 %). On average 44 % of the carbon is present as organic soil compounds, 42 % as live biomass (below and above ground), 8 % as dead wood and 5 % as litter, but there are large differences between biomes, with a higher proportion of carbon in living biomass in the tropics and more carbon in the soil of the boreal forest. Interestingly the largest part of the forest biomass consists of wood and bark: above ground this rises up to 98 % in tropical and temperate forests and 87 % in boreal forests, but also below ground much of the carbon is kept in woody materials, including coarse roots, a part of the detritus and even a substantial part of the fine roots contain secondary tissues. Heterotrophs (less than 1 %), tree foliage and herbaceous plants, although functionally vital, constitute only small fractions of the carbon stocks. It is estimated that 400 Pg carbon is stored in wood globally. Information on tree growth provides key information for a good understanding of patterns and processes within a forest ecosystem and, on a much larger scale, of planetary carbon fluxes. Projects include repeated diameter measurements and detailed analysis of growth patterns in the wood along a pith to bark gradient.