Above- and below-ground biomass, surface and volume, and stored water in a mature Scots pine stand

This study describes the amount and the spatial distribution of the above- and below-ground tree skeleton-defined as the woody structure of stem, branches and roots-in a mature Scots pine (Pinus sylvestris L.) stand in Belgium. Tree skeleton data were linked to the respective needle area, and as such, this work provides the background framework for modeling the tree hydraulic architecture and the carbon balance of the forest stand. Using validated allometric equations, we were able to calculate the amount of the volume, of the biomass and of the corresponding surface areas of individual trees in the stand. Total woody biomass of the 66-year-old forest stand was 155 Mg ha(-1), i.e., 126 Mg ha(-1) above ground and 29 Mg ha(-1) below ground. The total bio-volume of the woody mass of the stand was 314 m(3) ha(-1). The highest fraction of this value was the stem bio-volume, i.e., 236 m(3) ha(-1) or 75 % of the total. The total volume of all roots was 57 m(3) ha(-1) (18 % of the total volume), and the volume of branches was 20 m(3) ha(-1) (7 % of the total volume). The surface area of the roots ranged from 38,000 m(2) ha(-1) in the winter to 68,000 m(2) ha(-1) in the spring. The surface area of the stems was 2,700 m(2) ha(-1), and the surface area of all branches reached 4,400 m(2) ha(-1). The total above-ground water storage in the xylem was 94 m(3) ha(-1) (or 9.4 mm), while the accessible stored water was 2 mm of that quantity. A comparative analysis of the biometric parameters showed the balance between the different functionally connected, operational surface areas of the trees. The needle surface area was similar to the root surface area and in the same order of magnitude as the surface area of woody cambium. The results allow to link water uptake with transpiration and assimilation with respiration.