Comparison of three methods for determining the conductive xylem area of Scots pine (Pinus sylvestris)

Three methods for the estimation of conductive xylem area were compared in several stands of Scots pine in northern Germany: (1) computer tomography ( seven stands, 105 trees), (2) staining of increment cores (seven stands, 75 trees), and (3) resistance to penetration (two stands, 35 trees). The stai ning method gave significantly higher estimates of the proportion of conduc tive xylem area than the other methods. The results indicate that between true, stainable heartwood and conductive xylem there is a zone of relatively dry but chemically unaltered xylem, whi ch the staining method identified as sapwood. Therefore the use of staining methods to estimate functional sapwood in Scots pine seems to be prone to significant errors. Estimates of stand transpiration based on sapflux densi ty and sapwood area obtained by staining can result in an error of up to 15 per cent. This can be avoided by using techniques that are based on wood m oisture content. With a combination of computer tomography and staining tec hniques it is possible to estimate the extent of the three zones of xylem, viz. true sapwood, the transition zone, and true heartwood. Resistance to p enetration proved to be an efficient and inexpensive alternative to compute r tomography.