Current issue: 55(4)
Under compilation: 55(5)
The paper aimed at testing the potential of refining tree rot diagnostics carried out by means of electrical impedance tomography (EIT). Examined was the use of EIT datasets with electrical resistance values and sapwood proportion determined on the basis of tomograms. Making use of datasets with resistance values in EIT rot diagnostics is not a default method, although datasets stay unaffected by a fixed colour scale and subsequent subjective evaluation unlike tomograms. Tomography measurement was carried out for 27 individuals of Norway spruce (Picea abies [L.] Karst.) in two stands north-east of Brno, Czech Republic. Once felled down, radial cut-outs were sampled at the measurement site and used for localising rot and determining the extent of the area of decay. The results were subsequently compared with tomograms. EIT datasets containing values of electrical resistance found by measuring were statistically processed and compared with the extent of rot area identified within the cuts. Sapwood proportion values were also detected using the tomograms. The baseline assumption that sapwood proportion decreases as the rot area in the radial cut expands was confirmed. In trees with rot percentage to 35% approximately, sapwood proportion was exceeding 30% except one tree. In trees with rot percentage exceeding 35%, sapwood proportion was below 30%. On the basis of interpreted datasets, the trees can be split into three characteristic groups that correspond to the occurrence, extent and nature of the rot.
The effects of two alternative formulations of sapwood senescence on the behaviour of model LIGNUM (with parameter values adjusted for Scots pine (Pinus sylvestris L.) growing southern Finland) were studied. The two alternatives were autonomous sapwood senescence assuming a maximum age for the tree ring, and sapwood senescence that is controlled by the mortality of foliage. For the latter alternative two hypothetical further mechanisms were stipulated. All the formulations were implemented in LIGNUM. Simulations were made with all model variants for fertile and poor soil conditions using high, normal and low rates of foliage mortality. The simulation results were compared against of a data set consisting of 11 open grown Scots pine trees from southern Finland. Observations of heartwood proportion were used in this study. They show that heartwood starts to increase in trees from age of approximately 20 years onwards. The simulation results showed no differences between fertile and poor soil conditions as regards heartwood formation. Of the variants of foliage-controlled sapwood senescence the one where death of sapwood in a tree segment induces sapwood senescence in the tree parts below only slightly was the best. This and the autonomous sapwood senescence corresponded equally well to the observations. In order to make more refined conclusions additional data and simulations are necessary.
In laboratory studies the heartwood content seems to be the only natural property of a wood of different tree species influencing the decay resistance. Moistening and drying by diffusion happen quite slowly. Scots pine (Pinus sylvestris L.) sapwood takes moisture by capillary action quicker than pine heartwood and Norway spruce (Picea abies (L.) H. Karst.) wood. Swelling and shrinkage are also greatest in pine sapwood. Impregnation of pine sapwood can give it better hydrophobic and dimensional stability than that of pine heartwood.
The PDF includes an abstract in English.