In this paper, transversal stress wave velocity was measured in 30 trees of Serbian spruce (Picea omorika /Pančić/ Purk.) using a 2D sonic tomograph. Tomograms were analyzed and speed loss and average speed for Serbian spruce were calculated. Since there is no reference value for this species, in this research the reference value for stress wave velocity of Norway spruce (Picea abies /L./ H. Karst.) was used for comparison. The relative difference between referent and measured stress wave velocity indicates the amount of decay between the two sensors. The largest number of cross-sections had a speed loss of up to 10%, but there were also cross-sections with a speed loss of more than 50% in the transversal direction. This result shows that there are defects and damages in this direction that will reduce the strength of the wood. Summarizing data for trees with speed loss of less than 10%, the average stress wave velocity at the cross-sections is 1635 (1205-2170) m/s. Compared to Norway spruce, this velocity is higher, but not significantly.

The wood of northern red oak (Quercus rubra L.), considered to be a very high-quality material for processing in the wood industry, has not been tested in Serbia so far. To date, there are only small areas under northern red oak in Serbia, but there are significant stands of this species in the vicinity of Belgrade. In this paper, the basic physical and mechanical wood properties of northern red oak in Serbia were tested. The examined 57 years old tree was located in the forest of Lipovica, near Belgrade. The tree was cut down and two small logs were taken to the laboratory for analysis. The results show that the properties of wood of northern red oak do not differ significantly from the properties of native oak species in Serbia - sessile and pedunculate oak. In addition, the values of basic mechanical properties of wood of northern red oak in Serbia were similar to the relevant values obtained by other researchers in Europe and the USA. Thus, the utilization of wood of northern red oak in the local wood processing industry should be considered.