## 3 Results and Discussion
### Poplar Veneers  
Poplar is a fast-growing diffuse-porous hardwood species of high availability, whose utilization is restricted by its low density [3]. As regards the poplar wood veneers (Figure 10), the surface roughness parameters in the areas around the decay were found to be, in most of the cases (veneers V1, V3, V4 and V5), of lower surface roughness, compared to the wood surface of typical structures. Specifically, in the case of veneers V1 and V5, the differences were found to be statistically significant, with the roughness values of areas around decay to be the lowest ones (Table 5). The tests of Between-Subjects effects revealed that the factor of \"veneers\", referring to this progress of the different depths from V1 to V5, significantly affected the Ra variance, by 39%. In addition, 52.4% of Ra variance is attributed to the factor of \"Structure\", referring to the typical and non-typical structure of wood (around the decay area), while the interaction between the factors \"Veneers\" and \"Structure\" significantly affects the Ra variance, by 59.1%. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**Dependent Variable: Ra**} & & & \\ \hline
**Veneers** & **Structure** & **Mean** & **Std. Deviation** & **N** \\ \hline \multirow{3}{*}{V1} & Typical & 5.3760 & 0.54929 & 10 \\  & Irr.rings & 6.5480 & 0.51903 & 10 \\  & Total & 5.9620 & 0.79498 & 20 \\ \hline \multirow{3}{*}{V5} & Typical & 5.6860 & 0.45634 & 10 \\  & Irr.rings & 5.4680 & 0.67166 & 10 \\  & Total & 5.5770 & 0.56995 & 20 \\ \hline \multirow{3}{*}{V10} & Typical & 4.8020 & 0.36039 & 10 \\  & Irr.rings & 5.1000 & 0.20219 & 6 \\  & Total & 4.9137 & 0.33728 & 16 \\ \hline \multirow{3}{*}{Total} & Typical & 5.2880 & 0.58079 & 30 \\  & Irr.rings & 5.7985 & 0.80812 & 26 \\ \cline{1-1}  & Total & 5.5250 & 0.73531 & 56 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Descriptive statistics of dependent variable Ra measured on ash stump veneers of typical wood structure areas and areas of eccentric annual rings and discoloration. Figure 9: Surface roughness parameters Ra, Rz and Ry (\(\upmu\)m) of ash heartwood veneers (V1, V5, V10) on typical wood structure areas and in areas of eccentric annual rings (spiral grain) of the wood near the trunk base, also bearing discoloration. Concerning the roughness parameter values measured on the surface of poplar wood veneers (Figure 11, Table 6), around typical and non-typical wood structure areas, it was also revealed that the areas around the live knot detected were found to be, in each case, of significantly lower surface roughness compared to those of typical structure. The factor of \"veneers\", referring to this progress of the different depths from V1 to V5, significantly affected the Ra variance, by 70.4%. In addition, 60.9% of Ra variance is attributed to the factor of \"Structure\", referring to the typical and non-typical structure of wood around and on the irregularities of annual rings, while the interaction between the \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Dependent Variable: Ra** & & & & \\ \hline
**Veneers** & **Structure** & **Mean** & **Std. Deviation** & **N** \\ \hline \multirow{3}{*}{V1} & Typical & 11.0760 & 1.25466 & 10 \\  & Decay & 7.0540 & 0.89370 & 10 \\  & Total & 9.0650 & 2.31969 & 20 \\ \hline \multirow{3}{*}{V2} & Typical & 7.7180 & 0.70577 & 10 \\  & Decay & 8.5400 & 0.83865 & 10 \\  & Total & 8.1290 & 0.86424 & 20 \\ \hline \multirow{3}{*}{V3} & Typical & 8.4760 & 0.80899 & 10 \\  & Decay & 7.5660 & 0.52812 & 10 \\  & Total & 8.0210 & 0.81244 & 20 \\ \hline \multirow{3}{*}{V4} & Typical & 7.6540 & 0.61401 & 10 \\  & Decay & 7.0120 & 0.53705 & 10 \\  & Total & 7.3330 & 0.65089 & 20 \\ \hline \multirow{3}{*}{V5} & Typical & 9.2900 & 0.31035 & 6 \\  & Decay & 6.3250 & 0.59409 & 8 \\  & Total & 7.5957 & 1.59551 & 14 \\ \hline \multirow{3}{*}{Total} & Typical & 8.8039 & 1.54594 & 46 \\  & Decay & 7.3400 & 0.99082 & 48 \\ \cline{1-1}  & Total & 8.0564 & 1.48116 & 94 \\ \hline \hline \end{tabular}
\end{table}