A Qualitative Analysis of Sawn Timber Obtained from Various Sites Throughout Poland in The Aspect of Polish and European Standards of Quality

: The paper attempts to compare the classiﬁcation of sawn timber based on the norms used in Poland (PN—75 / D—96000) and those valid in the European Union (PN—EN 1611—1). For the research, long pine logs were taken from ﬁve research areas in Poland. The obtained sawn materials were divided according to their origin into lengths of the logs. It was shown that regardless of the origin of the stand, knots are the dominant defect, while the role of other wood defects is much lower. Direct comparison of the classiﬁcation according to Polish and European standards is very di ﬃ cult due to the di ﬀ erences in the acceptable range of individual wood defects. The raw material classiﬁed by the Polish standard shows a higher proportion of sawn timber of higher classes than the one classiﬁed by the European standard, so the Polish standard is less rigorous than the European one.


Introduction
Scots pine (Pinus sylvestris L.) is the essential forest-forming species in Poland: nearly 60% of our forests are pine forests. Most of the 40 million cubic meters of timber harvested in recent years have originated from pine trees. Pine timber has a number of applications, both in the round form (for construction shoring, as pit wood, poles and supports) and as timber [1]. Both these features and the available volume obtained from pine make it the most universally used material in sawmills and wood processing factories in Poland. The technological quality of pine wood is highly varied, depending on the region of Poland it comes from [2]. The qualitative variability of pine wood available in Poland as well as its applicability in industry and for construction purposes has drawn keen attention from researchers from the 1960s. Research works were carried out both by the faculties of forestry (for instance, Paschalis' studies on [3,4] the strength of Polish pine wood) and the faculties of wood technology in various universities, involving the conventional element method [5,6].
The choice of the right sawing method is based on the use of dedicated wood sawing systems [7]. In the final step of sawn timber production, the product is properly sorted. The separation of a certain amount of sawn timber having specific quality or dimensions is based on written product grading criteria (for instance, in the form of standards).
The aspect of proper and more rational utilization of timber in industrial production started to draw specialists' attention in the 1960s [8][9][10][11]. Currently, the proper functioning of sawmills and wood processing factories is approached in a more complex way: by acquiring the kind of timber that suits a given production profile, by increasing material efficiency of timber and by reducing production costs. The objective may be attained in several aspects. The technological progress we have been witnessing

Materials and Methods
The test material included pine timber from sawing mills in five different locations throughout Poland. The selected tree stands were characterized by comparable conditions of growth (habitat, site index), dimensions and quality so as to be a reference applicable to all Polish pine timber in the form of long logs. For this study, the authors selected pine timber of ages from 88 to 124, from a mixed forest habitat.  Table 1 shows a compilation of forest inventory parameters for selected surfaces. The tree stands were characterized by different tree height and site index and were of comparable technological quality.  Olesno  124  25  II  2  Kalisz Pomorski  90  28  I  3   Wymiarki  114  21  III  2  114  17  IV  2  Biała Podlaska  88  28  I  2  Dąbrowa Tarnowska  90  29  IA  2 Batches of about 50 m 3 of pine wood in the form of long logs were collected from each NFR for the tests. The wood was collected after tree stock survey the purpose of which was to match the qualitative structure (quality class) and dimensional structure (thickness grade) of the wood. The collected data were then analyzed and model trees were determined. This was intended to reflect the average quality and dimensions of pine timber in the form of long logs originating from Polish forests (most of it thickness Grade 2 WC0 material).
The timber was transported to the handling yard before being stored in the form of 3.5 m log logs. All the logs were sawn in the wood processing company KPPD Szczecinek (Koszalińskie Przedsiębiorstwo Przemysłu Drzewnego Spółka Akcyjna).
The sawing process provided edged timber with the nominal dimensions 45 × 140 × 3500 mm, for use in further analyses. The resulting sawn timber was classified according to the Polish Standard concerning coniferous timber for general use [27].
When determining its quality class, a specific board was assessed in terms of acceptable defects of wood. Such defects were categorized, counted, measured and their incidence was described (the incidence of defects on the worse surface and side was assessed). The method comprises two instances of divergence from the rule: (1) when the better surface of a component is free of defects and when the defects present on the worse surface result in the component being graded as Class 2, then the whole component is qualified as Class 1; (2) when there is only one defect and it is the reason why the component must not be graded as Class 2 timber, then the defect is not taken into account. When considering knots, the worse 1.0 m section of sawn timber was analyzed. The resulting sawn timber in the form of boards was graded in separate groups and the results were compiled taking into consideration both the origin of the test material and the type of defect. The resulting timber was graded based on both the Polish and European standards. Moreover, the authors compared both timber grading methods; the one based on the Polish Standard [27] and the European Standard [28].
The outcomes were subjected to statistical analysis. The data were collected using the Excel (2013) spreadsheet and handled by Dixon Q-test to reject outliers. The results were grouped for the whole batch of the material originating from a given site and were compared using the Statistica 13.1 package.
The distribution of the feature of interest was assessed based on the Shapiro-Wilk test. The homogeneity of variance was assessed with the Levene test. To assess the quality of sawn timber, a two-factor ANOVA analysis was performed. Depending on the results of the distribution and variance tests, the significance of the test results was assessed using the ANOVA or the Kruskal-Wallis test. Mean homogeneous groups were separated using the NIR test and Tukey's procedure.

Results
The assessment of the quality of sawn timber (according to PN-75/D-96000) obtained from the tested timber indicated variable timber quality depending on its origin. The highest quality was that of the sawn timber obtained from the Forest Divisions Olesno, followed by Wymiarki and Kalisz Pomorski. The sawn timber obtained from the trees from the Forest Divisions Dąbrowa Tarnowska and Biała Podlaska ( Figure 1) was of the poorest quality. As regards to the sawn timber quality class, Grade 3 dominated (Table 2). Class 3 timber originated mainly from middle and top logs.   As regards to the sawn timber quality class, Grade 3 dominated (Table 2). Class 3 timber originated mainly from middle and top logs. As regards the origin of the material, the percentage of quality Class 4 sawn timber for the top logs was confirmed in the respective sections of the model long logs. A small, but the highest, percentage of sawn timber of higher quality class (including Grade 1) was recorded in the butt-end logs ( Figure 2). It was observed as a regular feature in sawn timber from all sites that timber of the highest quality was obtained from the butt-end logs, the middle logs were the second best and the top logs were the third-best material. This confirmed the relationships between the exact section of long logs and the quality of the main timber ( Figure 3).  It was observed as a regular feature in sawn timber from all sites that timber of the highest quality was obtained from the butt-end logs, the middle logs were the second best and the top logs were the third-best material. This confirmed the relationships between the exact section of long logs and the quality of the main timber ( Figure 3).
Similar results as those for the Polish Standard were obtained using the European Standard PN-EN 1611-1. Grade 3 was the most numerous quality class of the sawn timber. Differences between the two grading procedures related to Grade 4, i.e., the lowest quality class. In the method based on the European standard, the amount of Grade 4 sawn timber was definitely larger. Compared with the method described in the Polish Standard, lower percentages of sawn timber represented, most of all, Grades 1 and 2 (Table 3). It was observed as a regular feature in sawn timber from all sites that timber of the highest quality was obtained from the butt-end logs, the middle logs were the second best and the top logs were the third-best material. This confirmed the relationships between the exact section of long logs and the quality of the main timber ( Figure 3).  Similar results as those for the Polish Standard were obtained using the European Standard PN-EN 1611-1. Grade 3 was the most numerous quality class of the sawn timber. Differences between the two grading procedures related to Grade 4, i.e., the lowest quality class. In the method based on the European standard, the amount of Grade 4 sawn timber was definitely larger. Compared with the method described in the Polish Standard, lower percentages of sawn timber represented, most of all, Grades 1 and 2 (Table 3).  Among the defects referred to in the standard, knots had a dominant effect on the quality grading of sawn timber regardless of the log zone they came from. The closer the top of the log, the higher the incidence of knots as the determinant of the quality class of sawn timber (Table 4). Table 4. The percentage of knots as a factor affecting the quality class of sawn timber in the longitudinal section of long logs. A similar relationship for the incidence of knots was observed for sawn timber collected separately for each forest division (Table 5).

Amount of Sawn Timber Logs
On the other hand, some differences were also observed. Compared with the other forest divisions, in the sawn timber from the Forest Division Olesno, the incidence of knots in the butt-end logs (as a determinant of its quality class) was the lowest. In the sawn timber from the other forest divisions, the effect of knots as the wood defect on the quality grading of the sawn timber was comparable ( Table 6).  I  II  III  IV  I  II  III  IV  I  II  III   Other wood defects considered in the sawn timber quality grading include bark pockets and resin pitches (Table 7).  I  II  III  IV  I  II  III  IV  I  II  III  The effect of bark pockets and resin pitches (considered collectively in PN-75/D-96000) on the quality grading of coniferous sawn timber is definitely less pronounced than that of knots (Table 8). Even though the impact of these two wood defects on its quality grading is rather low, the batches of sawn timber from the various sites differed a lot in this respect.
The most pronounced effect of the bark pockets and resin pitches on quality grading was observed for the sawn timber from the Forest Division Olesno ( Table 9). The other two defects considered and identified in the sawn timber did not have much impact on its quality grading. As a result of these defects, a small amount of sawn timber originating from butt-end logs and middle logs was regraded (from Grade 2) to Grade 3 (Tables 10 and 11).   I  II  III  IV  I  II  III  IV  I  II  III I  II  III  IV  I  II  III  IV  I  II  III  The results of verification of the quality of sawn timber based on the European Standard PN-EN 1611-1 were different from those based on the Polish Standard (the two highest grades, Grades 0 and 1 were combined). According to the European grading procedure, the percentage of the lowest grade timber (Grade 4) was the highest. Therefore, a material graded according to the Polish Standard comprises a higher percentage of sawn timber of higher grades than the same material graded based on the European Standard (Figure 4).  A compilation of sawn timbers representing the different quality class according to PN-EN 1611-1 confirmed that its requirements for coniferous timber were higher than those in the Polish Standard PN-75/96000 (Table 12). Such higher requirements resulted in the sawn timber being graded lower that the material graded based on the European Standard related to sawn timber from all the sites ( Figure 5). A compilation of sawn timbers representing the different quality class according to PN-EN 1611-1 confirmed that its requirements for coniferous timber were higher than those in the Polish Standard PN-75/96000 (Table 12). Such higher requirements resulted in the sawn timber being graded lower that the material graded based on the European Standard related to sawn timber from all the sites ( Figure 5).
As in PN-75/D-96000, knottiness was the defect with the highest impact on the quality grading of the sawn timber regardless of the log zone it came from, and such impact was noticeably lower than in the case of the Polish Standard (Table 13).
The same regularity was observed for the sawn timber originating from the respective forest divisions. The impact of knots as wood defect on the grading of sawn timber from the other forest divisions was comparable (Tables 14 and 15). As in PN-75/D-96000, knottiness was the defect with the highest impact on the quality grading of the sawn timber regardless of the log zone it came from, and such impact was noticeably lower than in the case of the Polish Standard (Table 13). The same regularity was observed for the sawn timber originating from the respective forest divisions. The impact of knots as wood defect on the grading of sawn timber from the other forest divisions was comparable (Tables 14 and 15).    Other types of wood defects considered in the sawn timber quality grading were bark pockets and resin pitches. In comparison with the Polish Standard, such defects had a considerable impact on the sawn timber quality grading. Specifically, this related to the sawn timber obtained from the middle sections of long logs (Table 16). Table 16. The percentage of bark pockets and resin pitches as a factor affecting the quality class of sawn timber in the longitudinal section of long logs.

Butt-End Log Middle Log Top Log
Total (pc) 1232 2061 689 With bark pocket and resin pitch (pc) 244 512 55 Percentage of bark pockets and resin pitches 20 25 8 These defects were observed regularly in the sawn timbers from all forest divisions (Table 17). Bark pockets and resin pitches have the most undesirable effect on the quality grading of sawn timber from the middle sections of long logs. For the various forest divisions, the defect spanned from 18% to 28% for the Forest Divisions Biała Podlaska and Olesno, respectively (Table 18).   The other two defects considered and identified in the sawn timber did not have much impact on its quality grading. They resulted in a small amount of sawn timber originating from all sections of long logs having to be regraded from Grade 3 to Grade 4, and were the most numerous in the butt-endand middle logs (Tables 19 and 20). Table 19. Amount of sawn timber by defect: rot (PN-EN 1611-1). In assessing the quality of pine timber, knots play a decisive role: they affect the quality of timber, graded in accordance with comparable Polish and European standards. As a result, the sawn timber is regraded, usually from Grade 3 under the Polish Standard to Grade 4 under the European Standard, or from Grade 2 to Grade 3.

Logs
Even after regrading, the presence of bark pockets and resin pitches is another important factor to be taken into account in assessing the quality of the sawn timber. These defects lead to less sawn timber being classified as Grade 2 or Grade 3 material.
Comparing the quality classes of sawn timber under the Polish Standard and the European Standard, one can observe that the same sawn timber represents different quality classes when classified according to different quality standards. The Polish Standard provides potentially higher quality classes than the European Standard. This regularity is best illustrated by comparing graphs showing quality classes for sawn timber originating from the butt-end, middle and top logs ( Figure 6). The European Standard emphasizes not only the presence of knots-the essential defect of sawn timber-but also the resin pitches that strongly and negatively affect gluing and surface finishing processes. The Polish Standard refers only to knots in sawn timber whereas the other defects (including resin pitches) have a marginal effect on the quality class of sawn timber, under the Polish Standard.
The graph showing the quality of sawn timber graded under the Polish Standard has a regular profile (Figure 6a). The quality of the sawn timber has a regular shape depending on the section of the long log it comes from. Sawn timber of the highest quality comes from the butt-end logs and the top logs provide timber of the poorest quality, whereas middle-quality timber is obtained from the middle logs. Such shape of the curve relates to sawn timber from every forest division. The curve showing the same relationship based on the European Standard for the various forest divisions had quite a different shape. For two forest divisions, namely Wymiarki and Kalisz Pomorski, the regular curve profile was maintained. For the forest divisions Olesno and Dąbrowa Tarnowska, the sawn timber of the best quality class came from the middle logs. On the other hand, in the forest division Olesno, sawn timber of the lowest quality class came from the top logs, and in Dąbrowa Tarnowska from the butt-end logs. In the sawn timber from the forest division Biała Podlaska, the arrangement of the quality classes of sawn timber was quite similar to that resulting from the Polish Standard, although the distances between the indicators of the quality of sawn timber obtained from the various log zones were not very large. Small differences between the indicators of quality for sawn timber were seen also in the method based on the Polish Standard. The reason why this occurred was probably that timber from that very site had the highest percentage of knots in its butt-end and middle sections. Comparing the quality classes of sawn timber under the Polish Standard and the European Standard, one can observe that the same sawn timber represents different quality classes when classified according to different quality standards. The Polish Standard provides potentially higher quality classes than the European Standard. This regularity is best illustrated by comparing graphs showing quality classes for sawn timber originating from the butt-end, middle and top logs ( Figure  6). The European Standard emphasizes not only the presence of knots-the essential defect of sawn timber-but also the resin pitches that strongly and negatively affect gluing and surface finishing processes. The Polish Standard refers only to knots in sawn timber whereas the other defects (including resin pitches) have a marginal effect on the quality class of sawn timber, under the Polish Standard.  The graph showing the quality of sawn timber graded under the Polish Standard has a regular profile (Figure 6a). The quality of the sawn timber has a regular shape depending on the section of the long log it comes from. Sawn timber of the highest quality comes from the butt-end logs and the top logs provide timber of the poorest quality, whereas middle-quality timber is obtained from the middle logs. Such shape of the curve relates to sawn timber from every forest division. The curve showing the same relationship based on the European Standard for the various forest divisions had quite a different shape. For two forest divisions, namely Wymiarki and Kalisz Pomorski, the regular curve profile was maintained. For the forest divisions Olesno and Dąbrowa Tarnowska, the sawn timber of the best quality class came from the middle logs. On the other hand, in the forest division Olesno, sawn timber of the lowest quality class came from the top logs, and in Dąbrowa Tarnowska from the butt-end logs. In the sawn timber from the forest division Biała Podlaska, the arrangement of the quality classes of sawn timber was quite similar to that resulting from the Polish Standard, although the distances between the indicators of the quality of sawn timber obtained from the various log zones were not very large. Small differences between the indicators of quality for sawn timber were seen also in the method based on the Polish Standard. The reason why this occurred was probably that timber from that very site had the highest percentage of knots in its butt-end and middle sections.

Conclusions
In some aspects, the implementation of the common European legislation in certain sectors of the Polish economy is not very smooth, even though Poland has been a member of the European Union since 2004. Among other things, this relates to wood as a material in the roundform and as processed wood, including timber. The Polish State Forests-the principal supplier of roundwood in

Conclusions
In some aspects, the implementation of the common European legislation in certain sectors of the Polish economy is not very smooth, even though Poland has been a member of the European Union since 2004. Among other things, this relates to wood as a material in the roundform and as processed wood, including timber. The Polish State Forests-the principal supplier of roundwood in Poland-follows its internal wood grading rules, based on the order of the Director-General of the State Forests defining the applicable technical requirements. In this respect, Poland is no exception among the EU states: some of them also have their own rules of standardization and quality grading of wood [29]. Despite some important dissimilarities between Poland and the European Union or any other EU member state, the grading rules applied have one thing in common, namely, wood defects. The timber quality grading rules depend on the acceptable range of intensity of these features (defects) according to any applicable national or European standard. Unfortunately, it would not be acceptable to use either the national or the European standards for timber quality grading. Timber quality grading is based on different methods of assessment of the defects and their acceptability. According to the examples shown above, the use of European standards in the quality grading of Polish coniferous timber results in a more stringent classification, especially as regards the higher quality grades. This is because the requirements of European Standards relating to knots and resinosis are more severe, in the first place. Even though the common economic and political space in Europe does exist, some regional (national) conditions in the European Union continue to prevail, and it is hard to predict when technical requirements and standards related to wood (and wood-based products, including sawn timber) in the whole European Union will be harmonized, if at all.

Conflicts of Interest:
The authors declare no conflicts of interest.