Quality of raw material and yield of exported sawn wood in the rational use of tropical timber from the Amazon

doi:10.21203/rs.3.rs-2437287/v1

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Quality of raw material and yield of exported sawn wood in the rational use of tropical timber from the Amazon

https://doi.org/10.21203/rs.3.rs-2437287/v1

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The low sawn timber yield of tropical species is caused by quality of the logs, among other factors. The objective was to evaluate the quality of logs and the sawn wood yield for export of the tropical species Dinizia excelsa Ducke, Hymenolobium heterocarpum Ducke, Dipteryx odorata (Aubl.) Willd., Astronium lecointei Ducke and Qualea paraensis Ducke. The log quality parameters analyzed were conicity, flattening, curving, buttresses, cracks, heartwood percentage and net volume. After sawing, the sawn wood yield was determined. The values of conicity (0.92 cm.m^− 1) and flattening (96%) did not differ between species. Qualea paraensis and Hymenolobium heterocarpum showed a better classification for curving. Astronium lecointei showed no buttresses. Qualea paraensis showed better classification for annular ring cracks and Dipteryx odorata for surface and diametrical cracks. Dipteryx odorata (86.75%) and Hymenolobium heterocarpum (82.4%) showed better results for heartwood percentage. Dinizia excelsa (90.1%), Dipteryx odorata (83.6%) and Hymenolobium heterocarpum (82.6%) logs showed higher net volume values. The yield of sawn timber for export differed between species and ranged from 23.9–40.2% for Dinizia excelsa and Qualea paraensis, respectively. There was variation in the quality of the logs and the yield of sawn timber for export due to the distinctive characteristics of the species evaluated.

Timber industry

sawmill

log classification

Amazon Forest

With the decrease in native forest areas, there has been an increase in inspection and the concern of society with the proper use of forest extraction areas in the Legal Amazon. Therefore, the practice of using logs with good quality for the production of sawn wood, especially when the international market has high demand, becomes important to reduce the number of trees to be extracted from the forest. Making good use of wood extracted from the forest means reducing waste generation, since the sawn wood yield will be higher, which contributes to the environmental conservation of forest resources.

Due to the large extent of the Amazon biome, Brazil stands out as the fourth largest producer and consumer of tropical logs in the world (ITTO 2021). Despite the good quality of tropical Amazon wood for log production, processing and commercialization are concentrated in a small group of species, which have greater commercial value. This fact puts pressure on these already consolidated species, and as an example, 54% of the total wood sold in Brazil in the period from 2012 to 2016 came from only 20 species (Brandes et al. 2020). Among these species, Dinizia excelsa Ducke, Hymenolobium heterocarpum Ducke, Dipteryx odorata (Aubl.) Willd., Astronium lecointei Ducke and Qualea paraensis Ducke stand out.

Part of the tropical sawn wood is destined for export due to the higher financial return. According to ABIMCI (2019), in 2018 the main Brazilian hardwood sawn wood exporting states were Pará, with 25%, and Mato Grosso, with 24% of exports. Already the main countries that imported Brazilian hardwood sawn wood were the United States, with 15%, the Netherlands, with 12% China, with 11%, Vietnam, with 10%, and France, with 9%.

However, despite the higher commercial value, the foreign market is more demanding for better wood quality. Normally, wood with the presence of sapwood and defects is not accepted, even if it is in small dimensions and quantities. This fact results in lower use of the raw material, lower yield and higher production of waste. Thus, the low percentage of raw material use is one of the major problems faced by the timber industry. Normally, this is manifested in generation of a large volume of waste, which causes an increase in the cost of the final product. Although recent studies have been conducted to evaluate the sawn timber yield of Amazonian species (Santos et al. 2017; Mendoza et al. 2019; Stragliotto et al. 2019; Lima et al. 2020). There is little information on the yield of tropical species for the Amazon region, despite the potential of wood and the important role of this region in supplying this raw material to the market (Luz et al. 2021).

It is known that the yield of sawn wood is influenced by several parameters, especially those related to the shape and quality of the logs (Melo et al. 2016; Santos et al. 2017; Marchesan et al. 2018; Luz et al. 2021). Few studies in the literature evaluate the yield of sawn timber of tropical Amazonian species, associating the quality of the logs as an important factor to explain the yield of certain species, such as the study by Luz et al. (2021). In general, the vast majority of studies in the literature analyzing this topic address only the log diameter class (Melo et al. 2019; Stragliotto et al. 2019; Lima et al. 2020).

Some quality characteristics of logs are important, such as conicity, flattening, curving, buttresses, cracks and net volume, as mentioned in the Standard for Classification of Hardwoods (IBDF 1984). This standard provides values for each characteristic to classify the logs into quality classes. The flattening of the logs when presented in a marked way hinders the production of the central block and this negatively affects the yield in sawn wood (Vital 2008). Luz et al. (2021), when evaluating 21 tropical Amazonian species, found flattening values ranging from 63.1 to 84.1%.

The conicity of a given log is characterized by a decrease in its diameter from the base to the top (Nassur et al. 2013). Burger and Ritcher (1991) indicate that conicity is more pronounced in isolated trees or in those located on the peripheries of the stands. The conicity is a natural characteristic of each species, tends to decrease over the years and has little genetic influence (Nassur et al. 2013).

According to Vital (2008), the curving of the logs affects the yield of the sawn wood because it limits the length of the pieces produced. Luz et al. (2021), when evaluating the bending in logs of 21 tropical species, found flattening values ranging from 0.0 to 4.7%.

According to IBDF (1984) the buttresses are considered a defect in the log when they are greater than or equal to 5%. During the formation of the buttresses in the trees, there is differentiated activity of the cambium cells, causing accentuated and disordered growth at the base of these trees. This differentiated growth results in the generation of irregular grains, with distinct characteristics of contraction and waste of raw material (Vital 2008). According to the same author, the buttresses are associated with genetic factors, species characteristics, soil growth and unfavorable climatic conditions.

The cracks in the tops of the logs, usually develop by the presence of radial parenchymal cells, whose mechanical strength is low (Jankowsky 1990). Additionally, according to the author, these cracks are caused by the difference between the tangential and radial contractions, negatively affecting the drying process of the cross sections of the logs, without them developing the cracks.

The incipient knowledge and lack of information on the variation in the yield of the log sawing process are barriers to production in the timber industry. Among the various obstacles to the improvement of the Amazon timber sector, we highlight the study of the quality of the raw material and the yield of sawn wood (LUZ et al. 2021). Therefore, it is essential that the quality of the extracted log wood be analyzed so that there is a higher yield of the sawn wood, especially in regard to sawn wood destined for export. Thus, the objectives of this study were to evaluate the quality of sawn timber of five tropical species from the Brazilian Amazon and to determine the yield of sawn timber for export.

Description of the study area and selection of species

This study was conducted at the Forest Management Unit III of the Jamari National Forest, located in the city of Itapuã do Oeste, state of Rondônia, Brazil. This area, with 46 thousand ha, is a concession of the timber industry and a source of raw material as its main activity, which is the monthly production of 1100 m of lumber for export, whose technological requirements are sawn pieces without defects and without sapwood. Five species were evaluated, with nineteen logs in each, with the following diametric characteristics (Table 1).

Table 1

Diametric characteristics of the species evaluated
Species	Diameter variation (cm)	Average diameter (cm)
Dinizia excelsa	71.3 a 147.8	98.8
Dipteryx odorata	60.0 a 99.8	79.8
Hymenolobium heterocarpum	62.5 a 135.5	83.5
Astronium lecointei	64.3 a 83.3	72.4
Qualea paraensis	45.3 a 82.5	59.5

The sawn wood produced from the log sawing process is destined for export. Thus, only the heartwood without defects was used for the species H. heterocarpum, D. odorata, A. lecointei and Q. paraensis due to the color requirements of the international market. For the Dinizia excelsa, wood from the heartwood and sapwood was used, also without defects. This fact is because the sapwood of this species is accepted in the international market due to its reddish color after drying, which is similar to the heartwood color.

Quality of the logs

The length and diameter of the logs were measured using a tape measure (precision of 1 mm). The perpendicular diameters were measured at the two ends of each log to determine the mean diameter. The volume of each log was calculated using the Smalian equation.

According to IBDF (1984), the quality parameters of all logs were evaluated by flattening, conicity, curving, buttresses, surface cracking, diametrical cracking, annular ring cracking and net volume. There were adaptations in the data collection of the annular ring crack, which were evaluated only when the crack length was greater than half a circumference and the number of cracks was not considered. The heartwood percentage was also calculated through the relationship between the heartwood volume and the total log volume.

The net volume was considered the volume effectively used for the production of sawn wood, without defects and without sapwood. It was calculated by the difference between the total volume and the sum of the defective wood volumes and the sapwood volume. The percentage of volume of defects in the central part of the sawn wood (heartwood rot, brittle and hollow heartwood) was determined according to the area of the defect present in the extremity with the largest amount of these defects. For the D. excelsa species, the sapwood volume was considered for the calculation of the net volume because the sapwood was also used for the production of sawn wood.

Based on the results of the quality parameters, the logs were classified according to the IBDF (1984) into Superior, Class I, Class II, Class III and Class IV, Class V (Table 2).

Tabela 2 Log quality classification according to adapted IBDF (1984).

Pr.	Superior	Class I		Class II			Class III			Class IV	Class V
C	≤ 3%	≤ 3%		≤ 4%			≤ 5%*			≤ 6%*	> 6%**
F	≥ 90%	≥ 80%		≥ 70%			≥ 60%			≥ 50%*	≥ 40%**
CU	≤ 3%	≤ 5%		≤ 5%	≤ 8%	≤ 5%	≤ 8%	≤ 5%		≤ 8%*	n.e.**
	N = 1	N = 1		N = 1	N = 1	N = 2	N = 1	N = 3		N = 2*	n.e.**
	L = Lt		L = Lt				L = Lt		L = Lt		n.e.**
B	≤ 10%	≤ 20%*		≤ 30%*			≤ 40%*			≤ 50%*	> 50%**
SC	≤ 5%	≤ 10%		≤ 20%			≤ 30%			≤ 40%	> 40%**
DC											n.e.**
RC	Ab, P **	Ce, Ce + P **		M **			M + P **			Ce + M **	Ce + M + P**
NV	≤ 95%	≤ 90%		≤ 80%			≤ 70%			≤ 60%	> 60%**
^{Pr.= Parameter; C= conicity; F= flattening; CU= curving; B= buttresses; SC= surface crack; DC= diametrical crack; RC= annular ring crack; NV= net volume; N= curving quantities; L = curving length; Lt = total log length; n.s. = not specified; Ldc = diametrical crack length; D= diameter; Ab= absent; Ce = central; M= median; P= peripheral *Adapted by the author}

Log splitting

The logs were unfolded in a simple vertical band saw, blade that is 200 mm wide and 3.3 mm thick; multiple circular saw, with three saws with 400 mm diameter and 5.5 mm thickness; and circular saw cutter, with 450 mm diameter and 5.5 mm thickness. The operator to obtain the best log yield according to the quality and type of sawn wood to be produced defined the sawing system adopted. In this type of unfolding, there is no cutting model that predicts the highest yield for each unfolded log.

Yield of sawn timber for export

After the sawing of logs, the lengths, widths and thicknesses of all the pieces obtained were measured. To calculate the yield of sawn timber for export, per log, the relationship between the volume of sawn wood and the total volume of the respective log was determined. The order and procedures to determine the quality of the log and the yield of the sawn wood are shown in Fig. 1.

Statistical analyses

The experiment was conducted in a completely randomized design, organized into five treatments (species) and 19 replicates (logs). The data on the conicity, flattening heartwood percentage, net volume and yield of sawn wood were subjected to analysis of variance (ANOVA) to verify the differences between the species evaluated. When significant differences were established between them, the Tukey test was applied (p < 0.05). The software used was R-Studio.

Bending, buttresses and surface cracks were not observed in some logs. Thus, the results are presented in two-axis graphs, with the mean value of the analyzed trait and the frequency of the logs with the presence of this trait. The diametral and annular ring crack data were presented in quality classes.

Quality of the logs

Table 3 shows the minimum, maximum, mean values, the coefficient of variation and multiple comparisons for the averages for the conicity, flattening, heartwood percentage and net volume of the logs of the five tropical species.

Table 3

Minimum, maximum, mean values, coefficient of variation and multiple comparisons for the averages for the conicity, flattening, heartwood percentage and net volume in lumber of five tropical species
Species	Values	Conicity (cm.m^− 1)	Flattening (%)	Heartwood Percentage (%)	Net volume (%)
Dinizia excelsa	Mínimum	0.0	86.4	50.0	49.5
	Maximum	2.1	99.7	90.5	100.0
	Mean	1.1 a	95.3 a	79.7 bc	90.6 a
	Coefficient of variation	61.3	3.8	12.0	13.5
Dipteryx odorata	Mínimum	0.1	87.0	79.8	54.7
	Maximum	3.2	97.1	92.2	92.2
	Mean	1.1 a	94.8 a	86.7 a	83.6 ab
	Coefficient of variation	76.7	2.6	4.3	10.0
Hymenolobium heterocarpum	Mínimum	0.0	88.9	70.0	70.0
	Maximum	1.6	100.0	89.1	89.1
	Mean	0.8 a	96.2 a	82.4 ab	82.4 ab
	Coefficient of variation	57.3	3.1	6.2	6.2
Astronium lecointei	Mínimum	0.0	90.5	57.8	57.8
	Maximum	2.2	99.6	78.8	78.7
	Mean	0.6 a	96.3 a	68.5 c	68.5 c
	Coefficient of variation	74.9	2.7	8.3	8.3
Qualea paraensis	Mínimum	0.0	94.1	49.2	49.2
	Maximum	2.4	100.0	83.1	87.8
	Mean	1.0 a	97.4 a	76.2 d	76.8 b
	Coefficient of variation	52.8	1.7	10.3	10.7

^{Means followed by the same letter in the column do not differ statistically from each other at 5% significance, according to the Tukey test}.

The mean values of conicity and flattening of the logs of the evaluated species did not differ from each other (p < 0.05).

The mean percentage values of the species evaluated (Fig. 4a) differed statistically from each other (p < 0.05). The heartwood percentage ranged from 68.5% for A. lecointei to 86.8% for D. odorata.

D. excelsa, D. odorata and H. heterocarpum showed no significant difference. For these species, the highest mean net volume values were obtained. D. odorata, H. heterocarpum and Q. paraensis (76.8%) showed no significant difference, while A. lecointei (68.5%) differed from the other species evaluated and showed the lowest mean value for the net volume of wood (Fig. 3) due to its low heartwood percentage.

Figure 2 shows the mean values and frequency of (A) curving, (B) buttresses and (C) surface cracks of logs from the five tropical species.

The percentage of curved logs varied from 5.3–52.6% for the species Q. paraensis and D. excelsa, respectively (Fig. 2a). Although D. excelsa had the lowest mean curving value (2.3%), 21% of its logs had a curvature greater than 3%, which is the maximum value allowed for not being considered a defect (Table 4). D. odorata was the species with the lowest curving value, with an average value equal to 4.2%, and only 74% of the logs had a curving less than or equal to 3% (Table 4).

The frequency of logs with the presence of buttresses was less than 30% for all species (Fig. 2b). The A. lecointei logs were classified in the superior class, which admits buttresses values lower than 10%, while the Q. paraensis and D. excelsa species presented 84.2% and 78.9% of the logs classified in the superior class, respectively (Table 4). The species H. heterocarpum and D. odorata presented 73.7% of the logs also classified in this class (Table 4).

The highest and lowest frequencies of surface cracks were observed for the species Q. paraensis (68.4%) and D. odorata (5.3%), respectively. Although D. odorata had a lower frequency, the species had the highest mean value of 29.8% for this property (Fig. 3c). The lowest mean surface crack value, 10.5%, was observed for the species A. lecointei (Fig. 3c). For the species D. odorata and H. heterocarpum, 94.7% and 89.7% of the logs, respectively, were classified as belonging to the superior class when the surface cracks were considered (Table 4). D. excelsa and A. lecointei had 79% and 73.7% of logs classified in the superior class, respectively (Table 4). Lower results were observed for Q. paraensis, in which only 53% of the logs were classified in the superior class (Table 4).

Table 4

Frequency of conicity, flattening, curving, buttresses, surface cracks, diametric cracks, annular ring cracks and net volume in lumber in quality classes of the five tropical species, in percentage
Espécie	Classes	C	F	CU	B	SC	DC	RC	NV
Dinizia excelsa	Superior	100.0	89.5	79.0	79.0	79.0	15.8	52.6	42.1
	I	0.0	10.5	10.5	0.0	5.3	5.3	15.8	15.8
	II	0.0	0.0	5.3	15.8	10.5	21.0	21.0	31.6
	III	0.0	0.0	5.3	0.0	0.0	10.5	0.0	5.3
	IV	0.0	0.0	0.0	5.3	5.3	21.0	5.3	0.0
	V	0.0	0.0	0.0	0.0	0.0	26.3	5.3	5.3
Dipteryx odorata	Superior	94.7	94.7	73.7	73.7	94.7	42.1	31.6	0.0
	I	0.0	5.3	5.3	10.5	0.0	47.4	47.4	15.8
	II	5.3	0.0	15.8	5.3	0.0	5.3	5.3	68.4
	III	0.0	0.0	0.0	5.3	5.3	5.3	0.0	10.5
	IV	0.0	0.0	0.0	0.0	0.0	0.0	15.8	0.0
	V	0.0	0.0	5.3	5.3	0.0	0.0	0.0	5.3
Hymenolobium heterocarpum	Superior	100.0	94.7	94.7	73.7	89.5	31.6	52.6	0.0
	I	0.0	5.3	5.3	5.3	0.0	36.8	36.8	0.0
	II	0.0	0.0	0.0	10.5	5.3	21.0	10.5	73.7
	III	0.0	0.0	0.0	0.0	5.3	10.5	0.0	21.1
	IV	0.0	0.0	0.0	10.5	0.0	0.0	0.0	5.3
	V	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
Astronium lecointei	Superior	100.0	100.0	94.7	100.0	73.7	0.0	73.7	0.0
	I	0.0	0.0	0.0	0.0	10.5	0.0	21.0	0.0
	II	0.0	0.0	5.3	0.0	10.5	15.8	0.0	0.0
	III	0.0	0.0	0.0	0.0	5.3	26.3	0.0	42.1
	IV	0.0	0.0	0.0	0.0	0.0	47.4	0.0	42.1
	V	0.0	0.0	0.0	0.0	0.0	10.5	5.3	15.8
Qualea paraensis	Superior	100.0	100.0	94.7	84.2	36.8	21.0	84.2	0.0
	I	0.0	0.0	0.0	10.5	15.8	36.8	10.5	0.0
	II	0.0	0.0	0.0	0.0	31.6	36.8	5.3	42.1
	III	0.0	0.0	0.0	5.3	0.0	5.3	0.0	47.4
	IV	0.0	0.0	5.3	0.0	10.5	0.0	0.0	5.3
	V	0.0	0.0	0.0	0.0	5.3	0.0	0.0	5.3
^{C= conicity; F= flattening; CU= curving; B= buttresses; SC= surface crack; DC= diametrical crack; RC= annular ring crack; NV= net volume}

For diametrical cracks (Table 4), D. odorata presented approximately 90% of logs classified in the Superior and I classes. This species also did not present logs classified in the two lower quality classes, showing that it had the best results.

For ring cracks, most of the logs evaluated were classified in the superior class and class I (Table 4). It is evident that more than 85% of the logs evaluated did not present ring cracks or had peripheral and/or central ring cracks. Q. paraensis, A. lecointei and H. heterocarpum obtained the best results for annular ring cracks. Among the species evaluated, Q. paraensis stood out with the highest percentage of logs (84.2%) in the superior class (Table 4).

Yield of sawn timber for export

Table 5 shows the minimum, maximum, mean, coefficient of variation and multiple comparisons of the averages for the lumber yield of the five tropical species.

Table 5

Minimum, maximum, mean values, coefficient of variation and multiple comparisons of the means for the sawn timber yield of the five tropical species
Species	Sawn timber yield values (%)
Species	Mínimum	Maximum	Mean	Coefficient of variation
Dinizia excelsa	18.9	66.6	40.2 a	28.6
Dipteryx odorata	16.2	47.3	35.2 ab	21.8
Hymenolobium heterocarpum	17.0	40.0	30.4 bc	31.5
Astronium lecointei	11.1	54.6	24.0 cd	36.9
Qualea paraensis	12.9	39.1	23.9 d	25.0

^{Means followed by the same letter do not differ at 5% significance according to Tukey’s test}.

There was a significant difference (p < 0.05) in the wood yield of the species evaluated (Table 5). For D. odorata, the average yield of sawn wood (35.2%) was statistically equal to that of D. excelsa (40.2%) and H. heterocarpum (30.5%) and different from those of other species. The lowest values of sawn timber yield for export were observed for the species A. lecointei and Q. paraensis, whose mean values were statistically equal.

Classification of log quality

The species Dinizia excelsa had the highest conicity value of 1.10 cm.m ^− 1 (Table 3), and its logs were classified in the superior class of quality. The higher the conicity value, the more conical the log will be. Considering the standard deviation, there is a large dispersion between the conicity data. However, according to data presented in Table 4, 95% of the logs were classified in the superior quality class for the conicity because the logs had values lower than 3 cm.m ^− 1, corroborating results found by Garcia et al. (2012) and Araújo et al. (2014). It was also observed that the highest taper was found in the basal part of the trees, and this phenomenon occurs because the taper is characterized by the decrease in diameter from the base to the top of the tree (Nassur et al. 2013). The logs evaluated were from a forest with an advanced stage of succession. This explains why the lower conicity values were found, since it is more pronounced in isolated trees or on the periphery of the plantations (Burger and Ritcher 1991)

Regarding flattening, more than 95% of the evaluated logs of the present study were classified as superior class (IBDF 1984), because they have mean flattening values greater than or equal to 90% (Table 4). The higher the flattening value, the more circular and less flattened is the log shape. This result indicates that there is no significant deviation in the circular shape of the logs and that flattening showed satisfactory results for the five tropical species evaluated. Thus, as flattening will not affect the production of a square center block and will not negatively interfere with lumber yield (Vital 2008). The average flattening values found for D. odorata and A. lecointei species were higher than those found by Luz et al. (2021), when evaluating the same species, showing better quality of the logs evaluated in this study.

The species H. heterocarpum, A. lecointei, and Q. paraensis showed the best curving results with 95% of the logs belonging to the superior class with a curving value of less than 3%. Q. paraensis showed the highest mean curving value (Fig. 2a). However, this characteristic was observed in only 5% of the logs of this species, which indicates satisfactory results. The results observed for A. lecointei showing that practically all logs were classified in the superior class corroborating with Luz et al. (2021). The higher curving values found for the species D. excelsa and D. odorata (Fig. 2a) may affect the yield of the sawn wood, as they may limit the determination of the length of the pieces produced and, consequently, decrease the yield of the sawn wood (Vital 2008). In this case, the sectioning processes in smaller logs result in a greater amount of waste due to the increase in the number of cuts. The results observed for the curving of D. odorata showed a mean of 4.22% and was present in 47.37% of the logs evaluated. These results were lower than those found by Luz et al. (2021), who observed average curving for the same species of less than 3%, the maximum value allowed for the superior class (IBDF 1984). In general, the divergence between the results observed in this study and the literature is associated with genetic factors, species characteristics, soil growth and unfavorable climatic conditions, as highlighted by Vital (2008).

The only species that did not present logs with buttresses was A. lecointei (Fig. 2b). The logs with the highest mean values for the length of the buttresses were those originating from the species H. heterocarpum, D. odorata and D. excelsa, which can be seen in Fig. 3g, 3b e 3e. Longer buttresses generate a greater amount of waste in the unfolding process because there is no industrial use of sawn wood from the region where the buttresses are present. This is because during the formation of the buttresses, there is differentiated activity of the cambium cells, causing marked and disordered growth at the base of the tree. This differentiated growth results in the deviation of the wood grain, in the alteration of the contractions and, consequently, in the waste of raw material (Vital 2008). The D. odorata data showed a high incidence of buttresses and high mean values (Fig. 2b and 3b), confirming the statement by Embrapa (2004) that buttresses of this species can reach one meter in length.

According to IBDF (1984), surface cracks are only considered a defect in the log when it is greater than 5%, negatively influencing the classification of logs. The lower number of surface cracks for the species D. odorata allowed us to classify it in the class of superior quality for the production of sawn wood (Table 4), corroborating Luz et al. (2021), who found similar mean values of surface cracks. The high frequency and high mean value of surface cracks observed for Q. paraensis species can affect the yield of sawn wood. In this species, the cracks reach both the outer region of the log, where the side board will be removed, and the core region that would be used for the manufacture of the sawn pieces. In this case, it is necessary to section the pieces since the destination market does not accept sawn wood with the presence of cracks or microfissures. In this case, the band saw operator decides the best positioning of the split log to obtain the best performance in sawn wood.

All species showed diametral cracks, which can be better understood by the presence of radial parenchymal cells, which according to Jankowsky (1990) has low mechanical strength and by the difference between tangential and radial contractions. D. odorata species showed lower values for these cracks.

The logs of A. lecointei showed larger diametral cracks (Table 4 and Fig. 3a). The high cracking rates are one of the main problems faced by the timber industries, which significantly reduce their yields, mainly due to the characteristics of the processed species and the low technological level, during the processing of tropical logs. The occurrence of these cracks causes greater generation of waste, which consequently results in waste of raw material and reduction in industry profits.

For the anullar ring crack, Q. paraensis, A. lecointei and H. heterocarpum presented higher numbers of logs classified in the superior class and class I. The superior class cracks are of the peripheral type and do not significantly affect the yield of the superior class sawn wood, as this part corresponds to the side board, shavings and sapwood regions, which will be removed during the sawing of the pieces. The cracks when they reach the center of the log (class I) mainly affect the part closest to the pith and have less influence on the yield of the sawn wood than when they reach the middle region of the log, which is the main region covered by the heartwood.

The highest mean values of heartwood percentage, observed for the species D. odorata and H. heterocarpum (Table 3), are important obtaining higher wood yields. This fact is more important when the wood produced is destined for the international market, which requires more homogeneous characteristics. Thus, the higher the proportion of heartwood in the logs, the greater the production capacity of sawn wood with uniform color, as indicated by Haselein et al. (2004). In addition, the wood from the heartwood region has greater natural durability due to the absence of nutritive materials and, mainly, due to the fact that the extractives are undesirable and/or toxic to xylophagous agents. The lower percentage of heartwood observed for the species A. lecointei contributes to greater waste generation during the sawing of logs, considering that, in the international market, the sapwood is not used for the production of sawn wood. Thus, for this species, approximately 32% of the volume of its logs was not used for timber production for export due to the high percentage of sapwood (Fig. 3d).

Except for D. excelsa, the net volume of the species represented the total volume of wood minus the sapwood volume. Therefore, for D. excelsa, the difference of approximately 10% for the total volume of logs (Table 3) is not due to the discount of the sapwood but to the fact that 70% of the logs of this species have heartwood and hollow rot (Fig. 3c and 3e). Logically, the incidence of rot or degrading agents in logs affects the yield of sawn wood. The lowest mean net volume for A. lecointei is due to its low heartwood percentage (Table 3). However, the species A. lecointei did not suffer damage caused by hollow logs, heartwood rot or pronounced cracks.

Yield of sawn timber for export

D. excelsa was the species with the highest production of sawn wood (Table 5), as expected, mainly due to the higher net volume (Table 3) available for the production of sawn wood, as sapwood was also used for this species. Despite the higher yield among the species evaluated, the amount of unprocessed sawn timber for export was high because approximately 60% of the sawn timber was not used for this purpose. It should be considered that approximately 70% of the logs had hollow wood and heartwood rot, as well as a high incidence of curving, surface cracks (Fig. 2a e 2c) and diametrical cracks (Table 3), which are characteristics that negatively affect the yield of the sawn wood. The lumber yield values for D. excelsa for export corroborate with the values found by Tonini and Ferreira (2004), are higher than those found by Santos et al. (2017) and lower than those found by Lima et al. (2020). However, this divergence is associated with the type of sawn wood accepted in the foreign market, which are pieces only without defects.

Among the species evaluated, D. odorata had the highest percentage of heartwood and net volume (Table 3), which probably explains why this species had the second highest yield (Table 5). This value could have been higher if the sapwood was also used and if the quality requirements for the exported wood were not so strict, since the logs of this species had a high incidence of curving and buttresses (Fig. 3f and 3b). The values found for this species were similar to those found by Lima et al. (2020) and higher than those found by Melo et al. (2019).

The species H. heterocarpum showed no hollow or heartwood rot that would interfere with the net volume value. However, this species had approximately 20% of the total volume with sapwood. If sapwood was used, the yield could increase and reach values close to or above 35%, which would be within the use standards of CONAMA 474/2016 (BRASIL 2016). No significant difference was observed between the timber yields of H. heterocarpum and A. lecointei. However, the higher value of 6% for H. heterocarpum contributes to less exploitation of the wood from the forests during the production of the same volume of wood, as well as less waste generation and higher profitability of the companies.

The lowest values of sawn wood yield were observed for the species A. lecointei and Q. paraensis, which can be explained by the smaller diameters (Table 1), corroborating the statement by Wade et al. (1992), by the percentage of heartwood and net volume (Table 3). In addition, the species A. lecointei showed the worst results for diametrical cracks (Table 4) and, as a result, a low yield of sawn timber for export (Table 5). However, the values found were higher than the values of Marchesan et al. (2018) when evaluating the yield of first quality wood, without defects and without sapwood. These authors reported that the logs analyzed showed attacks by xylophagous organisms, a fact that reduces the volume of wood to be accepted by the international market. The lumber yield of Q. paraensis was lower than those found by Melo et al. (2016) when evaluating Qualea sp. and by Stragliotto et al. (2019) when evaluating Q. paraensis. The higher yield percentages may be associated with the possibility of using processed wood with sapwood, which is not accepted for the production of sawn wood for the international market.

The species D. excelsa showed higher yields in sawn wood than that provided by CONAMA Resolution 474/2016 (BR ASIL 2016), which is 35%. The species D. odorata presented an average value of sawn wood yield consistent with the values proposed in this Resolution. However, the species H. heterocarpum, A. lecointei and Q. paraensis showed lower sawn wood yield values. However, it is noteworthy that all yields explored in this study only portray the yield values of sawn wood with an exclusive focus on the foreign market, which is already known to be more demanding in quality suits and does not allow wood with cracks of any magnitude and, or sapwood. Thus, although it was not the focus of this study, it was observed that part of the waste obtained, after separation for export, may still be reprocessed for the domestic market, even with smaller dimensions.

The experimental results confirm that to obtain higher yields of sawn timber from tropical forest trees, it is crucial to observe the quality of their logs as a determining factor to guide the felling of the trees. In addition, taking into account the stricter requirements for the commercialization of wood in the foreign market, the selection of logs, based on their quality, reduces the possibility of obtaining pieces with sapwood and defects, even if present in small magnitudes. These actions can avoid unnecessary disturbances to the forest ecosystem, as they make logging more efficient and help in the conservation of forest resources. Thus, it is possible to extract fewer trees to produce the desired amount of sawn wood. This fact is based on the efficiency of the splitting process of logs with superior quality, which will result in higher yields in sawn wood. In addition, lower waste production is observed, which is also one of the major problems faced by the mechanical wood processing industries.

There was great variability in the quality of the logs of the five species evaluated.

For all species, the conicity and flattening characteristics of the logs were classified in the superior class for most of the logs, which facilitates their unfolding process.

For the species H. heterocarpum, A. lecointei and Q. paraensis, curving was present and allowed 95% of their logs to be classified in the superior class based on this characteristic.

Only A. lecointei did not present buttresses, and 100% of its logs were classified in the superior class.

For the superficial and diametral cracks, the highest percentage of logs classified in the superior class was observed in the species D. odorata. For the ring cracks, the species A. lecontei and Q. paraensis had the highest percentage of logs in the superior class.

D. odorata wood had the highest percentage of heartwood, a decisive factor for sawn wood yield to be higher than 35%, as required by the Brazilian legislation.

Due to the use of sapwood in the production of sawn wood, the species Diniza excelsa had the best net volume percentages.

The surface cracks, the net volume and the presence of buttresses were more expressive in all species and promoted the classification of the highest number of logs in classes III, IV and V, which are considered inferior qualities and negatively affect the yield of sawn wood, especially for the international market.

In general, the yield of sawn timber for export of the species evaluated was low; among them, the species D. excelsa and D. odorata had the highest yields, and the species A. lecointei and Q. paraensis had the lowest yields.

The yields of sawn timber, targeting the international market, of the species H. heterocarpum, A. lecointei and Q. paraensis were lower than those by the Brazilian legislation, although the residues generated after classification for export can be reprocessed, and sold in the domestic market, which allows the use of parts of the lot with sapwood and with small defects.

Acknowledgments: The authors would like to thank the Brazilian agency "Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), and AMATA S.A.

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Availability of data and materials

The datasets supporting the conclusions of this article are included in the article. Besides, the datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests

On behalf of all authors, the corresponding author states that there is no conflict of interest. All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript.

Funding

This study was partially funded by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brazil (CAPES) - Finance Code 001 and AMATA S.A.

Code availability

Not applicable.

Authors' contributions

The manuscript is part of the master’s thesis of the first author. Bárbara Luísa Corradi Pereira, Aylson Costa Oliveira, Elaine Cristina Lengowski, Tatiana Paula Marques de Arruda and José Reinaldo Moreira da Silva contributed to the study conception and design. Material preparation, data collection and analysis were performed by Michelly Casagrande Stragliotto. The first draft of the manuscript was written by Michelly Casagrande Stragliotto and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

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Quality of raw material and yield of exported sawn wood in the rational use of tropical timber from the Amazon

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Abstract

Figures

Introduction

Materials And Methods

Description of the study area and selection of species

Quality of the logs

Log splitting

Yield of sawn timber for export

Statistical analyses

Results

Quality of the logs

Yield of sawn timber for export

Discussion

Classification of log quality

Yield of sawn timber for export

Conclusions

Declarations

References

Additional Declarations

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