Introduction

The wood is a versatile raw material that arouses interests due to its various properties that enables numerous uses. Considering its potential for construction and building structures, the wood is one of many forest products utilized around the world mainly because it presents a very favorable relationship between resistance and basic density, in comparison to other construction materials, wood reaches higher resistance with lower density which makes it able to be used with more efficiency in structures that carries much more than its own weight (^{Ramage et al . 2017}).

The utilization of wood in naval construction is very primitive, before the use of steel in shipbuilding industry, timber was widely used for building watercrafts such as boats and ships. Timber was applied in different parts of the boats, these in turn were designed, projected and manufactured according to the waterway characteristics (^{Tripati et al . 2005}; ^{Pommier et al . 2016}).

As reported by the Institute of National Historic and Artistic Patrimony ^{(IPHAN, acronym in Brazilian Portuguese) (2009)} greatest part of small boats in Brazil take advance of wood as a raw material. In the Amazon region, these handmade watercrafts are the means of transportation and subsistence for a significant proportion of the population, they are frequently hand manufactured by regional producers that uses mainly wood as a constructive material. Each selected specie is used according to their empirical knowledge to build components for the boats’ structure, however the lack of specialized technical knowledge leads to improper use of the wood, which may cause trouble both for the producers and for the consumers. It can be frequently observed the inadequate use of the timber due to mistakes committed during specie’s identification, this may compromise the life cycle of the boat and add to loss in biodiversity once it contributes to the disappearance of certain forest species that suffers from high exploitation pressure due to its commercial value.

The appropriate features for using woods as a raw material in shipbuilding varies in accordance to the environmental conditions of the navigation place (^{Melo Junior & Barros 2017}). Meanwhile, the naval carpentry industry demands understandment of the wood’s technological characteristics. Wood’s chemical, physical and mechanical properties, are sometimes, inferences of its anatomical characteristics (^{Baldin et al . 2018}) thus, the knowledge of these characteristics can be the basis for optimizing the boat’s production process, as just like a basic step for testing new species to be used in this productive process.

In this context, the traditional anatomical identification technics of wood are of fundamental importance to understand the distribution of species that are used and commercialized by popular names, which are often wrongly applied, because it provides subsidy for the appropriated and suitable usage of this raw material according to its specific technological properties (^{Gasson 2011}; ^{Muñiz et al . 2016}), as well as it improves forest biodiversity conservation. It also enables the introduction of new woody species with potential to replace those commonly employed in the market, and by having high exploitation demands they generally end up by having a reduction in population on its areas of occurrence and even enter the list of endangered species.

The lack of technological knowledge is pointed out as one of the main bottlenecks for the socioeconomic development of the sector of boat production in the state of the Pará. The city of Marabá, which represents the economical and political center of the southeast mesoregion of the state (^{Pena et al. 2014}), is also known for being the mesoregion that more contributes to the illegal deforestation of the Amazonian forest (^{INPE 2016}) for the accomplishment of this type of work.

Thereby, this research had as its objectives, the identification, anatomical characterization and determination of some physical properties of wood species that are used for building boats in the mesoregion of Marabá - Pará. Moreover to indicate wood’s ideal characteristics to be used for the naval industry, providing a rationally and sustainable use of these woods, and information on the anatomy of woody species that are used for boat production in the Amazon, and also on species protected by the Brazilian legislation that has been wrongly used for this purpose, which contributes to the conservation of the biome biodiversity.

Material and Methods

The survey of selected sites for the visits and for the collection of wood samples was placed on information obtained from fishermen and riverside population that lives in the region. They gave us the location of shipyards based in the city, since these enterprises are not registered in any municipal authority of control and supervision. There are in the area two shipyards, being both responsible for the construction of the largest number of boats used in the region, this number although reduced, represents the activity which is mostly empiric, of family heritage, and is running the risk of coming to an end because of the difficulty of disseminating and passing on the popular knowledge of handmade’s boat construction to new generations. The visited shipyards are located in the urban perimeter of the city of Marabá, state of Pará, Brazil, under the address: Transmangueira street, next to the Tocantins River (05°21’54’’S and 49°07’24’’W).

During the visits to the shipyards we collected samples of woods that were being used for boat construction. The enterprises’ owners provided us the popular names by which each wood is commercialized, this was done as a way to verify possible mistakes made in specie’s identification. For identification and posterior registration, at least 15 wood samples were cut for each specie, with the help of a hacksaw and a chisel, by each popular name provided by the owner. The wood samples were cut off of batches of wood stored in the yard of the shipyards.

The anatomical identification of the collected wood had the following workflow: (i) confection of the wood samples, properly orientated and defect free, with dimensions of 2 × 2 × 3 cm (tangential, radial and longitudinal directions, respectively); (ii) polishing of the transversal surface with slide microtool knife, to enhance the anatomic characteristics (iii) polishing of the transversal, longitudinal and tangential surfaces, with sandpaper with granulometry of 400 to 2500; (iv) surface cleaning with chamois paper; (v) analysis of its macroscopic anatomical structure using a special 10× magnifying glass and with a binocular stereomicroscope and (vi) identification of the species using an anatomical identification key from the IPT Manual of Wood Identification (^{Mainieri 1983}; ^{Corandin et al . 2010}; ^{Zenid & Ceccantini 2012}) (vii) lastly, confirmation of the identification made by comparing the species with standard samples from a xylotheque belonging to the Northern Agronomic Institute (IAN, acronym in Brazilian Portuguese) - Oriental EMBRAPA, state of Pará. The scientific nomenclature was adopted in accordance to the ^{BFG (2018)}. The identification of protected species was made based on the consultation of the “Official National List of Endangered Flora Species” (^{MMA 2014}) and also referred to the Red List of the flora of Pará (^{COEMA-PA 2007}). It was taken macrographic photos of the transversal plane of the woods identified in this study, with the help of a digital portable stereomicroscope branded “DinoLite AM4013ZT4”.

For the microscopic anatomical characterization, the samples used in the anatomical identification were reduced to the dimension of 2 cm³ and softened by cooking it in a solution of water and glycerin in the proportion of 4:1. Posteriorly, transversal, tangential longitudinal and radial longitudinal cuts were made in a slide microtome (Leitz 1208), with thickness varying from 16 to 20 µm. In the sequence, the histologic cuts were clarified in sodium hypochlorite 60%, colored with hydroalcoholic safranin 50% (^{Sass 1940}), dehydrated (^{Johansen 1940}; Sass 1940) and then used in the confection of permanent slides with synthetic resin. For measuring the dissociated anatomic elements, it was prepared a macerating solution in accordance with a method proposed by ^{Franklin (1945)}, lately colored with aqueous safranin 1% used to make semi-permanent slides with glycerin 50% (^{Strasburger 1924}). All anatomical characterization, measurement technics and terminology, followed the protocol proposed by the IAWA Committee (^{IAWA Committee 1989}). For those parameters 30 measurements were made. Counts or measurements were made to: Vessel per square millimeter (VF), Tangential diameter of vessel lumina (TDV), Vessel element length (VEL), Rays per millimeter (RF), Ray width (RW), Ray height (RH), Fiber length (FL), Fiber diameter (FD), Fiber lumina diameter (FLD), Fiber wall thickness (FWT). All anatomical measurements were made by using a light microscope ZEISS Primo Star HAL/LED, coupled to a digital camera Opton microscopio and a software to analyze the images (Image-Pro Express 6.0).

From the microscopic anatomical characteristics it was obtained the confirmation of the genus and species identified by macroscopy analyses, then confirmed by using specialized literature and the ^{InsideWood (onwards 2004)} website database.

15 wood samples for each specie were used to determine the wood’s physical properties. The wood’s basic density was determined by following the procedures established in the NBR 11941/2003 (^{Brazillian Association of Technical Norms - ABNT 2003} - Acronym in Brazilian Portuguese). For the linear and volumetric contractions, it was used a procedure stablished in the NBR 7190/1997 (^{Brazillian Association of Technical Norms - ABNT 1997}).

As to evaluate the anatomical and physical quantitative characteristics, it was applied a descriptive statistic test. The results are presented as mean values, standard deviation and units.

Results

In Table 1 there are presented the names of the identified species used as raw material in building boats, followed by the popular names given by the shipyard owners and botanic family.

The anatomical characteristics of the species identified in this work are briefly described in Tables 2 (quantitative characteristics) and 3 (qualitative characteristics) and illustrated in Figures 1 to 4.

Figure 1 a-d. Alexa grandiflora; e-h. Apuleia leiocarpa - a,e. Macroscopy 10× magnification; b,f. bright-field microscopy: transverse section; c,g. radial section; d,h. tangential section of the wood. Scale bar: a,e. 1 mm; b,f. 500 µm; c,d,g,h. 200 µm. 

Figure 2 a-d. Bagassa guianensis; e-h. Bertholletia excelsa - a,e. Macroscopy 10× magnification; b,f. bright-field microscopy: transverse section; c,g. radial section; d,h. tangential section of the wood. Scale bar: a,e. 1 mm; b,f. 500 µm; c,d,g,h. 200 µm. 

Figure 3 a-d. Caryocar villosum; e-h. Cedrelinga cateniformis - a,e. Macroscopy 10× magnification; b,f. bright-field microscopy: transverse section; c,g. radial section; d,h. tangential section of the wood. Scale bar: a,e. 1 mm; b,f. 500 µm; c,d,g,h. 200 µm. 

Table 4 shows the physical properties results for the species identified in this study.

From the anatomical characterization of the wood samples it was possible to successfully identify eight forest species of which timber is used in boats production. Among all identified species, Caryocar villosum and Apuleia leiocarpa stood out because they were found in higher frequency in shipyards and also because they could be used in different parts of the boats, depending on the needs. Gums and other depositions in heartwood vessels as well as prismatic crystals and in the parenchyma cells of A. leiocarpa were observed with more frequency (Fig. 1a-b,e,f), while tyloses in vessels of C. villosum were seen more frequently (Fig. 1a,b,e,f).

It was also observed that some popular names were erroneously applied to some species, the specie Dinizia excelsa was marketed with an erroneous popular name of “jatatobá” (Tab. 1). The more serious fact is in the stacking of different species, whose woods are commercialized by the same popular names (Tab. 1). In that way, the anatomical differentiation of these species was made.

The main erroneous grouping refers to the commercialization of the timber of “piquiá”, which was anatomically identified as two different species: Caryocar villosum , specie belonging to a botanic family named Caryocaraceae and Alexa grandiflora which belongs to the Fabaceae botanic family. Both woods from these species when observed to the naked eye, have similar organoleptic characteristics on the longitudinal sides, such as color and texture, nonetheless in a simple macroscopic evaluation of the transversal and longitudinal sides, with a 10× magnifying glass as well as a microscopic study of the timber, it is possible to identify these wood species (Tabs. 2; 3). C. villosum has an only visible axial parenchyma by using a 10× magnifying glass, apotraqueal diffuse and diffuse in aggregates with vessels totally obstructed by tyloses, presented both in transversal and longitudinal sides (Fig. 5a,c,e). A. grandiflora has an axial parenchyma visible to the naked eye, paratracheal aliform losangular; or confluent in short oblique stretches and in thin marginal lines, vessels unobstructed or partially obstructed with resinous oils (Fig. 5b,d,f).

Figure 5 Comparative images of the species: a,c,e. Caryocar villosum; c,d,f. Alexa grandiflora. Both marketed as "piquiá". Scale bar: a,b. 1 mm; c,d. 500 µm; e,f. 200 µm. 

Bagassa guianensis and Enterolobium schomburgkii were also found in the shipyards by the same popular name of “tatajuba”, though they are not only different species from different genus, they also belong to different botanic families. B. guianensis belongs to a botanic family named Moraceae and E. schomburgkii is attached to the Fabaceae botanic family. It is possible that the mistakes made in the commercialization of the timber of these two species is due to the similarities in its colors and basic density. Those mistakes would not occur if a brief comparison of the macroscopic anatomical structure of the woods was made, whereas they are from two very distinct genus (Tab. 2; 3). B. guianensis has an usually indistinct axial parenchyma, even with a 10x magnifying glass, classified as scarce, vessels are predominantly solitary with obstructions caused by tyloses, anyhow they are visible to the naked eye (Fig. 6a,c,e). E. schomburgkii has an axial parenchyma well contrasted to the naked eye, paratracheal aliform losangular forming short confluences and also can be vasicentric, the vessels are partially obstructed by a yellow substance and resinous oil (Fig. 6b,d,f).

Figure 6 Comparative macroscopic images of: a,c,e. Bagassa guianensis species; b,d,f. Enterolobium schomburgkii. Both marketed as "tatajuba". Scale bar: a,b. 1 mm; c,d. 500 µm; e,f. 200 µm. 

Discussion

The anatomical characteristics of the described woods have some similarities, except for Apuleia leiocarpa (Fig. 1a,b,c,e,f,g), the vessel frequency can be classified according to ^{Mainieri (1983)} as few (up to 3 per mm²) or as few in number (4 to 7 per mm²), it was also observed that the tangential diameter of vessel lumina was large, classified according to ^{IAWA (1989)}, as ≥ 200 µm. All species had an average fiber length of 900 to 1600 µm with fiber wall thickness classified as thin to thick. Likewise, all species have presented tyloses and/or any other deposition obstructing the vessel lumen. The evaluated physical properties have also shown similarities between the species, like 87.5% of them has, according to ^{IAWA (1989)}, a medium value of basic density (0.40 to 0.75 g.cm^-3), and 62.5% has shown, in accordance to ^{Durlo & Marchiori (1992)}, an excellent (1.2 to 1.5) or normal (1.5 to 2) coefficient of anisotropy. ^{Melo Junior and Barros (2017)} studying the wood used in the shipbuilding of “whaling canoes” in the Santa Catarina coast, Brazil, observed that 80% of the identified species presented medium density wood (0.53-0.65 g.cm ^-3), a result similar to that observed in this study.

The similarities in the values observed for some anatomical parameters and some physical properties between the different species, indicates that the choice of the best timber for naval construction, which is currently made based on empirical knowledge, actually has technological justification given to the common properties of these species.

According to ^{Sen et al . (2009)} and ^{Muller (2010)} hardwood’s timber are more durable in the marine environment in comparison to softwoods, specially timber of the heartwood region, due to the presence of several different natural substances such as resinous materials, gummy depositions, oils, alkaloids, silica, etc. Recently, the anatomical analyses of shipwrecks found in the west central coast of India, have indicated that the wood of “teca” ( Tectona grandis L.f.) has been largely used by Indians and others shipbuilders, mainly due to specifical timber properties, such as moderate basic density, high mechanical resistance, high dimensional stability and few defects during drying wood; to contain silica and resinous oils, conferring resistance to the attack by marine xylophages like “turu” ( Teredo navalis ) and also because it has high resistance to decomposition in terrestrial conditions (^{Tripati et al . 2005}, ^2016a, ^2016b). ^{Maineri & Chimelo (1989)} point out that the woods of C. villosum and A. leiocarpa , used more frequently on the se regional boats, have good resistance to attacks by xylophages’ organisms, being preferably indicated for naval construction, mainly for structural parts of the boats that are in contact with water, thus being more susceptible to attack by aquatic xylophages.

Among the wood species identified in this study, attention is drawn to Bertholletia excelsa H.B.K. for being found on the “Official National List of Endangered Plant Species” of the Brazilian Ministry of the Environment (^{MMA 2014}) and on the Red List of the Flora of Pará (^{COEMA-PA 2007}) categorized as vulnerable in the evaluation of risk of extinction, besides all that, the specie is protected by federal law (Decree 5.975/2006), thus cutting it is prohibited by law. It is known that the deforestation in the Amazon Rainforest has increased between 2015 and 2016, and the state of Pará stands out for having presented the largest deforested area (3025 km²) and one of the largest percentage increases (41%) between the years of 2015 and 2016 (^{INPE 2016}). The confirmation of the use of B. excelsa ’s wood in the production of boats in the region where this study took place also contributes to the aggravation of this scenario, because it is linked to the illegal commercialization of native wood.

According to ^{Ferreira et al. (2004)} the appropriate trade name for Dinizia excelsa is “angelim-vermelho”. The utilization of erroneous names for the wood of different species as being the same can bring damages and losses to the final product. Depending on the technical specification of the part of the boat to which the wood is going to be used, it could compromise all the boat’s structure. Some differences are pointed to the values of basic density and coefficient of anisotropy (Tab. 4), these differences can decrease the durability and quality of the final product, once that the basic density relates primarily to the workability in wood and, accentuated variations of the coefficient of anisotropy can ease the appearance of cracks, warping and twisting.

Conclusion

Eight species were identified as a raw material used for boat production in the region of Marabá- Pará (Dinizia excelsa, Bertholletia excelsa, Cedrelinga cateniformis, Bagassa guianensis, Enterolobium schomburgkii, Apuleia leiocarpa, Alexa grandiflora, Caryocar villosum ). The most used species were Caryocar villosum and Apuleia leiocarpa, each one was used in almost 30% of the constructive structures of the boats. The usage of Bertholletia excelsa ’s wood for this purpose called our attention, mainly because of the illegal timber trade in the region and the prohibition of cutting of this specie.

Most of the wood used in the production of boats has some anatomical and physical similarities such as, vessels ranging from few to few numerous (3-7 per mm²) with average diameter ≥ 200 µm; medium length fibers (900-1600 µm) and fiber wall thickness thin to thick-walled. For basic density, 87.5% presented medium density (0.40 to 0.75 g.cm^-3) and 62.5% presented anisotropic coefficient of medium to normal (1.2 to 2). Therefore, it suggests that these values indicate the quality of the wood for utilization in naval construction.

The results indicate anatomical and physical similarities in the woods used for boat production. Further, the obtained results can contribute as components for a database of the anatomy of wood species that are used for boat production in the Amazon region, besides subsidizing practices that contribute to a more effective control of the timber market in the region, as well as to promote better use of the raw material.