ARTÍCULOS

 

Mozambique's charcoals: anatomy of nine native species

Carbones de Mozambique: anatomía de nueve especies nativas

 

Cláudio Manuel Ismael Afonso ^a, Thaís Alves Pereira Gonçalves ^b, Graciela Inés Bolzon de Muñiz ^c, Jorge Luis Monteiro de Matos ^c, Silvana Nisgoski ^c*

^a Ministry of Agriculture, National Directorate of Land and Forestry, Av. Josina Machel, 537, Maputo, Mozambique, Africa.
^b Federal University of Parana, Doctoral Student of Forest Engineering. Av. Pref. Lothário Meissner, 632, Jardim Botânico, 80.210-170, Curitiba, PR, Brazil.
* Corresponding author: ^c Federal University of Parana, Department of Forest Engineering and Technology, Av. Pref. Lothário Meissner, 632, Jardim Botânico, 80.210-170, phone: (55) 41 - 3360-4275, Curitiba, PR, Brazil, silvana.ufpr@gmail.com

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SUMMARY

Most of the charcoal commercially produced in Mozambique is from natural forests, including high value species. This production often negatively affects the environment and one of the main reasons is the lack of sustainable forest management techniques. To facilitate forest control, we characterize the anatomy properties of charcoal made from Afzelia quanzensis, Amblygonocarpus andongensis, Combretum imberbe, Dalbergia melanoxylon, Guibourtia conjugata, Khaya nyasica, Millettia stuhlmannii, Pterocarpus angolensis and Swartzia madagascariensis. All these species possess high commercial value. The samples were carbonized at 450 °C for 1 h. Some shrinkage-related ruptures were present in charcoals, but the structure kept good definition of the cells features and did not influence the distinction of the species. The propagation of this knowledge would relieve pressure on valuable species and may also help with control of the charcoal supply chain.

Key words: carbonization, anatomical characteristics, commercial wood, wood anatomy.

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RESUMEN

La mayor parte del carbón producido en el comercio en Mozambique es de bosques naturales, incluyendo las especies de alto valor comercial. Esta producción afecta negativamente el medio ambiente y una de las principales razones es la falta de técnicas de manejo forestal sostenible. Para facilitar el control del uso de los bosques, se caracterizan las propiedades de anatomía de carbón vegetal a base de Afzelia quanzensis, Amblygonocarpus andongensis, Combretum imberbe, Dalbergia melanoxylon, Guibourtia conjugata, Khaya nyasica, Millettia stuhlmannii, Pterocarpus angolensis y Swartzia madagascariensis. Todas estas especies tienen un alto valor comercial. Las muestras fueron carbonizadas a 450 °C durante 1 h. Algunas rupturas relacionadas con las pérdidas estuvieron presentes en los carbones, pero la estructura mantuvo buena definición de las características anatómicas de las células y no influyeron en la distinción de las especies. La difusión de este conocimiento podría aliviar la presión sobre las especies valiosas y también puede ayudar con el control de la cadena de suministro de carbón.

Palabras clave: carbonización, características anatómicas, maderas comerciales, anatomía de la madera.

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INTRODUCTION

Mozambique has a great diversity of natural forests, and forestry biomass has an important role due to its environmental, social and economic dimensions (Vasco and Costa 2009). Biomass energy in the form of charcoal or firewood is used by over 85 % of urban households in Mozambique. Charcoal commerce covers an extensive value chain, from those at the production sites to those transporting and retailing it in the cities. Despite the dimension of this sector, it is a largely informal activity with limited recorded information (Vasco and Costa 2009, Cuvilas et al. 2010). Practically all the charcoal comes from natural forests. The production is characterized by a lack of sustainable forest management techniques; thus threatening natural resources (Bila 2005).

The estimated allowable cutting of trees in Mozambique is about two million cubic meters per year (Marzoli 2007). Regarding its commercial and scientific value, rarity, utility, resistance and quality, species which produce wood are classified into precious, first class, second class, third class and fourth class (Ministério da Agricultura). Some authors commented by Ali et al. (2008) explain that there are 118 wood species listed in the National Forestry Rules Guidelines classified in accordance with their value and some, classified as precious and first class, such as Berchemia zeyheri (Sond.) Grubov (pau-rosa), Spirostachys africana Sond. (sandalo), Swartzia madagascariensis Desv. (pau-ferro), Afzelia quanzensis Welw. (chanfuta), Milletia stuhlmannii Taub. (jambirre), Pterocarpus angolensis DC. (umbila), Androstachys johnsonii Prain. (mecrusse) and Combretum imberbe Wawra (monzo) are in declining availability in the Mozambican forests.

For energy purposes it is not allowed the use of wood from precious, first, second and third class, as well as those species that are scarce, protected or with historic and cultural value (Ministério da Agricultura 2002). Nevertheless, in Mozambique this is widely disobeyed by charcoal producers, because the choice of species for production depends on its availability and local culture (Bila 2005). In 2010 the use of firewood to produce charcoal was more than eleven million cubic meters (Steierer 2011). In African countries, the use of firewood and charcoal has been increasing as a consequence of urbanization and economic growth. This situation concerns environmentalists and those responsible for the management of forestry resources (Girard 2002, Clancy 2008).

Several studies have demonstrated that the anatomical structure of wood is maintained after carbonization (Kim and Hanna 2006, Gonçalves et al. 2012, Muñiz et al. 2013, Nisgoski et al. 2014). These authors have shown it is possible to identify species by examining charcoal samples. There are no scientific papers focusing on the features of charcoal made from species native to Mozambique. Along with this, literature on the anatomical features of arboreal species is not widely known in Mozambique, which contributes to the weak forestry control.

The present study characterizes the charcoal anatomy of nine species from Mozambique. All the species are prohibited for energetic purposes. We aim at contributing to the knowledge of these species and at helping to improve the forestry control.

METHODS

The samples were obtained from trees without a defined age growing in natural forests in Cabo Delgado (E39°17'01.70" S12°09'17.82) and Sofala (E34°50'34.79", S17°30'21.19"), provinces of Mozambique with annual average precipitation varying from 800 to 1,200 mm and predominant tropical and humid climate (INDE 2009). All the species chosen are native and possess high commercial value (table 1). For each species, three trees were randomly chosen for felling. The samples were taken as discs at breast height. The thickness of the discs was 5 cm with diameter of 18-35 cm outside the bark. All samples were free from defects. For the analyses, the samples were cut into blocks measuring 2.5 x 2.5 x 5 cm.

 

Table 1. List of species studied.
Lista de las especies estudiadas.

 

The samples were wrapped in aluminum foil and carbonized in an electric muffle furnace at 450 °C for 1 hour, with a heating rate of 7.5 °C per minute. After carbonization, the samples were cooled and weighed.

For anatomical analyses, the charcoal was broken by hand following the three structural planes of the wood and analyzed under a Zeiss Discovery v12 stereo microscope. The anatomical description was done based on the procedures of the Iawa Committee (1989). The images of charcoal were obtained by scanning electron microscopy with a tabletop microscope (Hitachi TM-1000). No metallic-sputter-coating was needed. The determination of qualitative anatomical features was based on 25 measurements of tangential vessel diameter (µm), vessel frequency (vessels mm^-2), ray frequency (rays mm^-1), ray width (µm) and ray height (µm).

RESULTS

The anatomical characteristics of the charcoal samples are summarized in quantitative (table 2) and qualitative (table 3) features, and illustrated in figures 1 - 3.

 

Table 2. Mean values and standard deviations of quantitative anatomical features of
charcoal from nine Mozambique species.
Valores medios y error estándar de las características anatómicas cuantitativas del carbón
de nueve Mozambique especies.

 

Table 3. Summary of qualitative anatomical features of charcoal from nine species.
Resumen de las características anatómicas cualitativas del carbón de nueve especies.

Legend: GR - growth ring; OD - other deposits; PP - perforation plates; IP - intervessel pits;
RW - ray width; RCC - rays: cellular composition; Rays: cellular composition: A - all ray cells
procumbent; B - body ray cells procumbent with one row of upright and/or square marginal
cells; C - body ray cells procumbent with mostly 2 to 4 rows of upright and/or square marginal
cells; D - rays with procumbent, square and upright cells mixed throughout the ray; SS -
storied structure; MI - mineral inclusions.

 

Figure 1. Scanning electron microscopy: images of transversal (A), radial
(B) and tangential (C) section of charcoal. Scale bar = 100 µm.
Microscopía electrónica de barrido: imágenes de la sección transversal (A),
radial (B) y tangencial (C) del carbón. Escala = 100 µm.

 

Figure 2. Scanning electron microscopy: images of transversal (A), radial
(B) and tangential (C) section of charcoal. Scale bar = 100 µm.
Microscopía electrónica de barrido: imágenes de la sección transversal (A),
radial (B) y tangencial (C) del carbón. Escala = 100 µm.

 

Figure 3.Scanning electron microscopy: images of transversal (A), radial
(B) and tangential (C) section of charcoal. Scale bar = 100 µm.
Microscopía electrónica de barrido: imágenes de la sección transversal (A),
radial (B) y tangencial (C) del carbón. Escala = 100 µm.

 

Shrinkage-related ruptures (figure 4) were observed in samples of Afzelia quanzensis, Amblygonocarpus andongensis, Dalbergia melanoxylon, Guibourtia conjugata, Khaya nyasica, Pterocarpus angolensis and Swartzia madagascariensis. Dalbergia melanoxylon presented ruptures in a parallel direction and perpendicular to the rays and P. angolensis only ruptures perpendicular to the rays. The other species only presented ruptures oriented in the direction of the rays.

 

Figure 4. Ruptures in Dalbergia melanoxylon
charcoal. Scale bar = 100 µm.
Rupturas en Dalbergia melanoxylon carbon.
Escala = 100 µm.

 

DISCUSSION

The qualitative anatomical structures of charcoal are the same as those observed in the description of the wood from these species analyzed in other studies. The database of Inside Wood (2012) contains the anatomical description of the hardwood species Afzelia quanzensis, Amblygonocarpus andongensis, Combretum imberbe, Dalbergia melanoxylon, Millettia stuhlmannii, Pterocarpus angolensis, Swartzia madagascariensis; Richter and Dallwitz (2000) described the hardwood of A. quanzensis, D. melanoxylon, Guibourtia conjugata, Khaya nyasica, M. stuhlmannii, P. angolensis, S. madagascariensis; and Ali et al. (2008) reviewed the anatomical characteristics of the hardwood of A. quanzensis, K. nyasica, P. angolensis, M. stuhlmannii.

The carbonization at 450 °C and 7.5 °C per minute of heating rate preserved well the structure of charcoal with good definitions of the cells features. Other works reported similar behaviors at different temperatures and/or heating rate, e.g: (i) Dichrostachys cinerea (L.) Wight et Arn. (Leguminosae) and Salix subserrata Willd. (Salicaceae) carbonized at 400 °C and 6.67 °C per minute (Prior and Alvin 1983); (ii) Quercus variabilis Bl. at 450 °C and 5 °C per minute (Kwon et al. (2009) (iii) Corymbia spp. and Eucalyptus spp. carbonized at 450 °C and 1.66 °C per minute (Gonçalves et al. 2014), (iv) Ocotea porosa (Ness et Mart.) Barroso carbonized at temperatures varying from 350-650 °C and heating rate from 1.04-1.24 °C per minute (Nisgoski et al. 2014). Kim and Hanna (2006), studying Quercus variabilis BL. observed destroyed fiber walls, explaining that this effect is due to the tensions created by the effect of temperatures over 400 °C. Prior and Alvin (1983) evaluated the anatomical changes as being due to the increase of temperature in the woods of Dichrostachys cinerea and Salix subserrata. They found that over 300 °C, the cell walls begin to acquire amorphous features in the charcoal, although the medium line of the lamella and primary wall could still be distinguished. Kwon et al. (2009) studied Q. variabilis and found that over 350 °C it was impossible to observe the fiber walls.

Ruptures are also observed in other works in: (i) rays -Corymbia citriodora (Hook.) K.D.Hill et L.A.S. Johnson, C. maculata (Hook.) K.D.Hill et L.A.S. Johnson, Eucalyptus dunnii Maiden, E. tereticornis Sm. and E. viminalis La-bill. (Gonçalves et al. 2014), Quercus variabilis, Q. robur L. (Kim and Hanna 2006) and Q. alba L. (McGinnes et al. 1971); (ii) axial parenchyma cells - E. dunnii (Gonçalves et al. 2014); (iii) fibers - Mimosa tenuiflora (Willd.) Poiret and M. ophthalmocentra Martius (Dias Leme et al. 2010). As the causes of ruptures are not yet explained, our results were expected and did not compromise the identification of the anatomical features. Moreover, ruptures apparently did not influence charcoal quality.

The charcoal of species studied presented prismatic crystals in the cells of axial parenchyma of Afzelia quanzensis, Amblygonocarpus andongensis, Dalbergia melanoxylon, Guibourtia conjugata, Millettia stuhlmannii, Pterocarpus angolensis and Swartzia madagascariensis. In the case of Combretum imberbe and Khaya nyasica, these were only observed in the ray cells.

CONCLUSIONS

Anatomical changes due to carbonization do not influence the distinction of species. The knowledge of charcoal anatomy can help in the control of the species in the charcoal supply chain. We hope this kind of study can be multiplied in order to contribute with nature conservancy in Mozambique.

ACKNOWLEDGEMENTS

We thank the Ford Foundation and Federal University of Paraná (UFPR), Brazil, for support and the opportunity provided to conduct this research.

 

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Recibido: 11.06.14
Aceptado: 20.01.15