Secondary forest biomass as a firewood source for cassava flour agroprocessing in tropical regions

Biomassa de vegetação secundária como fonte de lenha para o agroprocessamento de farinha de mandioca em regiões tropicais

ABSTRACT

In tropical regions, family farming often relies on firewood sourced from secondary vegetation. However, sustainable use of these forest resources requires an understanding of their physicochemical and energetic properties to assess energy potential and responsible management. This study evaluated the fuelwood quality of five species found in tropical secondary landscapes. We performed proximate analysis (moisture content, volatile matter, ash, and fixed carbon) and determined basic density, higher heating value (HHV), lower heating value (LHV), net heating value (NHV), and energy density. Our results showed favorable moisture contents (12.23% to 17.43%), supporting direct combustion. Basic density was moderate, with Banara guianensis (679 kg m^-³) and Vismia guianensis (653 kg m^-³) exhibiting the highest values. Connarus perrottetii , Lacistema pubescens, and Inga heterophylla presented balanced fuel profiles: high fixed carbon (22.01-22.91%), low ash (<2.1%), and lower volatile matter (74.97-76.44%), which favors slow combustion with reduced emissions. L. pubescens recorded the highest HHV (19.78 MJ kg^-¹) and LHV (18.42 MJ kg^-¹), while V. guianensis and I. heterophylla had the highest NHV (~15.6 MJ kg^-¹). Although B. guianensis showed the highest energy density (12.01 GJ m^-³), its elevated ash content suggests the need for proper residue management. Overall, the wood from secondary vegetation demonstrates potential as a sustainable energy source for cassava flour agroprocessing in tropical regions. Careful species selection and effective drying practices are crucial to optimizing combustion efficiency and ensuring the long-term viability of these valuable forest resources.

Index terms:
Fuelwood quality; Manihot esculenta Crantz; sustainable management; bioenergy potential; proximate analysis.

RESUMO

Em regiões tropicais, a agricultura familiar frequentemente depende de lenha proveniente de vegetação secundária. Contudo, o uso sustentável desses recursos florestais requer a compreensão de suas propriedades físico-químicas e energéticas. Este estudo avaliou a qualidade da lenha de cinco espécies comumente encontradas em vegetações secundárias tropicais. Realizamos a análise imediata (teor de umidade, materiais voláteis, cinzas e carbono fixo) e determinamos a densidade básica, poder calorífico superior (HHV), poder calorífico inferior (LHV), poder calorífico líquido (NHV) e densidade energética. Nossos resultados mostraram teores de umidade favoráveis (12,23% a 17,43%), adequados para a combustão direta. A densidade básica foi moderada, com Banara guianensis (679 kg m^-3 ) e Vismia guianensis (653 kg m^-3 ) apresentando os maiores médias. Connarus perrottetii, Lacistema pubescens e Inga heterophylla apresentaram perfis equilibrados: alto carbono fixo (22,01-22,91%), baixa cinzas (< 2,1%) e menores teores de voláteis (74.97-76.44%), favorecendo a combustão lenta com baixas emissões. L. pubescens registrou os maiores HHV (19,78 MJ kg^-1) e LHV (18,42 MJ kg^-1), enquanto V. guianensis e I. heterophylla tiveram o maior NHV (~ 15,6 MJ kg^-1). EmboraB. guianensis tenha apresentado a maior densidade energética (12,01 GJ m^-3 ), seu elevado teor de cinzas sugere a necessidade de um manejo adequado de resíduos. No geral, a madeira de vegetação secundária demonstra potencial como fonte de energia sustentável para o processamento de farinha de mandioca. A seleção criteriosa de espécies e secagem eficientes são fundamentais para otimizar a combustão e garantir a viabilidade a longo prazo desses recursos florestais.

Termos para indexação:
Qualidade da lenha; Manihot esculenta Crantz; manejo sustentável; potencial bioenergético; análise imediata

Introduction

Affordable and clean energy is a vital aspect of the 2030 global agenda because it is related to the Sustainable Development Goal - SDG (7), which aims to ensure access to affordable, reliable, sustainable, and modern energy for all. However, more than 2 billion people use firewood and other traditional biomasses for cooking purposes in special socially vulnerable regions (Food and Agriculture Organization of United Nations - FAOSTAT, 2022). Some areas are unable to extract firewood or wood for charcoal production sustainably; in this sense, the overall impact on the forest is high (FAOSTAT, 2022), making it difficult to achieve others SDGs, , which include climate action (13) and life on land (15). The gap between predatory logging and the need to use traditional fuels must be addressed in multiple ways, considering that many communities have no access to fuels or clean technologies for cooking food and other productive activities (Ngusa, 2025; Ooi et al., 2023).

This widespread dependence on solid biomass for household energy and local production is a persistent global phenomenon, driven by local resource endowments, economic constraints, and deep-rooted cultural traditions. In Africa, solid fuels remain the primary choice for residential cooking; in many countries firewood extraction from wild landscapes and community woodlots supplies essential activities (Adeeyo et al., 2022; Balume et al., 2025; Safari, Mwongerezi & Hyandye, 2022). Similarly, in Southern Asia, countries like India and Pakistan exhibit a strong rural connection to biomass, where firewood, crop residues, and animal dung constitute major energy sources despite growing grid and LPG infrastructure (Imran & Ozcatalbas, 2020; Ravindra et al., 2019). In Latin America, approximately 14% of the population still relies on biomass, with a stark contrast between rural (31%) and urban (5%) areas (Hartinger et al., 2025). This localized pressure is exemplified in specific tropical and peri-urban regions of Colombia and Mexico, where high per-capita firewood consumption drives deforestation risks (Pérez et al., 2022; Romero et al., 2025). Even in rapidly urbanizing nations like China, where modern infrastructure is widely accessible, a significant portion of rural households continue to utilize firewood, often driven by cultural preferences (Li, Y. et al., 2025; Tian et al., 2021). Within this global context, Brazil reflects a similar pattern, as approximately 11 million households regularly depend on firewood (Gioda, 2019).

In this framework, rural areas of the Brazilian Amazon represent complex territories reliant on firewood for cooking and agroprocessing (Mazzone, Cruz & Bezerra, 2021). Dynamic land use and cover changes continually modify the landscape, generating distinct mosaics of primary vegetation, agricultural zones, and secondary vegetation cover (Caballero et al., 2023). Within these mosaics, small-scale farming frequently relies on traditional slash-and-burn practices, a manual clearing and burning method used to prepare land for cultivation (Hauser & Norgrove, 2024). Although widely debated, such slash-and-burn systems function as refined resource management strategies, alternating short cultivation cycles with extended fallow periods (Pedroso Júnior, Murrieta & Adams, 2008; Rousseau et al., 2022). This agricultural model is intrinsically linked to cassava (Manihot esculenta Crantz) cultivation. It is widely used in family farming in the Brazilian Amazon, particularly in the state of Pará. As the leading national producer for approximately three decades, Pará yields around 4 million tons of cassava annually (Instituto Brasileiro de Geografia e Estatística - IBGE, 2024). Alves and Modesto Júnior (2022) emphasize that cassava stands out as a zero-waste crop of paramount economic, social, and cultural importance, employing over 83,000 people across regional agribusinesses. While biomass demands vary, firewood is used extensively in the processing of cassava-based products, including tapioca, starch, maniva, tucupi, and especially cassava flour (Alves & Modesto Júnior, 2022). For cassava flour manufacturing, firewood with suitable combustion properties enhances energy efficiency and supports the traditional processing practices of small-scale farmers. Consequently, understanding firewood quality is fundamental to improving thermal performance, minimizing fuel consumption, and shortening processing times, ultimately strengthening the economic viability and resilience of rural Amazonian communities.

In general, the production of cassava flour by smallholder farmers is highly dependent on the use of firewood. Alongside this, the traditional consumption of cassava flour stands out for its strong sociocultural significance. Its heritage traces back to Indigenous and riverine communities and remains a staple in the daily diet of Amazonian populations (Barghini & Cereda, 2025). Consequently, firewood must remain within this product chain, which occurs appropriately, through the sustainable use of accessible and affordable raw materials by rural communities employing traditional techniques. Slash-and-burn practices, for example, create areas of secondary vegetation during fallow periods, which can serve as a potential source of firewood for cassava flour processing. In this scenario, this paper aimed to assess the potential use of firewood derived from secondary vegetation in the traditional processing of cassava flour by smallholder farmers. For this research, five wood species were characterized to identify those with physicochemical and energy-related properties. The central hypothesis is that the proximate composition, basic density, and moisture content of secondary vegetation firewood provide suitable thermal properties and energy availability to meet the requirements of traditional roasting systems, proving their viability as sustainable firewood sources.

Material and Methods

Firewood collection and energy analysis

The study area was a rural property in the municipality of Igarapé-açú, Pará, Brazil (Latitude: 1° 7’ 37’’ South, Longitude: 47° 37’ 4’’ West). For reference, the criteria used to classify this smallholder property were based on Brazilian legislation (Brasil, 1993, 2006), which limits small family farms in this municipality to a maximum area of 220 hectares and specifies a predominantly family-based labor force.

The region relies heavily on traditional cassava (M. esculenta) agroprocessing, where biomass is the primary energy source for flour roasting (Figure 1A). The roasting process occurs in artisanal ovens, where firewood is burned to provide the thermal energy necessary for moisture reduction and flour gelatinization (Neves et al., 2020) (Figure 1B). This traditional practice illustrates the direct dependence of smallholder income on the quality and availability of locally sourced secondary vegetation.

Figure 1:
Artisanal cassava flour production process in Igarapé-Açú, Pará, Brazil. (A) Firewood used as the primary energy source. (B) Traditional roasting system, where biomass combustion provides the thermal energy required for flour processing.

Initially, 1 hectar of secondary vegetation was inventoried to identify the species with the highest Importance Value Index (IVI). The IVI was calculated based on phytosociological criteria (Curtis & McIntosh, 1950), considering the relative abundance, frequency, and dominance of each species. Five woody species were responsible for 40.13% of IVI, namely Banara guianensis Aubl.; Connarus perrottetii (DC.) Planch.; Inga heterophylla Willd.; Lacistema pubescens Mart. and Vismia guianensis (Aubl.) Choisy.

Three individuals per species (average Diameter at Breast Height: 3.12-5.12 cm) were collected and sample discs and wedges were prepared for analysis. Two opposing wedges were used to determine the basic density, according to ASTM D2395-17 (American Society for Testing and Materials - ASTM, 2022), and for moisture content, following the oven-drying method (ASTM, 2025). Moisture content was determined as part of the physical characterization of the biomass. The remaining material was granulometrically reduced with the aid of a drill and knife mill. Then, we classified the resulting biomass on a 40 and 60-mesh sieve for proximate analysis in accordance with the ASTM E870-82 standard (ASTM, 2024). The proximate analysis included the determination of volatile matter, ash content, and fixed carbon content, with fixed carbon calculated by difference. The energetic attributes were estimated using Equation (1) by Parikh et al. (2005), for the higher heating value, Equation (2) for the lower heating value, and Equation (3) for the net heating value, employing the values from the proximate analysis, hydrogen, and moisture content, as highlighted below.

$HHV=0.3536\cdot CF+0.1559\cdot VM-0.0078\cdot ASH$ (1)

$LHV=PCS-\left(2.5116\cdot 0.09\cdot H\right)$ (2)

$NHV=\left(PCI\cdot \left(1-\left(0.01\cdot U\right)\right)\right)-\left(2.5116\cdot 0.01\cdot U\right)$ (3)

Where: HHV, higher heating value (MJ.kg^-1); LHV, lower heating value (MJ.kg^-1); NHV, net heating value (MJ.kg^-1); FC, fixed carbon (%); VM, volatile matter content (%); ASH, ashes (%); H, hydrogen content (%); MC, moisture content (%).

We consider the hydrogen content to be 6%. We determine the energy density (ED) by the product between the lower calorific value in MJ.kg^-1 and the basic density in kg.m^-3.

Experimental design and data analysis

A random balance design was used with five treatments, three repetitions for the physical parameters, proximate analysis, and energetic estimation. The species were considered as factors. The data residues were performed to the Shapiro-Wilk and Bartlett tests at 95% probability. After proving normality and homogeneity of variance, we performed univariate analysis of variance and applied the Tukey test at 5 % significance for multiple comparisons of means. The logarithmic transformation was attempted to normalize non-normally distributed and heteroscedastic data. Additionally, a Pearson correlation analysis was conducted to assess the linear relationships between the studied properties.

Results and Discussion

The moisture content for all species was below 14.73 ± 2.05%, with I. heterophylla (13.49%) and V. guianensis (12.23%) exhibiting the lowest values. The average moisture content for each species is shown in Figure 2A. Notably, wood intended for firewood is typically harvested with a moisture content above the fiber saturation point (>30%). Thus, meteorological and storage conditions are crucial for reducing wood moisture content (Souza et al., 2019), as they govern the loss of free and bound water to the environment. In this study, the species were stored in a dry, well-ventilated environment, which facilitated water loss.

Figure 2:
Comparative distribution of (A) moisture content (%) and (B) basic wood density (kg m^-³) among five species of secondary vegetation: Connarus perrottetii (CP), Lacistema pubescens (LP), Vismia guianensis (VG), Inga heterophylla (IH), and Banara guianensis (BG). Violin plots represent the distribution of data points, with white dots indicating medians and gray boxes showing interquartile ranges. Different lowercase letters above the bars indicate statistically significant differences between species based on Tukey’s test (p < 0.05).

High moisture content negatively affects combustion efficiency. Additionally, it increases emissions of particulate matter (PM_2.5), carbon monoxide (CO), and nitrogen oxides (NO_x) (Deng et al., 2023). Studies suggest that firewood with a moisture content of around 10% provides optimal combustion performance (Tucho et al., 2023). In contrast, firewood with ~30% moisture content suffers from reduced combustion efficiency, as substantial energy is consumed in water evaporation before useful heat release (Lai et al., 2024). This leads to prolonged processing times and increased these pollutant emissions, negatively impacting both fuel ignition and combustion dynamics (Dominic & Baidurah, 2025; Peng et al., 2023).

Given this, effective firewood storage is essential to maintain its quality as a fuel. This challenge is particularly acute in the Brazilian Amazon, where the study area (Maracana River region) experiences a total annual precipitation of 2,488 mm, with a pronounced rainy season from February to April (Raiol et al., 2025). Under these humid conditions, maintaining firewood at suitable moisture levels is a significant obstacle for smallholder farmers. Prolonged periods of heavy rainfall, especially during the peak rainy season, make outdoor firewood storage particularly difficult (Souza et al., 2019). Therefore, implementing proper storage techniques, such as covering the base and top of fuel stacks, is essential to mitigate the effects of the local climate, ensuring fuel quality and enhancing energy efficiency throughout the year (Eliasson et al., 2020).

The analyzed species exhibited an average basic density of 578 ± 76.89 kg m⁻³. The average density for each species is shown in Figure 2B. Basic density values varied significantly among species, except for I. heterophylla (507 kg m⁻³) andC. perrottetii (500 kg m⁻³), which were statistically similar.B. guianensis recorded the highest density at 678 kg m⁻³, followed byV. guianensis (653 kg m⁻³) andL. pubescens (553 kg m⁻³). All evaluated woods are classified as moderate (Csanády, Magoss & Tolvaj, 2015), indicating that B. guianensis presents more material to be consumed during combustion. From an energy perspective, the density dictates the mass of dry combustible material available per unit of volume. Lower values reduces the heat release and shortens its combustion time (Gao & Dai, 2026). Additionally, species with higher basic density inherently yield greater volumetric energy density, a parameter relevant for biomass fuel logistics (Strandgard et al., 2021). Within this framework, B. guianensis and V. guianensis stand out as promising energy sources, as their higher density indicates a greater mass of fuel within a concentrated spatial footprint. Conversely, lower-density species, such as C. perrottetii and I. heterophylla, may require larger volumes of wood to meet the same thermal demand.

The species studied are young individuals with reduced diameter, whose wood processing does not yet reflect heartwood formation (Yang et al., 2025). Species within this context, particularly those with low basic density values, tend to retain higher moisture content. This is partly due to the juvenile characteristics of the wood, such as shorter fiber lengths, thinner cell walls, and higher vessel frequency, which contribute to increased adsorption rates (Soares et al., 2019), as well as greater internal space for free water storage. In this study, maximum moisture content ranged from 82.43% to 134.88% across the species. Although all species were classified as having moderate basic density, three statistically distinct groups were identified for maximum moisture content, as illustrated in Figure 3A. This variation indicates that, even among woods with similar density classification, the capacity for water retention may differ substantially among species. Given this, biomass with higher maximum moisture content may require longer drying periods, especially under humid tropical conditions, where storage conditions strongly influence water loss from wood (Souza et al., 2019).

Figure 3:
Comparative distribution of (A) maximum moisture content (%) and (B) variation in net heating value (MJ kg^-¹) as a function of moisture content (%) among five species of secondary vegetation: Connarus perrottetii (CP), Lacistema pubescens (LP), Vismia guianensis (VG), Inga heterophylla (IH), and Banara guianensis (BG). Violin plots represent the distribution of data points, with white dots indicating medians and gray boxes showing interquartile ranges. Different lowercase letters above the bars indicate statistically significant differences between species based on Tukey’s test (p < 0.05).

This relationship is further demonstrated in Figure 3B, where moisture content reduces the net heating value of the biomass - the amount of available energy released during combustion, excluding the energy required to evaporate water. Therefore, selecting species with low moisture retention and high net heating value is critical for energy efficiency, as these properties maximize useful heat release while minimizing combustion losses. For cassava flour agroprocessing, this is particularly important because the roasting process requires continuous and stable heat supply. Additionally, it reinforces the importance of storage and drying management, since the storage period significantly affects moisture content and the energy efficiency of wood fuels (Stolarski et al., 2023). Thus, species that combine moderate density, lower moisture retention, and higher net heating value may contribute to greater combustion efficiency and more stable thermal performance in small-scale flour production systems.

During the dry season, characterized by low relative humidity and high temperatures, water loss from wood to the environment accelerates. In the study area, this hydrological deficit period typically occurs between August and November (Raiol et al., 2025). Harvesting during this time would reduce the required storage period for firewood. Even during rainy seasons, wood stored in a dry, covered environment continues to lose moisture (Souza et al., 2019), albeit at a slower rate.

Cassava cultivation in the eastern Amazon is characterized as a low-input, manually managed crop typically grown by smallholders within shifting cultivation systems (Abrell et al., 2024; Denich et al., 2005). In this framework, land preparation often involves slash-and-burn in short-fallow locations, with cassava harvested as needed for processing, generally after 12 months (Alves & Modesto Júnior, 2022). While some firewood can be obtained during this initial land clearing, farmers will likely require additional woody material over time to sustain the constant demand for cassava flour agroprocessing.

It is well-established that vegetation felling is facilitated during dry seasons (Vilpoux, 2024), and that warmer, drier conditions also favor the natural drying of harvested firewood. However, these climatic variations pose significant logistical challenges for smallholders. Balancing the highly demanding tasks of harvesting and processing cassava into flour with the concurrent activities of harvesting, transporting, and properly storing firewood poses a significant challenge. This can lead to substantial energetic expenditure for workers. For instance, small-scale cassava farms in Nigeria, relying mostly on manual labor for operations reported a total energy consumption of 4904.87 MJ.ha^-1 (Adekanye & Oni, 2022). Furthermore, prolonged rainy periods hinder natural drying and complicate outdoor firewood storage (Souza et al., 2019), forcing smallholders to dedicate more effort to manage moisture content and ensure fuel efficiency.

The proximate analysis of wood species is crucial for understanding their energy potential and combustion behavior during agroprocessing cassava flour. Regarding the studied wood species, as illustrated in Figure 4A, we observed an average volatile matter content of 76.66 ± 1.66%, with four distinct groups among the species. V. guianensis stood out with the highest value (79.60%), while I. heterophylla had the lowest (74.97%). The overall average ash content was below 1.8%, with three distinct groups observable in Figure 4B. For B. guianensis, the average was 3.26%, whereas V. guianensis had the lowest value (0.35%). Finally, the average fixed carbon content across all species was 21.55 ± 1.26%. I. heterophylla presented the highest value (22.9%), while V. guianensis and B. guianensis had the lowest (~20.0%).

Figure 4:
Comparative distribution of (A) volatile matter (%), (B) ash content (%), and (C) fixed carbon content (%) among five species of secondary vegetation: Connarus perrottetii (CP), Lacistema pubescens (LP), Vismia guianensis (VG), Inga heterophylla (IH), and Banara guianensis (BG). Violin plots represent the distribution of data points, with white dots indicating medians and gray boxes showing interquartile ranges. Different lowercase letters above the bars indicate statistically significant differences between species based on Tukey’s test (p < 0.05).

In general, wood combustion initially involves the burning of volatile compounds, followed by the glowing combustion of charcoal (Jiang et al., 2014; Li, J. et al., 2025). As biomass is heated, volatile compounds release CO and flammable hydrocarbons (Mierzwa-Hersztek et al., 2019), which account for approximately 75% of the total energy released by firewood combustion (Kumar, Kumar & Tyagi, 2013). In addition, higher volatile matter content ignite more easily and sustain enhanced thermal intensity. During combustion, the volatile flame gradually expands, smoothly enveloping the fuel particle through gas-to-gas phase reactions. This phenomenon indicates a homogeneous ignition mechanism driven by devolatilization dynamics (Bora & Mahapatra, 2025), representing a highly desirable performance profile for traditional cassava flour roasting. Conversely, fixed carbon content is inversely proportional to volatile content and promotes a slower, more sustained burn. A balanced proportion of both characteristics enhances energy production while reducing gas emissions and particulate matter (Vieira et al., 2023).

In this context, the proximate analysis indicates that the species C. perrottetii , L. pubescens, and I. heterophylla exhibit the most suitable fuel profile for firewood use in agroprocessing. This suitability is primarily driven by their higher fixed carbon content and lower volatile matter. A higher fixed carbon content contributes significantly to the heating value and promotes a slower, more sustained combustion essential for continuous processing demands, while lower volatile matter reduces initial emissions and favors controlled flame intensity. Additionally, the ash content of the evaluated species ranged from 0.4% to 3.2%, with a general average of 1.78%. For four of the studied species, this value strictly aligns with the typical 1-2% range reported for woody feedstocks, which implies higher initial ash deformation temperatures and substantially reduces the risks of slag formation and furnace fouling during thermal conversion (Wu, Beutler & Baxter, 2020; Zhai et al., 2021). Consequently, these favorable ash contents directly support operational and commercial decisions for local smallholders, ensuring the continuous and safe grid performance of traditional cassava roasting systems.

The evaluated secondary species exhibited high energy storage capacity, with an average higher heating value (HHV) was 19.56 ± 0.29 MJ kg^-1, and the lower heating value (LHV) was 18.20 ± 0.29 MJ kg^-1. The species were grouped into four statistically distinct categories, as illustrated in Figures 5A and 5B. L. pubescens consistently showed the highest values, with an HHV of 19.78 MJ kg^-1 and an LHV of 18.42 MJ kg^-1. It was closely followed by I. heterophylla (HHV: 19.77 MJ kg^-1; LHV: 18.42 MJ kg^-1) and C. perrottetii (HHV: 19.69 MJ kg^-1; LHV: 18.33 MJ kg^-1). These results are highly competitive when benchmarked against other tropical fuel studies: our values are consistent with the HHV average of 19.91 MJ kg⁻¹ reported for rural firewood in Tanzania (Menéndez & Curt, 2013) and fall well within the range observed for diverse firewood species in Mexico (18.33-22.07 MJ kg⁻¹; Fuente-Carrasco et al., 2022). Furthermore, our species outperform several tropical dry forest varieties, which typically exhibit lower values (16.2-18.5 MJ·kg^-¹; Rodríguez-Jiménez, Duarte-Aranda & Canché-Escamilla, 2019).

Pearson correlation analysis resolved the specific interactions between proximate analysis parameters and heating values (S1). Our results indicated a strong and significant positive correlation between fixed carbon and both HHV and LHV (r = 0.82, p < 0.001). This trend confirms the decisive role of fixed carbon in governing the energy content of secondary species, aligning with thermodynamics of solid biomass combustion (Manyatsha, Hattingh & Edokpayi, 2025; Matsunari et al., 2025). Conversely, a weak negative correlation was observed between volatile matter and HHV/LHV (r= −0.32, p = 0.243), indicating this relationship was not statistically significant at the 5% level. Furthermore, ash content exhibited a moderate negative correlation with HHV/LHV (r= −0.50, p = 0.055). Although this negative impact did not reach strict statistical significance, the mathematical trend corroborates the energetic penalties imposed by inorganic fractions on biomass fuel quality (Yongtie et al., 2022). Ultimately, fixed carbon shows a positive and expressive impact on the energy content of the fuelwood, while volatile matter and ash content have a negative, though marginally significant, impact on this property. This provides essential guidance for species selection in agroprocessing.

We identified only two distinct groups for the net heating value (NHV) (Figure 5C), which accounts for wood moisture content in energy availability calculations and is particularly relevant for applications such as cassava flour agroprocessing. The highest average NHV values were observed for V. guianensis (15.61 MJ kg⁻¹) and I. heterophylla (15.59 MJ kg⁻¹). We observed that C. perrottetii and L. pubescens were excluded from this group of species with the highest heating values due to their high moisture content. Conversely, V. guianensis consistently stood out among the species with the highest NHV. These results underscore the impact of moisture on the energy quality of fuelwood (Lima et al., 2020), thus reinforcing the importance of proper drying practices to maximize the energy potential of wood biomass for efficient use in agroprocessing systems.

Figure 5:
Comparative distribution of (A) higher heating value (MJ kg^-¹), (B) lower heating value (MJ kg^-¹), (C) net heating value (MJ kg^-¹), and (D) energy density (GJ m^-³) among five species of secondary vegetation: Connarus perrottetii (CP), Lacistema pubescens (LP), Vismia guianensis (VG), Inga heterophylla (IH), and Banara guianensis (BG). Violin plots represent the distribution of data points, with white dots indicating medians and gray boxes showing interquartile ranges. Different lowercase letters above the bars indicate statistically significant differences between species based on Tukey’s test (p < 0.05).

Energy density calculations resolved the evaluated biomasses into four distinct statistical groups (Figure 5D), with the highest averages recorded for B. guianensis (12.01 GJ m⁻³) and V. guianensis (11.85 GJ m⁻³). High energy density functions as a primary indicator for maximizing biomass transportation efficiency (Halba, Vidyarthi & Arora, 2022; Tumuluru et al., 2024). For smallholder farmers utilizing wood from secondary vegetation, this parameter is equally critical as it directly impacts the efficiency of storage, minimizing the required volume for a given energy output (Carvalho et al., 2020). Since traditional firewood extraction typically requires extended periods for natural moisture reduction under limited infrastructure, superior energy density becomes paramount. Maximizing the energy stored per unit of volume inherently optimizes constrained household storage spaces and reduces the total handling effort required by traditional family farmers.

In terms of energy stock, B. guianensis provides the highest energy per unit volume but exhibits a substantial ash content, requiring smallholders to manage the mineral residues left after combustion. In this regard, species-derived ash can be integrated into agricultural practices to replenish soil nutrients and mitigate soil acidification (Wu et al., 2024). For V. guianensis, the volatile matter-to-fixed carbon ratio suggests a clear mechanism for accelerated devolatilization and faster combustion kinetics. Consequently, its application in traditional ovens requires careful air-to-fuel ratio adjustments to ensure optimal thermal stability (Martinez-Sarache et al., 2025). L. pubescens had an average energy density of 10.20 GJ m⁻³, placing it in the second-highest group. This species exhibits a high fixed carbon content and low volatile matter and ash, representing a stable fuel profile that optimizes solid-phase char burning and heat preservation (Bora & Mahapatra, 2025; Tarlinski et al., 2024; Wu et al., 2024), which is ideal for the continuous demands of traditional cassava flour roasting systems.

Practical applications and future perspectives

The evaluation of firewood from secondary vegetation provides a technical alternative to primary forest exploitation (González-González et al., 2024), supporting biodiversity conservation and mitigating deforestation in the Amazon. Beyond these environmental gains, this approach empowers rural communities by generating income and providing smallholders with reliable energy for cassava agroprocessing. Given that cassava roasting is a complex thermal process, involving simultaneous mass and heat transfer (Sruthi et al., 2021), the quality of the final product is highly sensitive to heat supply stability. In this context, the selection of appropriate firewood is a key operational control.

Species such as C. perrottetii, L. pubescens, and I. heterophylla emerge as high-potential energy sources, as their favorable fixed carbon and volatile matter ratios ensure superior heating values (Brčić et al., 2024) and a stable combustion profile suitable for the thermal demands of roasting (Das, Duarah & Purkait, 2023). Furthermore, firewood with high energy density and low moisture content improves combustion efficiency, significantly mitigating smoke emissionsand enhancing indoor air quality (Massuque, Assis & Trugilho, 2024; Zhao et al., 2021). To optimize these benefits, smallholders should prioritize species with higher basic density (V. guianensis and B. guianensis) which enhance energy efficiency and reduce harmful emissions (Sahu et al., 2026), while adhering to effective storage practices to prevent moisture-related performance losses (Tomczak, Tomczak & Jelonek, 2020; Tucho et al., 2023).

The selection of secondary vegetation species with favorable energy properties, as analyzed in this study, can directly contribute to achieving Sustainable Development Goals (SDGs) 7 (Affordable and Clean Energy), 12 (Responsible Consumption and Production), 13 (Climate Action), and 15 (Life on Land) (United Nations, 2015). The sustainable management of secondary vegetation in the Amazon represents a practical strategy for balancing environmental conservation with socioeconomic development. It reduces pressure on primary forests, enhances biomass quality for energy use, and strengthens energy security in rural communities. To maximize these benefits, public policies and capacity-building initiatives should be promoted through rural extension programs, disseminating firewood management and storage techniques while ensuring the sustainable use of resources and the preservation of Amazonian ecosystems. This approach is supported by empirical evidence, which demonstrates that field days and structured training sessions significantly increase the adoption rates of technical practices (Marenya, Usman & Rahut, 2021).

Future research should adopt an interdisciplinary approach to optimize firewood management in the cassava production chain and investigate emissions from firewood species used by smallholders, including their health impacts. In addition, firewood collection from the studied species should balance their physicochemical and energy properties with their ecological roles in secondary vegetation communities, ensuring the sustainability of this practice in these ecosystems. Such studies could enhance environmental sustainability through renewable energy alternatives, economic viability via low-cost solutions, and social development by strengthening rural communities.

Conclusions

Secondary forest species show potential as renewable fuelwood sources for cassava agroprocessing. Efficient selection must integrate moisture behavior, basic density, proximate composition, heating value, and energy density. Species with favorable combustion profiles (C. perrottetii, L. pubescens, and I. heterophylla) and higher energy stocks (B. guianensis and V. guianensis) can support stable heat supply when properly dried and stored. These sustainable biomass options optimize traditional oven efficiency, reduce pressure on primary native forests, and secure cleaner energy for tropical smallholder farmers.

Acknowledgments

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001, Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação de Apoio à Pesquisa do Espírito Santo (FAPES) Grant: 240/2025 - P: 2025-9TN3T. The authors also thank the Universidade Federal Rural da Amazônia (UFRA) for the institutional and logistical support provided during the fieldwork.

Data Availability Statement

Data available upon request to authors.

References

• Abrell, T. et al. (2024). Shifting cultivation in decline: An analysis of soil fertility and weed pressure in intensified cropping systems in Eastern Amazon. Agriculture, Ecosystems & Environment, 360:108793.
• Adeeyo, R. O. et al. (2022). Determinants of solid fuel use and emission risks among households: Insights from limpopo, South Africa. Toxics, 10(2):67.
• Adekanye, T., & Oni, K. C. (2022). Comparative energy use in cassava production under different farming technologies in Kwara State of Nigeria. Environmental and Sustainability Indicators, 14:100173.
• Alves, R. N. B., & Modesto Júnior, M. de S. (2022). Potencialidades da cultura da mandioca no Estado do Pará. In A. K. O. Homma. Sinergias de mudança da agricultura amazônica: Conflitos e oportunidades Brasilia, DF: Embrapa, (pp.310-338).
• American Society for Testing and Materials - ASTM. (2022), ASTM D2395-17: Standard test methods for density and specific gravity (Relative Density) of wood and wood-based materials Available in: https://store.astm.org/d2395-17.html
  » https://store.astm.org/d2395-17.html
• American Society for Testing and Materials - ASTM. (2025), ASTM D4442-20(2025): Standard test methods for direct moisture content measurement of wood and wood-based materials Available in: https://store.astm.org/d4442-20r25.html
  » https://store.astm.org/d4442-20r25.html
• American Society for Testing and Materials - ASTM. (2024). ASTM E870-82(2019): Standard test methods for analysis of wood fuels Available in: https://store.astm.org/e0870-82r19.html
  » https://store.astm.org/e0870-82r19.html
• Balume, B. S. et al. (2025). Charcoal and firewood use in urban areas of developing countries: Drivers, consequences, and the need for clean cooking solutions. Renewable and Sustainable Energy Reviews, 217:115745.
• Barghini, A., & Cereda, M. P. (2025). Traditional amerindian cassava-based foods and drinks in the Amazon region. In M. P. Cereda., & O. F. Vilpoux. Traditional products and their processes Elsevier. (pp.129-154).
• Bora, A., & Mahapatra, S. (2025). Experimental study on combustion characteristics of Bambusa tulda and petcoke at varying blending ratios. Energy, 320:135383.
• Brasil. Ministério da Agricultura. (1993). Lei nº 8.629 de 25 de fevereiro de 1993. Dispõe sobre a regulamentação dos dispositivos constitucionais relativos à reforma agrária, previstos no Capítulo III, Título VII, da Constituição Federal. Diário Oficial da União: seção 1, 26/02/1993, pág. nº 2349.
• Brasil. Ministério Do Desenvolvimento Agrário. (2006). Lei nº 11.326 de 24 de julho de 2006. Estabelece as diretrizes para a formulação da Política Nacional da Agricultura Familiar e Empreendimentos Familiares Rurais. Diário Oficial da União: seção 1, 25/07/2006, pág. nº 1.
• Brčić, M. et al. (2024). Influence of crop management on the agronomic and combustion properties of spelt (Triticum spelta L.). Biomass and Bioenergy, 188:107313.
• Caballero, C. B. et al. (2023). Transformation of Brazil’s biomes: The dynamics and fate of agriculture and pasture expansion into native vegetation. Science of The Total Environment, 896:166323.
• Carvalho, A. C. D. et al. (2020). Produção de energia da madeira de espécies da Caatinga aliada ao manejo florestal sustentável. Scientia Forestalis, 48(126):e3086.
• Csanády, E., Magoss, E., & Tolvaj, L. (2015). Quality of machined wood surfaces Springer International Publishing.
• Curtis, J. T., & McIntosh, R. P. (1950). The interrelations of certain analytic and synthetic phytosociological characters. Ecology, 31(3):434-455.
• Das, P. P., Duarah, P., & Purkait, M. K. (2023). Fundamentals of food roasting process. In S. M. Jafari. High-temperature processing of food products Elsevier. (pp.103-130).
• Deng, M. et al. (2023). How to improve pollutant emission performances of household biomass cookstoves: A review. Energy and Buildings, 295:113316.
• Denich, M. et al. (2005). A concept for the development of fire-free fallow management in the Eastern Amazon, Brazil. Agriculture, Ecosystems & Environment, 110(1-2):43-58.
• Dominic, D., & Baidurah, S. (2025). A review of biological processing technologies for palm oil mill waste treatment and simultaneous bioenergy production at laboratory scale, pilot scale and industrial scale applications with technoeconomic analysis. Energy Conversion and Management: X, 26:100914.
• Eliasson, L. et al. (2020). Managing moisture content during storage of logging residues at landings - Effects of coverage strategies. Renewable Energy, 145:2510-2515.
• Food and Agriculture Organization of United Nations - FAOSTAT. (2022). The State of the World’s Forests 2022 FAO. Available in: https://openknowledge.fao.org/items/4c8bd12f-d6b8-4755-a82f-1284c41bf012
  » https://openknowledge.fao.org/items/4c8bd12f-d6b8-4755-a82f-1284c41bf012
• Fuente-Carrasco, M. E. et al. (2022). Energy properties of 22 timber species from Oaxaca, Mexico. South-east European forestry, 13(2):107-113.
• Gao, X., & Dai, H. (2026). Autothermal hydrogen production from wood biomass based on low-temperature alkaline glycerol pretreatment synergized with efficient heat storage media. Journal of Cleaner Production, 551:147930.
• Gioda, A. (2019). Residential fuelwood consumption in Brazil: Environmental and social implications. Biomass and Bioenergy, 120:367-375.
• González-González, C. A. et al. (2024). The importance of secondary vegetation for sustainable use of timber forest products in Calakmul, Campeche. Revista Chapingo Serie Ciencias Forestales y del Ambiente, 30(3):19-34.
• Halba, A., Vidyarthi, P. K., & Arora, P. (2022). Gasification as a potential solution for forest fires in the Indian Himalayan Region: A review. Bioresource Technology Reports, 19:101162.
• Hartinger, S. M. et al. (2025). The 2025 Lancet countdown Latin America report: Moving from promises to equitable climate action for a prosperous future. The Lancet Regional Health - Americas, 52:101276.
• Hauser, S., & Norgrove, L. (2024). Slash and burn agriculture, effects of. Encyclopedia of Biodiversity, 4:208-227.
• Imran, M., & Ozcatalbas, O. (2020). Determinants of household cooking fuels and their impact on women’s health in rural Pakistan. Environmental Science and Pollution Research, 27(19):23849-23861.
• Instituto Brasileiro de Geografia e Estatística - IBGE. (2024). Produção agrícola Municipal: Culturas temporárias e permanentes Available in https://www.ibge.gov.br/estatisticas/economicas/agricultura-e-pecuaria/9117-producao-agricola-municipal-culturas-temporarias-e-permanentes.html?=&t=destaques
  » https://www.ibge.gov.br/estatisticas/economicas/agricultura-e-pecuaria/9117-producao-agricola-municipal-culturas-temporarias-e-permanentes.html?=&t=destaques
• Jiang, T. et al. (2014). Fire performance of oak wood modified with N-methylol resin and methylolated guanylurea phosphate/boric acid-based fire retardant. Construction and Building Materials, 72:1-6.
• Kumar, M., Kumar, S., & Tyagi, S. K. (2013). Design, development and technological advancement in the biomass cookstoves: A review. Renewable and Sustainable Energy Reviews, 26:265-285.
• Lai, Y. et al. (2024). Characterisation of wood combustion and emission under varying moisture contents using multiple imaging techniques. Fuel, 373:132397.
• Li, J. et al. (2025). Reinforcing flame retardancy, dimensional stability, and high strength of woods for structural applications through surface densification and chemical modification. Industrial Crops and Products, 223:120175.
• Li, Y. et al. (2025). Cooking fuel choice of rural households in China: The impact of horizontal occupational differentiation and vertical income differentiation. Energy, 335:138250.
• Lima, M. D. R. et al. (2020). Logging wastes from sustainable forest management as alternative fuels for thermochemical conversion systems in Brazilian Amazon. Biomass and Bioenergy, 140:105660.
• Manyatsha, K., Hattingh, B. B., & Edokpayi, J. (2025). First study on the characterisation of preferred fuelwood species for various energy applications in Limpopo Province. Scientific African, 30:e03062.
• Marenya, P. P., Usman, M. A., & Rahut, D. B. (2021). Community-embedded experiential learning and adoption of conservation farming practices in Eastern and Southern Africa. Environmental Development, 40:100672.
• Martinez-Sarache, H. A. et al. (2025). Experimental research on the countercurrent fixed-bed combustion of biomass. Progress in Energy and Combustion Science, 109:101233.
• Massuque, J., Assis, M. R., & Trugilho, P. F. (2024). Characterization of Miombo species used by rural communities as fuelwood in Northern Mozambique. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 46(1):16175-16184.
• Matsunari, S. et al. (2025). Elucidation of char combustion behaviors for various types of biomass by reaction kinetic analysis. Journal of the Japan Institute of Energy, 104(10):122-128.
• Mazzone, A., Cruz, T., & Bezerra, P. (2021). Firewood in the forest: Social practices, culture, and energy transitions in a remote village of the Brazilian Amazon. Energy Research & Social Science, 74:101980.
• Menéndez, A., & Curt, M. D. (2013). Energy and socio-economic profile of a small rural community in the highlands of central Tanzania: A case study. Energy for Sustainable Development, 17(3):201-209.
• Mierzwa-Hersztek, M. et al. (2019). Assessment of energy parameters of biomass and biochars, leachability of heavy metals and phytotoxicity of their ashes. Journal of Material Cycles and Waste Management, 21:786-800.
• Neves, E. C. A. et al. (2020). Classificações e características nutricionais e tecnológicas de farinhas de mandioca comercializadas em Belém, Pará, Brasil. Brazilian Journal of Food Technology, 23:e2019143.
• Ngusa, D. A. (2025). Barriers to the adoption of clean cooking energy technologies in rural households within selected lower-middle-income countries: A bibliometric analysis. Energy Strategy Reviews, 61:101834.
• Ooi, W. C. et al. (2023). Biomass fuel production through cultivation of microalgae Coccomyxa dispar and Scenedesmus parvus in palm oil mill effluent and simultaneous phycoremediation. Agriculture, 13(2):336.
• Pedroso Júnior, N. N., Murrieta, R. S. S., & Adams, C. (2008). A agricultura de corte e queima: Um sistema em transformação The slash-and-burn agriculture: A system in transformation. Boletim Museu Paraense Emílio Goeldi. Ciências Humanas, 3(2):153-174.
• Peng, Y. et al. (2023). Emission characteristic of OVOCs, I/SVOCs, OC and EC from wood combustion at different moisture contents. Atmospheric Environment, 298:119620.
• Pérez, G. et al. (2022). Socioeconomic and environmental aspects of traditional firewood for cooking on the example of rural and peri-urban Mexican households. Energies, 15(13):4904.
• Raiol, L. L. et al. (2025). Assessment of environmental degradation and conservation in the Maracanã River Basin, eastern amazon. Frontiers in Environmental Science, 12:1506701.
• Ravindra, K. et al. (2019). Trend in household energy consumption pattern in India: A case study on the influence of socio-cultural factors for the choice of clean fuel use. Journal of Cleaner Production, 213:1024-1034.
• Rodríguez-Jiménez, S., Duarte-Aranda, S., & Canché-Escamilla, G. (2019). Chemical composition and thermal properties of tropical wood from the Yucatán dry forests. BioResources, 14(2):2651-2666.
• Romero, T. E. R. et al. (2025). The energy potential of agricultural biomass residues for household use in rural areas in the department la guajira (Colombia). Sustainability, 17(3):974.
• Rousseau, G. et al. (2022). Potential of slash-and-mulch system with legumes to conserve soil attributes and macrofauna diversity in Eastern Amazon. Pedobiologia, 95:150840.
• Safari, J. G., Mwongerezi, J. K., & Hyandye, C. B. (2022). Patterns and predictors of household fuel choices in Maswa District, Tanzania. Cogent Social Sciences, 8(1):2137963.
• Sahu, D. et al. (2026). Gaseous pollutant emissions from solid fuel combustion: Comparative study of real-world and simulated chamber-based experiments. Atmospheric Pollution Research, 17(3):102798.
• Soares, B. C. D. et al. (2019). Behavior of juvenile and Mature Eucalyptus cloeziana wood subjected to drastic drying. Floresta e Ambiente, 26(3):e20170872.
• Souza, A. P. D. et al. (2019). Variação anual da umidade de equilíbrio e da cor de madeiras amazônicas submetidas a ensaios de campo. Revista Ciência da Madeira - RCM, 10(3):223-235.
• Sruthi, N. U. et al. (2021). An overview of conventional and emerging techniques of roasting: Effect on food bioactive signatures. Food Chemistry, 348:129088.
• Stolarski, M. J. et al. (2023). Changes in commercial dendromass properties depending on type and acquisition time. Energies, 16(24):7973.
• Strandgard, M. et al. (2021). Use of modelling to compare the impact of roadside drying of Pinus radiata D.Don logs and logging residues on delivered costs using high capacity trucks in Australia. Biomass and Bioenergy, 147:106000.
• Tarlinski, D. et al. (2024). Combustion of single walnut shell particles in a laminar flow reactor under oxy-fuel conditions: Optical measurements and particle sampling. Fuel, 369:131613.
• Tian, Z. et al. (2021). The health effect of household cooking fuel choice in China: An urban-rural gap perspective. Technological Forecasting and Social Change, 173:121083.
• Tomczak, K., Tomczak, A., & Jelonek, T. (2020). Effect of natural drying methods on moisture content and mass change of scots pine roundwood. Forests, 11(6):668.
• Tucho, B. G. et al. (2023). Effect of wood moisture content on the performance of wood burning cook stoves. International Journal of Sustainable Engineering, 16(1):1-10.
• Tumuluru, J. S. et al. (2024). Energy-based break-even transportation distance of biomass feedstocks. Frontiers in Energy Research, 12:1347581.
• Vieira, T. A. S. et al. (2023). Impact of chemical composition on eucalyptus wood clones for sustainable energy production. Forests, 14(11):2240.
• Vilpoux, O. F. (2024). Cassava starch processing units: Comparison of industrial technologies from China, Thailand, and Brazil. In M. P. Cereda., & O. F. Vilpoux. Starch industries: Processes and innovative products in food and non-food uses Academic Press, Elsevier. (pp.9-35).
• Wu, R., Beutler, J., & Baxter, L. L. (2020). Non-catalytic ash effect on char reactivity. Applied Energy, 260:114358.
• Wu, S. et al. (2024). Substantial CO2 uptake by biomass ashes under natural condition in China. Science of The Total Environment, 954:176460.
• Yang, S. et al. (2025). Advances in the study of heartwood formation in trees. Life, 15(1):93.
• Yongtie, C. et al. (2022). Morphology, mineralogy and rietveld texture analysis of ash deposits from a moving grate boiler. Fuel, 314:122737.
• Zhai, J. et al. (2021). New insights into biomass combustion ash categorisation: A phylogenetic analysis. Fuel, 287:119469.
• Zhao, N. et al. (2021). Dynamic relationships between real-time fuel moisture content and combustion-emission-performance characteristics of wood pellets in a top-lit updraft cookstove. Case Studies in Thermal Engineering, 28:101484.

• Editor de seção:
  Renato Paiva http://orcid.org/0000-0001-5107-0285

Publication Dates

• Publication in this collection
  17 Aug 2026
• Date of issue
  2026

History

• Received
  08 May 2026
• Accepted
  16 July 2026