The wood samples of T. foetidissima and T. copelandii were collected at the Maguindanao del Norte (07°08′ N; 124°16′ E), BARMM, Philippines, with an elevation ranging from 85-110 meter above sea level (masl) Figure 1, displaying a tropical monsoon climate (Classification: Am).

Three matured trees (approximately 10 to 20-year-old) were selected per tree species with a diameter of greater than 20 cm. Wood samples were extracted at three different locations within the DBH level (1.3 m) of the trees which were free from defects, knots, and injuries, using a 5.15 mm diameter by 100 mm long alloy steel increment borer, with a fine-threaded tip. After extraction, wood samples were placed in the respective ziplock bags with proper labelling for safe keeping, while the holes in the trees caused by increment borer were patched with wood and painted to keep away from the degrading organism (i.e., insect and fungi).

Matchstick-sized samples were prepared from the collected wood samples and then macerated in equal volume (1:1) of acetic acid and hydrogen peroxide (50% concentration), following the procedure of (Espiloy et al., 1999). The maceration was done in a water bath and heated for three hours at 100 oC until the samples became white, soft and easy to separate into individual fibers. Afterward, the samples were washed with distilled water to become acid-free, and then subjected to microscopic observation and measurement without staining.

Before fiber measurement, the macerated samples inside the test tubes were shaken to ensure the separation of different structural elements. Twenty-five undamaged fibers were observed per replicate under the Euromex compound microscope and measured using ImageJ Software (ImageJ 1.45). The length, diameter, and lumen diameter of each fiber were measured in accordance to the International Association of Wood Anatomists (IAWA) standard (Wheeler et al., 1989), while the cell wall thickness was determined based on the difference between the fiber diameter and lumen diameter. Cell wall fraction (1) was also calculated following the equation used by (Eloy et al., 2024):

Cell wall fraction = 2 x Cell wall thickness x 100 (1)

Fiber diameter

Based on the fiber morphology data, the derived values such as Runkel ratio (2), Slenderness ratio (3), Flexibility ratio (4), Muhlsteph ratio (5), and Rigidity coefficient (6) were computed using the equation used by (Hartono et al., 2022), while the Luce’s shape factor (7) was determined using the equation followed by (Wood properties related to pulp and paper quality in two Macaranga species naturally regenerated in secondary forests, 2016). These values were used to further evaluate the potential of T. foetidissima and T. copelandii as raw materials for pulp and paper production, and other applications.

Runkel ratio = 2 x Cell wall thickness (2)

Lumen diameter

Slenderness ratio = Fiber length (3)

Fiber diameter

Flexibility ratio = Lumen diameter x 100 (4)

Fiber diameter

Mublsteph ratio(%) = Fiber diameter² - lumen diameter² x 100 (5)

Fiber diameter²

Rigidity coefficient = Cell wall thickness (6)

Fiber diameter

Luce' s shape factor = Fiber diameter² - Lumen diameter²(7)

Fiber diameter² +Lumen diameter²

A t-test analysis was used to compare the fiber morphology and derived values of T. foetidissima and T. copelandii wood. This analysis was carried out using Jamovi version 2.3 (Jamovi Project 2023).

Results of the study showed that the fibers of T. foetidissima and T. copelandii measured 1.613 mm and 1.677 mm, respectively. The analysis indicated no significant difference in fiber length between the two species, with a P-value of 0.668, suggesting that the fiber lengths are comparable. The average fiber length results of the present study were relatively longer compared to other Terminalia spp. like T. arjuna (1.176 mm), T. bellerica (1.131 mm), T. myriocarpa (0.991 mm) in India (Singh et al., 2013), T. ivorensis (sapwood, 1.314 mm & heartwood, 1.413 mm) in Ghana (Antwi-Boasiako & Apreko-Pilly, 2016), T. arjuna (0.512 mm), T. bellerica (0.262 mm), T. chebula (0.445 mm), and T. elliptica (0.490 mm) in India (Ranjan et al., 2025). These findings were relatively comparable to the fiber length of T. foetidissima (1.650 mm) in Philippines (F.P.R.D.I., 1996) and T. catappa (1.673 mm) in Nigeria (Aina et al. 2019). Compared to some underutilized native wood species in the Philippines (Villareal et al., 2025) such as Alstonia scholaris (1.79 mm), Ficus callosa (1.82 mm), and Ficus variegata (2.73 mm), both T. foetidissima and T. copelandii possessed shorter fibers, except for Broussonetia luzonica (1.44 mm). Moreover, T. foetidissima and T. copelandii fibers were relatively longer than the fibers of Falcataria moluccana (3-, 5-, and 7-year-old trees: 1.160, 1.140, and 1.170 mm, respectively), a fast-growing plantation species in the country commonly used for veneer, plywood, pulp and paper, and other light construction applications (Alipon et al., 2021).

(Salehi, 2001) grouping, both the fibers of T. foetidissima and T. copelandii fall under the second group, which is characterized by having an average fiber length ranging from 0.9 to1.9 mm. These results indicate that the fibers of T. foetidissima and T. copelandii could befavorable raw materials for composite products considering that fibers ranging from 1.0 to 5.0 mm in length can potentially be used for composite products (Madsen et al., 2013). Long fibers with thin cell walls were much preferable for pulp and paper manufacturing since thelongerthe fiber, the higher the paper's tearingresistance (Sharma et al., 2011). (Suansa & Al-Mefarrej, 2020) also stated that fibers with an average of greater than 0.4mm are considered suitable raw materials for papermaking. Based on the fiber length results,T. foetidissima andT. copelandiifi bers would befavorable for pulp and paper production. Additionally, the DENR Administrative Order No.2000-63 also classifies both species as suitable materials for furniture and construction applications. However, further research is needed to thoroughly evaluate the potential of these species for various applications

The findings of this study revealed that the T. foetidissima fiber diameter was 41.345 µm, while T. copelandii fiber diameter was 34.992 µm. Statistical analysis revealed no significant difference in the fiber diameter between these two species, with a P-value of 0.307. The average fiber diameter of T. foetidissima and T. copelandii was relatively smaller than those of Terminalia spp. reported by (Singh et al., 2013) such as T. arjuna (160.40 µm),T. bellerica (171.00 µm), T. chebula (125.40 µm) and T. myriocarpa (256.90 µm) (Singh et al., 2013), but larger to T. foetidissima (27.00 µm) (F.P.R.D.I., 1996) and T. ivorensis (sapwood, 21.69 µm and heartwood, 19.79 µm) (Antwi-Boasiako & Apreko-Pilly, 2016). Moreover, the observed fiber diameter of T. catappa (36.37 mm) (Aina et al. 2019), and 3-, 5-, and 7-year-old F. moluccana (35.40, 37.40, and 38.00 µm) (Alipon et al., 2021) were comparable to the present results. Compared to some underutilized native species reported by (Villareal et al., 2025), the fiber diameters of T. foetidissima and T. copelandii were smaller than A. scholaris (49.50 µm), F. callosa (52.83 µm), and F. variegata (52.13 µm), except for B. luzonica (35.83 µm).

Relative to lumen diameter, the results showed that T. foetidissima fiber has an average lumen diameter of 28.296 µm and T. copelandii fiber has a lumen diameter of 23.495 µm. The analysis revealed no significant results with a P-value of 0.402, indicating a comparable result for the lumen diameter of T. foetidissima and T. copelandii fibers. The average lumen diameters of T. foetidissima and T. copelandii were relatively larger than those of T. foetidissima (17.00 µm) (F.P.R.D.I., 1996), T. ivorensis (sapwood, 15.47 µm & heartwood, 13.33 µm) (Antwi-Boasiako & Apreko-Pilly, 2016), T. catappa (10.00 µm) (Aina et al. 2019). Compared to the findings of (Villareal et al., 2025) on A. scholaris (38.73 µm), F. callosa (37.40 µm), and F. variegata (33.07 µm), both T. foetidissima and T. copelandii fibers’ lumen diameter were smaller, except for B. luzonica (26.33 µm). Moreover, (Alipon et al., 2021) report larger lumen fibers of 5 and 7-year-old F. moluccana with 30.90 and 31.70 (µm), respectively, while 3-year-old F. moluccana seems to be comparable to T. foetidissima fiber. Basically, the lumen diameter significantly influences the beating process of pulp and paper production, as liquid penetrates the empty spaces in the fibers (Kiaei et al., 2014). Furthermore, the physiological growth of wood, including tree ages, diameter increase, and species, can influence lumen diameter (R & M, 2007); (Anupam et al., 2016). The present lumen diameter results suggest that the beating process of T. foetidissima and T. copelandii fibers could probably be favorable.

Results of this study indicated that T. foetidissima has 6.524 µm and T. copelandii has 5.748 µm cell wall thickness. These average results were relatively thicker than those of the cell wall of some Terminalia spp. reported by (Singh et al., 2013) on T. arjuna (2.30 µm), T. myriocarpa (2.20 µm), T. bellerica (2.10 µm), and T. chebula (1.80 µm), while thinner than T. catappa (16.67 µm) (Aina et al. 2019). (F.P.R.D.I., 1996) also reported a slightly thinner cell wall of T. foetidissima with an average of 5.00 µm. Moreover, the cell wall of T. ivorensis (sapwood, 6.22 µm & heartwood, 6.46 µm) reported by (Antwi-Boasiako & Apreko-Pilly, 2016) seems to be comparable with the present result of T. foetidissima fibers. As compared to 3-, 5-, and 7-year-old F. moluccana (3.30, 3.20, 3.1 µm, respectively) (Alipon et al., 2021), A. scholaris (5.40 µm) and B. luzonica (4.73 µm) (Villareal et al., 2025), the cell walls of both T. foetidissima and T. copelandii were thicker, but thinner than F. callosa (7.70 µm), and F. variegata (9.57 µm) (Villareal et al., 2025). Basically, cell wall thickness increases toward maturity which is dependent on the accumulated metabolic products like holocellulose, lignin, and waxes (Ververis et al., 2004);(Shmulsky & Jones, 2019). Fibers with thick walls adversely affect the bursting strength, tensile strength, and folding endurance of paper (Kiaei et al., 2014);(Shmulsky & Jones, 2019). Based on the present result, T. foetidissima and T. copelandii fibers could be relatively rigid and may produce less dense paper but higher tearing strength, considering the impact of cell wall to the fiber flexibility and bulkiness of paper (Sharma et al., 2011).

The result showed that T. copelandii recorded 33.688% cell wall fraction, while T. foetidissima recorded 31.842% exhibiting 5.634% difference. Although, no significant difference was observed with a P-value of 0.691. This present result was relatively lower compared to other hardwood species usually used for construction purposes like Peltophorum dubium (64.00%), Parapiptadenia rigida (57.80%), and Eucalyptus grandis × Eucalyptus urophylla (55.20%) (Eloy et al., 2024), while higher than those of underutilized native species in the Philippines (A. scholaris, 21.82%; B. luzonica, 26.40%; F. callosa, 29.15%; F. variegata, 36.72%) (Villareal et al., 2025), and underutilized fast-growing species in Indonesia (Macaranga bancana, 7.00% and M. pearsonii, 8.00%)(Wood properties related to pulp and paper quality in two Macaranga species naturally regenerated in secondary forests, 2016). A higher cell wall fraction slows a material's drying rate by reducing its capacity to hold moisture. This property also serves as a key indicator for industrial use, where a value below 40% suggests suitability for pulpwood and is linked to greater bending resistance through fiber flexibility (Kollmann & Côté, 1968); (Wood properties related to pulp and paper quality in two Macaranga species naturally regenerated in secondary forests, 2016); (Eloy et al., 2024). Additionally, the cell wall fraction is directly linked to wood’s basic density and inversely linked to its moisture content. Moreover, a higher cell wall fraction increases wood density and enhances its mechanical strength, making it more resistant (Sette Junior et al. 2012; (Lima et al., 2014); (Tanabe et al., 2016); (Eloy et al., 2024). The present results indicated that T. copelandii wood may have a slower drying rate, while T. foetidissima may exhibit a faster drying rate. These findings also suggest that both wood species could be suitable for pulpwood production.

Derived values of T. foetidissima and T. copelandii wood species, such as the Runkel ratio, Slenderness ratio, Flexibility ratio, Muhlsteph ratio, Rigidity coefficient, and Luce’s shape factor are presented in Table 2.