Fiber Morphology and Extractive Content of Aquilaria cumingiana (Decne.) Ridl. Wood
from Davao Oriental, Philippines
Jayric F. Villareal1,2*, Willie P. Abasolo1, Rosalie C. Mendoza1, and Lerma S.J. Maldia3
1Department of Forest Products and Paper Science, College of Forestry and Natural Resources, University of the Philippines Los Baños,
College, Laguna 4031 Philippines
2College of Agroforestry and Forestry,
Don Mariano Marcos Memorial State University, North La Union Campus, Bacnotan, La Union 2515 Philippines
3Department of Forest Biological Sciences, College of Forestry and Natural Resources, University of the Philippines Los Baños,
College, Laguna 4031 Philippines
The fiber morphology and extractive content of Aquilaria cumingiana (Decne.) Ridl. wood collected in Davao Oriental, Philippines were determined to gather pioneering information about the properties of A. cumingiana for better characterization and classification. Wood samples were classified according to color with the aid of a Nix Mini 1 Color Sensor and labeled as A, B, C, and D. The result of the study showed an increasing trend of color lightness percentage from samples A (32.74%) to D (74.96%). Morphologically, both samples C and D (1.03 mm) showed the longest fiber, sample A showed the largest fiber (35.41 µm) and lumen diameter (27.77 µm), and sample C showed the thickest cell wall (4.71 µm). On the other hand, the highest Runkel ratio, slenderness ratio, and flexibility ratio were shown in samples B (0.49), C (33.00), and A (78.13), respectively. The amount of extractives obtained in the study decreases from samples A to D regardless of the solvents used. Statistically, the color lightness, morphological properties, and extractive content were significant across sample classifications. Among solvents used, the extractive content showed a significant result. The color lightness and extractive content showed a negative relationship, which signifies that the color lightness may be used to evaluate the amount and quality of extractives in A. cumingiana wood. Based on the morphological properties, A.
cumingiana fibers are found favorable in pulp and paper production. The classification and characterization of A. cumingiana wood properties along the infected portions of a tree and chemical profiling of the extracts would be relevant information to consider.
Keywords: agarwood, Aquilaria cumingiana, color lightness, derived values, extractive content, fiber morphology, solvents
*Corresponding author: [email protected]
ISSN 0031 - 7683
Date Received: 24 Nov 2021
INTRODUCTION
Agarwood is an exceptional non-timber forest product that is extremely expensive and has been traded around the world for hundreds of years. It is characterized as a dark aromatic resin embedded heartwood derived mainly from the wounded or infected wood of Aquilaria and Gyrinops under the Thymelaeaceae family that is commonly used for incense, medicines, and religious ceremonies (Chowdhury 2018). Normally, Aquilaria wood is soft, light in density, elastic, and white to yellowish-white in color (Lim et al. 2016). However, it turns dark and becomes denser and harder when the wood gets wounded or infected associated with the formation of wood resin (Karlinasari et al. 2017).
As reported in The Plant List (2013), 21 Aquilaria species were recorded worldwide, and 13 species of which were reported to produce fragrant resin, whereas the remaining eight species are subjected to further investigation.
Interestingly, the Philippines is considered one of the richest among the agarwood-producing countries where different Aquilaria species were found – namely, A.
brachyantha, A. decemcostata, A. parvifolia, A. apiculata, A. citrinicarpa, A. urdanetensis, A. malaccencis, and A.
cumingiana (The Plant List 2013; Yin et al. 2016).
Unfortunately, all natural Aquilaria species have been listed in Appendix II of CITES since 2005. As of 2009, eight species were listed on the IUCN Red List of Threatened Species as endangered species (IUCN 2009).
Under the Updated National List of Threatened Philippine Plants and Their Categories, A. cumingiana was listed as Vulnerable (DENR 2017). Despite the protective measures implemented, indiscriminate cutting of naturally grown Aquilaria trees was continually reported due to its expensive value and rarity with great demand worldwide.
However, only the small resin-embedded wood portions were utilized, whereas the healthy wood that constitutes the greater portion of the tree was usually ignored as if it is worth next to nothing (Tan et al. 2019). For that reason, the fiber morphology of Aquilaria wood was characterized to evaluate its suitability for pulp and paper production – particularly the healthy wood – in order to provide potential uses to this commonly ignored portion of the wood.
Moreover, A. cumingiana is a lesser-known Aquilaria species, and no particular study has been reported on the anatomical and extractive content of this species in the Philippines; hence, this is a pioneering study. To assess the quality of A. cumingiana wood and its agarwood produced, it is vital to characterize and understand its basic properties for proper utilization and classification.
This study aims to [1] characterize the fiber morphology and extractive content of A. cumingiana wood at different color lightness, [2] identify the most efficient solvent to
extract extractive content of A. cumingiana wood using the Soxhlet extraction method, and [3] determine the relationship between the extractive content and the color lightness. This study provides significant information on the characteristics of A. cumingiana species, specifically on the fiber morphology and extractive content, which are useful not only for scientific purposes but mainly for the agarwood industry and wood-based and chemical industries. It shall also facilitate the development of reliable and consistent standards for agarwood grading.
MATERIALS AND METHODS
Plant Materials and Samples
A. cumingiana wood samples were collected by chopping the wood portion of A. cumingiana trees at Mount Hamiguitan Range Wildlife Sanctuary (MHRWS), Davao Oriental, Philippines. Particularly, the infected portion and the healthy portion of A. cumingiana trees were used, replicated three times. Due to the very limited wood samples available, the samples were classified into four samples (A, B, C, and D) based on their color regardless of the portions of trees where they were taken (Figure 1).
Color Lightness Determination
The color lightness of the classified wood samples was determined to further assess its color using the Nix Mini 1 Color Sensor (Nix Sensor Ltd., Ontario, Canada), as well as the extracted extractives (after extractive content analysis). Using the RGB value (red, green, blue) of the samples directly acquired in the color sensor readings, the color lightness ranging from 0% (black) to 100% (white) was computed as (Cmax + Cmin)/ 2 x 100 (Nishad and Chezian 2013). The RGB values were divided by 255 to change the range from 0–255 to 0–1: R' = R/255; G'
= G/255; B' = B/255; Cmax = max (R' or G' or B'); Cmin = min (R' or G' or B'). The average results of the color lightness (three replicates) from both wood samples and extracted extractives were computed.
Fiber Morphology of A. cumingiana Wood
Fiber characterization. Matchstick-sized samples were prepared and macerated in equal volumes of 50% acetic acid and 50% hydrogen peroxide (50% concentration), following the procedure of Espiloy et al. (1999).
Maceration was done in a water bath and heated for 2–3 h at 100 °C until the samples turned white and soft. Thirty (30) undamaged fibers were observed per replicate under the microscope and measured using the Optika ISview software version 3.6.9. The length, diameter, and lumen diameter of the fibers were measured, whereas the cell
wall thickness was determined based on the difference between the fiber and lumen diameters.
Derived values. Using the data measured from fiber characterization, the derived values such as Runkel ratio (1), slenderness ratio (2), and flexibility ratio (3) were computed using the equation used by Saikia et al. (1997).
(1) (2) (3)
Extractive Content of A. cumingiana Wood
The extractive content analysis was carried out using the Soxhlet extraction method in accordance with TAPPI (1988) test methods (T 257 cm-85, T 204 cm-88, and T 207 cm-88). Wood samples were chipped into pieces and then
ground into powder (0.5 mm) using a Wiley mill. Prior to grinding, the wood samples were initially air-dried up to 12% moisture content or lower to avoid a lower recovery rate, longer grinding time, and possibly overheating mill due to clogging at the screen. Soxhlet extraction is a well-established standard technique with wide industrial applications, better reproducibility and efficiency, and less extract manipulation. Hence, ethanol, cyclohexane-ethanol (2:1 v/v), and water were used as solvents in the study.
Two (2.0) g powdered wood of A. cumingiana were prepared and then placed into filter paper extraction thimbles and in Soxhlet extraction tubes. A volume of 150 mL of each solvent (ethanol, cyclohexane-ethanol, and water) was added individually to the boiling flasks and placed on the hot plate. The extraction was conducted for four hours with a rate of approximately four siphoning per hour at a constant temperature of 60 °C. After extraction, the thimbles were removed from the Soxhlet tubes and quantitatively transferred to the tared 150-mL round- bottomed flask and washed with fresh solvent to remove traces of extractives. The washings were added to the flasks, subjected to rotary evaporation, and dried at 105 ± 2 °C for 8–12 h. Prior to weighing, the extracted samples
Figure 1. Sample classification of A. cumingiana: [A] relatively dark in color and solid; [B] moderately dark and chips in size; [C] lighter than sample B and chips in size; sample [D] healthy wood.
were cooled in the desiccator. The extractive content was calculated as a percentage of the oven-dry weight of the extracted samples with three replicates.
Statistical Analysis
One factor analysis of variance (ANOVA) was used to compare the difference in fiber properties, whereas two- factor ANOVA was used for extractive content at different color lightness. Tukey's honest significant difference was used to determine the significant differences between and among the mean values of the data. Also, Pearson’s linear correlation coefficient was utilized to determine the relationship between the extractive content and the color lightness. All statistical analyses were generated using SAS (Statistical Analysis System) software version 9.
RESULTS
Color Lightness of A. cumingiana Wood
Figure 2 shows the average color lightness from the sample classification of A. cumingiana wood. The highest average color lightness was observed in sample D with 74.96%, followed by samples C (55.79%), B (47.32%), and A (32.74%), respectively. Statistical analysis showed that the color lightness among sample classifications was significantly different. From samples A to D, a significant increase in color lightness was observed. However, there were no significant differences in the color lightness of the three solvents, as well as their interaction with the sample classifications.
Fiber Morphology of A. cumingiana Wood
Table 1 shows the result of the fiber morphology and its derived values such as fiber length, fiber diameter, lumen diameter, cell wall thickness, Runkel ratio, slenderness
ratio, and flexibility ratio of A. cumingiana wood.
The average fiber length of A. cumingiana was 0.98 mm. Both samples C and D were 1.03 mm, and samples A and B were 0.92 mm. The average fiber diameter of A. cumingiana was 32.11 µm. The highest value was recorded in sample A with 35.41 µm, whereas the lowest was in sample B with 28.97 µm. Moreover, the lumen diameter had an average of 23.40 µm, and the highest value was recorded in sample A with 27.77 µm – followed by samples D (23.74 µm), C (22.45 µm), and B (19.63 µm). The average cell wall thickness of A. cumingiana was 4.36 µm, whereas sample C showed the highest value with 4.71 µm. However, with the highest fiber and lumen diameter, sample A showed the lowest value of cell wall thickness at 3.82 µm.
The average Runkel ratio of A. cumingiana was 0.39, where sample B (0.49) had the highest value, whereas sample A (0.28) had the lowest. For the slenderness ratio, the average result in this study was 30.39. The highest value was recorded in sample C (33.00), and the lowest was recorded in sample A (26.32). However, the average flexibility ratio result was 72.31, where the highest value
Means with different letters are significantly different at 5% level by Tukey’s post hoc test
Figure 2. The average color lightness of A. cumingiana wood.
Table 1. Fiber morphology and its derived values of A. cumingiana wood.
Anatomical properties Classification
Average P-value
A B C D
Fiber length (mm) 0.92b 0.92b 1.03a 1.03a 0.98 2.00E–16*
Fiber diameter (µm) 35.41a 28.97c 31.88b 32.18b 32.11 2.00E–16*
Lumen diameter(µm) 27.77a 19.63d 22.45c 23.74b 23.40 2.00E–16*
Cell wall thickness (µm) 3.82c 4.67a 4.71a 4.22b 4.36 2.00E–16*
Derived values
Runkel ratio 0.28d 0.49a 0.44b 0.36c 0.39 2.00E–16*
Slenderness ratio 26.32b 32.01b 33.00a 32.45a 30.95 2.00E–16*
Flexibility ratio 78.13a 67.50d 70.02c 73.58b 72.31 2.00E–16*
Means in the same row followed by common letters are not significantly different at 5% level by Tukey’s post hoc test; *significant
was recorded in sample A (78.13), whereas the lowest value was recorded in sample B (67.50). Statistical analysis showed that the fiber morphology and its derived values were significantly different among the sample classification at a 5% probability level. This is probably due to the classification of collected samples, which disregarded the portions of trees where it was taken.
Extractive Content of A. cumingiana Wood
Figure 3 shows the average extractive content of A.
cumingiana wood from the sample classification using three solvents (ethanol, cyclohexane-ethanol, and water).
The average extractive content from ethanol solvent was relatively higher than those from cyclohexane-ethanol and water solvents. Relative to the sample classification of A. cumingiana wood, the highest average extractive content was observed from sample A (13.32, 10.75, and 6.66%) –followed by the samples B (12.11, 9.78, and 5.83%), C (5.05, 4.90, and 4.59%), and D (2.59, 2.38, and 4.36%), for ethanol, cyclohexane-ethanol, and water solvents, respectively.
Relationship between the Color Lightness and the Extractive Content
Figure 4 shows the result of the linear correlation coefficient between the color lightness and the extractive content of A. cumingiana wood from three different solvents. The result showed that the color lightness was significantly correlated to the extractive content.
Particularly, the color lightness and the extractive content of A. cumingiana wood have a negative relationship with P-values of 0.0003, 0.0006, and 0.0115 (for ethanol, cyclohexane-ethanol, and water extracts, respectively) – which means as the color lightness increases, the extractive content decreases.
Means with different letters are significantly different at 5% level by Tukey’s post hoc test
Figure 3. The extractive content of A. cumingiana wood extracted from three different solvents for different sample classifications.
The result showed significant differences in the extracted extractive content of A. cumingiana wood among the sample classification and the solvents at a 5% probability level. Likewise, the interactions between the sample classification and solvents were significantly different, which signifies its contribution to the variation of the extractive content result. Depending on solvents, the efficiency of extraction of the extractives increases from water to ethanol, and a significant decrease in extractive content was observed from samples A–D, regardless of solvents (Figure 3).
Figure 4. The linear correlation coefficient between the color lightness and extractive content of A. cumingiana wood from three different solvents.
DISCUSSION
Color Lightness of A. cumingiana Wood
The color lightness result of the study relates to the findings of Zich and Compton (2002) that the quality of agarwood is determined by its color (where the darker the color, the more valuable or higher grade of agarwood), and fragrance intensity. Likewise, it was reported that dark wood correlates with good quality agarwood; however, there are exceptions or some factors that need to be considered such as the origin of samples, consumer’s country, the portion of trees where the sample was taken, and fragrance (Lee and Mohamed 2016; Karlinasari et al. 2021).
Fiber Morphology of A. cumingiana Wood
The average fiber length result of the present study corroborates with the findings observed by Dwianto et al.
(2019) on Gyrinops versteegii (an agarwood-producing species), where the non-injured wood (0.94 mm) showed longer fiber than the injured wood (0.86 mm) but with almost similar fiber diameter and cell wall thickness. This indicates that the infection in the wood might reduce the
rate of cell length development (Dwianto et al. 2019).
The average fiber length of A. cumingiana was shorter compared to softwoods (3.5 mm), hardwoods (1.0 mm), as well as bamboo (1.8 mm) (Anupam et al. 2016).
However, it was relatively higher compared with other Aquilaria species (0.61 mm for seedlings and 0.55 mm for trees) (Nugroho et al. 2018). Based on the groupings devised by Salehi (2001), the fibers of A. cumingiana fall under the second group, which is characterized to have an average fiber length ranging from 0.9–1.9 mm.
Generally, fiber length influences the tearing strength of the paper, and the longer the fibers, the higher the tearing resistance of the paper (Sharma et al. 2011). Based on the result, paper made from A. cumingiana fibers tends to be less resistant to tears.
For the fiber diameter of A. cumingiana, the result was relatively higher than those of hardwoods (25.0 µm) and other Aquilaria species (14.91 µm for seedlings and 21.80 µm for trees) (Nugroho et al. 2018), whereas it was slightly lower than those of softwoods (35.0 µm) (Kiaei et al. 2014) and G. versteegii (35.58 for non-injured and 35.87 µm for injured) (Dwianto et al. 2019).
Kiaei et al. (2014) stated that lumen diameter affects the beating process in pulp and paper production due to liquid penetration in the empty spaces of the fibers. The average result of the study was higher compared to other Aquilaria species (12.43 µm for seedlings and 19.20 µm for trees) characterized by Nugroho et al. (2018). Based on the result, the beating process of A. cumingiana will be favorable.
Moreover, the result showed that the fiber of sample A will be more flexible and could probably produce dense and well-formed paper than samples B, C, and D since cell wall thickness governs the fiber flexibility and the bulkiness of paper (Sharma et al. 2011). According to Yin et al. (2016), Aquilaria wood fibers are characterized by thin to very thin walls with more bordered pits. The result of the present study was relatively lower compared to G. versteegii (4.51 µm for non-injured and 4.38 µm for injured) (Dwianto et al. 2019), whereas relatively higher than the result of other Aquilaria species (1.24 µm for seedlings and 1.34 µm for trees) (Nugroho et al. 2018).
According to Istek (2006), a Runkel ratio below 1.0 is expected to have thin-walled fibers, which conforms to the result of the present study. Istek also added that good mechanical strength properties are usually observed with the fibers having Runkel ratio of below 1.0. Based on the Runkel ratio result, the fiber of A. cumingiana is suitable for pulp and paper production. With regard to slenderness, the result was slightly lower than the acceptable value, which is more than 33.00 (Kiaei et al. 2014). Based on the flexibility groupings devised by Bektas et al. (1999), the observed wood fibers of A. cumingiana were considerably
elastic to highly elastic indicating efficiency and suitability for paper production. The flexibility ratio expresses the potential of fibers to collapse during beating or during drying of the paper web. The collapsed fibers provide more bonding area, and the degree of fiber bonding depends greatly on the flexibility of individual fibers (Zobel and van Buijtenen 1989).
The anatomical characteristics were a considerably good basis for wood utilization, especially in the pulp and paper making industry. Paper properties are significantly influenced by the fiber properties, anatomy, and separation method of the fibers (Zobel and van Buijtenen 1989). The fiber length, fiber diameter, lumen diameter, cell wall thickness, Runkel ratio, slenderness ratio, and flexibility ratio are the fiber characteristics that significantly influence the quality and properties of paper. Lim et al. (2016) also reported that Aquilaria not being an important timber species for construction/
building purposes is a concern, where its wood produced is soft, light in density (335-400 kg/m3 air dry), and not resistant to decay. It is commonly used for making boxes or packing crates, plywood, disposable chopsticks, as well as resin-embedded wood. This finding of Lim et al.
(2016) supported the result of the present study having a low Runkel ratio, indicating the unsuitability of materials for building/construction purposes.
Extractive Content of A. cumingiana Wood
As seen in Figure 3, the extractives content of A.
cumingiana wood was highly soluble in ethanol solvent than in cyclohexane-ethanol and water solvents. However, the amount of extractives obtained in the study is not the total amount present in the samples since some of the compounds/components cannot be extracted by just using one solvent and did not undergo a series of extraction using different solvents.
In the study of Hoque et al. (2019), the ether extracts of three categories of agarwood (A. malaccensis) – namely, white agarwood, screw injected agarwood, and insect- infested agarwood – were 1.80, 20.49, and 11.08%, respectively. The results of the present study were relatively higher than the extracts of the white agarwood sample, whereas they were relatively lower than that of the screw-injected agarwood sample. However, only samples A and B from the ethanol extracts of the present result showed a higher value relative to the ether extracts from the insect-infested agarwood sample. Moreover, the average extractive content results of A. cumingiana were relatively higher than the results obtained from the ethanol extracts of A. crassna with 2.0% (Novriyanti et al. 2010), A. agallocha with 2.3% (Habibur et al. 2012), and A. malaccensis with 1.67% (Sulaiman et al. 2015) using n-hexane solvent.
On the other hand, Zhang et al. (2012) reported the production of high-quality agarwood by whole tree induction technology compared with different levels of ethanol-soluble extractives from the wild agarwood samples. The average resin levels of induced agarwood were 19–22% higher than the average results of this study. In relation to the 10% requirement extracts for traditional Chinese medicine, only the ethanol extracts from samples A and B and the cyclohexane-ethanol extracts from sample A met this requirement. The yield and qualities of agarwood extracts varied considerably due to different factors like agarwood species, biological characteristics of trees, the origin of samples, solvents used in extraction, and methods of inoculation (natural and artificial) (Chowdhury 2018). Basically, the chemical compounds such as sesquiterpenes, chromones, fatty acids, and phenolic compounds secreted by plants are the main ones responsible for the distinctive fragrance of Aquilaria agarwood when burnt and also provide protection against external attacks or infection (Jong et al. 2014).
Relationship between the Color Lightness and the Extractive Content
Based on the result, the color lightness may be a good indicator to significantly evaluate the extractive content of agarwood and its quality. The degree of extractive/
resin determines the market value of the product, and the wood with darker color correlates significantly with the high-quality agarwood (Lee and Mohamed 2016).
The dark color of agarwood indicates the presence of agarwood resin in the wood, which corroborates the result of the study. Presently, each agarwood-producing country developed its own grading system, which is typically based on the concentration of resin within the wood. The amount of extractives/resins and the secondary metabolites of agarwood have a direct relationship with its quality (Liu et al. 2017). These extractive components that are soluble to some solvents such as sesquiterpenes, chromones, fatty acids, and phenolic compounds were the main ones responsible for the fragrance of agarwood and contribute to the change of color and agarwood quality (Jong et al. 2014). Thus, the higher the extractive content tends to display higher agarwood quality associated with different secondary metabolites/components.
Soehartono and Mardiastuti (1997) stressed that the yield of Aquilaria resin does not correspond with tree diameter or timber volume, even in trees with similar indications of infection. The result of the present study will contribute to the development of a reliable and consistent evaluation of the resin/extractive content of agarwood and may address the complexity of agarwood grading systems, which sometimes involved personal interest.
CONCLUSION
The fiber morphology and extractive content of A.
cumingiana wood collected at MHRWS, Davao Oriental, Philippines were characterized in this study. The fiber properties (fiber length, diameter, lumen diameter, and cell wall thickness) and their derived values (Runkel ratio, slenderness ratio, and flexibility ratio) varied significantly across sample classifications. On the other hand, the extractive content was significantly different among the sample classification and the solvents used.
Relative to the sample classification, sample A showed the highest extractive content, and a significant decrease was observed from samples A–D, respectively. Moreover, ethanol showed the highest extractive content, and the efficiency of extraction increased from water to ethanol.
In addition, the linear correlation coefficient result showed that the color lightness has a negative relationship with the extractive content of A. cumingiana wood – signifying that as the color lightness increases, the extractive content decreases, relative to the solvents. The results suggest the suitability of A. cumingiana fibers for pulp and paper production, which will minimize wood wastes and maximize the utilization, particularly the healthy wood.
Paper made from A. cumingiana fibers tends to be less resistant to tear but will have a favorable beating process.
Also, the color lightness will be a good indicator to significantly evaluate the extractive content of agarwood and its quality. The darker the color of the wood the higher the extractive content, indicating potentially higher quality agarwood.
ACKNOWLEDGMENT
The authors would like to express deep gratitude to the Department of Environment and Natural Resources (DENR) Region XI for giving the Wildlife Gratuitous Permit No. XI-2019-28 and Wildlife Transport Permit No. 2020-004 to collect and transport wood samples of Aquilaria cumingiana. The authors are also grateful to F. Sanchez Jr., O. Marasigan, R. Obias, R. Magcantara, M. Laspiñas, L.F. Casiple, Y. Sarmiento, and to the PENRO, CENRO/PASU, MHRWS-PAMO of Davao Oriental and to the rest of the MHRWS personnel for the technical assistance and support during the conduct of the study. Special thanks to the Accelerated Science and Technology Human Resource Development Program–
National Science Consortium of the Department of Science and Technology for the scholarship grant given to Mr. Villareal.
REFERENCES
ANUPAM K, SHARMA AK, LAL PS, BIST V.
2016. Physicochemical, morphological, and anatomical properties of plant fibers used for pulp and papermak- ing. Fiber Plants 235–248.
BEKTAS I, TUTUS A, EROGLU H. 1999. A study of the suitability of Calabrian pine (Pinus brutia Ten.) for pulp and paper manufacture. Turkish Journal of Agriculture and Forestry 23: 589–599.
CHOWDHURY M. 2018. Production of agarwood through aeration method into the agar tree [master’s thesis]. Bangladesh Agricultural University, Mymens- ingh. Retrieved from https://www.researchgate.net/
publication/327152856
[CITES] Convention on International Trade in Endangered Species of Wild Flora and Fauna. 2005. The trade and use of agarwood in Taiwan, Province of China.
TRAFFIC East Asia–Taipei. Retrieved from http://
cites.org/sites/default/files/common/com/pc/15/X- PC15-07-Inf.pdf
[DENR] Department of Environment and Natural Re- sources. 2017. Updated national list of threatened Philippine plants and their categories. Retrieved from http://server2.denr.gov.ph/uploads/rmdd/dao-2017-11.
DWIANTO W, KUSUMAH SS, DARMAWAN T, LAK- SANA RPB, DAMAYANTI R. 2019. Anatomical observation and characterization on basic properties of Agarwood (Gaharu) as an Appendix II CITES. IOP Conference Series: Earth and Environmental Science 374: 012062.
ESPILOY ZB, ESPILOY EB, MORAN SR. 1999. Basic properties of two – lesser used bamboo species: laak (Bambusa sp. 2) and kayali (Gigantochloa atter).
Forest Product Research and Development Institute Journal 25 (1–2): 1–18.
HABIBUR R, VAKATI K, ESWARAIAH MC. 2012. In vivo and in vitro antiflammatory activity of Aquilaria agallocha oil. International Journal of Basic Medical Sciences and Pharmacy 2: 7–10.
HOQUE MN, KHAN MMH, MONDAL MF. 2019. Insect infested agarwood: a newly prized product of agarwood market in Bangladesh. Fundamental and Applied Agri- culture 4(1): 689–692. DOI: 10.5455/faa.1693 ISTEK A. 2006. Effect of Phanerochaete chrysospori-
um white rot fungus on the chemical composition of Populus tremula L. J Cellulose Chem Technol 40(6):
475–478.
[IUCN] International Union for Conservation of Nature.
2009. 2008 IUCN red list of threatened species. Re- trieved from http://www.iucnredlist.Org
JONG PL, TSAN P, MOHAMED R. 2014. Gas chro- matography-mass spectrometry analysis of agarwood extracts from mature and juvenile Aquilaria malaccen- sis. International Journal of Agriculture and Biology (Pakistan) 16: 644–648.
KARLINASARI L, DANU MI, NANDIKA D, TUJA- MAN M. 2017. Drilling Resistance Method to Eval- uate Density and Hardness Properties of Resinous Wood of Agarwood (Aquilaria malaccensis). Wood Research 62(5): 683–690.
KARLINASARI L, PRATAMA NA, PURWANTO YA, TURJAMAN M. 2021. Evaluation of Agarwood (Aquilaria malaccenis) from Bintan Island Based on Indonesian Standard. Journal of Tropical Forest Sci- ence 33(4): 435–443.
KIAEI M, TAJIK M, VAYSI R. 2014. Chemical and bio- metrical properties of plum wood and its application in pulp and paper production. Ciencia y Tecnología 16(3):
313–322. DOI:10.4067/S0718-221X2014005000024 LEE SY, MOHAMED R. 2016. The origin and domesti- cation of Aquilaria, an important agarwood-producing genus. In: Agarwood, Tropical Forestry. Mohamed R ed. Springer Science + Business Media Singapore. DOI 10.1007/978-981-10-0833-7_1
LIM SC, NORDAHLIA AS, ABD. LATIF M, GAN KS, RAHIM S. 2016. Identification and properties of Ma- laysian Timbers. Malaysian Forest Records No. 53.
Forest Research Institute Malaysia, Kepong.
LIU XM, TAO TT, MENG XX, ZHANG WW, CHANG J, XU F. 2017. Cloning and expression analysis of a farnesyl diphosphate synthase (FPPS) gene from Cha- maemelum nobile. Not Bot Horti Agrobo Cluj-Na 45:
2. DOI: 10.15835/nbha45210858
NISHAD PM, CHEZIAN RM. 2013. Various colour spaces and colour space conversion algorithms. Journal of Global Research in Computer Science 4(1): 44–48.
NOVRIYANTI E, SANTOSA E, SYAFII W, TURJAMAN M, SITEPU IR. 2010. Antifungal activity of wood extract of Aquilaria crassna Pierre ex Lecomte against agarwood-inducing fungi, Fusrium solani. Journal of Forestry Research 7: 155–165.
NUGROHO WD, PUJIARTI R, TIYASA NP. 2018. Wood anatomical characteristics of agarwood-producing species (Aquilaria sp.) Wood Research 64(5): 759–768.
SAIKIA SN, GOSWAMI T, ALI F. 1997. Evaluation of pulp and paper making characteristics of certain fast-growing plants. Wood Sci Technol 31: 467–475.
SALEHI K. 2001. Study and determine the properties of chemi-mechanical pulping high yields from bagasse.
Wood and Paper Research No. 232. Research Institute of Forests and Rangelands.
SHARMA AK, DUTT D, UPADHYAYA JS, ROY TK.
2011. Anatomical, morphological and chemical characterization of Bambusa tulda, Dendrocalamus hamiltonii, Bambusa balcooa, Malocana baccifera, Bambusa arundinaceae, and Eucalyptus tereticornis.
Bioresources 6(4): 5062–5073.
SOEHARTONO T, MARDIASTUTI A. 1997. The cur- rent trade in gaharu in West Kalimantan. Jurnal Ilmiah Biodiversitas Indonesia 1(1).
SULAIMAN N, IDA IDAYU M, RAMLAN AZ, NUR FASHYA M, NOR FARAHIYAH AN, MAILINA J, NOR AZAH MA. 2015. Effects of extraction methods on yield and chemical compounds of gaharu (Aquilaria malaccensis). Journal of Tropical Forest Science 27(3):
413–419.
TAN CS, ISA NM, ISMAIL I, ZAINAL Z. 2019. Agar- wood induction: current developments and future perspectives. Front Plant Sci 10: 122. DOI: 10.3389/
fpls.2019.00122
[TAPPI] Technical Association of the Pulp and Paper Industry Standards. 1988. Wood extractives in etha- nol-benzene mixture. Atlanta, USA.
THE PLANT LIST. 2013. The Plant List: a working list of all plant species, Version 1.1. Retrieved on 26 Jan 2020 from http://www.theplantlist.org/
YIN Y, JIAO L, DONG M, JIANG X, ZHANG S. 2016.
Wood resources, identification, and utilization of agarwood in China. Retrieved from https://www.
researchgate.net/publication/303729493
ZHANG LX, LIU YY, WEI JH, YANG Y, ZHANG Z, HUANG JQ, CHEN HQ, LIU YJ. 2012. Production of high-quality agarwood in Aquilaria sinensis trees via whole-tree agarwood-induction technology. Chinese Chemical Letters 23: 727–730.
ZICH F, COMPTON J. 2002. The final frontier: towards sustainable management of Papua New Guinea’s agarwood resource.
ZOBEL BJ, VAN BUIJTENEN JP. 1989. Wood variation:
its causes and control. Berlin, Heidelberg, New York:
Springer-Verlag.
