Does Agarwood Always Improve with More Time?

Agarwood is fragrant wood formed by the accumulation of resin in a tree. When trees are deliberately wounded to induce agarwood formation, does waiting longer improve quality? In 2025, Ming Li and colleagues compared agarwood from cultivated “Qi-Nan” lines at six months, one year, and two years after inducing resin formation.

The researchers wanted to understand how cultivated line and formation time affect chemical components used to assess quality. Here, time refers to the interval between wounding a living tree and harvest, not to aging harvested fragrant wood in storage.

Comparing four cultivated lines at three time points

The study examined four graft-propagated clones of Aquilaria sinensis grown in Guangdong Province, China: YYZ, AS, RH, and XGY. A clone is a line propagated to retain the characteristics of its original individual. In the paper, Qi-Nan refers to cultivated material of this kind.

The researchers drilled holes into the trunks of healthy trees grown for three years to stimulate resin formation. Agarwood formation involves the tree’s defensive response to stimuli such as injury. Resin-rich wood was collected at 6, 12, and 24 months after treatment.

There were three replicates for each combination of four clones and three time points. Each replicate used material from five trees randomly selected from different locations. Ordinary A. sinensis agarwood and low-resin white wood were also examined for comparison.

Measuring “quality” with four chemical indicators

The indicators were the proportion of ethanol-extractable material, the compound agarotetrol, and two phenylethylchromones. Chromones are a group of compounds present in agarwood, treated in the paper as clues for evaluating aroma and quality.

First, dried, powdered wood was extracted with ethanol, and the mass of recovered material was divided by the original dry wood mass. This gives the extract proportion. Liquid chromatography combined with mass spectrometry was then used to examine the amounts of particular compounds.

“Quality” in this study is an assessment combining these chemical indicators. It is not a direct measurement of people’s comparisons of burning agarwood, market prices, or grades in the Japanese incense tradition. A high extract proportion is not the same as an aroma that everyone considers superior.

Three clones scored highest at two years

For YYZ, AS, and RH, the ethanol-extract proportion initially fell between six months and one year, then reached its highest value at two years. The two-year proportions all exceeded 46%. They did not simply increase steadily over time.

The patterns of increase and decrease in the two chromones also varied by clone and compound. Even so, in the overall assessment that combined the four weighted indicators, these three clones scored highest at 24 months among the three time points examined.

This overall score is a calculation that combines several components into a single measure. Because it depends on the indicators selected and how they are weighted, it is not a unique score representing every aspect of agarwood’s value.

XGY scored higher at one year

XGY, by contrast, followed a different course. Its ethanol-extract proportion increased from six months to one year, reaching 51.49% at one year, before decreasing at two years. Both chromones examined also peaked at one year and then decreased.

The combined chemical assessment likewise gave XGY a higher score at 12 months than at 24 months. Among all 12 conditions, XGY at 12 months ranked near the top, behind YYZ and AS at 24 months.

The authors suggest that this clone may reach a high chemical quality score in less time than the others. A major implication is the need to consider formation time clone by clone, rather than waiting the same number of years before harvesting all of them.

However, only three time points were examined: 6, 12, and 24 months. The study does not establish whether XGY’s true optimum is exactly 12 months, or what would happen at more closely spaced time points or beyond two years.

One component alone is not enough either

Agarotetrol is used in agarwood assessment, but its levels in the Qi-Nan samples were lower than in the ordinary agarwood comparison samples. By contrast, extract proportions and the two chromones were higher in Qi-Nan.

A material that scores highly on one indicator therefore does not necessarily score highly on another. One reason the authors assessed multiple components together is that the chemical characteristics of Qi-Nan are difficult to capture through the amount of a single substance.

The measurement method also has limitations. One of the two chromones was quantified using the calibration curve of the other, structurally similar compound rather than its own dedicated standard. The figures cannot be treated as an absolute quality benchmark that would be identical under any measurement method.

Why do accumulation patterns differ among clones?

The researchers also reported genetic differences among the four clones. Differences in internal tissue structure, capacity to supply precursors, or defensive responses could affect the rate and composition of resin accumulation.

Another possibility involves the relationship between fungi within the trees and defensive responses. Drawing on earlier studies, the authors discuss how changes in fungal communities during formation, or a decline in fungi as defensive compounds accumulate, might alter subsequent compound synthesis.

In addition, conversion of one chromone into another form could reduce the amount of a particular measured chromone without eliminating the resin as a whole. Such transformations are another possible explanation for lower values after a longer wait.

However, this comparison did not manipulate fungal changes, plant-hormone pathways, or the tissue structure of each clone to identify the causes. Why XGY reached a high score earlier remains a question for future mechanistic research.

Considering both clone and indicator when choosing harvest time

The results show that managing cultivated agarwood requires attention not only to formation time but also to the line being grown. The authors suggest that chemical measurements can inform clone selection and harvest planning, supporting Qi-Nan production and quality assessment.

However, the study was limited to one area of Guangdong, four clones, and one drilling-based induction method. The same rankings or time intervals cannot be applied to other environments, induction methods, or wild agarwood in general. The relationship to aroma during heating and to preferences, which matters to people using the fragrance, also needs separate investigation.

The research was supported by the Fundamental Research Funds of the Chinese Academy of Forestry. The authors declared no financial conflicts of interest or personal relationships that could have influenced the results.

Summary

The relationship between resin-formation time and chemical indicators was not the same across the four graft-grown Qi-Nan clones. Three clones scored highly at 24 months, while XGY did so at 12 months. The results did not show a uniform improvement with longer waiting.

The key is not to see agarwood production as a matter of time alone. Understanding how components are produced and transformed in each clone, then choosing harvest timing with indicators suited to the purpose, is important. The authors show that linking differences in genetic material with chemical assessment offers a way to make cultivated agarwood quality management more specific.

References

Li, M., Yang, Z., Hong, Z., Xu, D., Li, Z., & Wang, S. (2025). Effects of different clones and inducing time on agarwood quality in grafted Qi-Nan Aquilaria sinensis (Lour.) spreng. PLOS One, 20(7), e0327514. DOI: 10.1371/journal.pone.0327514. Full text. © 2025 Li et al. The original article is published under CC BY.