Chemistry in Action: How Chemistry Facilitates the Survival of the Fir Tree

Keywords: Chemical properties, cellulose, oleoresin, pH, intermolecular forces, metabolites, symbiosis, Fir tree

Abstract

This paper examines key members of the highly varying chemical compounds found in fir trees and the multitude of solutions they provide. The structure of the tree’s cell walls is provided by the polymer’s cellulose and lignin. These polymers have very different chemical makeups, bonding patterns, hydrophilicity, and rigidity. The cell walls use these two materials to form a load-bearing network that is strong and resilient. Fir trees produce several secondary metabolites, most notably phenolic compounds and terpenoids, which are multifunctional. These compounds provide antioxidative protection against reactive oxygen species to antimicrobial and antifungal protection from infection. While they’re integral to the survival of fir trees, their production is carefully managed for metabolic efficiency. Derivatives of terpenoids are also used for an integral defense mechanism: resin. Through self-sealing wounds and releasing toxic chemicals, resin protects the tree from infections and insects. In addition, fir trees regulate soil pH for optimal acidity through leaf litter. A symbiotic relationship with fungi releases organic acids from needles for better nutrient absorption. The combination of the beneficial uses of these compounds and strategies with metabolic efficiency is the key to the survival of fir trees.

Introduction

As seen in the paper Wonders of Forest Giants: Physical Properties Governing Fir Trees, fir trees are a tree species that can live for hundreds of years and reach impressive heights, towering over all other living organisms in the surrounding area. However, despite being very large, the survival mechanisms, structural components, and way of existence are governed by tiny molecules, composed primarily of carbon, hydrogen, and oxygen. This may surprise; however, carbon, hydrogen and oxygen are essential to all life forms on earth (Remick & Helmann, 2023). For fir trees, these tiny atoms make up molecules many orders of magnitude over their own size, resulting in a functional, cohesive living organism which can sustain a prosperous existence. Fir wood is composed of cellulose, a polysaccharide, and lignin, a polyphenol. Together, they make up the primary source of strength in the fir tree's structure (Viera Kučerová et al., 2019). The molecular structure of cellulose and lignin allows for water to interact with each molecule differently, resulting in different advantages. For example, cellulose has numerous OH groups, allowing it to interact and retain ample amounts of water, thanks to intermolecular forces like hydrogen bonding (O’Neill et al., 2017). However, lignin, on the other hand, interacts very differently with water because it is hydrophilic. This makes its interaction with water an opposite to that of cellulose. On top of lignin and cellulose, phenolic compounds, characterized by the presence of phenol groups, are the source of a lot of the smell we associate with fir trees. However, they also have important antioxidative effects, which prevent damage to the cell by being oxidized (Xu & Wang, 2025). Additionally, terpenoids are another molecule that we find present in fir trees. Terpenoids are characterized by an isoprene skeleton, and due to this large nonpolar structure, many essential oils are derived from them (Kim et al., 2024). For the fir tree, protecting itself from outside threats is also achieved thanks to various chemical processes, such as the biosynthesis of oleoresin. Oleoresin, which is composed of terpenoids, a mixture of turpentine and resin, is what fir trees produce to seal up any wounds they may have sustained. Due to the oxidative and reactive properties of turpentine and resin, once in contact with air, the turpentine will evaporate, leaving the resin to oxidize and develop a hard shell, creating the protective defense the fir tree needs to protect itself (Phillips & Croteau, 1999). Furthermore, fir trees utilize their dead needles, which litter the ground to decrease the pH of the soil around its base, which allows the breakdown of vital nutrients thanks to symbiotic help from fungi (Virzo De Santo et al., 2002). Throughout this paper, we will further explore how fir trees use chemistry to not only survive but also prosper in the wild.

Cellulose and Lignin

Abies wood is a complex bio-composite consisting of two main biopolymers: cellulose and lignin. In silver fir (Abies alba), cellulose consists of 40-49% of the wood's dry mass, and lignin accounts for 27-30% (Viera Kučerová et al., 2019). These biopolymers form a structure in the cell walls, where cellulose fibres are embedded in a lignin-hemicellulose matrix. The major structural differences between cellulose and lignin are outlined in the table below.

The chemical composition of polymers, as outlined in table 1, is what gives wood remarkable strength and moisture-specific responsiveness. Cellulose is a linear polysaccharide composed of β-D-glucopyranose units linked by β (1-4) glycosidic bonds. Each unit is rotated 180 degrees relative to neighbouring units; the pair is called cellobiose. The result is a flat ribbon-like polymer chain; cellulose is highly polar due to its three OH groups and forms an extensive network of hydrogen bonds as seen in Figure 2. The degree of polymerization can reach thousands.

Cellulose chains further aggregate to form an organized bundle called a microfibril, all held together by a dense network of intrachain hydrogen bonds. Each microfibril contains cellulose molecules running parallel to one another. Glucose ribbons within the microfibril are organized into monoclinic or triclinic crystal structures (Yao et al., 2016). Interchain hydrogen bonds link OH groups of one chain to O groups in adjacent chains. Figure 1 below shows how the cellulose binds to one another.

Bravais lattices describe potential, distinct, three-dimensional arrangements of points in a crystal, classified into 14 types based on symmetry and geometry. Among these lattices, the triclinic and monoclinic systems exhibit the lowest degrees of symmetry.

Triclinic: all axes and angles are unequal, with no right angles-the most asymmetric lattice type. Native cellulose is triclinic.

Monoclinic: two axes are inclined while one is perpendicular, featuring a single mirror plane. Regenerated cellulose is monoclinic.

Fig. 1. Cellulose in an inter-intra Hydrogen-bonded network with two cellulose monomers (https://vitroid.github.io/water-science/water/cellulose.html).

The network holds chains together in a sheet-like conformation, with hydrophobic faces rich in CH groups stacking, resulting in high crystallinity and tensile strength. However, cellulose is not entirely crystalline. In these microfibrils, amorphous regions exist where the molecular ordering is disrupted. These regions occur at chain ends or where H-bonds are disrupted. Amorphous regions are more accessible to water and enzymes, facilitating enzymatic hydrolysis and allowing crystallites to be partially hydrolyzed (Michael Ioelovich, 2024). During self-assembly, cellulose chains spontaneously align and aggregate due to extensive intermolecular hydrogen bonding and van der Waals interactions. Linearity and stiffness are provided by β-(1→4)-linked D-glucose to allow compressed chain packing in parallel or antiparallel modes. Molecular alignment results in elementary fibrils, which aggregate to form microfibrils and fibres of larger dimensions according to thermodynamic favourability. Hydroxyl group alignment results in hydrogen-bonding networks that stabilize crystalline triclinic and monoclinic lattice structures.

Lignin, the second major biopolymer, is aromatic and results from the coupling of phenylpropanoid monomers. Abies are softwoods, which means lignin is built mainly from guaiacyl units derived from coniferyl alcohol and a small proportion of p-hydroxyphenyl units instead of syringyl units, which are found in hardwoods (Viera Kučerová et al., 2019). From this, we can extrapolate that the difference between hardwoods and softwoods is the proportion of various lignin units. Unlike cellulose, lignin, and hemicellulose, form a complex nonlinear network which occurs through different bond linkages, the most common being the Beta-O-4 ether linkage. The comparison of linear to non-linear networks in these molecules is observed in Figure 2.

Fig. 2. Molecular diagram depicting the linear network of cellulose and non-linear networks of lignin and hemicellulose, and how they compose the plant cell wall (Nazari et al., 2021)

Lignin's structure can be interpreted as a random cross-linked polymeric network. It is a random coil of aromatic rings connected by aliphatic linkages; it is entirely amorphous and does not form ordered crystals. Lignin’s synergistic effects thus result in a stronger summation of properties then the individual strength. This assembly creates a composite system in which cellulose serves as a reinforcing phase and lignin as a load-distributing matrix, together vesting rigidity and resilience.

Fig. 3. Chemical structure of cellulose, which the fir tree uses to amplify its strength and rigidity. Carbon atoms are depicted in black, oxygen in red, and hydrogen in white. (https://commons.wikimedia.org/wiki/File:Cellulose-Ibeta-from-xtal-2002-3D-balls.png).

Within a biological context, the self-assembly process illustrates an evolutionary design solution; molecular-level architecture optimized by trees to balance strength, flexibility, and resilience. Crystalline regions provide mechanical stability and compression resistance, while amorphous areas provide flexibility and water accessibility, enabling controlled deformation and adaptive growth. Cellulose self-assembly is a natural blueprint for durable, responsive materials synthesized by chemical processes.

Water-binding properties

Water, being a polar molecule, interacts differently with cellulose and lignin. Cellulose is hygroscopic: its numerous OH groups form excess H bonds with water molecules. Water access, however, depends on cellulose morphology. Due to the crystalline structure, the H bonding sites are engaged in inter-chain bonding, and the tight packing leaves little room; liquid water, therefore, is unable to penetrate the crystalline core (Miyamoto et al., 2014). The amorphous regions in the cellulose and the surfaces of microfibrils are the only parts capable of absorbing water, this is observed in Figure 4.

Fig. 4. Crystalline region (in red) shown alongside amorphous region (in blue). Free OH in the amorphous region allow bonding to water. (Nathawat POOPAKDEE & Warut THAMMAWICHAI, 2024)

Thus, two classes of water arise in relation to cellulose. Bound water is tightly associated with cellulose and can withstand freezing at subzero temperatures, while free water, also called capillary water, is held in the spaces between microfibers. Bound water forms a layer on the cellulose surface, plasticizing it. Above 220K (-53.15 ), the water can diffuse, but below that, it forms a rigid glass-like layer. Given the habitat of fir trees, water bound by cellulose rarely freezes since temperatures below 220K are highly uncommon in the mainland United States of America and parts of Canada where fir trees are native (Climate Data, n.d.). Around 260K (-13.15 ) the water in the cell pores becomes mobile, and when saturated, the bound water content is quite significant. Dry amorphous cellulose can take up to 30% of its weight, softening and swelling. The residual moisture content after air-drying is due to bound water. In microcrystalline cellulose, far less water is absorbed as it is confined to the surface. Higher crystallinity correlates with lower moisture content, as fewer OH groups can bind to water. Experimentally, pure crystalline cellulose remains stable when exposed to water until external layers are saturated. Amorphous cellulose, when exposed to water, rapidly gains weight and flexibility upon imbibing water. Amorphous fractions and defects in microfibrils are the primary source of water uptake (O’Neill et al., 2017). For fir tree these properties are quite important since it allow them to be resistant to drought by having internal water stores as well as being resistant to the effects of freezing water during the colder months of the year.

Lignin is much less hydrophilic than cellulose; it was historically considered hydrophobic because it lacks abundant hydroxyl groups. Lignin will absorb some moisture due to a few polar sites that physically entrap water in its pores, but it does not form extensive hydrogen bonds with water. As a result, the water in lignin tissue resides in the matrix of hemicelluloses and amorphous cellulose. Lignin with hemicellulose (a more hygroscopic compound than cellulose) swells readily with water, forming a gel-like matrix. In silver fir, when cell walls absorb water, it is observed that hemicellulose and lignin are the main areas of water storage.

Water molecules are attracted into the lignin-hemicellulose matrix, turning it from a stiff, dry state to a swollen state. This exerts an expansive force, pushing microfibrils apart. Hydration of the polar groups lowers the system's enthalpy but increases the volume (Bertinetti et al., 2016). Hydration forces drive swelling, and restraining forces, such as covalent bonds, resist swelling. Together, this contributes to the structural integrity of the fir tree while also ensuring that the tree is saturated with enough water to sustain growth.

Secondary Metabolites

Fir trees, as well as all other plants, produce some organic molecules which are not directly involved with growth. These secondary metabolites are nonetheless essential for the survival of the plant, with a diverse range of functions that manage the plant’s interactions with the environment. In the genus Abies, around 327 secondary metabolites have been identified, with a majority falling under the two major categories of phenolic compounds and terpenoids (Kim & Park, 2018). These two groups of compounds in fir trees will be explored, looking at their antioxidative and antimicrobial effects. Outside of these groups, fir trees also possess a smaller variety of other organic compounds. For example, see Figure 5 for major components found in Abies koreana (Korean fir). Compounds outside of the major groups include steroids and maltol, which is used as a flavor enhancer.

Fig. 5. Major metabolites found in Abies koreana grouped by compound type. Adapted from (Kim & Park, 2018).

Phenolic compounds

Phenolic compounds are characterized by the presence of a phenol group, which is an aromatic ring (a carbon ring with delocalized electrons) with hydroxyl (OH) groups. Figure 6 shows the basic classification of phenolic compounds. Monomeric phenolic compounds include flavonoids, which have two aromatic rings connected by a three-carbon chain, and non-flavonoids, which comprise simple phenols and stilbenes.

Fig. 6. Classification of phenolic compounds with representative examples (Xu & Wang, 2025).

Polymeric phenolic compounds include hydrolysable tannins, which can be hydrolyzed to form acids, condensed tannins, and complex tannins, composed of hydrolysable and condensed subunits. Lignin, a major component of cell walls as mentioned previously, as well as lignans, which have a lower molecular weight, are derived from phenolic compounds (Xu & Wang, 2025).

Phenols have several different functions, one of the most important being their antioxidative effects. When reactive oxygen species, such as superoxide, over accumulate, they can oxidize membranes, nucleic acids, and proteins, causing severe damage to cells (Xu & Wang, 2025). Many phenols are considered antioxidants due to their ability to prevent damage to the cell by being oxidized preferentially. The hydroxyl group within a phenol group is highly susceptible to oxidation, which reduces the reactive oxygen species and renders it harmless (Latos-Brozio et al., 2021).

In addition, cell walls that are saturated with phenolic compounds restrict water movement, essential during drought conditions. Some phenolic compounds also have antibacterial effects by disrupting the cell membrane of harmful bacteria. Phenolic compounds can act as signalling molecules to trigger the plant’s defences in various signalling pathways (Xu & Wang, 2025). It has also been found that phenolic compounds present in the leaves of Abies nephrolepis (Khingan fir) play a role in the protection of gap junction intracellular communication, where neighbouring cells exchange compounds through membrane channels. Khingan needle extract and the catechin epigallocatechin gallate can prevent the inhibition of this communication by hydrogen peroxide, but the effect was not seen with isolated antioxidative substances. This could indicate that the phenolic compounds have another mechanism to protect the tree (Lee et al., 2004). Clearly, the effects of phenols are far-reaching.

The synthesis of phenolic compounds is flexible – phenols accumulate in response to water and salt stress when their presence is most essential and can vary from tissue to tissue (Xu & Wang, 2025). The wood of Abies alba (silver fir) contains lignans, phenolic acids, and flavonoids. Figure 7 shows the different types of wood present. The compounds are found in higher concentrations towards the surface of the wood —sapwood —than in the centre —heartwood —where they are better positioned to inhibit the growth of harmful fungi (Vek et al., 2021).

Fig. 7. Diagrams labelled with wood regions of a tree trunk. (a) Horizontal cross section showing heartwood and sapwood regions. (b) Vertical cross section showing heartwood, sapwood, branchwood, and knotwood regions (Vek et al., 2021).

The phenolic content of the bark of the silver fir is largely comprised of tannins, which make the bark taste less appetizing to insects and animals which prey on the trees. The distribution of tannins is not uniform, but increases towards the crown of the tree, likely due to the greater ability to photosynthesize required for the pathway for tannin synthesis (Brennan et al., 2020). The phenolic content of wood also decreases along the length of branches as they get further from the trunk, where damage is less detrimental to the survival of the tree (Schoss et al., 2022). Cones contain a significant amount of catechins, as well as terpenoids, with significant antioxidative effects. These effects were found to be stronger in the Korean fir, a member of the genus Abies, compared to the Douglas fir, which is not (Latos-Brozio et al., 2021). Cones house the reproductive organs of the tree, making their safety a top priority.

In summary, the synthesis pathways of phenolic compounds find a delicate balance between protection and conservative metabolism to maximize the propagation of the species (Xu & Wang, 2025). The phenolic compounds are produced according to ability, with more high density where photosynthesis is more efficient, use, with antifungal compounds and tannins found near the surface of the bark, and importance of protection, with the trunk and reproductive organs being most important for the propagation of the species.

Terpenoids

Terpenoids are a group of organic molecules characterized by an isoprene skeleton, which can be seen in Figure 8. They are generally classified by the number of 5-carbon units (Abdallah & Quax, 2017).

Fig. 8. Classification of terpenoids (Abdallah & Quax, 2017).

Essential oils derived from fir trees are primarily composed of terpenoids since they are largely nonpolar and therefore lipid soluble (Kim et al., 2024). Phenolic compounds, by contrast, are largely water-soluble attributable to the presence of a polar OH group. Essential oils extracted have been used for a wide variety of medicinal effects. For example, it has been reported that the essential oil extracted from the needles of Abies holophylla (Manchurian fir) inhibits respiratory bacteria. The main substances in this essential oil are the terpenoids D-Limonene, 3-Carene, α-Pinene, and β-Bisabolene, with relative abundances varying with time of year. The compounds in the essential oil have been found to have strong antioxidative effects (Kim et al., 2024), however, evidence shows little to no antibacterial effects from the terpenoids in fir (Yang et al., 2009). This suggests that terpenoids support the antioxidant role of phenolic compounds, but phenolic compounds are more active in terms of fighting infection.

Outside of phenols and terpenoids, vitamin C (ascorbic acid) and vitamin E (⍺-tocopherol) are also important antioxidants. While both compounds can function as antioxidants, they are most effective when present in a ratio of 10:1 to 15:1 vitamin C to vitamin E, with vitamin C being used to restore vitamin E after it is oxidized (Kunert & Ederer, 1985). Vitamin C is significantly present in fir needles, though the amount is not especially high compared to other conifers (Ain Raal et al., 2018). As fir needles age, the amount of vitamin E increases faster than the amount of vitamin C, an imbalance which leads to more damage from free radicals (Kunert & Ederer, 1985).

Resin as a Defense Mechanism

For all living organisms, nature is an unpredictable and dangerous place where anything can occur. For trees in particular, strong storms, insects, fungi and more can have a detrimental effect on their well-being. Unfortunately for fir trees, any damage that they sustain must be self-repaired. For fir trees, this presents a challenge since even the smallest of wounds can act as an entry for harmful bacteria and insects. Thus, to solve this issue, fir trees utilize a natural chemical product known as resin. Resin is characterized by not being soluble in water, hardening when exposed to air and being a product that does not play a fundamental role in the general functionality of the tree outside of protection (https://www.fs.usda.gov/wildflowers/ethnobotany/resins.shtml). Given the versatile properties of resin, it plays numerous roles for the fir tree, helping it to protect itself from outside threats by acting as a self-sealing healing tool. In Figure 9, many possibly damaged fir cones have resin dripping from them, thus showing how resin acts as a sealant to external wounds.

Fig. 9. Fir cones of the Spanish fir with resin coming out of them (https://www.treeguideuk.co.uk/spruce-and-fir-tree-cones).

To fully understand why resin is so beneficial to fir trees, it is essential to understand the chemistry that leads to its eventual properties. Resin, as we see in Figure 7, on the fir cones, is not what fir trees directly produce. Rather, resin is the result of evaporation and polymerization. Oleoresin is what fir trees produce and is what initially comes out of the tree. It is a mixture of terpenoids, which consist of turpentine and resin. Turpentine is a mixture of monoterpene and sesquiterpene, and resin is composed of diterpene (Phillips & Croteau, 1999). Figure 10 shows the different molecules that make up monoterpene, sesquiterpene and resin.

Fig. 10. Monoterpenes , sesquiterpenes , and diterpenes , which comprises oleoresin (Phillips & Croteau, 1999).

Once exposed to the atmosphere, turpentine, which is more volatile, evaporates, leaving behind the diterpene resin acids, which then oxidatively polymerize. The polymerization of the diterpene resin is what makes the resin develop a hardened outer shell, which seals the injured area of the tree. This harder outer shell can trap invading insects and microbial pathogens, preventing them from spreading throughout larger parts of the tree. This process of only hardening once in contact with air allows the wound to be internally sealed by the viscous mixture and allows any damage to the healed wound to be resealed should the already oxidized layer be punctured. By design, this allows the fir tree to maximize its ability to seal off any damage. Contrary to other conifer trees, which also employ resin to prevent invasion, fir trees store relatively small amounts of resin in little cyst-like resin blisters and respond to being attacked by producing oleoresin in adjacent tissues to the area of attack. This form of defence has advantages in that it does not require transport of oleoresin from one part of the tree to another when being attacked, allowing for a more efficient local defence. The turpentine components of oleoresin, which are needed by the tree to produce resin, can be utilized by bark beetles to cause more harm than good to the tree. Certain bark beetle species, like the Western Balsam Bark beetle, can convert turpentine components to oxygenated derivatives, which are then used by the beetles as sex attractants to signal a large mating event (Ministry of Forests, 2025). However, these monoterpene compounds that the beetles utilize to attract more beetles are actually toxic to the beetles, presenting an interesting conundrum for both the beetle and the fir tree (Phillips & Croteau, 1999).

Biosynthesis of Oleoresin

Terpenoid biosynthesis is a very important component in producing oleoresin. In the plastids of higher plants, the pyruvate-glyceraldehyde-3-phosphate pathway initiates the diversion of carbohydrate metabolism to terpenoid biosynthesis. In Figure 11, the pyruvate-glyceraldehyde-3-phosphate pathway is shown, whereby after the production of isopentenyl diphosphate (IPP) and then dimethyl diphosphate (DMAPP) by isomerization of IPP, a series of condensation reactions occur, which involve either the addition of one, two or three IPP units to DMAPP. The addition of one IPP unit yields the precursor to monoterpenes: geranyl diphosphate (GPP), the addition of two IPP units yields the precursor to sesquiterpenes: farnesyl diphosphate FPP, and the addition of three units of IPP precursor to diterpenes: anylgeranyl diphosphate (GGPP).

Fig. 11. Pathway summarization of the biosynthesis of terpenes in higher plants (Phillips & Croteau, 1999).

Following the production of GPP, FPP and GGPP, the desired end products are generated through terpenoid synthases, which use enzymes that operate through electrophilic reaction mechanisms which employ certain organic cofactors to generate electrophilic species (Phillips & Croteau, 1999).

The production of the resin acids utilizes the pathway set up to produce monoterpenes, sesquiterpenes and diterpenes by utilizing GGPP. The first step in the formation of resin acid is the protonation of the terminal double bond of GGPP, and the second step is the ionization of the formed diphosphate ester. This is summarized in Figure 12, where there is an illustration of the formation of the resin acids.

Fig. 12. Process by which resin acids are formed following the production of GGPP by the pyruvate-glyceraldehyde-3-phosphate pathway (Phillips & Croteau, 1999).

Through these various chemical reactions, the fir tree can produce the necessary components it needs to produce oleoresin, which then allows it to seal off any wounds or protect against infection from insects or fungi. Without these chemical reactions, fir trees would fall victim to their surroundings and not be able to allow themselves the long life that is typical for the species.

The Soil Chemistry of Fir Trees

One of the most interesting components of fir trees is the very specific nature of the soil they grow in. To prosper, these trees require soil with a rather acidic pH. The reason for this is that a lower acidity in soil increases the availability of the micronutrients in soil. An interesting note is that phosphorus is also a very necessary nutrient absorbed by fir tree roots; however, the most available phosphate compound in soil is dihydrogen phosphate (H₂PO₄⁻), which is typically only soluble with a soil pH of 6-7.5 (USDA, 2014). Given the tree’s soil with a low pH, phosphorus is made available for intake from the roots with the assistance of fungi. (Van Sundert et al., 2018). Essentially, when phosphorus binds to ions and becomes insoluble at the low pH, the fungi help break down this fixation to the ions and makes phosphorus soluble.

Given the importance of soil acidity and the availability of nutrients in the soil, fir trees require a way to maintain this condition. Hence, fir trees utilize what’s called “needle littering” (Zhang et al., 2025). A defining feature of fir trees is their needle-like leaves that offer many photosynthetic and structural benefits. However, these leaves also benefit the tree once they have fallen from its branches. They collect at the bottom of the tree, forming an organic layer at the tree’s base. As this layer is decomposed, organic acids descend into the soil. This not only results in a decreased pH of the soil, but it also adds absorbable molecules to soil. As seen in Figure 13 many beneficial nutrients are made available, namely minerals like Zinc (Zn) and Copper (Cu). While some potentially toxic substances like Lead (Pb) and Cadmium (Cd) are produced, this detriment is outweighed by the benefit of the lower pH and essential nutrients.

Fig. 13. This diagram depicts the give and take nature of the leaf litter below the tree. It lowers the soil’s pH and offers helpful minerals (Zn, Cu), while producing a few unnecessary minerals (Pb, Cd) as well (Zhang et al., 2025).

For this organic layer of littered needles to properly alter the fir tree’s soil chemistry and provide the necessary nutrients, it cannot simply decompose itself. Rather, this process relies on the symbiotic help of fungi that break down this layer over time. In essence, the fungi found on the litter layer undergo a process called mycelium growth (Virzo De Santo et al., 2002). In this process, long fungal filaments called hyphae are grown from the fungus and reach down into the soil, as seen in Figure 14.

Fig. 14. This image depicts the mycelium growth of the hyphae from the fungus below the tree. As depicted, the hyphae overlap with the tree roots to increase absorption of nutrients (Holewinski, 2025).

These extensions aim to help break down organic substances, primarily nitrogen- and phosphorus-containing compounds, which are absorbed by the fir tree’s roots as nutrients. As mentioned above, these fungi help make the phosphorus (from H₂PO₄⁻) soluble and thus absorbable. More specifically, the primary class of fungi found in the litter layer of fir trees are called hyphomycetes (Virzo De Santo et al., 2002). These fungi are the type that grow the fastest on the organic layer then die off. While some trees like pines experience growth of other fungi, such as basidiomycetes, fir trees rely primarily on these rapid hyphomycetes (Figure 15). This fungal relationship is symbiotic, seeing as the tree benefits from the litter decomposition and provides a suitable growth environment for the fungus.

Fig. 15. Graphs depicting fungal species growing in four different trees. Plot A highlights the high hyphomycete presence in fir trees (A. Alba) early on. Plot B also shows the early growth of hyphomycetes, primarily in firs. Plots C and D portray the growth of basidiomycetes and ascomycetes, respectively, which are present after longer time periods in other trees, primarily pines (Virzo De Santo et al., 2002).

Hence, the soil chemistry is maintained via a series of subsequent steps that are intended for the tree’s survival. By shedding the needle leaves from the fir branches, the tree is able to maintain an organic layer of needle litter at its base, which allows for a decrease in the soil’s pH along with the addition of important minerals. This acidic soil is more suitable for the desired fungi, namely hyphomycetes, and these fungi extend their hyphae into the soil to offer the tree more nutrients, which are necessary for survival.

Conclusion

From a chemical standpoint, fir trees have many intricate design solutions that allow them to grow and prosper. Regarding its structural chemistry, the tree utilizes compounds such as cellulose and lignin to distribute the load of the tree, increasing rigidity. Additionally, both compounds are essential for water retention. Cellulose and lignin utilize biopolymer interactions to allow fir trees to retain large amounts of water during droughts while also ensuring that water in the tree does not freeze during the coldest months. For the fir tree, this is very useful since it allows them to combat different weather events regardless of how extreme they are. Also, since cellulose can retain water, it keeps the wood flexible, decreasing stiffness. Lignin, for its part, acts as a water barrier to stop over-swelling of the tree, ensuring that an equilibrium of water saturation is achieved, maintaining an ideal level of flexibility. Moreover, it was determined that fir trees use other chemical attributes, namely secondary metabolites, for needs outside of growth. For instance, they use phenolic compounds to prevent damage from oxygen species and droughts, and their terpenoids serve as a source of antioxidative effects for the tree. To protect itself from exterior threats like beetles and fungi, fir trees produce oleoresin. This chemical allows for the tree to seal external and internal wounds throughout the tree by having turpentine evaporate from Oleoresin, leaving resin to create a hard layer by oxidative polymerization. By having a solution to external wounds, fir trees can survive external wounds and combat large mating events by external organisms. Finally, the design advantages of the fir tree’s soil chemistry were observed. As described, the tree’s fallen needles leave form layer at the tree’s base, which acidifies the soil to the tree’s needed conditions and invites fungi to grow hyphae for further absorption of beneficial nutrients. Without fungi, the fir tree would not be able to extract the same amount of nutrients and minerals from the soil, which are essential for growth. If it were not for many of these advantageous design solutions in the tree’s chemistry, it would lack many of its most important survival mechanisms. Given the amount of nutrients and protection from the environment required of this tree, this design solutions are critical for the tree’s well-being.