A Big Tree Made of Tiny Interactions: A Look into the Chemistry of Sequoia Trees

Keywords: sequoia, chemistry, fungi, oil, bark, roots, serotinous cones, fire resistance

Abstract

Although sequoia trees are among the largest trees in the world, they have evolved to interact and solve problems on small scales. This essay presents how the sequoia deals with certain problems using chemistry. To maintain a stable soil composition, the sequoia’s fallen needles and cones are rich in calcium ions, which serve to maintain nutrients and soil structure. Sequoia trees also form relationships with various species of fungi. In the tree’s roots, fungal networks increase the sequoia’s ability to absorb nutrients, while the tree provides its helper with sugars. Relationships with fungi are also present in sequoia foliage where the tree uses chemical compounds in its oil to control the population of fungi. In addition, the chemical properties of the sequoia’s bark and wood make the tree resistant to compressive forces, fires, and insects. A relatively high amount of lignin, a molecule found in wood, allows the sequoia to better withstand compressive forces. The lignin along with other compounds are also used to deter insect attacks. Meanwhile, a high concentration of tannin in the tree’s bark gives the sequoia increased fire resistance. The serotinous cones of the sequoia tree store a crystalline substance, which allows preservation of the seeds while also inhibiting germination. Thus, the sequoia tree has adapted to its environment by employing a variety of solutions at a cellular and chemical level.

Introduction

Sequoia trees have had over 200 million years to evolve to their immense size, lifespan, and durability. And with the entire populations of both the giant sequoia and the coast redwood being confined to the state of California, their survival depends on how well each species can withstand their specific climates. For the coast redwoods, which, as its name suggests, lives on the Californian coast, that entails calm, yet cool and foggy weather conditions. Meanwhile, the giant sequoia learned to take advantage of their habitat’s dry and stormy climate in the center of California, which often leads to intense droughts and forest fires. Our last paper discussed the physics (see Sequoia Physics) behind the sequoia tree’s mechanisms for survival. This paper follows up by exploring the chemistry that drives those same mechanisms. The first topic discussed will be the big tree’s approaches to fungi regulation and defense against insect invaders, including an analysis of the sequoia’s oils’ composition. The next topic discussed is the big tree’s bark composition, followed by serotinous cones, its soil’s microbial communities, its heartwood components and terpenoid volatiles.

Soil Composition

The Sierra Nevada’s fluctuating rain patterns can pose a unique danger to the giant sequoia population that inhabits this mountain range. Notably, periods of intense rainfall and alternatively prolonged droughts cause major fluctuations in soil chemistry and structure. During periods of high rainfall, the increased percolation of water can lead to wetter and more acidic soils, which in turn promotes the toxic solubilization of metals such as iron or manganese (Zinke & Stangenberger, 1994). Thus, to buffer these chemical swings and maintain a stable soil environment throughout the rain cycles, the sequoiadendron will engage in a remarkable form of pedological management through its litter deposition. The fallen needles, bark and cones, which are especially rich in the base cation Ca²⁺ (see Table 1.), result in an increased extractable calcium level in the upper mineral soil (Carey et al., 2020).

Table 1. Total elemental weight (in grams) in fallen old-growth sequoiadendron parts at Whitaker Forest. (Zinke & Stangenberger, 1994).

Note that among all elements, calcium exhibits a remarkably elevated concentration, making up 46.53% of the entire tree composition.

This continuous input of calcium from the sequoia litter increases the soil’s base concentration and subsequently its pH, which functions as a method of effectively neutralizing the acidity generated in wetter years. In doing so, the giant sequoia is a more chemically balanced microsite that resists both acidification and the consequent release of toxic ions. Additionally, these elevated calcium levels allow the formation of calcium carbonates that immobilize nutrients in mineral form (Zinke & Stangenberger, 1994). This process acts as a safeguard against nutrient loss, conserving them during periods of high precipitation, where leaching would otherwise be severe. Furthermore, the presence of calcium ions contributes directly to the physical organization of the soil matrix. Calcium serves as a bridging agent between negatively charged clay particles and humic acids, encouraging the formation of aggregates which improve soil structure and porosity (Allison et al., 2007). This resulting aggregation is essential for improving aeration and allowing rainwater to infiltrate more efficiently through the upper horizons as opposed to running off the surface. This is especially critical for maintaining moisture availability in coarse drought prone soils above the sequoia belt (Zinke & Stangenberger, 1994).

Through these combined effects, the sequoiadendron effectively engineers a soil environment that is simultaneously buffered against chemical instability and optimized for water and nutrient retention.

Fungi-Root Symbiosis

While this calcium enriched soil created by the giant sequoias' own litter plays an important role in maintaining a hospitable environment, it also introduces a new physiological challenge. In order to maintain its large size, the giant sequoia requires a massive nutrient intake. However, the high calcium content and pH present in the sequoiadendrons’ local soil, allow for very little zinc and notably phosphorous solubility (Carey et al., 2020). To overcome this limitation, the sequoiadendron relies on an intricate biological partnership with the arbuscular mycorrhizal fungi (AMF), a symbiosis that effectively extends the functional range of the tree root system into the surrounding soil matrix (Carey et al., 2020).

Within this association, the fungal symbiote forms unique, tree-like structures known as arbuscules inside the cortical cells of the giant sequoia’s fine roots (Fig. 1) (Cargill et al., 2025). These finely branched, intracellular networks dramatically increase the surface area available for nutrient exchange between the tree and the fungus. At the cellular interface, the arbuscular trunk (AT) resides within the peri-arbuscular membrane (PAM) which acts as an expansion of the plant plasma membrane, additionally containing shared protein markers with the AT.

Fig. 1. Structure of arbuscule within a plant root cortical cell. The arbuscule consists of a main trunk (1) that forms the base of the fungal structure and is enveloped by the peri-arbuscular membrane (PAM) (2). Between the PAM and the fungal hyphae lies the peri-arbuscular space (PAS) (3), an apoplastic compartment which mediates nutrient and signal exchange between the symbionts. The final hyphal branches (4) are surrounded by the branch domain of the PAM, where the phosphate transport proteins reside. (Cargill et al., 2025).

Communication between these partners begins when the fungus releases signaling molecules such as chitooligosaccharides, which are partially hydrolyzed products of chitin. They enter the PAM and are recognized by plasma membrane localized receptors on the tree side, called symbiosis receptor kinase (SYMRK). This interaction will trigger a cascade of ion fluxes, opening both the potassium channels DM1 and calcium channels CNGCN15 to induce peri-nuclear calcium oscillations. These oscillations subsequently serve as primary intracellular signals that activate key enzymes like calcium and calmodulin-dependent kinase (CCaMK). Once activated, CCaMK will phosphorylate the transcription factor CYCLOPS, consequently activating RAM-1 and other GRAS-domain regulators to drive the expressions of genes required for nutrient exchange and arbuscule development, as seen in Fig 2. (Luginbuehl & Oldroyd, 2017)

Fig. 2. Signaling network regulating arbuscular mycorrhizal symbiosis in plant root cells. (Luginbuehl & Oldroyd, 2017).

In exchange for this highly regulated access to nutrients, the fungus receives a continuous supply of sugars, such as photosynthate, produced by the sequoia’s vast canopy. In return, the AMF, attached to the roots of its host plant, will extend its hyphae far beyond the depletion zone of the root system, penetrating soil microhabitats where phosphorous remains soluble or biologically available (Molina, 2003). Moreover, this fungus possesses a saprophytic ability, secreting specialized enzymes that can break down complex organic structures to release bound phosphorous and nitrogen, which are otherwise completely inaccessible to the roots. (Molina, 2003). However, since AMF is not as effective as true saprotrophs like penicillin or Trichoderma, it must instead make use of phosphate-solubilizing bacteria (PSB). Functioning as a sort of “fungal highway”, the AMF physically carries PSB to isolated organic-P patches. The bacteria migrate within a water film coating the hyphal surface, where the hyphal exudates glucose to provide the energy needed for bacterial chemotaxis and proliferation. At the patch, PSB will express alkaline phosphatase genes that hydrolyze organic phosphates such as phytate into inorganic phosphate which the plant is able to process (Jiang et al., 2021). Once these nutrients are transferred back to the peri-arbuscular space, plant transporters such as MtPT4 will bring them to the root symplast where they can be delivered to other parts of the plant (Luginbuehl & Oldroyd, 2017).

This represents an elegant dual solution to resource management. By working with soil microbial communities, the giant sequoia can gain the benefit of both alkalinizing the environment around it and retaining the ability to access nutrients from long distance unmodified soil.

Relationship Between Foliage Fungi and Sequoia Oil

Fungi Composition

Sequoia sempervirens hosts a multitude of fungal species on its leaves with at least 81.4% of its leaves being colonized. (Rollinger & Langenheim, 1993). These fungi are referred to as endophytes, since they are often found within the leaves of plants, though most of them are not harmful to the plants they colonize (Carroll, 1988; Espinosa-García & Langenheim, 1991).

The community of endophytes living in the sequoia’s leaves is diverse (Espinosa‐García & Langenheim, 1990). As shown in Table 2, sequoia sprouts have a relatively even distribution of fungi on their leaves. However, as the sprout ages, the fungus Pleuroplaconema sp. starts to dominate the competition, composing 50% of the total fungi population in sequoia trees (Espinosa‐García & Langenheim, 1990).

Table 2. Percentage of fungal species colonizing the leaves of a sequoia tree (Espinosa‐García & Langenheim, 1990).

Although most endophytes in Table 2 are harmless to adult trees, some fungi in the list such as Pestalotiopsis funereal are harmful to seedlings and older individuals (Espinosa-García & Langenheim, 1991). Thus, the sequoia tree needs a way to regulate the population of fungi on their leaves.

Effects of Sequoia Oil on Fungi Growth

One way sequoia trees regulate their fungi population is by secreting volatile oils. As shown in Fig. 3, the oil is composed of many compounds, and the chemical composition of the oil varies for each individual tree (Espinosa-García & Langenheim, 1991).

Fig. 3. Percentage of each terpenoid, a type of chemical compound, found in the oil of Sequoia sempervirens. A, tricyclene; B, thujene; C, α-pinene; D, camphene; E, β-pinene; F, sabinene; G, myrcene; H, α-phellandrene; I, limonene; J, β-phellandrene; K, y-terpinene; L, p-cymene; M, terpinolene; N, caryophyllene (Espinosa-García & Langenheim, 1991).

Testing the phenotypes on Pleuroplaconema sp. and Pestalotiopsis funereal, Espinosa-García and Langenheim (1993) found that at higher doses, sequoia oil reduced the growth of the fungi up to 89.1% and 73% respectively (Espinosa-García et al., 1993). However, as shown in Fig. 4, lower doses of the oil encouraged the growth of Pleuroplaconema sp. while slightly inhibiting the growth of Pestaltiopsis funereal (Espinosa-García et al., 1993).

Fig. 4. Growth of Pleuroplaconema sp. and Pestalotiopsis funereal depending on sequoia oil dose (Espinosa-García et al., 1993).

This leads to the sequoia’s second approach when dealing with fungi populations, which is its relationship with Pleuroplaconema sp. Although these interactions are understudied, it is theorized that Pleuroplaconema sp. inhibits the growth of other fungi (Espinosa-García et al., 1993). Thus, a larger population of this mutualistic fungus reduces the chances of other fungi attacking the seeds and more vulnerable individuals of the sequoia population.

As such, the effect of sequoia oil on Pleuroplaconema sp. could explain the fungus’ dominance in adult trees. Sequoia sprouts produce approximately three times more monoterpenes, compounds found in sequoia oil, per gram of dry leaf (Hall & Langenheim, 1986). Thus, the growth of Pleuroplaconema sp. is possibly inhibited in sprouts, while adult sequoias promote the fungus’ spread.

Varying Oil Compositions

The relative amount of oil produced in sprouts isn’t the only thing that differentiates them from their mature counterpart. The proportions of the compounds present in sequoia oil also change. As shown in Fig. 5, sprouts and newer foliage of sequoia trees have a higher limonene proportion with sprouts containing nearly double the limonene percentage compared to the mature foliage of grown trees (Hall & Langenheim, 1986). In addition, Hall and Langenheim (1986) noticed that the production of limonene can be induced via external stress such as herbivory, which includes damage or removal of leaves. A year after the leaves of a sprout were removed, the percentage amount of limonene increased by 5%, which shows that limonene plays a role in animal deterrence (Hall & Langenheim, 1986).

Limonene is not the only compound with a noticeable change in proportion over time. In the same study, Hall and Langenheim (1986) found that the percentage amount of y-terpinene, another compound found in sequoia oil, significantly changes over time. Though unlike limonene, the proportion of y-terpinene increases as the sprout ages, which can be observed in Fig. 6 (Hall & Langenheim, 1986).

Fig. 5. Change in percentage amount of limonene in a sequoia sprout, modified from Hall and Langenheim, 1986 (Hall & Langenheim, 1986).

Fig. 6. Change in percentage amount of y-terpinene in a sequoia sprout, modified from Hall and Langenheim, 1986 (Hall & Langenheim, 1986).

y-terpinene is shown to be inhibitory to fungi, and the increase in percentage amount of this compound suggests that mature trees are better at retaliating against fungi (Espinosa-García & Langenheim, 1991; Hall & Langenheim, 1986). Thus, combining these two observations suggests that young sequoias are under a different selection of pressure than adults (Hall & Langenheim, 1986). Sprouts are lower to the ground, which makes them vulnerable to herbivores, whereas mature sequoias do not face this problem due to their big size.

Chemical Composition and Synthesis of Sequoia Bark

Bark Composition

The previous paper of this series discussed the mechanical properties of the sequoia’s bark, which were found to rely on the hierarchical nature of its fibrous material (see Sequoia Physics). The bark’s resistance does not solely rely on its networked nature, as it also depends on its chemical composition. Sequoia bark has been found to contain high lignin concentrations, a characteristic that is attributed to its increased resistance (Bold et al., 2020). It is, however, very difficult to quantitively measure the lignin content in bark, as it is almost intrinsically linked to cellulose and hemicellulose (Rowell et al., 2005). We can, however, visually compare stained micrographs of sequoia bark to micrographs of other tree’s bark, as is done in Fig. 7 below.

Fig. 7. (A) Photomicrograph of S. giganteum bark stained with toluidine blue, which makes lignified tissues appear bluish turquoise, seen here in rows of rectangular shapes (Adapted from Bold et al., 2020). (B) Photomicrograph of Luehea divaricate bark stained with toluidine blue, which shows lignified tissues as greenish blue, as visible in the lower third of the image (Modified from Pace, 2019).

These two slides next to each other make clear that sequoia bark is more lignified than other tree’s barks. In the above example, the Luehea divaricate sample is lignified in lower concentrations, as visible by the subtle greenish tint of the stain near the bottom of Fig. 7B. Sequoia bark, however, contains distributed rows of densely lignified tissue between the thin-walled parenchymatous cells, as indicated by the strong turquoise coloring of the fiber cells containing the lignin (Bold et al., 2020). As shown in Fig. 8, these highly lignified fiber cells are present throughout the bark tissue in a uniform linear pattern.

Fig. 8. Photomicrograph of S. giganteum bark stained with toluidine blue, showing the highly lignified fiber cells in bluish turquoise. The arrows indicate the linear arrangement pattern of the lignin in the bark tissue (Bold et al., 2020).

It has been found that high lignification leads to higher compressive strength in wood, an observation that can realistically transfer to bark tissue. In agreement with the findings relating to the compression behavior of sequoia bark reported by Bold et al., wood that contains more lignin has been found to show no observable compression failures (Gindl, 2002). Again, as discussed in the previous paper, compression strength and elasticity are primordial in enabling sequoia trees to withstand the harsh impacts imposed by frequent rockfall in their habitat.

Lignin is the second component by mass of vascular plants, as it comprises of 24% to 33% of the weight of softwood trees (Gargulak et al., 2015). Every lignin unit is composed of a phenylpropanoids monomer that forms the lignin polymer proper. Lignin possesses a complex three-dimensional structure that gives it its strength. This structure results from the multiple types of bonds formed between lignin monomers in a typical softwood lignin structure, as shown in Fig. 9.

Fig. 9. Model of lignin structure in spruce trees, a softwood tree (Gargulak et al., 2015).

Lignin units are linked by carbon-carbon and ether bonds. The handful of different types of lignin, which differ slightly in their chemical formulas, make it possible for lignin to adopt a networked approach to polymerisation, as opposed to a more linear type of arrangement that would be possible with more symmetrical monomers, like some plastics. Fig. 9 illustrates the branching structure of the lignin polymer. The specific strength of each type of bond present in softwood lignin is as follows in Table 3.

Table 3. Prevalence of common bond types in softwood lignin, and the typical bond dissociation enthalpy (BDE) of each bond in aqueous environments. Frequency data are adapted from Gargulak and coworkers, 2015 (Gargulak et al., 2015). BDE data are adapted from Qin and colleagues, 2014 (Qin et al., 2014).

According to the frequency values above, softwood lignin uses significant proportions (approx. 25%) of the stronger β-5 and 5-5 bonds, which have BDEs in the 130-140 kcal/mol range, without relying exclusively on them (Qin et al., 2014). It can be hypothesized that, since biological tissues can heal, this makes lignin a balanced material that allows for macroscopic deformations at the expense of higher rigidity, but at the gain of better elasticity.

The chemical composition of sequoia bark gives new insight in how its elasticity- and compression strength-optimized characteristics are achieved, not only through the hierarchal material of their fiber networks, but also through the synthesis of lignin typical to most softwoods. This lignin, as discussed above, has itself an arrangement characteristic of fiber networks in its polymer form and its varied bond strengths between units.

Bark Resistance Against Invaders

In the Sierra Nevada, the native habitat of giant sequoias and coast redwoods, intense and widespread bark beetle invasions, involving species native to the territory, are common. They pose numerous threats, such as tree mortality, and increasing the likelihood of forest fires due to accumulation of dead wood (Fettig et al., 2021). To survive the threat of invasive insects, sequoias have adapted (1) the composition of their bark to make it harder to penetrate and (2) to produce chemicals that inhibit colonization attempts.

Lignified tissue does not only play a role in the compression strength and elasticity of sequoia bark but is also a primordial component of their resistance to bark beetles. As seen in Fig. 8, the lignin content of sequoia bark is distributed in repeating rows. It has been found that this kind of lignified pattern is a strong beetle deterrent, as it leads the invaders to dig significantly narrower galleries in more lignified trees than less lignified trees, which greatly limits the damage these galleries can inflict on the tree. It has also been found practically impossible for bark beetle larvae to establish galleries and lay eggs deep within the wood (Wainhouse et al., 1998).

Many conifers, including sequoias, synthesize terpenes to defend themselves against invading species. There are about 30,000 known terpenes, which make it one of the largest groups of natural plant products. At their base, terpenes are C₅ units bonded together, forming mono-, di- and sesqui-terpenes (Krokene, 2015). The biosynthesis mechanism of terpenes is shown below in Fig. 10.

Fig. 10. Synthesis mechanism of terpenes (Krokene, 2015).

Sequoias store terpenes under pressure, in ducts distributed inside their bark. If an insect punctures a duct, the terpenoid resin will flow out and forcibly remove the insects into the gallery, enabling the trees to flush out or trap gallery-digging invaders. Terpenes are also involved in the wounding process of sequoias, which gives an ability to recover quickly after the resin-flooding process (Krokene, 2015). However, terpenes are not merely a mechanical defense system, as they have proven to be toxic to beetles. Experiments involving four different monoterpenes have shown that higher concentrations of said monoterpenes cause beetle mortality. The process of the beetles’ detoxification involves water loss by excretion of terpene toxins, and the death of the beetles is therefore suspected to be attributed to dehydration (Reid et al., 2017).

Sequoias also use protein-based defense mechanisms to deter insects. Some of these include amylase inhibitors, that prevent the beetles from breaking down the starch they need to survive into simpler sugars, thus preventing them from profiting off their host. Sequoias can also produce enzymes that promote the lignification of tissue, essentially creating additional barriers making insect’s entry harder. Such protein-based chemical defenses can be of very high specificity and target specific organisms (Franceschi et al., 2005), although no readily available research on sequoia’s use of specific enzymes and inhibitors could be found.

The Role of Tannin in Fire Resistance

Due to its fire-prone ecosystem, the giant sequoia had to adapt to survive periods of intense heat. An experiment found that, when comparing fire-resistant tree bark, like the giant sequoia’s, with the technical reference polymer ABS (Fig. 11), the polymer burned by leaving only 2.6% solid behind, while fire-resistant tree bark only carbonized when it was burned, leaving up to 60% solid behind (Tributsch & Fiechter, 2008).

Fig. 11. The chemical structure of ABS (Acrylonitrile Butadiene Styrene). Its chemical formula is (C₈H₈·C₄H₆·C₃H₃N)_n. (SpecialChem, 2025).

In the specific case of the giant sequoia, it was observed that when exposed to fire, larger compact pieces of sequoia bark react differently than small samples. The surface larger pieces of bark tend to carbonize rapidly, however, once the fire is remove, oxidation does not continue to proceed unless the bark is exposed to an extremely long and intense period of fire. In smaller samples of the bark, the flames were able to oxidize the material and left more coarse structured fibres behind. This creates a layer of ash around the structure, which becomes thicker until the entire sample is oxidized (Tributsch & Fiechter, 2008). Since the giant sequoia is so thick, the behaviour of the larger bark pieces in the first scenario represents best what happens to the tree in its habitat. Additionally, when the bark is exposed to a very high temperature with limited access to oxygen, the sample will carbonize but not oxidize. This is because the carbonized layer can shield the underlying bark from oxidation under the lack of oxygen. This fire-retardant quality is the sequoia’s design solution to surviving its dry environment. Many fires are bound to happen throughout its long lifespan, so this big tree had no choice but to adapt fire-proof bark. To put the giant sequoia’s resistance to fire in comparison with ABS and other fire-resistant trees, Figure 12 depicts the thermogravimetric mass loss for different materials (Tributsch & Fiechter, 2008). 

Fig. 12. Comparison of thermogravimetric mass loss from 0°C to 600°C for ABS, different tree barks, and tannin, a component of many tree barks. At 600°C, the giant sequoia still retains 43% of its carbonized solid mass. Tannin extracted from the bark of the Quebracho tree reaches 49.5% of solid mass retained, and tannin extracted from the giant sequoia showed a similar behaviour (Tributsch & Fiechter, 2008).

A closer look at the giant sequoia’s bark during thermogravimetric heating can be seen in Figure 13, depicting the mass spectroscopically measured gases that escape from the bark as the temperature rises. From 0°C to 100°C, mostly water vapour escapes the sample. Before reaching 200°C, some organic compounds of mass to charge ratio (m/q) 107 and 108 in the bark start escaping as gas as well. Between 200°C and 300°C, oxidized compounds, like CO and CO₂ gas, begin to be detected (Tributsch & Fiechter, 2008).

Fig. 13. Percent mass of the giant sequoia’s bark compared to the spectroscopically determined gases escaping as the temperature rises (Tributsch & Fiechter, 2008).

The reason the giant sequoia’s tree bark fares so well under intense heat is that the big tree’s bark contains tannic acid, which is a type of tannin (Fig. 14) (Vakulenko, 2018). Tannin is a large, planar, polyphenol that can form complexes with proteins and alkaloids, which they precipitate, as well as polysaccharides such as cellulose. Tannin also reduces radicals and oxidants efficiently through its electron donation ability (Tributsch & Fiechter, 2008).

Fig. 14. The chemical structure of Tannic acid, with the chemical formula C₇₆H₅₂O₄₆. (American Chemical Society, 2018).

When in the presence of a fire, tannin’s oxidation is suppressed and instead the molecule is transformed into a similarly structured graphitic component with properties that allow it to slow or stop the spread of the fire. Tannin as a polyphenol, is able to chemically reduce and inactivate radicals formed, which would otherwise continue to ignite the material. It can also donate electrons from its excited state, which generates a higher reducing power for it to produce, and in turn, slow down the fire front (Tributsch & Fiechter, 2008). This process is visualized in Figure 15 below.

Fig. 15. Two schemes explaining the fire resistance strategy of the giant sequoia tree bark. On the left, the strategy of polyphenols (tannins) through carbonization is depicted. On the right, the thermoreduction of radicals is shown (Tributsch & Fiechter, 2008).

Serotinous Cone Crystals

As a serotinous conifer, the giant sequoia seeds are found in its cones, and this big tree relies on forest fires to reproduce. Besides having the ability to keep seeds safe during periods of intense heat, these cones have adapted another design solution to give them the upper hand in their reproduction: inside of the serotinous cones lie red, water-soluble crystalline substances, also known as cone crystals. The role of cone crystals is to preserve the sequoia seeds for many years, which is important because these seeds can remain in their cones for decades at a time (Prknovà, 2019). However, another interesting aspect of these cone crystals is their ability to totally inhibit germination— even their own (Fig 16).

Fig. 16. Comparison of Norway spruce seeds (A) with cone crystals and (B) without cone crystals, depicting the substance’s germination inhibition properties (Prknovà, 2019).

It is estimated that sequoia cones contain 1.2-2.6% of this crystal. The components of cone crystals, which are also referred to as cone pigments or reddish tannin, are 66% water-soluble material and 4.2% soluble in ethyl ether. Some of the degradation products of the cone solids include pyrogallol, catechol, phloroglucinol, gallic acid, and protocatechuic acid. This mixture of substances is what gives the crystal its preservatory and inhibitory qualities. Even though the pigment inhibits its own seeds (Fig. 17), it relies on rainfall and water to rinse the substance away, leaving the giant sequoia seeds to successfully germinate (Prknovà, 2019). This design solution goes well with the cone’s previously discussed pyrohydriscence in the paper on the tree’s physics (see Sequoia Physics), which in simple terms means the cone only opens after the initial presence of fire followed by water. This ensures that when the seeds are finally released, the crystal substance is bound to be quickly rinsed off, which makes it an incredible design solution that optimizes the seed’s chances at survival by ensuring the right conditions for germination while eliminating nearby competition.

Fig. 17. Comparison graph of the number of giant sequoia seedlings over time after sawing. Variant I are sequoia seedlings with cone crystals, while Variant II are rinsed seedlings (Prknovà, 2019).

Conclusions

Sequoias leverage chemistry in many ways to thrive in their environment. The first challenge discussed in this paper is that of the high soil acidity of the Sierra Nevada region. To fight back, sequoia deposit calcium-rich litter in their cones, needles and bark to increase soil pH, form nutrient-immobilizing calcium carbonates and improve soil porosity. Another challenge faced by sequoias is that the high calcium concentration creates to mitigate the previous issues is beneficial but lowers the solubility of essential nutrients like zinc. Sequoias form symbiotic relationships with fungi that extend the root system of sequoias, increase their surface area and break down phosphorus for the tree’s consumption to remediate, in exchange for sugars given to the fungi. Sequoias also host fungi on their foliage, and control their population through the secretion of volatile oils that inhibit the growth of harmful fungi but catalyzes the growth of beneficial ones like Peuroplacomena sp. These oils vary with the age of the tree: saplings are more disposed to herbivore control via limonene, and mature trees produce more γ-terpinene to control fungi. As the Sierra Nevada experiences frequent rockfall, sequoia bark is highly lignified, which makes it highly compression resistant and gives it an elastic character through its variety of bond types. The lignin also helps deter invasive insects from digging wide galleries, helping to minimize the integral damage to the tree. Terpenes are also secreted in the bark, flooding insect-made galleries when their ducts are punctured and acting as poison to bark beetles, causing mortality through water loss. Another danger of the Sierra Nevada is its frequent forest fires. To defend themselves, sequoias have large amounts of tannin in their bark. Tannin carbonizes when exposed to heat, which helps isolate the core of the tree from flames. Finally, to ensure that germination conditions are optimal, sequoias use serotinous cones that only open when exposed to forest fire heat, which is enabled by crystals that preserves seeds for decades until the conditions are optimal. To summarize, sequoias use many different chemicals to ensure its safety from environmental threats, while making impressively many use cases for each substance it synthesises.