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Article

Study on the Natural Durability of Quercus pyrenaica Willd. to Wood Decay Fungi and Subterranean Termites

by
Sara M. Santos
1,*,
María Teresa de Troya
1,
Lee Robertson
1,
Saúl Gutiérrez
2,
Gonzalo Caballé
2 and
José Luis Villanueva
2
1
Institute of Forest Sciences (ICIFOR), National Institute of Agrarian and Food Research and Technology (INIA), Superior Council for Scientific Research (CSIC), Ctra. de la Coruña km 7, 28040 Madrid, Spain
2
Center for Forestry and Industry Services of Castilla León (CESEFOR), Pol. Ind. las Casas, Calle C Parcela 5, 42005 Soria, Spain
*
Author to whom correspondence should be addressed.
Forests 2025, 16(9), 1486; https://doi.org/10.3390/f16091486
Submission received: 10 July 2025 / Revised: 10 September 2025 / Accepted: 16 September 2025 / Published: 18 September 2025
(This article belongs to the Section Wood Science and Forest Products)
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Abstract

Evaluating wood’s natural durability is essential when establishing the level of protection that is required depending on the end use to extend its service life. Natural durability is defined as the intrinsic resistance of wood against the attack of destructive organisms. There are standardized methods for estimating a durability value. In Europe, the EN 350:2016 standard is responsible for establishing the basic guidelines, as well as the necessary tests to determine this value. This standard applies to commercial wood, both native and imported, and helps to improve and obtain better construction applications depending on the final use. This work aimed to study the natural durability of Quercus pyrenaica Wild. against Basidiomycetes (Coniophora puteana (Schumacher ex Fries) Karsten and Trametes versicolor (Linnaeus) Quélet) and termites (Reticulitermes grassei Clément). The standards applied were EN 113-2:2021 and EN 117:2023. The heartwood of the Quercus pyrenaica is highly durable against both xylophages basidiomycetes and subterranean termites. The sapwood is moderately durable against Coniophora puteana, slightly durable-not durable against Trametes versicolor, and moderately durable against termites. These results open the door for commercialization of this species, and it is expected to be included in EN 350:2016, where Q. pyrenaica is not included.

1. Introduction

Wood has been one of the most widely used materials in construction throughout history, both for its decorative value and its excellent physical and mechanical properties. Wood’s characteristics, such as its high mechanical strength, sound insulation, and easy processing, make it a widely used material [1]. Furthermore, wood is a renewable and environmentally friendly material with carbon storage capacity, making it suitable for carbon neutrality [2], thus contributing to the mitigation of greenhouse gas emissions [3]. Currently, with growing concerns about preserving our historical heritage and the use of renewable materials, the construction industry has turned to wood as a structural element. The range of applications for wood is increasing every day thanks to these characteristics and advantages.
However, wood also has disadvantages. As an organic material, it is susceptible to degradation due to biotic and abiotic damage caused by insects and fungi, dimensional variations with temperature and humidity, discoloration, and photodegradation [4,5,6]. This deterioration depends primarily on the wood’s chemical composition and anatomy. When wood is used outdoors, these disadvantages are accentuated [7,8], depending on the climatic conditions of the location, as this influences the presence of decomposing organisms, such as fungi or termites. Furthermore, with climate change, outdoor wood is expected to become increasingly vulnerable to decay [9,10,11]. The reason for this is that fungal decay is influenced by temperature and moisture content. Since climate change scenarios predict increases in temperature and wood moisture content due to increased precipitation in the future, wood will be more exposed to such decay.
When using wood, it is not only important to consider the exposure to the climate, product design, and class use, but also the natural durability against biological deterioration. Natural durability is an inherent property of each species, defined as “the property of wood that makes it resistant to attack by chemical, physical, and biological degrading agents without any preservation treatment” [12]. Estimating natural durability is essential, as it forms the basis for recommendations for optimal use based on the risk conditions at final installation and for determining the degree and type of protection that the wood will require to extend its service life. This avoids the need for constant replacement, contributing to the survival of a system as complex as forests by reducing tree felling [13,14,15].
Natural durability is defined by a series of properties that directly influence the establishment of organisms that can degrade it and are related to the composition of the cell wall, the anatomy of the xylem, the availability of nutrients, the quantity and composition of heartwood extractives, and the presence of moisture-regulating components [16]. More specifically, extractives and lignin are routinely described as the main factors explaining wood’s resistance to decay, with a highly significant negative correlation between mass loss and relative lignin content [15,17,18,19].
The composition and structure of the cell wall is fundamental for the durability of wood [20,21]. The availability of cellulose and hemicellulose is essential, since most fungi and bacteria present cellulase and/or hemicellulase enzyme activities [22]. However, lignin can make the cell wall more impenetrable and more resistant to biodegradation [23]. In gymnosperms, the lignin monomer is guaiacyl, which is compact and difficult to oxidize, while angiosperms contain both guaiacyl and syringyl [24]. It should be noted that up to 95% of the xylem of gymnosperms is formed by tracheids, while angiosperms have more specialized cell types, larger conductive elements, and a higher proportion of parenchymal cells [25]. In conclusion, it can be said that gymnosperms generally have greater natural durability when compared to angiosperms, although there is wide variation in durability within both softwoods and hardwoods
It is known that [26] for the same wood species, heartwood is more resistant to decay than sapwood due to the higher concentration of toxic extractive compounds, such as alkaloids, phenols, and terpenes. During heartwood formation, relatively large quantities of these secondary metabolites are deposited, in which the types and quantities depend on the species and location. These compounds are thought to act as deterrents to pathogen attacks in many species [27,28]. Tannins are phenolic compounds, primarily ellagitannins, with oxidative properties [29]. The amount of extractive compounds is known to increase from the pith to the outer part of the heartwood, reaching a maximum in the transition zone between heartwood and sapwood. Furthermore, the durability of sapwood is usually greater in species with a durable heartwood than in those with a less durable heartwood.
Among the biotic factors that are involved in wood degradation, fungi and insects cause more or less damage according to climate conditions [30,31]. Wood that is decayed by fungi experiences a significant loss of strength [32,33]. Examples include brown rot and white rot, which utilize enzymes and metabolites at different rates, thus generating distinct decomposition patterns [34]. Humidity, temperature, condensation processes, or natural fungal substances influence the types of fungi that can attack wood; therefore, the fungi growing in sapwood and heartwood differ. For example, certain fungal species that tolerate concentrations of tannins or other polyphenols can establish in heartwood [35]. Brown rot fungi primarily decompose cellulose and hemicellulose in wood, leaving modified lignin residues. Coniophora puteana is one such fungus, which can cause up to 70% mass loss in softwood structures, thereby reducing the mechanical strength [36,37]. Furthermore, white rot fungi degrade lignin, which affects the wood’s compression strength. More than 90% of wood decaying fungi in standing and felled trees in the north of America and Iran are caused by white rot fungi such as Trametes versicolor [38].
Termites are a group of social insects that live in warm regions, with the ability to degrade both softwood and hardwood through the production of mechanisms such as endogenous enzymes. Subterranean termites (Rhinotermitidae) are the most widely distributed termite family in Europe [39], forming large colonies (several hundred thousand to millions of individuals) in the soil at depths of 70 to 100 cm and exploring wood sources in their surroundings (radius of less than 10 m) [40]. They require high levels of humidity to survive.
In many parts of the world, there are standardized methods adapted to geographical areas, which allows for the testing of natural durability. The deterioration of wood in service in Europe is studied according to the standards indicated in EN-350:2016 [41], which defines the testing protocols for assessing the natural durability of commercially important wood species in Europe [42,43,44]. This standard establishes the application of EN 113-2:2021 [45] to assess durability against wood-boring basidiomycete fungi and EN 117:2023 [46] against subterranean termites. The EN-350:2016 standard [41] also provides a list of species whose natural durability has already been studied and is therefore known. It should be noted that wood is a heterogeneous material, and its durability varies between species and even between populations within the same species. However, the EN 350:2016 [41] standard establishes a durability criterion, classifying wood’s natural durability against fungi into five classes, from 1 to 5, where 1 is very durable and 5 is not durable, and against insects, termites, and marine organisms, into three classes: durable, moderately durable, and susceptible.
Quercus pyrenaica covers approximately 1.1 million hectares in Spain, accounting for around 3.9% of the national forest area and about 21% of the country’s broadleaved woodlands [47]. Despite its ecological relevance and regional abundance, Q. pyrenaica is not currently listed in the European EN 350:2016 standard [41].
This omission is notable, as the species presents promising structural and aesthetic properties, positioning it as a potentially valuable alternative for the timber industry. Furthermore, studies have highlighted the species’ resilience to climate change, exhibiting strong drought tolerance, efficient resprouting, and adaptive flexibility in mixed stands [48,49,50]. Evaluating its natural durability against biotic and abiotic agents is essential to determine its viability for long-term industrial use, especially in sustainable construction systems, where resistance to environmental stress is a priority. Recent research also confirms that the mechanical performance of Q. pyrenaica wood meets the criteria for structural applications, supporting its inclusion in future durability assessments and standardization efforts [51].
To estimate the resistance against attack by wood decay fungi, some researchers use the values of the concentration of various substances in the wood, such as some extracts or chemicals that accumulate during duraminization [52,53]. Some authors [42,54,55] found clear correlations between the mass loss and the amount of extractives in European Quercus species [53]. In other studies on durability, a marked influence of the region of origin of the wood was observed; however, they did not determine the final cause (genetic, soil type, climate, type of wood decay agents, etc.) for these significantly different behaviors [44,56,57]. As for the relationship between some physical properties of wood and durability, some authors obtained meaningful relationships, albeit limited, between some physical properties of Quercus petraea Liebl. and its natural durability [58]. Recently, a decrease in durability with the current climate change conditions has been observed [59].
It must be taken into account that if a wood type is not durable for the type of use and climate where it will be used, a protective treatment must be applied. Chapter 3 of the SE-M Basic Document on Timber Structures, Durability [60], lists the biological risk classes (currently called use classes) that structural timber is exposed to depending on the conditions of its use and climate, as well as the preventive and/or curative treatments that must be applied.
For this reason, the main goal of this work is to determine the natural durability of Pyrenean oak (Quercus pyrenaica) against wood decay Basidiomycetes causing brown and white rot and subterranean termites based on the standards indicated in EN-30:2016 [41]. This paper presents the results obtained using sapwood and heartwood specimens of Pyrenean oak (Quercus pyrenaica) compared with the reference species Pinus sylvestris L., as specified in the corresponding regulations. Additionally, Fagus sylvatica L. test tubes were added, because Quercus pyrenaica is a leafy species.

2. Materials and Methods

2.1. Materials

The study was conducted on heartwood and sapwood of Quercus pyrenaica Wild., using Pinus sylvestris L. and Fagus sylvatica L. as reference species. Once dry, the wood was cut into blocks of 50 × 25 × 15 mm, which were selected in the number and orientation required by each test standard (EN 113-2:2021 [45] for fungi, and EN 117:2023 [46] for termites).
The wood decay organisms used are the following:
  • Basidiomycete fungi: Coniophora puteana (Schumacher ex Fries) Karsten, strain BAM Ebw 15, and Trametes versicolor (Linnaeus) Quélet, strain CTBA 863A.
  • Social insect: the species Reticulitermes grassei (Clément), a subterranean termite, most frequent found in the Iberian Peninsula, from the ICIFOR-INIA hatchery DAGARD Iberica (Madrid, Spain).

2.2. Methods

As previously mentioned, the European EN 350:2016 standard [41] establishes the principles for testing and classifying the main wood species in Europe. This standard sets out the regulations to be followed to classify the impregnability and durability of wood, depending on the type of xylophagus agent.

2.2.1. Natural Durability Test Against Basidiomycete Fungi

To establish durability against wood decay Basidiomycete, the European EN 113-2:2021 standard [45] was followed. According to the standard, pure cultures of the fungal strains Coniophora puteana and Trametes versicolor were grown in a malt–agar medium (1.5% agar; 3% malt). Once the fungi had developed on the surface of the medium, wood specimen blocks were placed in contact with each other under sterile conditions and incubated for 16 weeks in a climate chamber at 22 ± 2 °C and 70 ± 5% relative humidity. After this time, degradation was calculated using the percentage mass loss (ML) under anhydrous conditions and the ratio between the ML (%) of the test specimens and the reference wood specimens. The class of resistance to fungal degradation was graded according to the EN 350:2016 standard [41] (Table 1).

2.2.2. Natural Durability Test Against Reticulitermes Grassei

To determine the durability against termites, the European EN 117:2023 standard was applied [46]. The standard establishes that each wooden block test must be in contact with a colony of termites according to the following methodology: Each test container was composed of moistened sand, to which one colony made up by 250 workers, 2–3 soldiers, and nymphs, was introduced. After 2–3 days, wooden blocks were added to each container. The test containers were incubated in the culturing chamber during a period of 8 weeks, with air circulation, at 28 ± 2 °C and a relative humidity of 80 ± 5%. At the end of the test, the wood specimens were removed from each container for the visual examination, according to the following criteria: 0: no attack; 1: attempted attack (superficial erosion); 2: slight attack (erosion of 1 mm in depth and/or single tunneling to a depth of up to 3 mm); 3: average attack (erosion of <1 mm in depth and/or isolated tunneling of a depth > 3 mm not enlarging to form cavities); and 4: strong attack (erosion of >1 mm to <3 mm in depth and/or tunneling penetrating to a depth > 3 mm and enlarging to form a cavity in the body of the test specimen). In addition, the total number of termites still living in each test container was counted, and the survival level of the workers determined, as well as the presence of living soldiers and/or nymphs. Although it is not a requisite of the standard, the mass loss of each block test was determined.
The natural durability classes against Reticulitermes grassei according to the EN 350:2016 standard [41] are presented in Table 2.

2.2.3. Statistical Study

The results obtained from the percentage of weight loss in both sapwood and heartwood of the test blocks that were inoculated with Coniophora puteana and Trametes versicolor, as well as the test blocks that were attacked by Reticulitermes grassei, were compared using the Kruskal–Wallis test (IBM SPSS statistics version 22 software) in order to determine the significant differences between sapwood and heartwood and the differences within each of them that were induced by the inoculation of the fungi and the attack of the termites.

3. Results

The results are shown separately below according to the standard applied for each xylophagous organism under study.

3.1. Natural Durability Test Against Basidiomycete Fungi

The results obtained against basidiomycete fungi are shown in Table 3 for the sapwood and heartwood of Quercus pyrenaica compared to the control species P. sylvestris and F. sylvatica.
Figure 1 shows the appearance of Q. pyrenaica sapwood wooden blocks with C. puteana and T. versicolor. Figure 2 shows the appearance of the heartwood samples against both fungi. Figure 3 shows the degraded appearance of the control pine and beech samples.

3.2. Natural Durability Test Against Reticulitermes Grassei

Table 4 shows the data obtained after the application of EN 117:2023 [46] against subterranean termites (Reticulitermes grassei) in Q. pyrenaica wood compared to the controls, and an example can be seen in Figure 4.

3.3. Statistical Study

Table 5 shows the results of the statistical analysis and the application of the Kruskal–Wallis test on the differences in weight loss of Quercus pyrenaica after fungal inoculation and termite attack. The probability (p) and the H index between the sapwood and heartwood are shown. Within each of these zones, the differences found due to the action of the fungi and termites are indicated.

4. Discussion

The wood of certain species of oak is known to be susceptible to decay by white rot fungi and brown rot fungi [30,45]. Similarly, insects that can attack older oak wood, including Bostrychus capucinus L. and Anobium punctatum De Geer. Recently, ants (Formica sp.) have become more common in wood, including oak [61,62]. Therefore, species-by-species durability testing is essential.
The results obtained after applying EN 113-2:2021 [45] (Table 3) to evaluate the durability against brown and white rot, in addition to the results of the statistical study (Table 5), indicate that there are significant differences in the degradation (mass loss) caused by the fungi. This is significantly greater (p < 0.01) in the sapwood than in the heartwood. The degradation is so low (mean ± standard deviation 1.98 ± 1.91) that the wood is considered durable even after fungal inoculation. The effect of fungi on the sapwood is much more significant, and the resulting mass loss makes the wood considered not durable according to the criteria of EN 350:2016 [41]. In both inoculated areas of the wood, the fungus Trametes versicolor caused significantly greater weight loss than Coniophora puteana (p < 0.01 on the sapwood and p < 0.05 on the heartwood).
Table 4 shows the results relating to the durability of Q. pyrenaica against subterranean termites after applying the EN 117:2023 standard [46]. The results show that the heartwood is also durable without any degree of attack or survivors, while the two reference species studied (scots pine and beech) are susceptible. However, the sapwood of Q. pyrenaica is moderately durable. Neither the pine or beech controls exhibited durability. The Kruskal–Wallis test (Table 5) showed no significant differences (H = 2.21; p = 0.13) between the sapwood and heartwood with respect to the mass loss caused by termites. The greater standard deviation in the durability of sapwood is due to its greater susceptibility to biological attacks, because it contains living cells and fewer protective substances such as tannins, unlike heartwood. This low natural durability implies greater variability in its resistance to degradation, which translates into a higher standard deviation compared to heartwood. Heartwood, being the innermost and biologically inactive part, is naturally more resistant. Its more compact structure and high content of protective extractives give it greater durability, resulting in a lower standard deviation.
Several points could explain the durability found in Quercus pyrenaica. It is known that species belonging to the genus Quercus (Quercus sp.) have a ring-porous structure and a wide ranging density ranging from 390 kg/m3 to 930 kg/m3 [63]. As previously stated, density positively influences durability within the same ring-porous species, with denser wood being more durable than wood with lower density [64]. Large vessels in earlywood are typical of oak (diameters greater than 200 μm), and small, radially oriented vessel clusters are typical of latewood. Quercus pyrenaica, in particular, has broad uniseriate and multiseriate rays and abundant axial parenchyma. It is important to note that the distribution and proportion of wood cell types, as well as the presence of intercellular spaces, influence the penetration and colonization capacity of fungal hyphae and determine whether the fungus can access nutrient sources and sufficient oxygen in the wood. The data obtained are consistent with previous literature which concludes that, in ring-porous species, such as Quercus robur L., fibrous tracheids also have a higher guaiacyl content than fibers [65], therefore being more resistant to soft rot and white rot fungi [66].
Although the durability of Quercus pyrenaica has not been studied to date, other species of the same genus, Quercus rubra L., Quercus petraea L., Quercus robur L., etc., are known to be among the most durable according to the EN 350:2016 standard [41]. According to various studies, pines, oaks, chestnuts, and walnuts, which naturally contain tannins, resist natural conditions better than other wood species [67]. Specifically, the high natural durability of some oak heartwood is mainly due to the presence of polyphenols. Their quantity, type, and distribution in oak trunks depend on factors such as tree age, growing conditions, and wood density [68,69,70,71]. Subsequent studies evaluating the fungicidal effect of each of the eight major ellagitannins [29] and the phenolic monomers of oak wood also confirmed this idea. In the same way, the absence of toxic elements in the extracts of certain oak species could explain their non-durable nature [72]. This is the case of Quercus sideroxyla Bonpl., a non-durable species with a high degree of degradation [73].
Several studies have also shown that the concentration of soluble ellagitannins in oak trees decreases from the sapwood–heartwood transition zone to the pith, with a concomitant increase in the concentration of insoluble ellagitannins [68,74]. This could explain why the sapwood shows a slightly greater loss against Trametes versicolor and moderately durable against subterranean termites.
Also, it has to be taken into account that tyloses are common in some species, representing a protrusion of a parenchyma cell into the lumen of adjacent vessels [75]. They may be associated with heartwood formation but also occur naturally in the sapwood after cavitation caused by water stress and may appear in sections of the stem that have been injured or infected [76]. Although there is much controversy about the role of tyloses in the natural durability of wood, it has been concluded that tyloses of Quercus montana Willd. contribute to resistance to fungal decay, either by slowing water uptake for decomposition or by preventing the movement of fungal hyphae through the lumen [52]. A similar conclusion was reached [77] when studying the durability of Quercus petraea and Quercus robur, indicating that the presence of wood tyloses in oak heartwood seems to show that there is a negative correlation between tyloses and the biodegradation of oak wood. The chemical analysis of Q. pyrenaica also revealed a weighted average cellulose content of 48.23%, while hemicellulose and lignin contents were 18.48% and 19.71%, respectively, [78]. The presence of tyloses in Quercus pyrenaica, as well as fibrillar networks, gums, starch grains, and crystals, has also been observed [79]. All these morphological and compositional characteristics could explain the high durability of Quercus pyrenaica.
It is also worth noting that durable wood species such as Quercus pyrenaica can also be a valuable source of active chemical compounds for the treatment of fungal diseases, both in plants and humans [80].
The values obtained in this study serve as a reference for possible inclusion in the natural durability classifications of Quercus pyrenaica, a species that is not included in the European EN 350:2016 standard [41]. The results suggest that Quercus pyrenaica heartwood could offer superior natural durability compared to other commonly used European hardwoods, such as Quercus robur L. (European oak), Castanea sativa Mill. (chestnut), and Fagus sylvatica L. (beech). Its potential to replace species such as oak and chestnut in products such as decking, landscaping elements, or exterior carpentry could reduce the need for synthetic preservatives and align with sustainability and circular bioeconomy goals. For example, while European oak is typically classified as durable (Class 2) according to EN 350:2016 [41], field trials have shown that its performance can decline to Classes 4–5 (non-durable) when exposed to soil over time [81]. Similarly, while chestnut is generally considered durable (Class 2), some studies report moderate durability (Class 3), depending on growing conditions and wood anatomy [82]. In contrast, beech and ash are consistently classified as slightly or not at all durable (Classes 4–5), limiting their use to indoor applications unless treated. Based on current findings, Quercus pyrenaica can be placed between Classes 1 and 2 in natural durability, surpassing most of these species in its resistance to decay and termite attacks and demonstrating potential for outdoor use without the need for chemical treatments.

5. Conclusions

  • The heartwood of Quercus pyrenaica is highly durable against both xylophages basidiomycetes and subterranean termites.
  • The sapwood of this species is moderately durable against Coniophora puteana and slightly durable–not durable against Trametes versicolor.
  • The sapwood of Quercus pyrenaica is moderately durable against termites.
These results open the door for commercialization of this species, and it is expected to be included in EN-350, where Quercus pyrenaica is not included yet.

Author Contributions

Investigation, S.M.S., M.T.d.T., L.R., S.G., G.C. and J.L.V.; Writing—original draft, S.M.S., M.T.d.T. and L.R.; Writing—review & editing, S.G., G.C. and J.L.V. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the European LIFE call, within the LIFE +REB project [LIFE 20 CCM/ES/001778], and carried out in the Wood Protection laboratories of the Forest Products Department of the Institute of Forest Sciences (ICIFOR) of the INIA-CSIC.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

We thank Francisco Llinares of Universidad San Pablo CEU, who made the statistical study.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Forests 16 01486 g001
Figure 1. Appearance of the sapwood specimens of Q. pyrenaica after 16 weeks of incubation: (a) tested against Coniophora puteana; (b) tested against Trametes versicolor.
Figure 1. Appearance of the sapwood specimens of Q. pyrenaica after 16 weeks of incubation: (a) tested against Coniophora puteana; (b) tested against Trametes versicolor.
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Forests 16 01486 g002
Figure 2. Appearance of the heartwood specimens of Q. pyrenaica after 16 weeks of incubation: (a) tested against Coniophora puteana; (b) tested against Trametes versicolor.
Figure 2. Appearance of the heartwood specimens of Q. pyrenaica after 16 weeks of incubation: (a) tested against Coniophora puteana; (b) tested against Trametes versicolor.
Forests 16 01486 g002
Forests 16 01486 g003
Figure 3. Example of the appearance of the control specimens: (a) Pinus sylvestris tested against Coniophora puteana; (b) Fagus sylvatica tested against Trametes versicolor.
Figure 3. Example of the appearance of the control specimens: (a) Pinus sylvestris tested against Coniophora puteana; (b) Fagus sylvatica tested against Trametes versicolor.
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Forests 16 01486 g004
Figure 4. An example of the deterioration following termite attack in the sapwood (top left) and heartwood (top right) specimens of Quercus pyrenaica compared to the control specimens of Pinus sylvestris (bottom left) and Fagus sylvatica (bottom right) after 8 weeks of incubation.
Figure 4. An example of the deterioration following termite attack in the sapwood (top left) and heartwood (top right) specimens of Quercus pyrenaica compared to the control specimens of Pinus sylvestris (bottom left) and Fagus sylvatica (bottom right) after 8 weeks of incubation.
Forests 16 01486 g004
Table 1. Durability classes of wood to fungal attack (basidiomycete fungi) (EN 350:2016 [41]).
Table 1. Durability classes of wood to fungal attack (basidiomycete fungi) (EN 350:2016 [41]).
Durability ClassDescriptionPercent of Loss in Mass
1Very durablex 1 ≤ 5
2Durablex 1 > 5 but ≤10
3Moderately durablex 1 > 10 but ≤15
4Slightly durablex 1 > 15 but ≤30
5Not durablex 1 > 30
1 x = higher of the median mass losses (in %) determined for test specimens exposed to each of the used test fungi.
Table 2. Durability classes (DC) of wood to termite attack (EN 350:2016 [41]).
Table 2. Durability classes (DC) of wood to termite attack (EN 350:2016 [41]).
Durability ClassDescriptionClassification Criteria
DDurable≥90% “0, 1”, max. 10% “2” *
MModerately durable<50% “3, 4”
SSusceptible≥50% “3, 4”
* 90% of the test pieces classified with an attack grade of 0 or 1 and a maximum of 10% of test pieces with an attack grade of 2 and 0% “3 and 4”.
Table 3. Durability results against Basidiomycetes fungi.
Table 3. Durability results against Basidiomycetes fungi.
Wood SpeciesConiophora puteanaTrametes versicolor
Mass Loss (%)Durability ClassMass Loss (%)Durability Class
Q. pyrenaicaSapwood12.360Moderately durable29.125Slightly durable–Not durable
Heartwood0.027Very durable0.055Very durable
ControlP. sylvestris39.861Not durable20.273Slightly durable
F. sylvatica35.125Not durable42.455Not durable
Table 4. Durability classes of wood to termites (Reticulitermes grassei) attack (EN 350:2016 [41]).
Table 4. Durability classes of wood to termites (Reticulitermes grassei) attack (EN 350:2016 [41]).
Wood SpeciesAttackSurvivals (%)Mass Loss (%)Durability Class
Q. pyrenaicaSapwood1.973.604.76Moderately durable
Heartwood001.1Durable
ControlP. sylvestris475.2212.12Susceptible
F. sylvatica2.756.895.30Susceptible
Table 5. Statistical study of the durability of Quercus pyrenaica.
Table 5. Statistical study of the durability of Quercus pyrenaica.
Mass Loss (%)SapwoodHeartwood
Mean ± Standard Deviation20.71 ± 14.441.98 ± 1.91
Kruskal–Wallis TestH (p)
14.40 (p < 0.01)
FungusC. puteanaT. versicolorC. puteanaT. versicolor
Mean ± Standard Deviation12.36 ± 10.0829.06 ± 13.350.52 ± 0.453.45 ± 1.68
Kruskal–Wallis TestH (p)H (p)
36.46 (p < 0.01)8.11 (p < 0.05)
TermitesSapwoodHeartwood
Mean ± Standard Deviation4.29 ± 5.901.10 ± 0.29
Kruskal–Wallis TestH (p)
2.21 (p = 0.13)
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Santos, S.M.; de Troya, M.T.; Robertson, L.; Gutiérrez, S.; Caballé, G.; Villanueva, J.L. Study on the Natural Durability of Quercus pyrenaica Willd. to Wood Decay Fungi and Subterranean Termites. Forests 2025, 16, 1486. https://doi.org/10.3390/f16091486

AMA Style

Santos SM, de Troya MT, Robertson L, Gutiérrez S, Caballé G, Villanueva JL. Study on the Natural Durability of Quercus pyrenaica Willd. to Wood Decay Fungi and Subterranean Termites. Forests. 2025; 16(9):1486. https://doi.org/10.3390/f16091486

Chicago/Turabian Style

Santos, Sara M., María Teresa de Troya, Lee Robertson, Saúl Gutiérrez, Gonzalo Caballé, and José Luis Villanueva. 2025. "Study on the Natural Durability of Quercus pyrenaica Willd. to Wood Decay Fungi and Subterranean Termites" Forests 16, no. 9: 1486. https://doi.org/10.3390/f16091486

APA Style

Santos, S. M., de Troya, M. T., Robertson, L., Gutiérrez, S., Caballé, G., & Villanueva, J. L. (2025). Study on the Natural Durability of Quercus pyrenaica Willd. to Wood Decay Fungi and Subterranean Termites. Forests, 16(9), 1486. https://doi.org/10.3390/f16091486

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