Abstract
Results of research on the diversity of wood-rot fungi found in buildings and outdoor wooden engineering structures in Poland are presented in this article. A total of 47 species and genera of wood-rot fungi from Basidiomycota (19 brown rot fungi, 28 white rot fungi) and 1 genus from Ascomycota (1 fungus that does not cause wood decay) were found in damaged buildings. The greatest number of wood-rot fungi was reported on outdoor wooden engineering structures (33 species), followed by unoccupied residential buildings (30 species). The lowest diversity was found in occupied residential buildings (20 species). A total of 34 species and genera of fungi were found in all examined structures, out of which 17 species caused brown rot, 16 caused white rot, and 1 did not cause wood decay.
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Diversity of Indoor Wood Decaying Fungi in Poland
Bogusław Andres,* Krzysztof J. Krajewski, and Izabela Betlej
Results of research on the diversity of wood-rot fungi found in buildings and outdoor wooden engineering structures in Poland are presented in this article. A total of 47 species and genera of wood-rot fungi from Basidiomycota (19 brown rot fungi, 28 white rot fungi) and 1 genus from Ascomycota (1 fungus that does not cause wood decay) were found in damaged buildings. The greatest number of wood-rot fungi was reported on outdoor wooden engineering structures (33 species), followed by unoccupied residential buildings (30 species). The lowest diversity was found in occupied residential buildings (20 species). A total of 34 species and genera of fungi were found in all examined structures, out of which 17 species caused brown rot, 16 caused white rot, and 1 did not cause wood decay.
DOI: 10.15376/biores.17.3.4856-4869
Keywords: Diversity; Frequency; House-rot fungi; Wood-decaying fungi
Contact information: Institute of Wood Sciences and Furniture, Warsaw University of Life Sciences (SGGW), 159 Nowoursynowska St., 02-776 Warsaw, Poland;
* Corresponding author: boguslaw_andres@sggw.edu.pl
INTRODUCTION
Due to its high load-bearing capacity, insulation, and low carbon footprint, wood is an important material used in construction. However, if not properly preserved, it is subject to degradation by a variety of biotic components. Fungi are one of the main causes of degradation of wooden buildings (Schmidt 2007). House-rot fungi do not specialize exclusively in wood degradation of buildings. They are saprotrophic fungi inhabiting dead wood in forests or outdoors, and they colonize building materials in structures due to favorable conditions for their development (Lloyd and Singh 1994). These conditions usually occur due to flawed design, mistakes made during construction, or improper use. House-rot fungi attack wood in structures according to their temperature and moisture content preferences (Schmidt 2006). For example, fungi that decompose fallen trees and tree stumps are observed in damp and cool basements.
According to the classification presented by Blanchette (2000), taking into account the macroscopic appearance of wood biodegradation, three types of decomposition caused by fungi associated with these decompositions have been distinguished: white rot – caused by fungi that degrade cellulose, hemicelluloses and lignin; brown rot – caused by fungi that degrade cellulose, hemicelluloses and do not degrade lignin; and soft rot – caused by fungi that degrade cellulose and hemicelluloses but only at surface level.
In the Northern Hemisphere, the most commonly used wood for structural timber is derived from coniferous trees. Brown rot fungi causes the most economic damage to European and North American buildings (Schmidt and Huckfeldt 2011). Because of progressive decay, wood attacked by fungi loses its original properties. The mechanical strength of structural timber is reduced, resulting in major building failures or disasters.
The terms house-rot fungi and dry-rot fungi are used exclusively for wood-destroying fungi in buildings. Fungi destroying stored wood and structural timber outdoors constitute a separate group. Due to differences in the classification of fungi destroying structural timber indoors and outdoors dating back to the 1930s (Skupieński 1937), species destroying structural timber indoors, structural timber outdoors, and stored wood are all referred to as “house-rot fungi”. The first classification of house-rot fungi in Poland was presented by Ważny (1951); this classification was modified several times (Ważny 1957; 1958; 1963; 1970; 1983). Its latest version (Table 1) was published in 2001 (Ważny 2001). Publications by other authors, which appeared in later years (Krajewski and Witomski 2012; Karyś 2014), did not introduce any changes to the Ważny (2001) classification. Thus, despite being published over 20 years ago, the last update of the classification of house-rot fungi by Ważny (2001) is still considered up to date and accurate in Poland. This classification includes the location of damage, developed on the basis of reliable field studies.
Only the most important species are discussed in national monographs on wood-destroying fungi indoors and outdoors. Thus, the list of house-rot fungi in domestic monographs is limited to 8 to 13 species. In contrast, 6 to 26 species of house-rot fungi are discussed in foreign monographs (Table 1). A higher number of species discussed in foreign monographs is connected, among other things, with more frequent use of hardwood in housing construction (Andres et al. 2019).
Table 1. House-rot Fungi from Basidiomycota Discussed in Poland Monographs (Andres et al. 2019)
However, the diversity of indoor wood-decaying fungi is much higher, as evidenced by numerous articles presenting the results of field studies carried out in Europe. Alfredsen et al. (2005) presented a list of 31 species and genera of indoor decay fungi in southern Norway. Schmidt (2007) published a list of 74 species and genera of wood-infesting fungi in buildings in Germany. Fraiture (2008) reported a list of 101 species and genera of indoor wood-decay fungi in Belgium. Irbe et al. (2008) presented a list of 23 species of wood infesting fungi in historic buildings in Macedonia. Vampola (2008) published a list of 40 species of indoor wood-decay fungi in the Czech Republic. Schmidt and Huckfeldt (2011) reported a list of 117 species and genera of indoor wood-decay fungi in Germany. Irbe et al. (2012) presented a list of 46 species and genera of fungi destroying the exterior of wooden buildings in Latvia. Haas et al. (2019) reported a list of 40 species of fungi infesting wood in buildings in Styria (Austria).
Interesting results on the biodiversity of fungi found in buildings in France were presented by Slimen et al. (2020). The authors of the study, using multidisciplinary analytical tools, identified in the 18th century wooden building fungi causing brown and white rot, in particular S. lacrymans and Coprinellus aff. radians and numerous species of fungi belonging to the Ascomycota.
Gabriel and Švec (2017) analyzed data on the occurrence of wood-decaying fungi in the Albania, Belgium, Czech Republic, Denmark, Estonia, Finland, France, Germany, Latvia, Norway, Poland and Romania. The most abundant fungi causing deep wood decay in buildings in the indicated countries, except Norway, were S. lacrymans and C. puteana. In Norway, however, A. vaillanti (currently F. vaillantii) was the dominant wood-decaying species.
Materials that are used in newly constructed and renovated buildings should improve the management of humidity and thermal comfort, which should reduce the incidence of indoor fungal growth and in particular that of white and brown rot agents. However, some conceptual and design solutions that do not consider the regional climate, the tendency to shorten the construction time to the bare minimum, and the use of old technologies (wet construction systems with high water requirements/consumption) encourage the development of indoor fungi. These characteristics of the modern construction industry, which increase the risk of fungal infestation, have prompted the authors of this publication to conduct a survey study on the diversity of indoor and outdoor wood-decay fungi. This work reviews the diversity of indoor wood-decay fungi in Poland and compares the results with other European studies.
EXPERIMENTAL
The study was conducted in late 2019 and early 2020 to review the list of house-rot fungi found during mycological and building inspections. Mycological and mycological-construction experts associated with the Polish Association of Building Mycologists (PABM) took part in the research. All members of this group had appropriate, certified specialist knowledge and skills in the field of building mycology. Mycological and mycological-construction experts PABM took part in the research, after obtaining informed consent from the PABM Main Board. Participation in the research process was voluntary. The applied research procedures were compliant with the principles of ethics contained in the Code of Ethics for Research Workers – Polish Academy of Sciences.
In order to efficiently collect research results from PABM experts, a data entry form was created and made available to experts online. The data entry form consisted of 21 species of fungi selected based on current publications discussing the occurrence of house-rot fungi in Europe. The species were selected based on the frequency of their occurrence in Central-Western European buildings and based on observations made during mycological and building surveys in Poland. Before providing data on the frequency and location of the fungus species, the experts could read a note containing the technical name, a synonym of the current Latin name, and a brief description of morphological structures of the fungus (macro- and microscopic). When filling out the form about the frequency of occurrence, the experts had to choose one of the following options: very often (more than 50% of observations), often (up to 50% of observations), rarely (up to 25% of observations), occasionally (up to 5% of observations), or not found. Additionally, there was an open question in which the respondent experts could provide names of observed fungal species that were not included in the form.
After determining the frequency of occurrence of a given species, the expert could indicate the type of structure in which they found morphological structures of the fungus. When answering this question, one or more answers could be chosen from: occupied residential buildings (RB), unoccupied residential buildings (URB), other buildings: sheds, wood shelters, etc. (OB), structural timber outdoors (STO) and other locations: mines, abandoned churches, railroad ties, etc. (OL).
The following was stated in a description, which immediately preceded the data entry form: Sending back the completed form is tantamount to the respondent expert being in possession of appropriate photographic documentation and/or desiccated fungi samples of the observed fungal species.
The experts taking part in the study were tasked with providing percentage values for the frequency of occurrence of given fungal species in controlled structures. The data for filling in the form by the experts came from mycological research they conducted during their inspections of fungus-damaged buildings.
The frequency of occurrence of given fungal species, presented in Table 2 (column 3) and Table 3 (column 8), was determined according to Eq. 1,
(1)
where f is the frequency of occurrence of given fungal species, is the weighted arithmetic mean based on values indicated by experts, and n is the number of observed fungal species and genera (n = 48). The frequency of occurrence of fungal species in given object categories was determined in a similar fashion (Table 2, columns 4 through 8).
Statistical error was calculated using the statistical calculator provided on the NETSTEL Software website (naukowiec.org) assuming a confidence level of α = 0.95 and a fraction size of 0.5 (in the absence of information on the distribution of the statistical characteristic in the studied population).
The names of fungi are provided according to systematics updated on a regular basis in the Index Fungorum database (2022).
RESULTS AND DISCUSSION
Based on the results of an internet query, the number of PABM experts actively performing expert reports in 2019 was determined to be 100. For the assumed confidence interval (α = 0.95), it was calculated that collecting 81 questionnaires research forms from mycological and mycological-construction experts would guarantee a study statistical error of 5%. The study involved 73 experts, so the statistical error was 6%. All questionnaires were filled out correctly, i.e., there were no logical errors. The results of the questionnaire are presented in Table 2. The table shows the total frequency of fungal occurrence in the inspected objects divided into object categories, in which fungal morphological structures were detected. The fungi were sorted in descending order based on the total frequency of occurrence in buildings.
The study conducted focused on large Basidiomycota fungi (macromycetes), i.e. with fruiting bodies larger than 5 mm. Therefore, a number of micromycetes (e.g. from Ascomycota) found in the fungus infested buildings were not presented in the results of the study.
The experts provided a total of 48 types of fungi (43 species and 5 fungi recognized to genus): 47 species and genera of wood-degrading Basidiomycota (including 41.7% brown rot fungi and 58.3% white rot fungi) and 1 genus from Ascomycota (Table 2). The highest species diversity of wood-rot fungi was found on outdoor structures (STO) – 33 species. The second location in terms of diversity was unoccupied residential buildings (URB) – 30 species. The lowest diversity was found in occupied residential buildings (RB) – 21 species.
Table 2. Total Frequency of Fungal Occurrence in Control Sites and Locations of Fungal Morphological Structures
Thirty-four species and genera of fungi were found in buildings (RB, URB, and OB), including 33 wood-rot fungi (51.5% brown rot fungi and 48.5% white rot fungi). A total of 87.3% of fungal species and genera observed in buildings were brown rot fungi, 12.3% were white rot fungi, and 0.4% did not cause wood decay (concerns Peziza sp. fungi, which are not classified as wood destroying fungi).
Table 2 (columns 4 through 8) can be used to track which buildings were most frequently infested by given fungal species. In the case of species entered by experts (fungi outside the list of 21 species included in the questionnaire), Table 2 does not show their percentage occurrence in each category but only indicates these categories by “x”. The other locations category (OL), which was filled out by experts, proved to be the most diverse. Experts indicated following locations: structures on forested land, mines, lumber yard stores, railroad sleepers, and others.
The results of field investigations published in the form of articles generally present a much broader spectrum of wood-rot fungi in buildings than it is described in monographs. There are relatively few national publications (articles) on the species diversity of house-rot fungi because for over 40 years, no data on the occurrence of wood-decaying fungi in buildings were published in Poland. Few publications refer to selected areas of Poland (Ważny and Czajnik 1973; 1974a; 1974b; Konarski 1974) or focus on a specific category of objects (Ważny and Czajnik 1963a; Ważny et al. 1999; Andres 2011). Only the publication by Ważny and Czajnik (1963b) provides data for the entire country on wood rot fungi in buildings (Table 3). In the publication from the 1960s (Ważny and Czajnik 1963b), a list of 26 species was provided (including 61.5% brown rot fungi and 38.5% white rot fungi), whereas the experts taking part in the study provided a total of 33 wood rot fungi. In addition to the increase in diversity, it can be concluded that the proportions of species causing brown rot and white rot of wood have slightly changed. In the 1960s, the total frequency of observations of brown rot fungi in buildings was 95.4%. In this study, the total number of observations of brown rot fungi was 86.7%. The obtained results could have been significantly influenced by the revitalization programs implemented in the country after 2004 (after Poland’s accession to the European Union) and since 2015 widely implemented under the Municipal Revitalization Programs (Ministry of Development Funds and Regional Policy). These programs are aimed at, inter alia, counteracting the degradation of the urban structure of cities and striving for reconstruction of cities’ historical identities. As part of integrated revitalization projects, the following are renovated: historical market squares, tenement blocks, and 19th century postindustrial complexes (according to nomenclature adopted in this publication: RB, URB and OB). The observations of the authors of this article confirm that buildings intended for revitalization are often heavily damaged, and due to the high moisture inside of them, favorable conditions for the development of white rot fungi occur.
It should be noted, however, that despite the indicated noticeable differences between the results from the 1960s and the current state of fungal infestation in buildings in Poland, both studies had different methodologies for obtaining data.
Table 3. Abundance of (%) Wood-Decaying Fungi in Buildings