Spalting is any form of wood coloration caused by fungi. Although primarily found in dead trees, spalting can also occur in living trees under stress. Although spalting can cause weight loss and strength loss in the wood, the unique coloration and patterns of spalted wood are sought by woodworkers. [1]
Spalting is divided into three main types: pigmentation, white rot, and zone lines. Spalted wood may exhibit one or all of these types in varying degrees. Both hardwoods (deciduous) and softwoods (coniferous) can spalt, but zone lines and white rot are more commonly found on hardwoods due to enzymatic differences in white rotting fungi. Brown rots are more common to conifers, although one brown rot, Fistulina hepatica (beefsteak fungus), is known to cause spalting among deciduous trees. [2]
Pigmentation is caused when fungi produce extracellular pigments inside wood. Bluestain is also a form of pigmentation; however, bluestain pigments are generally bound within the hyphae cell walls. [3] [4] A visible color change can be seen if enough hyphae are concentrated in an area. [5] Pigmenting fungi classified as spalting fungi do decay wood, they simply do so at a slower rate (soft rotting) than white rotting fungi. [6] [7] The most common groups of pigmentation fungi are the imperfect fungi and the ascomycetes. [8] Mold fungi, such as Trichoderma spp., are not considered to be spalting fungi, as their hyphae do not colonize the wood internally and they do not produce the enzymes necessary to digest the wood cell wall components.
The mottled white pockets and bleaching effect seen in spalted wood is due to white rot fungi. Primarily found on hardwoods, these fungi "bleach" by consuming lignin, which is the slightly pigmented area of a wood cell wall. [9] Some white rotting can also be caused by an effect similar to pigmentation, in which the white hyphae of a fungus, such as Trametes versicolor (Fr.) Pil., is so concentrated in an area that a visual effect is created. [10]
Both strength and weight loss occur with white rot decay, causing the "punky" area often referred to by woodworkers. Brown rots, the "unpleasing" type of spalting, do not degrade lignin, thus creating a crumbly, cracked surface which cannot be stabilized. [5] Both types of rot, if uncontrolled, will render wood useless.
Dark dotting, winding lines and thin streaks of red, brown and black are known as zone lines. This type of spalting does not occur due to any specific type of fungus, but is instead an interaction zone in which different fungi have erected barriers to protect their resources. [8] They can also be caused by a single fungus delineating itself. The lines are often clumps of hard, dark mycelium, referred to as pseudosclerotial plate formation. [11]
Zone lines themselves do not damage the wood. However, the fungi responsible for creating them often do. Spalted wood is also sometimes known as web wood.
Conditions required for spalting are the same as the conditions required for fungal growth: fixed nitrogen, micronutrients, water, warm temperatures and oxygen. [5] [12]
Water: Wood must be saturated to a 20% moisture content or higher for fungal colonization to occur. Wood placed underwater lacks sufficient oxygen, and colonization cannot occur. [13]
Temperature: The majority of fungi prefer warm temperatures between 10 and 40 °C, [13] with rapid growth occurring between 20 and 32 °C. [14]
Oxygen: Fungi do not require much oxygen, but conditions such as waterlogging will inhibit growth. [15] [16]
Time: Different fungi require different amounts of time to colonize wood. Research conducted on some common spalting fungi found that Trametes versicolor, when paired with Bjerkandera adusta , took eight weeks to spalt 1.5 inch (38 mm) cubes of Acer saccharum . [1] Colonization continued to progress after this time period, but the structural integrity of the wood was compromised. The same study also found that Polyporus brumalis, when paired with Trametes versicolor, required 10 weeks to spalt the same size cubes.
The Ohio Department of Natural Resources found that pale hardwoods had the best ability to spalt. [17] Some common trees in this category include maple (Acer spp.), birch (Betula spp.) and beech (Fagus spp.). However, recent research suggests that sugar maple (Acer saccharum) and aspen (Populus sp.) are preferred by both white rot and pigment fungi. [18] [19]
One of the trickier aspects to spalting is that some fungi cannot colonize wood alone; they require other fungi to have preceded them to create favorable conditions. Fungi progress in waves of primary and secondary colonizers, [4] where primary colonizers initially capture and control resources, change the pH of the wood and its structure, and then must defend against secondary colonizers that then have the ability to colonize the substrate. [4] [20]
Ceratocystis spp. (Ascomycetes) contains the most common blue stain fungi. [21] Other pigmenting fungi include Chlorociboria aeruginascens , Chlorociboria aeruginosa , Scytalidium cuboideum , and Scytalidium ganodermophthorum . [22] Trametes versicolor , (Basidiomycetes) is found all over the world and is a quick and efficient white rot of hardwoods. [4] Xylaria polymorpha (Pers. ex Mer.) Grev. (Ascomycetes) has been known to bleach wood, but is unique in that it is one of the few fungi that will erect zone lines without any antagonism from other fungi. [23]
Initial lab work was conducted on spalting in the 1980s at Brigham Young University. A method for improving machinability in spalted wood using methyl methacrylate was developed in 1982, [24] and several white rot fungi responsible for zone line formation were identified in 1987. [25] Current research at Michigan Technological University has identified specific time periods at which certain spalting fungi will interact, and how long it takes for said fungi to render the wood useless. [1] Researchers from this university also developed a test for evaluating the machinability of spalted wood using a universal test machine. [26]
Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The defining feature of this fungal group is the "ascus", a microscopic sexual structure in which nonmotile spores, called ascospores, are formed. However, some species of the Ascomycota are asexual, meaning that they do not have a sexual cycle and thus do not form asci or ascospores. Familiar examples of sac fungi include morels, truffles, brewers' and bakers' yeast, dead man's fingers, and cup fungi. The fungal symbionts in the majority of lichens such as Cladonia belong to the Ascomycota.
Polypores are a group of fungi that form large fruiting bodies with pores or tubes on the underside. They are a morphological group of basidiomycetes-like gilled mushrooms and hydnoid fungi, and not all polypores are closely related to each other. Polypores are also called bracket fungi or shelf fungi, and they characteristically produce woody, shelf- or bracket-shaped or occasionally circular fruiting bodies that are called conks.
Intraspecific antagonism means a disharmonious or antagonistic interaction between two individuals of the same species. As such, it could be a sociological term, but was actually coined by Alan Rayner and Norman Todd working at Exeter University in the late 1970s, to characterise a particular kind of zone line formed between wood-rotting fungal mycelia. Intraspecific antagonism is one of the expressions of a phenomenon known as vegetative or somatic incompatibility.
Trametes versicolor – also known as Coriolus versicolor and Polyporus versicolor – is a common polypore mushroom found throughout the world. Meaning 'of several colors', versicolor reliably describes this fungus that displays a variety of colors. For example, because its shape and multiple colors are similar to those of a wild turkey, T. versicolor is commonly called turkey tail. A similar looking mushroom, commonly called false turkey tail, which is from a different order, may sometimes be confused with the turkey tail mushroom due to appearance. Another lookalike is the multicolor gill polypore.
Chlorociboria is the type genus of in the fungal family Chlorociboriaceae within order Helotiales. The genus includes 23 species.
Xylaria is a genus of ascomycetous fungi commonly found growing on dead wood. The name comes from the Greek xýlon meaning wood.
Lignin-modifying enzymes (LMEs) are various types of enzymes produced by fungi and bacteria that catalyze the breakdown of lignin, a biopolymer commonly found in the cell walls of plants. The terms ligninases and lignases are older names for the same class, but the name "lignin-modifying enzymes" is now preferred, given that these enzymes are not hydrolytic but rather oxidative by their enzymatic mechanisms. LMEs include peroxidases, such as lignin peroxidase, manganese peroxidase, versatile peroxidase, and many phenoloxidases of the laccase type.
A wood-decay or xylophagous fungus is any species of fungus that digests moist wood, causing it to rot. Some species of wood-decay fungi attack dead wood, such as brown rot, and some, such as Armillaria, are parasitic and colonize living trees. Excessive moisture above the fibre saturation point in wood is required for fungal colonization and proliferation. In nature, this process causes the breakdown of complex molecules and leads to the return of nutrients to the soil. Wood-decay fungi consume wood in various ways; for example, some attack the carbohydrates in wood, and some others decay lignin. The rate of decay of wooden materials in various climates can be estimated by empirical models.
Mycelial cords are linear aggregations of parallel-oriented hyphae. The mature cords are composed of wide, empty vessel hyphae surrounded by narrower sheathing hyphae. Cords may look similar to plant roots, and also frequently have similar functions; hence they are also called rhizomorphs. As well as growing underground or on the surface of trees and other plants, some fungi make mycelial cords which hang in the air from vegetation.
Xylaria polymorpha, commonly known as dead man's fingers, is a saprobic fungus. It is a common inhabitant of forest and woodland areas, usually growing from the bases of rotting or injured tree stumps and decaying wood. It has also been known to colonize substrates like woody legume pods, petioles, and herbaceous stems. It is characterized by its elongated upright, clavate, or strap-like stromata poking up through the ground, much like fingers. The genus Xylaria contains about 100 species of cosmopolitan fungi. Polymorpha means "many forms". As its name suggests, it has a very variable but often club-shaped fruiting body (stroma) resembling burned wood.
Kretzschmaria deusta, commonly known as brittle cinder, is a fungus and plant pathogen found in temperate regions of the Northern Hemisphere on broad-leaved trees, also found in Argentina, South Africa, and Australia.
Coriolopsis gallica is a fungus found growing on decaying wood. It is not associated with any plant disease, therefore it is not considered pathogenic. For various Coriolopsis gallica strains isolated, it has been found, as a common feature of the division Basidiomycota, that they are able to degrade wood components, mainly lignin and to lesser extent cellulose, which results in a degradation area covered by the accumulating -white- cellulose powder. Therefore, C. gallica might generically be called, as with many other basidiomycetes, a "white-rot" fungus.
Daedaleopsis confragosa, commonly known as the thin walled maze polypore or the blushing bracket, is a species of polypore fungus in the family Polyporaceae. A plant pathogen, it causes a white rot of injured hardwoods, especially willows. The fruit bodies are semicircular and tough, have a concentrically zoned brownish upper surface, and measure up to 20 cm (8 in) in diameter. The whitish underside turns gray-brown as the fruit body ages, but bruises pink or red. It is found all year and is common in northern temperate woodlands of eastern North America, Europe, and Asia. The species was first described from Europe in 1791 as a form of Boletus, and has undergone several changes of genus in its taxonomic history. It acquired its current name when Joseph Schröter transferred it to Daedaleopsis in 1888.
Lenzites elegans, also known as Trametes elegans and Daedalea elegans, is a common polypore and wood-decay fungus with a pantropical distribution found on hardwood hosts in regions including Australia, New Zealand, and Japan. Though it is referred to as Lenzites elegans on this wikipedia page, The Species Fungorum places it current name as Trametes Elegans. It has recently been considered a complex that is split into three different species: T. elegans,T. aesculi, and T. repanda.
Trametes pubescens is a small, thin polypore, or bracket fungus. It has a cream-colored, finely velvety cap surface. Unlike most other turkey tail-like species of Trametes, the cap surface lacks strongly contrasting zones of color.
Meripilus giganteus is a polypore fungus in the family Meripilaceae. It causes a white rot in various types of broadleaved trees, particularly beech (Fagus), but also Abies, Picea, Pinus, Quercus and Ulmus species. This bracket fungus, commonly known as the giant polypore or black-staining polypore, is often found in large clumps at the base of trees, although fruiting bodies are sometimes found some distance away from the trunk, parasitizing the roots. M. giganteus has a circumboreal distribution in the northern Hemisphere, and is widely distributed in Europe. In the field, it is recognizable by the large, multi-capped fruiting body, as well as its pore surface that quickly darkens black when bruised or injured.
The Echinodontiaceae are a family of crust fungi in the order Russulales. Species of this family, divided amongst two genera—Echinodontium and Laurilia—have a widespread distribution, although they are especially predominant in north temperate zones. They are parasitic or saprobic on wood, and may cause white rot of angiosperms and gymnosperms.
Panellus stipticus, commonly known as the bitter oyster, the astringent panus, the luminescent panellus, or the stiptic fungus, is a species of fungus in the family Mycenaceae, and the type species of the genus Panellus. A common and widely distributed species, it is found in Asia, Australia, Europe, and North America, where it grows in groups or dense overlapping clusters on the logs, stumps, and trunks of deciduous trees, especially beech, oak, and birch. During the development of the fruit bodies, the mushrooms start out as tiny white knobs, which, over a period of one to three months, develop into fan- or kidney-shaped caps that measure up to 3 cm (1.2 in) broad. The caps are orange-yellow to brownish, and attached to the decaying wood by short stubby stalks that are connected off-center or on the side of the caps. The fungus was given its current scientific name in 1879, but has been known by many names since French mycologist Jean Bulliard first described it as Agaricus stypticus in 1783. Molecular phylogenetic analysis revealed P. stipticus to have a close genetic relationship with members of the genus Mycena.
Catherine Gross Duncan (1908-1968) was an American mycologist from the early 20th century. Her major area of focus was wood-decay fungi.
Scytalidium ganodermophthorum is an anthroconidial ascomycete fungus in the Scytalidium genus. It is also known by its teleomorph name Xylogone ganodermophthora. It is the cause of yellow rot in lingzhi mushrooms and it is used in spalting as a pigmenting fungi.