Airborne fungal colonisation of coarse woody debris in North Temperate Picea abies forest : impact of season and local spatial scale Rimvydas VASILIAUSKAS 1 *, Vaidotas LYGIS 1 , Karl-Henrik LARSSON 2 and Jan STENLID 1 1 Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, Box 7026, SE-750 07 Uppsala, Sweden. 2 Botanical Institute, Go ¨teborg University, Box 461, SE-405 30 Go ¨teborg, Sweden. E-mail : [email protected]Received 27 August 2004; accepted 24 November 2004. Coarse woody debris is important for mycodiversity in forest ecosystems, but its availability in managed stands is reduced. Leaving dead wood during felling is suggested as an option to sustain and restore the diversity. However, little is known what fungi would colonise freshly cut wood left on managed sites, and how the colonisation process is influenced by ecological factors. During summer and autumn, 120 freshly cut Picea abies stem sections over 8 cm in diameter were placed upright in mapped locations over two discrete plots separated by 100 m in a north-temperate forest. After seven weeks the sections were collected, and isolation and identification of fungi was done from their upper surfaces. In all 943 fungal strains were isolated, representing 97 species. Species richness in the summer survey was 42.5 % higher than during the autumn survey. Low species similarity characterized the different seasons (Sorensen indices : S S =0.36 and S N =0.34) and for 21 species (22 %) observation frequency was significantly affected by season. As a result, community structures in summer and autumn differed notably (z-test ; P<0.001). Species richness between the two plots differed by less than 10%, but there were 64 species (66%) found only in one of them, thus qualitative similarity was low (S S =0.49). Quantitative similarity was higher (S N =0.63), indicating that the dominant species colonised wood to a similar extent in both areas. Fungal community structure differed significantly among the two plots (z-test ; P<0.001). Our data showed that freshly cut CWD contributed to mycodiversity in managed north-temperate forest, providing habitats for numerous individuals from over 100 species. The fungal community within a single stand differed markedly both across small distances and over the seasons. In order to sustain and enhance mycodiversity in managed stands, coarse wood should always be left during harvesting. This study also demonstrates the importance of molecular identification and ITS sequence databases for exploring fungal diversity in natural communities. INTRODUCTION Coarse woody debris (CWD) includes various types of dead wood, e.g. snags, logs, large branches and roots. The size used to define CWD varies among studies, but generally it is supposed to exceed 7 cm diam (Harmon et al. 1986, Samuelsson, Gustafsson & Ingelo¨g 1994). The importance of CWD for the function of forest ecosystems and to biodiversity of a broad range of organisms (e.g. mammals, birds, amphibians, invert- ebrates, plants, lichens, and saprobic fungi) is now widely recognized (Maser & Trappe 1984, Harmon et al. 1986, Samuelsson et al. 1994, McComb & Lindenmayer 1999). In particular, CWD is of vital importance to lignicolous fungi that play a crucial role in wood decomposition and nutrient cycling within the ecosystem. Many studies have shown that species rich- ness of wood-inhabiting fungi and non-vascular plants (threatened species in particular) increases with the amount of CWD in a stand (Bader, Jansson & Jonsson 1995, Ohlson et al. 1997, Lindblad 1998, Humphrey et al. 2000, Kruys 2001, Sippola, Lehesvirta & Renvall 2001). The presence of logs with high degree of decay and of large dimensions was initially thought to be one of the strongest determinants of fungal diversity within a given forest site (Bader et al. 1995, Høiland & Bendiksen 1996, Kruys et al. 1999). However, more recent studies have shown the importance also of smaller logs (Kruys & Jonsson 1999, Czederpiltz 2001, Heilmann-Clausen 2003). Intensively managed forest stands are characterized by uniform tree species, size, age and spacing, and absence of CWD (Hansen et al. 1991). Such reduced availability (or complete absence) of suitable substrates * Corresponding author. Mycol. Res. 109 (4): 487–496 (April 2005). f The British Mycological Society 487 doi:10.1017/S0953756204002084 Printed in the United Kingdom.
Transcript
Airborne fungal colonisation of coarse woody debris in
North Temperate Picea abies forest : impact of season and
local spatial scale
Rimvydas VASILIAUSKAS1*, Vaidotas LYGIS1, Karl-Henrik LARSSON2 and Jan STENLID1
1Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, Box 7026, SE-750 07 Uppsala,Sweden.2Botanical Institute, Goteborg University, Box 461, SE-405 30 Goteborg, Sweden.
Received 27 August 2004; accepted 24 November 2004.
Coarse woody debris is important for mycodiversity in forest ecosystems, but its availability in managed stands isreduced. Leaving dead wood during felling is suggested as an option to sustain and restore the diversity. However, littleis known what fungi would colonise freshly cut wood left on managed sites, and how the colonisation process is
influenced by ecological factors. During summer and autumn, 120 freshly cut Picea abies stem sections over 8 cm indiameter were placed upright in mapped locations over two discrete plots separated by 100 m in a north-temperate forest.After seven weeks the sections were collected, and isolation and identification of fungi was done from their upper
surfaces. In all 943 fungal strains were isolated, representing 97 species. Species richness in the summer survey was 42.5%higher than during the autumn survey. Low species similarity characterized the different seasons (Sorensen indices:SS=0.36 and SN=0.34) and for 21 species (22%) observation frequency was significantly affected by season. As a result,community structures in summer and autumn differed notably (z-test ; P<0.001). Species richness between the two plots
differed by less than 10%, but there were 64 species (66%) found only in one of them, thus qualitative similarity was low(SS=0.49). Quantitative similarity was higher (SN=0.63), indicating that the dominant species colonised wood to asimilar extent in both areas. Fungal community structure differed significantly among the two plots (z-test ; P<0.001).
Our data showed that freshly cut CWD contributed to mycodiversity in managed north-temperate forest, providinghabitats for numerous individuals from over 100 species. The fungal community within a single stand differed markedlyboth across small distances and over the seasons. In order to sustain and enhance mycodiversity in managed stands,
coarse wood should always be left during harvesting. This study also demonstrates the importance of molecularidentification and ITS sequence databases for exploring fungal diversity in natural communities.
INTRODUCTION
Coarse woody debris (CWD) includes various types ofdead wood, e.g. snags, logs, large branches and roots.The size used to define CWD varies among studies, butgenerally it is supposed to exceed 7 cm diam (Harmonet al. 1986, Samuelsson, Gustafsson & Ingelog 1994).The importance of CWD for the function of forestecosystems and to biodiversity of a broad range oforganisms (e.g. mammals, birds, amphibians, invert-ebrates, plants, lichens, and saprobic fungi) is nowwidely recognized (Maser & Trappe 1984, Harmonet al. 1986, Samuelsson et al. 1994, McComb &Lindenmayer 1999). In particular, CWD is of vitalimportance to lignicolous fungi that play a crucial rolein wood decomposition and nutrient cycling within the
ecosystem. Many studies have shown that species rich-ness of wood-inhabiting fungi and non-vascular plants(threatened species in particular) increases with theamount of CWD in a stand (Bader, Jansson & Jonsson1995, Ohlson et al. 1997, Lindblad 1998, Humphreyet al. 2000, Kruys 2001, Sippola, Lehesvirta & Renvall2001). The presence of logs with high degree of decayand of large dimensions was initially thought to be oneof the strongest determinants of fungal diversity withina given forest site (Bader et al. 1995, Høiland &Bendiksen 1996, Kruys et al. 1999). However, morerecent studies have shown the importance also ofsmaller logs (Kruys & Jonsson 1999, Czederpiltz 2001,Heilmann-Clausen 2003).
Intensively managed forest stands are characterizedby uniform tree species, size, age and spacing, andabsence of CWD (Hansen et al. 1991). Such reducedavailability (or complete absence) of suitable substrates* Corresponding author.
Mycol. Res. 109 (4): 487–496 (April 2005). f The British Mycological Society 487
doi:10.1017/S0953756204002084 Printed in the United Kingdom.
inevitably leads to a decrease in species richness ofmany organisms, including lignicolous fungi (Siitonen2001, Edman 2003). Therefore, one possible option tosustain or even to restore the mycodiversity in managedforest areas could be leaving certain amounts of deadwood during forest operations. For temperate standsof central Europe, suggested amounts comprise 1–2%of the total number of trees in mature stands, and5–10 m3 hax1 in other stands (Ammer 1991, Utschick1991). However, little is known about which fungiwould colonise freshly cut wood left on managed forestsites, and how the colonisation process is influenced byecological factors, such as season or spatial scale. Thestructure of the primary decayer community is animportant determinant for subsequent fungal suc-cession and for species richness at later stages of wooddecomposition (Hudson 1968, Cooke & Rayner 1984,Renvall 1995).
The primary aims of the present work are to inves-tigate fungal community in freshly cut CWD, artifici-ally distributed in managed forest of Norway spruce(Picea abies), and to estimate the impact of season andspatial scale during the early stages of communityestablishment. In addition the distribution of myceliainside the wood was examined. To date, distribution offungal individuals in freshly exposed wood has beenextensively studied only in logs of Fagus sylvatica(Coates & Rayner 1985c). Related studies on P. abiesCWD concerned mapping of individual mycelia inolder and well-decayed substrates mainly (Gustafsson2002, Kauserud & Schumacher 2002, 2003).
MATERIALS AND METHODS
Study area and fieldwork
The study was carried out in the experimental areaS9-Ramsjon of the Swedish Forest Research Institute(Skogforsk), located in central Sweden about 150 kmnorth-west of Stockholm (Thor 1997). It comprises a 40old plantation of Picea abies that was thinned once,4 yr prior to our study. The experiment was conductedin two discrete 20r10 m plots separated by about100 m. It included 120 freshly cut sound-looking sprucestem sections (baits) over 8 cm diam cut from one treeon each occasion. Average parameters of the baits arepresented in Table 1. The fieldwork was repeated twicewith identical settings : in Oct.–Nov. (autumn) 2000,and in July–Aug. (summer) 2001. During each season,60 baits were placed upright in each of two plots (35and 25, respectively). Their exact locations were map-ped in relation to the number of a neighbouring stump(all trees and stumps within the area are permanentlynumbered). Consequently, all them were placed inabout the same location during both seasons. Thebottom part of each bait was marked, and wrappedinto double plastic sheets in order to protect it from soilcontact. After 7 wk in the field, the baits were collected,individually placed in plastic bags, brought to the
laboratory and stored at +5 xC for another sevenweeks.
Isolation and identification of fungal strains
After storage, pieces of wood (about 5r5r10 mm)were cut off with a knife directly from the surface ofexposed wood at the upper cross-section of the baits(Fig. 1). From each disc at least six samples were taken,sampling its central, intermediate and outer parts, andincluding possibly more diverse areas of colonisedwood. When a high fungal diversity was observed inexposed wood, additional samples were taken fromdistinctly colonised areas. Wood samples were surfacesterilised under a flame and placed onto an agarmedium in 9 cm diam Petri dishes. Procedures of fungalisolation from the wood samples and sub-culturingof fungal strains were similar to those performed inearlier studies (Vasiliauskas & Stenlid 1998a, Lygis,Vasiliauskas & Stenlid 2004a). The extent of sampling,
Fig. 1. Patterns of fungal colonisation of Picea abies stemsections (baits) following 7 wk exposure in north-temperate
forest ; (a) cross-section of the bait, showing the presence ofdiverse fungal individuals (separated from each other by darklines) and one sampling locality (indicated by an arrow); (b)longitudinal section of the bait, showing penetration depth of
discoloration beyond the exposed surface (black arrow), andsound-looking wood that remained encased by the bark(white arrow). Sizes of white quadrats in the background are
isolation, and strains obtained are shown in Table 1.Isolated strains were either identified by observingmorphological characteristics of the mycelium or bycomparing nuclear ribosomal ITS sequences with alibrary of sequences from identified fruit bodies.Morphological identification was partly done bythe Centraal bureau voor Schimmelcultures (CBS,Utrecht). All strains isolated are deposited in thecollection of fungus cultures of the Department ofForest Mycology & Pathology, Swedish Universityof Agricultural Sciences, Uppsala.
The molecular identification included DNA extrac-tion, PCR amplifications and DNA sequencing; andfollowed protocols already established at our lab(Karen et al. 1997). The ribosomal ITS region wassequenced using two primers (ITS1 and ITS4) for everyspecimen (White et al. 1990). Sequences obtained werechecked against those available in our databases(Department of Forest Mycology and Pathology,Swedish University of Agricultural Sciences, Uppsala,and Botanical Institute, Goteborg University). Thetwo latter databases consist of sequences of wood-inhabiting fungi, obtained either directly from fruitbodies or from spore cultures of known species. Inaddition, the NCBI BLAST database (Altschul et al.1997) was checked.
Distribution of fungal mycelia in wood
Distribution of fungal mycelia was examined in a woodsection SK-93 that, for this part of the work, wasrandomly selected from among the other baits. It wasapprox. 13 cm in length and 8.5 cm diam, nine samplesfrom its surface were taken previously during the initialsampling. The section was stored in a plastic bag at 5 x
for another six months, making a total of almost ninemonths in storage.
The analysis consisted of : (1) additional samplingand isolation from the surface of the bait and from itsdeeper layers, and mapping the isolates ; (2) trackingcolumns of discoloured wood inside the bait, drawingtheir configurations, and modelling them in three-dimensional (3-D) shape; (3) vegetative compatibilitytests among the strains of the same species. At first, anadditional 14 samples were taken at the top surface(depth 0–0.4 mm) of the bait. Then, the bait wasdissected into 24 discs 1.5 mm thick, starting from thetop. Thus, a 72 mm long section of the bait, comprisingabout half of the total length, was sectioned into discs.Fungal isolations were carried out from patches ofdiscoloured wood on six discs at different depths,taking 5 samples from each disc (Table 2).
The shape of discoloured columns was analysed in23 wood discs (top disc was discarded). Prior to theanalyses, they were washed in running water andwrapped into moist paper towels. Then, borders ofdiscoloured areas on each disc were encircled with amarker by hand and photographed using digitalcamera JVC 3-CCD (light source from below the
discs). Obtained images were processed by PC softwareImage-Pro1Plus (version 4.0). Marked areas andvolume of continuous discoloration columns through-out the examined discs were calculated by softwareImage-Pro1Plus (version 4.0). Computerised 3-Dreconstruction and visualization of discolorationcolumns were carried out at the Wood UltrastructureResearch Centre, Department of Wood Science,Swedish University of Agricultural Sciences ; 3-D re-constructions were generated from the stack of imagesobtained from the 23 serial sections of the block. Theimages were processed and integrated in a CAD-basedcomputerized modelling system using Non-UniformRational B-Splines (NURBS) for the extraction ofshapes (Bardage 2001). Vegetative compatibility testswere carried out as in one of our earlier studies(Vasiliauskas & Stenlid 1998b).
Statistical analyses
The aim of statistical analyses was to elucidate possibledifferences in species richness and structure of fungalcommunities in two pairs of datasets : autumn vs sum-mer, and plot 1 vs plot 2. Species richness was analysedby calculating species accumulation curves (SACs),that show the relationship between the cumulativenumber of species found and the sampling intensity(Colwell & Coddington 1994). SACs were calculatedusing R computer language (Ihaka & Gentleman 1996).Community structure was compared in two ways: (1)by calculating qualitative (SS) and quantitative (SN)Sorensen similarity indices (Magurran 1988); (2) bymeans of paired z-test, designed to compare number ofpairvise observations from two communities influencedby a common factor (Eason, Coles & Gettinby 1986).Furthermore, the occurrence of each particular speciesin autumn vs summer baits, and in plot 1 vs plot 2 wascompared using chi-squared test ; the presence/absencedata was calculated from actual no. of strains observedamong the total no. of samples taken in respective setof baits (Fowler, Cohen & Jarvis 2001).
RESULTS
Among 1063 samples taken (8.9 per bait on average),715 (67.3%) yielded fungal cultures (the remaining32.7% were either surface-contaminated or sterile).From those, we subcultured 943 fungal strainsrepresenting 97 species, 82 (84.5%) of which wereidentified at least to genus (Table 1). The surface ofthe baits was usually colonized by many differentfungal genotypes (Fig. 1a). Their penetration down-wards into the wood was not extensive, and was limitedto 3 cm at most according to visual estimates from fivesplit summer baits. Wood that was encased by the barkappeared sound (Fig. 1b).
The season had a pronounced impact on speciesrichness of fungi colonizing freshly cut CWD on our
a Actual no. of strains of each species observed in total no. of samples (and not the percentages in total amount of strains, presented in the
Table) were compared by chi-squared tests in two datasets: autumn vs summer, and plot 1 vs plot 2. Underlined percentage value indicates that
the test was statistically significant for given species within the respective dataset. The levels of significance are shown as: *–P<0.05;
**–P<0.01; ***–P<0.001.
R. Vasiliauskas and others 491
study sites. Thus, 511 samples taken in the autumnyielded 42 different species, whereas 552 taken in sum-mer yielded 76 (Table 1, Fig. 2a). Decreasing samplingeffort in summer baits to the same figure as in autumnbaits (511) would give a calculated 73 different species(Fig. 2a). The difference between summer and autumnbaits is statistically significant (chi-squared test ; P=0.004). Thus our data indicate that the diversity offungi colonizing wood within the same area of a north-temperate forest during summer months can be almosttwice that observed during the late autumn (42.5%higher).
Autumn and summer communities differed con-siderably in species composition. As a result, qualitat-ive and quantitative Sorensen similarity indices wereonly SS=0.36 and SN=0.34, respectively when differ-ent seasons are compared (Fig. 2a). A certain numberof species were found only during one of the seasons.Thus we found 55 unique ‘summer species’ and 21‘autumn species ’ (Table 1). Most conspicuous amongthe ‘summer species’ were the basidiomycetes Resini-cium bicolor, Phlebiopsis gigantea, and Phanerochaetesordida, which dominated the community during July–Aug., but were completely absent during Oct.–Nov.(Table 1). Although other species, were present duringboth seasons, season had a significant impact on theirfrequency\ies of occurrence. Thus, the basidiomycetesHypholoma capnoides and Sistotrema brinkmannii,together with the ascomycetes, Nectria viridescens andRosselinia desmazieressii, and the conidial fungusCylindrocarpon didymum, dominated in the communityduring the autumn months, but were seldom observedin summer. In contrast, the colonization frequency of
root rot basidiomycetes in the genus Heterobasidiondecreased significantly in Oct.–Nov. (Table 1). In total,there were 21 species (22%), the colonization frequencyof which was significantly affected by season (Table 1).As a result, the community structures of fungi colon-izing wood in summer and autumn differed signifi-cantly (z-test ; P<0.001).
The species richness in plots 1 and 2, separatedwithin the investigated plantation by about 100 m, wasmore or less the same. When sampling effort is kept to356 in both plots, the estimated number of speciesrecorded in plot 1 is 57 while 52 species were recordedin plot 2, a difference in species richness of less than10% (Fig. 2b). However, 64 species (66% of the total)were found only in one of the plots (Table 1). As aresult, qualitative Sorensen similarity index (SS) amongthe communities in plot 1 and plot 2 was only 0.49. Thequantitative index, on the other hand, was higher(SN=0.63), indicating that the dominant species in theplots colonised wood to a similar extent (Fig. 2b). Theresults show that communities of wood-inhabitingfungi may differ significantly (z-test ; P<0.001) at amoderately local scale.
Extended sampling and isolation from the baitSK-93 (39 new samples down to 7 cm depth) revealed18 species, 14 of which were new for that particularbait, and nine of which were new for the wholecommunity. This raises the total number of species en-countered during the investigation to 106. The result isquite expected but also indicated by the raising speciesaccumulation curves (Fig. 2). Even with the extendedsampling of bait SK-93 our sampling is not at allexhaustive and certainly many other species of fungi
Table 2. Isolation of fungi from wood section (bait) SK-93 as a result of increased sampling effort and depth.
Note : Underlined species were not isolated during the initial sampling, and are new for the whole community (not present in Table 1). +,
isolation of single strain of a given fungus; *, strains vegetatively compatible with each other and representing one genetic individual of the
fungus.
Fungi in coarse woody debris 492
are likely to inhabit baits at these plots in addition tothose presented in the Table 1.
Sectioning of the bait has revealed a high number ofpatchy areas of discoloured wood, which, however,were hard to map. Only three discrete decay columnswere found to expand continuously throughout theexamined half of the bait (Fig. 3). Several species werepresent inside each of the columns, but the isolates ofthe same species (e.g. Peniophora piceae, Trichodermapolysporum) were always vegetatively compatible(Fig. 3, Table 2). When originating from different dis-coloured areas inside the bait, the isolates were alwaysincompatible. Initial and extended sampling yielded thesame fungal genotypes of Hormonema dematioides,Ophiostoma piceae, and Phlebiopsis gigantea. (Table 2).
DISCUSSION
We demonstrate that season and short distances insidea forest stand might have a profound impact on the
establishment of airborne wood-inhabiting fungi inCWD on north-temperate Picea abies forest sites. Themuch higher species richness observed during thesummer months (76 species in summer vs 42 in autumn)probably reflects more colonisers of fresh woodsporulating in summer than in mid- to late autumn.Nevertheless, our data also revealed the presence oftypical late season colonizers. We do not know if suchspecies really are adapted to fruiting during the coolerperiod of the year, or if they are simply out-competedin summertime.
While season had an impact on both species richnessand similarity (Fig. 2a), local distance (ca 100 m) in-fluenced community structure and not species richness,which remained more or less constant across the stand(Fig. 2b). The distinct difference in species compositionbetween our plots indicates that the local spore sourceis an important determinant of fungal communitystructure. A study of Heterobasidion spp., commonwood-decay polypore in the temperate zone (recordedalso during the present work; Table 1), demonstratedthat the spore deposition gradient is very steep withinthe first 100 m from a fruit body (Stenlid 1994). Asimilar result was obtained in a study of corticioidwood-decomposer, Phlebia centrifuga (Norden &Larsson 2000). Recent work demonstrates the import-ance of landscape composition on spore deposition of
Fig. 3. Computerised three-dimensional picture of three
discrete discoloration columns inside Picea abies stem section(approx. 8.5 cm in diameter) starting from the top. P.p.,Peniophora piceae ; T.v., Trametes versicolor ; T.p.,
level from which each species was isolated within respectivecolumns is indicated by the bars.
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SS=0.36
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Autumn
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Fig. 2. Sampling effort and species richness of fungi in Picea
abies stem sections (baits) following 7 week exposure innorth-temperate forest. The datasets are compared from thebaits that were (a) exposed during July–August (summer) vs.
October–November (autumn), and (b) distributed in twodiscrete plots (plot 1 and plot 2) separated by a distance ofabout 100 m. The structure of fungal communities iscompared by qualitative (SS) and quantitative (SN) Sorensen
indices of similarity.
R. Vasiliauskas and others 493
wood-inhabiting fungi, although on a larger (1–3 km)spatial scale (Edman et al. 2004a, b).
Our data suggest that even freshly cut CWDcontributes to mycodiversity on managed north tem-perate sites. However, our study was not designed toshow how soon and to what extent (if at all) freshly cutwood could help in restoring primeval mycodiversity.An expanded long-term study close to old-growth siteswith a known flora of saprophytic fungi would bedesirable. Studies in tropical forest have shown thatspecies richness of wood-inhabiting fungi returns tothe level of the primary forest when the woody debrisis retained and there is a patch of original forest in thevicinity (Lindblad 2002). In the present work the com-munity structure of fungi within a single stand wasfound to differ significantly both over small distancesand over different seasons. This implies that in order tosustain and enhance fungal diversity in managed standssome coarse wood should always be left wherever andwhenever harvesting takes place.
Freshly cut wood sustains a highly diverse fungalcommunity after just a few weeks of exposure toairborne colonisation (Fig. 1a). Different species ofbasidiomycetes were found to co-exist in close prox-imity within the same small column of discolored wood(Fig. 3). In a similar experiment, high diversity wasobserved in aerial cut surfaces of Fagus sylvatica logs,where up to 30 mutually antagonistic fungal in-dividuals of several species were found cmx3 (Coates &Rayner 1985a). Buried cross-sections, however, werecolonised by a less diverse community (Coates &Rayner 1985b). Similarly, hundreds of fungal specieswere reported from stumps of spruce some weeks afterthey were cut and available for airborne colonisation(Woods1996,Woodward2003,Vasiliauskas et al. 2004).Stumps are in most cases the only source of CWD inmanaged stands but it should be remembered that afreshly cut stump is ecologically different from a stemsection, since stumps remain attached to the root sys-tem for a considerable time (Redfern & Stenlid 1998).
We demonstrated the ability of Mycena spp. andCollybia spp. to abundantly colonise freshly cut CWD(Table 1). In another study, Mycena galopus was foundto inhabit living stems of pine (Lygis et al. 2004b).These findings contribute to a new picture of theecology of those fungi. They were previously knownprimarily as decomposers of litter and of well decayedresidues of wood, on which their fruiting bodies arecommonly observed (Rodionova 1970, Stepanova1975, Hansen & Knudsen 1992, Ryman & Holmasen1998). We also discovered that several ‘combative’species are already present in freshly exposed substrate.According to Cooke & Rayner (1984), so calledcombative species have a secondary resource capturestrategy: they arrive late, displace from the woodspecies that were already present and take over theirpreviously colonised domain. The following speciesfrom Table 1 could be classified as combative:Hypholoma capnoides, Phanerochaete spp., Resinicium
bicolor, Sistotrema brinkmannii, and Trametes versi-color (Holmer & Stenlid 1996). It is likely that thosespecies will be able to persist in baits for several years.In general, the basidiomycete macrofungi reported inthis study are common throughout the forests of NorthEurope (Hansen &Knudsen 1992, Ryman &Holmasen1998).
Among 74 species of microfungi reported in thepresent work (Tables 1–2), many related species(belonging to at least the same genera) have beenpreviously encountered in woody substrates in north-temperate and boreal forests. Thus, 44 (59%) of thosewere found to inhabit stumps, snags and living trees ofspruce, pine and birch in Sweden and Lithuania (Lygiset al. 2004a, b, Vasiliauskas et al. 2004, 2005). Among60 microfungi that were identified (Tables 1–2), 27(45%) related species were isolated from spruce stumpsin Scotland (Woods 1996), and thirty-seven (or 62%)from decomposing logs of Douglas-fir, spruce andaspen in North America (Crawford, Carpenter &Harmon 1990, Lumley, Gignac & Currah 2001).
About 15% of species found remained unidentified(Tables 1–2). In other studies, where the identificationwas based on morphological characters of themycelium, unidentified species comprised 25–35%(Woods 1996, Lumley et al. 2001). This indicates thatmorphological identification of fungal cultures in manycases is difficult, but also that sequence coverage inGenBank and our local sequence databases is farfrom exhaustive. We can expect that some of theseunidentified sequences represent unknown speciesespecially among micromycetes with inconspicuousfruit bodies. It is estimated that the majority of fungihave not yet been isolated and identified (Kennedy &Clipson 2003). An example concerning wood-inhabit-ing species is a recent survey of microfungi from rottingwood in Canada, during which 49 species of asco-mycetes were isolated, 15 of which were new forCanada, and seven were new for North America; 20species had not previously been reported from wood(Lumley, Abbot & Currah 2000, Sigler, Lumley &Currah 2000). During recent work in our laboratoryfour previously unknown species of dark septate fungi(Phialocephala spp.) have been detected in woodysubstrates (Menkis et al. 2004). The availability ofcomprehensive and well-documented sequencedatabases will markedely increase the efficacy ofmycodiversity studies, in particular when analysingfungal DNA directly from environmental samples(Johannesson & Stenlid 1999, Vainio & Hantula 2000,Kennedy & Clipson 2003).
ACKNOWLEDGEMENTS
We thank Olov Pettersson for technical assistance, and Stig Bardage
for help in detailed wood analyses. This work was supported by
grants from the Swedish Research Council for Environment,
Agricultural Sciences and Spatial Planning (FORMAS) and the
Foundation for Strategic Environmental Research (MISTRA).
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