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Influence of decay fungi, construction characteristics, and environmental conditions on the quality of wooden check-dams.


Wooden crib dams are widely used for torrent control in mountainous regions. Their life span is limited by geomorphological processes and decay. We examined the species composition and population structures of basidiomycetes in crib dams in the northern Swiss Alps and related the presence of the dominating fungi to specific ecological conditions within such constructions. The most dominant fungi were (in decreasing order) Fomitopsispinicola, Antrodia serialis, Sistotrema brinkmannii s.l., Gloeophyllum sepiarium, Armillaria cepistipes, and Gloeophyllum odoratum, amounting to 75 percent of all basidiomycetes. Presence of these fungi correlated strongly with the degree of wood deterioration. The decay fungi occurred more frequently on the wings of the dams than on the lateral abutments or on those parts which were constantly covered by flowing water. Correspondingly, decay was most advanced in the wings. Decay of check dams in south facing torrents was more pronounced than in those in channels facing north and decay was more intense in check dams below elevations of 900 m asl. The diameter of the logs, the age of the check dams and the wood species, Norway spruce (Picea abies) or European white fir (Abies alba), did not affect either the degree of decay or the presence of any species of fungi. Most individual mycelia (genets) were small(up to 87 genets ofF. pinicola were found on a single dam) and spread of individual thalli to adjacent logs was very rare. The implications of these findings for constructing and maintaining crib dams are discussed.

In mountainous regions, infrastructure and many human settlements are exposed to the effects of erosion, which is mostly caused by the action of torrents. In torrent control, the flow of water is regulated by check dams, which are frequently constructed of wood (crib dams, Fig. 1). The life span of such structures is limited by geomorphological processes and also by the rate of decomposition of the wood by fungi. Crib dams provide a specific habitat for fungi due to the use of fresh logs for construction, soil contact and fluctuating moisture. To predict decay dynamics and to improve the construction of the dams, the behavior of the decay fungi must be known. Therefore, we studied species composition and population structures of basidiomycetes on selected crib dams in the Swiss Alps and related the presence of the dominant species to specific ecological conditions within such constructions. The study is based on data of Noetzli (2002) which have been re-evaluated using an improved statistical model.

Materials and methods

Locations, environmental parameters, and construction characteristics

Nine crib dams were selected in eight different catchments within an area of approximately 30 by 20 km on the northern slope of the Swiss Alps in cooperation with the local forest service (for details see Noetzli 2002).

The parameters altitude ([e.sub.1] in Table 1), exposure ([e.sub.2]), and geographical location ([e.sub.3]) of the check dams were inferred from the Swiss National Maps (1:25,000). The ages of the dams ([m.sub.3]) were found in the documentation of the responsible forest services. The diameter ([m.sub.2]) of each log was measured. The construction was similar for all dams, and the different sections ([m.sub.4]) of the check dams, i.e., wings, lateral abutments, and water section, were according to Figure 2. The wood species ([m.sub.5]) of each log was determined microscopically according to Phillips (1970) and Schweingruber (1990). Only European white fir (Abies alba Mill.) and Norway spruce (Picea abies L. Karst) were employed for construction of the investigated crib dams. Fruitbodies of decay fungi often occurred on the cut side of anchoring logs.


Degree of decay

A resistograph (Typ 1410, Frank Rinn Distribution, Heidelberg, Germany) was employed to test the soundness of the wood (Rinn et al. 1996). Drillings for resistance measurements were made at intervals of 60 cm along each log of each dam. According to Noetzli (2002), results based on measurements at 30-cm intervals did not differ significantly from those for 60-cm intervals (p-value = 0.81). The drillings occurred radially or, in anchor logs, axially to a maximum depth of 20 cm. The degree of decay, i.e. the ratio between healthy and decayed wood, was determined according to Noetzli (2002) for each drill resistance profile and was given as proportion (values 0 to 1), e. g. in statistical analyses (Table 1) or in Figure 3.


Isolation of decay fungi

Drilling cores of 10 cm length were taken horizontally every 60 cm with a SUUNTO[R] core bit of 5 mm inner diameter (Bazzigher et al. 1985, Kramer and Akca 1995) adjacent to each drill hole that resulted from resistance measurements (Fig. 4). Prior to each sample drilling, the core bit and the surface of the borehole location were flame-sterilized with ethanol (96%). The samples were individually packed in [gamma]sterilized PVC tubes (Becton Dickinson, Le Pont de Claix, F) and subsequently processed for isolation and cultivation according to the protocols of Holdenrieder et al. (1994) and Sieber (1995). Pure cultures were identified by comparisons with reference cultures from fruitbodies, by the use of the key of Stalpers (1978) or, for Armillaria isolates, by testing sexual compatibility with haploid tester strains of known species origin (Korhonen 1978). The abundance of each species was determined (Noetzli 2002).



Colonization patterns

The size of individual thalli of the most abundant species (Fomitopsis pinicola (Sw.:Fr.) P. Karst., Antrodia serialis (Fr.) Donk, Gloeophyllum sepiarium (Wulf.) P. Karst., and Armillaria cepistipes Velen.) was determined based on vegetative compatibility (vc) tests following the protocols of Mounce (1929) and Noetzli (2002). Heterocaryotic isolates of the same species were considered genetically different if a zone displaying mycelial antagonism (demarcation line, barrage zone) was formed between the isolates (Malik and Vilgalys 1999). The size of individual thalli was estimated based on the number of somatically compatible isolates from each sampled crib dam (Worrall 1997).

Statistical analysis

All data were analysed with the software package R 2.4.0 (R Development Core Team 2006). A generalised linear model (R-function glm) was applied with quasi-binomial error distribution and the logit link function. The default model consisted of the numeric response variable "degree of decay" and the explanatory variables, all represented as factors (Table 1). Treatment contrasts were associated with the factors where each level contrasts with the baseline level; the latter is omitted. Besides the main effects, all twofold interactions were considered among the different fungi as well as between the different fungi and the other variables (Eq. [1]):

Default model: y - ([f.sub.1] +, ... , +[f.sub.6]) ([m.sub.1] +, ... , + [m.sub.5] + [e.sub.1] + , ... , + [e.sub.3]). [1]

The final model was selected starting from the complex one that contains possible simpler equations as special cases but has little explanatory and predictive power. A stepwise backward selection process was applied to find a more parsimonious and explanatory model from a significance point of view (Stahel 2000, Venables and Ripley 2002). Analysis of deviance tables were computed for the complex and final fitted model objects to test for significant loss of explained deviance.

Residual analysis was conducted to check the compliance of the assumptions required and the fit of the final model. For that purpose, residuals against fitted values (TukeyAnscombe plot) and against leverages (hat matrix) were analysed as well as the partial and the deviance residuals against the explanatory variables, respectively.

The generic R-function confint (confidence interval), based on profile likelihoods, was applied to compute confidence intervals, particularly to test the different levels of the multilevelled factors ([m.sub.2], ... , [m.sub.5]) against each other. Furthermore, Pearson's Chi-squared test was performed to test contingency tables.


Degree of decay

In total 972 drill resistance profiles were evaluated. The resulting distribution of the degree of decay is shown in Figure 3. The median is at 10.14 percent with a corresponding median absolute deviation of [+ or -] 13.56 percent.

Decay fungi

A total of 979 drilling cores and 655 fruit-bodies were collected. After processing, 1378 samples of basidiomycetes were noted. At least one basidiomycete was detected at 59 percent (582) of the sample locations. The most frequent species were Fomitopsis pinicola (Sw.: Fr.) P. Karst, Antrodia serialis (Fr.) Donk., Sistotrema brinkmanni (Bres.) J. Erikss., Gloeophyllum sepiarium (Wulf.) P. Karst., Armillaria cepistipes Velen., and Gloeophyllum odoratum (Wulf.: Fr.) Imazeki (Table 2). These six species constitute 74 percent of the total number of basidiomycetous samples (1378).


Other identified basidiomycetes were (in decreasing order of frequency) Heterobasidion annosum s.l., Gloeophyllum abietinum (Bull.: Fr.) Karst., Postia caesia (Schrader) P. Karsten, Trichaptum abietinum (Fr.) Ryv., Gloeophyllum trabeum (Pers). Murrill., Bulbillomycesfarionosus Bres. (Jill.), Coprinus sp., Flammulina velutipes (Curt.: Fr.) Sing. and Riessia semiophora Fres. Additionally, a total of 241 mycelia and fruit-bodies, probably basidiomycetes, that could not be identified were recorded at 182 sample locations.

Colonization patterns

The frequency of colonization by basidiomycetes of the three check dam sections considered in this study was significantly different ([chi square]-test, p < 0.05). About 76 percent of the samples from the wing sections, 43 percent of the lateral abutments, and 41 percent of the water section hosted at least one basidiomycete (Fig. 5). This significant difference was found likewise for each of the six most abundant species (Table 3).

VC-groups were small and mostly limited to the corresponding sample location as indicated by vegetative compatibility tests among pure cultures of Fomitopsis pinicola (163 vc-groups), Antrodia serialis (125), Gloeophyllum sepiarium (115), and Armillaria cepistipes (16). The largest vc-groups were restricted to single logs, except for six cases ofF. pinicola, where isolates of two adja cent logs were compatible--a finding, that was not observed for A. serialis and G. sepiarium. As far as Armillaria cepistipes was concerned, some vc-groups occurred all over a check dam and were occasionally detected at sampling points several meters apart from each other (Table 4).

Statistical model

The stepwise backward model selection process based on the default model considering main effects and all twofold interactions among the different fungi as well as between the different fungi and the other variables, resulted in a noticeably simpler, but, more parsimonious and explanatory model, without significant loss of power (Table 5). The comprehensive analysis of the residuals did not reveal any obvious deviations associated with the model assumptions.

A summary of the reduced, generalized linear model (Rfunction glm) including estimates and significance levels (p values) is given in Table 6. Except for Armillaria cepistipes ([f.sub.1] which was not considered in the selected model, the most significant main effects on the decay process were found for the five most abundant decay fungi ([f.sub.2] ... [f.sub.6]), the sections of the check dams ([m.sub.4]) and the exposure ([e.sub.2]).

Among the decay fungi, Antrodia serialis was the most effective wood decomposer, followed by Fomitopsis pinicola, Gloeophyllum odoratum, G. sepiarium, and Sistotrema brinkmannii.

Compared to the wing sections of the check dams, the lateral abutments and the water section ([m.sub.4]) showed significantly lower degrees of decay, without significant difference between the latter two. No significant main effect was ascertained for the other material parameters, i.e. front side of anchor logs ([m.sub.1]), diameter of logs ([m.sub.2]), and age of the check dams ([m.sub.3]). The parameter wood species ([m.sub.5]) that differentiated between spruce, fir, and undeterminable wood was not considered in the selected model. Also the geographic location of the check dams ([e.sub.1]) was dropped by the backward selection process and, therefore, in this study it is not of importance for the decay process. However, both environmental parameters of the model had significant effects on the decay process. Check dams with a southern exposure were more decayed than those with a northern exposure ([e.sub.2]). Less decay occurred on check dams of regions above 900 m asl than on those beneath ([e.sub.1]). The estimates of the interaction between the different fungal species were all negative, indicating mutual exclusion and a decreasing effect on the decay process. This behavior was most distinctive in interactions of Antrodia serialis with Gloeophyllum odoratum and Fomitopsis pinicola, followed by the interactions of F. pinicola with Sistotrema brinkmannii and G. sepiarium.

The interaction effects between the sections of the check dam and fungal species were quite different (Table 6). Compared to the wing sections, the decay effect of A. serialis was significantly higher at the water section. Exactly the opposite was true for F. pinicola. Gloeophyllure sepiarium produced more decay at the lateral abutments compared to the wing sections. A further positive estimate was found for the interaction effect of A. serialis with the front side of the anchor log, indicating that this fungus occurred and developed its decomposition activities preferably on the front compared to the rest of the log. Furthermore, A. serialis was registered less often and, therefore, produced less decay on check dams above 900 m asl and on logs with diameters between 30 and 40 cm compared to those with less than 30 cm. This latter effect was found also for F. pinicola and S. brinkmannii. F. pinicola and G. sepiarium had higher decay activities on young (0 to 10-year-old) than on 11 to 20-yr-old check dams. Based on the comparison of the confidence intervals, decay caused by G. sepiarium was also significantly less severe on 11 to 20-year-old than on 21 to 30-year-old check dams. This was the only case of a multi-levelled factor with more than one significant difference.


Degree of decay

Resistography was found to be a reliable technique for decay detection for dry and for water saturated wood, confirming earlier studies on standing tree stems (Gruber 2001).

Spruce and true fir wood is commonly regarded as slightly or nonresistant to decay (Simpson and TenWolde 1999). Nevertheless European white fir is ranked as more durable than Norway spruce by Knigge and Schulz (1966), and forest practicioners in Switzerland frequently regard European white fir more durable than Norway spruce in crib dam constructions (Zeller 1987, Rickli 1997). However, no difference in durability between spruce and fir wood was found in our study.

Surprisingly, no significant differences in decay of older (> 10 years) and younger ([less than or equal to]10 years) dams were found, showing that within crib dams environmental conditions are probably more decisive for the decay processes than the age of the dams. However, there were negative and significant interaction effects between 0 to 10-yr-old dams and the two species F. pinicola and G. sepiarium, and 11 to 20-year-old dams and the two species. Both species had a stronger effect on decay in 0 to 10-year-old than in 11 to 20-year-old logs. Furthermore, G. sepiarium had more influence on decay in logs with an age of 21 to 30 years compared to those with an age of 11 to 20 years.

The activity of fungi is strongly influenced by temperature (Toljander et al. 2006, Schmidt 2006) and global warming may contribute to an increase of natural hazards also by accelerating decomposition of crib dams. For example, A. serialis shows a strong negative interaction effect with the altitude (Table 6), and possibly its frequency at higher elevation will increase with warming.

Decay fungi and colonization patterns

The colonization of various crib dam sections by basidiomycetes reflects their sensitivity to water logging. Shortage of oxygen and diffusion of exoenzymes inhibit mycelial growth and wood decomposition processes (Rayner and Boddy 1988). Nevertheless, the water sections of the dams were also colonized by basidiomycetes (Table 3) which can survive under waterlogged conditions for many years and become active again during periods of exposure to air (Webber and Gibbs 1996, Borman et al. 2006).

Only four species (A. serialis, F. pinicola, G. odoratum, G. sepiarium) were significantly associated with decay. Few basidiomycete species are known to decay wood under very moist conditions, e.g. Physisporinus vitreus (Schmidt et al. 1996), Bulbillomyces farinosus (Breitenbach and Kranzlin 1986) and Armillaria spp. (Metzler and Hecht 2004), of which the latter two were recorded in our study, too. Armillaria cepistipes occurred at relatively low frequency (Table 3). Armillaria spp. can form very extended thalli. Thalli covering areas of up to 4000 [m.sup.2] in managed forests of the Alps are quite common (Prospero et al. 2003a). Most crib dams, however, were colonized by only a small number of thalli of limited extent (Table 4), for details see appendix II in Noetzli 2002). The distribution pattern of A. cepistipes genets within crib dams shows that these constructions are either not very susceptible to attack by basidiospores from the air or by rhizomorphs of genets within the vicinity. This contrasts with stumps, which are very effectively captured by genets which are already present in the soil (Prospero et al. 2003b). Nevertheless, the removal of potential inoculum sources near dams might reduce the risk of infection (see Shaw and Kile 1991) but would be difficult to realize in practice. The polypore Bulbillomycesfarinosus is a rare species. However, due to its capability to form asexual propagules (Aegerita anamorph) that are disseminated by water, it may be able to infect various dams along a stream.

Among the most frequent fungi, those causing brown rot (F. pinicola, A. serialis and G. sepiarium) formed relatively small genets which are indicative for basidiospore infection and showed limited subsequent vegetative spread. Therefore, chlamydospores, which are formed by F. pinicola and G. sepiarium (Stalpers 1978), are apparently not involved in the local spread of these fungi. The age of these infections is hardly determinable from our data. In contrast to snags or logs on the ground, the growth rates of the mycelia are possibly restricted under the specific ecological conditions that prevail within crib dams. The time frame for spore infection by the main decay fungi may be narrow on crib dams and relatively simple measures (e.g. timing of construction, physical or biological wood treatment) could help to reduce infections. For example, the cut surface of Norway spruce stumps are susceptible to infection by the polypore Heterobasidion annosum for only a few weeks (Bendz-Hellgren 1997) and may be protected by a variety of treatments during that period (Holdenrieder and Greig 1998, Pratt et al. 1998). However, decay fungi can be already present in the green timber before construction starts and cause damage later on (Dietz and Wilcox 1997, Baum et al. 2003). The succession of fungi within crib dams deserves further study and the nondecayed logs of dams may provide a source of microorganisms with potential for biological control of decay (see also Schoeman et al. 1999).

Besides A. cepistipes, only F. pinicola was able to spread to adjacent logs in a few cases (6 out of 163). Spreading of thalli may have been stopped by antagonism of the microbial community present in the contact zone or by deadlock between different genets. Fomitopsispinicola is a dominant decay fungus of conifer stems after wind throw and bark beetle attack. In these substrates, the genets are restricted to single logs (Luschka 1993, HSgberg et al. 1999, Hamdan et al. 2005, Ammann 2006). Within transverse sections of the same log, up to 5 genets were found, but their longitudinal extension has not been studied (Ammann 2006).

For A. serialis and G. sepiarium, we were unable to find any published data on the population structure. Our results show that basidiospore infection dominates also in these species, and only a small proportion of thalli colonized a substrate volume comprising more than 2 sample points (Table 4). A. serialis was frequently associated with decay on the water section (Table 6), and it showed a strong negative interaction effect with G. odoratum. Conversely, F. pinicola showed a strong negative interaction effect with the water section, as well as with A. serialis. The presence of different fungal species in a single sample was frequently associated with reduced decay (Table 6). This finding contrasts observations from wood chips in microcosms for which a positive correlation was found between decay and fungal diversity (Toljander et al. 2006). Basidiomycetes interact with each other using a versatile set of mechanisms (Boddy 2000); e.g.F, pinicola produces various antimicrobial steroids (Keller et al. 1996, Rosecke and Konig 1999), but its inability to form melanised pseudosclerotial plates may reduce its competitiveness (McDougall and Blanchette 1996).

Fomitopsis pinicola affects mostly dam components that are relatively easy to replace. Junctions between individual logs are apparently not associated with an increased risk of spreading of mycelia, despite the fact that release of iron from bonding nails may enhance the activity of wood decayers (Noetzli et al. 2007). Therefore, replacement of single weakened crib dam components can significantly increase the life span of these constructions, thereby supporting earlier recommendations. In principle, the construction of wings by gabions or rock boulders will also increase the lifespan of a log crib check dam, but it has to be considered that such wings are quite heavy and that the resulting forces acting on the timber structure may have destabilizing effects and/or can cause deformation and local crushing of log-joints unless the crib wall is quite rigid. Gabion and boulder wings as well as rigid log crib walls require a lot of stones (and boulders!) which are not always readily available in a torrent (Boell et al. 1999). For a few years, oak, sweet chestnut and European larch have been used in Switzerland for wings and other parts of log dams susceptible to decay (and damage due to sediment transport). Modern fastening techniques like bolts or steel-wire anchors have also been employed to easily replace or repair decayed parts of the log dams. Although reliable evidence of positive effects is not yet available, such procedures seem quite promising and will be studied in detail as a continuation of this project.

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The authors are, respectively, Research Scientist (during this work) and now a Forest Officer, Swiss Forest Service, Zfirich, Switzerland (; Research Scientist, WSL, Swiss Federal Institute for Forest, Snow and Landscape Research, Research Group: Mountain Torrents, Erosion and Landslides, Birmensdorf, Switzerland (; Research Scientist, WSL, Swiss Federal Institute for Snow and Avalanche Research, Research Group: Alpine Ecosystems, Davos Dorf, Switzerland (; and Research Scientist and Professor, ETH Zurich, Forest Pathology and Dendrology, Institute of Integrative Biology (IBZ), Zurich, Switzerland (, The authors wish to thank the local forestry staff of the Cantons Schwyz (Felix Cuny), Nidwalden (Urs Braschler), Obwalden (Joseph Hess), and Glarus (Pascal Heldher) for providing the study objects, Prof. Florin Florineth (Univ. of Natural Resources and Applied Life Sciences, Vienna) for stimulating discussions, and Dr. Colin Millar for linguistic revision. This research was conducted as part of the project "Ursachen und Dynamik yon Faulen an Holzkonstruktionen im Bachverbau," funded by the Swiss Federal Office for the Environment (BAFU). This paper was received for publication in March 2007. Article No. 10339.
Table 1.--Parameters considered in the statistical model to explain
decay in wooden crib dam components.

 Response variable

y degree of decay

 Explanatory variables

[f.sub.1] Armillaria cepistipes [f.sub.4] Gloeophyllum odoratum
[f.sub.2] Antrodia serialis [f.sub.5] Gloeophyfum sepiarium
[f.sub.3] Fomitopsis pinicola [f.sub.6] Sistotrema brinkmannii
[m.sub.1] sample at front side of anchor log
[m.sub.2] diameter of logs
[m.sub.3] age of the check dam
[m.sub.4] section of the check dam
[m.sub.5] wood species
[a.sub.1] altitude
[a.sub.2] exposure
[a.sub.3] geographical location of the check dams
 (Noetzli 2002; p. 12)


y numerical [0,1 ]; (y [member of] R)

 Factor levels

[f.sub.2] 0: not found 1 : found
[m.sub.1] 0: no 1: yes
[m.sub.2] 1: d < 30 cm 2: 30 cm [less 3: d [greater than
 than or equal or equal to] 40 cm
 to] d < 40 cm
[m.sub.3] 1: 0 to 10 years 2: 11 to 20 years 3: 21 to 30 years
[m.sub.4] 1: wing 2: lateral 3: water section
[m.sub.5] 1: fir 2: spruce 3: indeterminable
[a.sub.1] 0: below 900 m asl 1: above 900 m asl
[a.sub.2] 0: north (including east) 1: south (including west)
[a.sub.3] 1: Trepsental A 4: Speichenrus 7. Heitlibach
 2: Trepsental B 5: Chratzerlibach 8: Ebenmattgraben
 3: Steingraben 6: Durrenbach 9: Stengraben

Table 2.--Frequency of the six most common basidiomycete species on
crib dams in northern Switzerland (isolates from drilling cores and
 Crib dam number

 1 2 3 4 5 6 7 8
Number of sampling
 locations per dam 148 159 51 141 117 69 130 66
 Fomitopsis pinicola 64 27 12 9 33 3 22 1
 Antrodia serialis 31 37 -- 23 2 12 3 9
 Sistotremp brinkmannii 17 27 2 16 10 10 3 10
 Gloeophyllum sepiarium 13 18 -- 23 8 2 8 9
 Armillaria cepistipes 1 2 1 -- 3 2 24 7
 Gloeophyllum odoratum 1 2 -- 13 -- -- 4 3
 Various basidiomycetes * 28 28 8 30 6 17 34 23

 Crib dam number

 9 Total
Number of sampling
 locations per dam 98 979
 Fomitopsis pinicola 18 189
 Antrodia serialis 7 124
 Sistotremp brinkmannii 4 99
 Gloeophyllum sepiarium -- 81
 Armillaria cepistipes 8 48
 Gloeophyllum odoratum 7 30
 Various basidiomycetes * 8 182

* Mostly non-sporulating, septate, hyaline mycelia that exhibited
growth on ascomycete-inhibiting thiabenda-zole medium.

Table 3.--(A) Total number of sampling points with presence/absence of
basidiomycetes. (B) Occurrence of the most common basidiomycete species
on the various components of crib dams (wings, abutments, and water
section; see Fig. 1).

 Number of sampling Number of sampling Total of
 points with points without sampling
(A) basidiomycetes basidiomycetes points

wings 388 124 512
abutments 69 91 160
water section 125 182 307
Total 582 397 979

 Sampling Sampling Sampling Sampling
 points points points points
(B) with without with without

 F. pinicola A. serialis

wings 144 368 92 420
abutments 11 149 13 147
water section 34 273 19 288
Total 189 790 124 855

 G. sepiarium A. cepistipes

wings 72 440 27 485
abutments 7 153 14 146
water section 2 305 7 300
Total 81 898 48 931

 Sampling Sampling
 points points
(B) with without

 S. brinkmannii

wings 76 436
abutments 13 147
water section 10 297
Total 99 880

 G. odoratum

wings 24 488
abutments 4 156
water section 2 305
Total 30 949

Table 4.--Thallus size of the most common basidiomycetes. The first
column (size) shows the number of sampling points with the same genet,
the other columns show the percentage of vc-groups of a specific size
class for each species.

 Species of decay fungi

 Gloeophyllum Fomitopsis Antrodia Armillaria
 sepiarium pinicola serialis cepistipes

Number of 115 163 125 16
[right arrow]

size (percent)
 1 81 72 84 31
 2 13 13 8 6
 3 3 7 3 25
 4 2 3 4 0
 5 1 2 1 0
 6 0 1 0 6
 7 0 1 0 13
11 0 0 0 13
18 0 0 0 6

Table 5.--Default and selected model (R syntax) and comparison of the
default againstthe selected model using Chi-squared test statistics (R
Development Core Team 2006).

 Analysis of Deviance Table

 Resid. Df Resid. Dev. Df Deviance P(>|Chi|)

1 861 227.691
2 935 254.433 -74 -26.742 0.058

Table 6.--Summary of the function glm (R Development Core Team 2006)
used for the model calculation with the degree of decay as the response
variable y and the explanatory variables as indicated in Table 1.
glm(formula = y ~ [f.sub.3]([f.sub.2] + [f.sub.5] + [f.sub.6]) +
[f.sub.2]([f.sub.4] + ([f.sub.3] + [f.sub.5])([m.sub.3] + [m.sub.4]) +
[f.sub.2]([m.sub.1] + [m.sub.2] + [m.sub.4] + [e.sub.1]) + [m.sub.2]
([f.sub.3] + [f.sub.6]) + [e.sub.3], family=quasibinomial(logit),
data =dat1)

 Deviance residuals:

Min 1Q Median 3Q Max
-1.6513 -0.3299 -0.1237 0.1863 2.2869


 Std. codes
 Estimate error t value Pr(>|t/) (a)

(Intercept) -1.7366 0.1904 -9.121 <2E-016 ***
A.serialis 2.9134 0.4370 6.667 4.44e-11 ***
F. pinicola 2.7282 0.2489 10.963 <2E-016 ***
G. odoratum 2.3637 0.3303 7.156 1.68e-12 ***
G. sepiarium 1.1785 0.2392 4.928 9.84e-07 ***
S. brinkmannii 0.8908 0.2811 3.169 0.001582 **
front-sample 0.1661 0.1182 1.405 0.160281
diameter 30 to 40 0.1552 0.1860 0.834 0.404390
diameter >40 0.2355 0.2102 1.121 0.262747
age 11 to 20 0.3879 0.2107 1.841 0.065976 ****
age 21 to 30 -0.3019 0.1753 -1.722 0.085346 ****
lateral abutment -0.8245 0.1957 -4.212 2.77e-05 ***
water section -1.0223 0.1638 -6.243 6.50e-10 ***
altitude >900 -0.3686 0.1826 -2.018 0.043863 *
southern exposure 0.7705 0.2004 3.845 0.000129 ***
A. serialis: -2.2856 0.4102 -5.572 3.30e-07 ***
 altitude >900
A. serialis: G. -2.6597 0.5066 -5.250 1.88e-07 ***
A. serialis: 1.0304 0.2857 3.606 0.000327 ***
A. serialis: -1.2021 0.3867 -3.109 0.001934 **
 diameter 30 to 40
A. serialis: -0.6318 0.3998 -1.580 0.114367
 diameter >40
A. serialis: lateral 0.5269 0.4698 1.121 0.262410
A. serialis: water 1.7471 0.3518 4.967 8.10e-07 ***
F. pinicola: A. -1.3801 0.4099 -3.367 0.000792 ***
F. pinicola: G. -0.7905 0.3807 -2.077 0.038112 *
F. pinicola: S. -1.1737 0.5075 -2.313 0.020960 *
F. pinicola: 30 -0.6901 0.2882 -2.394 0.016844 *
 to 40 diameter
F. pinicola: -0.2060 0.3381 -0.609 0.542485
 diameter >40
F. pinicola: age 11 -0.7687 0.2989 -2.572 0.010277 *
 to 20
F. pinicola: age 21 -0.3388 0.3424 -0.989 0.322755
 to 30
F. pinicola: lateral -0.2858 0.4363 -0.655 0.512622
F. pinicola: water -1.2376 0.3502 -3.534 0.000430 ***
G. sepiarium: age 11 -0.8502 0.3299 -2.577 0.010109 *
 to 20
G. sepiarium: age 21 0.7357 0.4799 1.533 0.125594
 to 30
G. sepiarium: lateral 1.4269 0.5962 2.394 0.016882 *
G. sepiarium: water -1.0633 1.1511 -0.924 0.355870
S. brinkmannii: -1.1116 0.3555 -3.127 0.001822 **
 diameter 30 to 40
S. brinkmannii: -0.6209 0.3966 -1.566 0.117760
 diameter >40

(a) Signif. codes: *** < 0.001; ** < 0.01; * < 0.05; **** < 0.1
Dispersion parameter for quasibinomial family taken to be 0.2922121
Null deviance: 493.97 on 971 degrees of freedom
Residual deviance: 254.43 on 935 degrees of freedom
Adjusted RZ = 0.501
Deviance explained = 48.5 percent
Number of Fisher scoring iterations: 5
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Author:Noetzli, Konrad; Boell, Albert; Graf, Frank; Sieber, Thomas N.; Holdenrieder, Ottmar
Publication:Forest Products Journal
Geographic Code:1USA
Date:Apr 1, 2008
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