Discoloration following bark stripping wounds on Fraxinus excelsior

A total of 101 Fraxinus excelsior trees 8–32 cm in d.b.h. with bark stripping wounds caused by Alces alces and Cervus elaphus in Lithuania were cut, dissected and examined. The injuries ranged in age from 5 to 18 years, when the trees were 22–40 years old and were in the size range 6–24 cm d.b.h. For 5-10 years old wounds, the mean length of associated wood discoloration was 804 × 201 cm, while in 16–18 years old wounds it was 912 × 144 cm. There was no correlation between wound age and extent of discoloration in the stems examined (r = 0.11). Tree d.b.h. and wound size (initial width × length) were correlated with the extent of discoloration (r = 0.43 and r = 0.20, respectively). The presence of complete wound occlusion had no significant effect on the length of columns of discoloration associated with wounds of 10 or more years old. The average occlusion rate during the first 10 years was 128 × 28 mm or 13 mm/year, correlating positively with the radial increment (r = 0.42). Amongst a total of 500 F. excelsior trees with wounds, 29 trees (5.8%) bore basidiomycete fruiting bodies. Most common was Phellinus punctatus, found on 12 (2.4%) stems, followed by Coniophora puteana (1.6%), Peniophora limitata (0.4%) and Datronia mollis (0.4%). Fungi most commonly isolated from discoloured wood were ascomycetes Phaeoacremonium rubrigenum, Phialophora malorum, Hypoxylon rubiginosum, Coniothyrium sporulosum, Libertella spp., Ophiostoma sp., and basidiomycetes Ischnoderma benzoinum, Ischnoderma resinosum, Tyromyces sp.     

Stem-rot damage and the progress of causal fungi in old-aged Japanese larch trees at the foot of Mt. Fuji

Damage caused by stem-rot and the progress of the causal fungi in old-aged Japanese larch (Larix kaempferi (Lamb.) Carr.) was investigated at the foot of Mt. Fuji. Stem-rot was found in 75% of 108 trees investigated, and volume of rot was 6% of the total wood volume in the forest investigated. Stem-rot damage was much greater than the damage by butt-rot.Stereum sanguinolentum (Alb. and Schw. ex Fr.) Fr. infected larch trees at the greatest incidence (49.4%). However,Porodaedalea chrysoloma (Fr.) Imaz. caused the most volume loss to the trees.S. sanguinolentum infected larch stems mainly through stem wounds, and decay caused by the fungus progressed 9.75×10² cm³/year on average.P. chrysoloma infected larch stems mainly through dead branches and wounds, and the average rate of decay progress for the fungus was 2.74×10³ cm³/year.     

Bark phenolics of American beech (Fagus grandifolia) in relation to the beech bark disease1

The amount of total extractable phenols was determined for bark sections obtained from behind cankers naturally induced by Nectria coccinea var. faginata and from behind mechanically inflicted wounds on stems of American beech. Healthy bark from susceptible trees was found to contain a similar level of phenolics as bark from trees determined to be resistant to the beech bark disease. Six months after wounding, wound-altered bark from susceptible trees was found to be lower in phenols than woundaltered bark from resistant trees. Inoculation of wounds with N. coccinea var. faginata resulted in decreased phenolic levels in bark sections nearest the wound surface, and increased phenolic levels in sections nearest the vascular cambium, several mm distant. Phenolic levels in injured or infected bark appear to follow similar patterns as those resulting from injury or infection of xylem tissues.     

Penetration of Picea sitchensis root bark by Armillaria mellea,Armillaria ostoyae and Heterobasidion annosum

Penetration of root bark tissues of Picea sitchensis by Armillaria ostoyae, Armillaria mellea and Heterobasidion annosum was examined in the absence of wounds, in superficial wounds (rhytidome tissues removed to expose the secondary phloem) and in wounds to the depth of the vascular cambium (deep wounding). Both species of Armillaria penetrated bark without prior wounding, but neither species formed rhizomorphs in this treatment. Armillaria ostoyae penetrated to 39 cell layers in depth by 48 days after inoculation of unwounded bark, whereas A. mellea penetrated 25 cell layers in the same time. Armillaria mellea penetrated superficial wounds significantly more rapidly than did A. ostoyae. Both species produced rhizomorphs within wounded host tissues. Inoculation of deep wounds with Armillaria resulted in a greater depth of bark necrosis with A. mellea than with A. ostoyae. In the absence of wounding, H. annosum failed to penetrate root bark tissues, but in both superficial and deep wounds hyphae penetrated beyond the ligno–suberized boundary zone (LSZ) by 12 days after inoculation. Where no inoculations were made, superficial or deep wounding led within 25 days to the restoration of a structurally continuous LSZ, and by day 48 the wound periderm (WP) was fully differentiated. In inoculated wounds, however, formation of the LSZ and WP was delayed or inhibited in most trees, particularly following inoculation with A. ostoyae or A. mellea. Suberization in the LSZ and WP remained diffuse and discontinuous 48 days after inoculation. Moreover, the presence of WP did not prevent further penetration of the tissues by the pathogens. Variations between trees in the depth of pathogen penetration were noted, possibly indicating differing susceptibilities of individual host genotypes. The possible host factors involved in resistance to penetration of root bark tissues by Armillaria and Heterobasidion are discussed.     

Decay in Norway Spruce Caused by Stereum sanguinolentum Alb. & Schw. ex Fr. Developing from Extraction Wounds

In two stands of Norway spruce (Picea abies (L.) Karst.), plantedin 1952 and 1929 in Yair Hill Forest and Glentress Forest, BordersRegion, two per cent of the trees examined in 1983 had extractiondamage on stems and superficial roots. Extraction wounds were4 and 8 years old respectively and ranged in size from 52 to1099 cm². Infection frequency of the damaged trees was 47 percent and 54 per cent respectively. Stereum sanguinolentum wasthe most common fungus isolated, accompanied by Trichodermaviride Fr; Chaetomium cochlioides Palliser and Heterobasidionannosum (Fr.) Bref. The frequency of isolation of S. sanguinolentumincreased progressively in samples taken from the outside ofstems inwards, whereas the other microorganisms present showedthe opposite pattern. In four trees, T. viride overgrew S. sanguinolentumin the the decay columns. Positive correlations were demonstratedbetween surface area of wounds and vertical extension of decay,tree volume and decay volume, and diameter of stem at breastheight (DBH) and decay volume; whereas a negative correlationoccurred between number of growth rings per 5 cm (measured inwardsfrom the outside of the bole) and radial penetration of decay.The results confirm the importance of S. sanguinolentum as awound pathogen.     

Signs and symptoms associated with Heterobasidion annosum and Armillaria ostoyae infection in dead and dying mountain pine (Pinus mugo ssp. uncinata)

Symptoms and signs associated with root rot caused by Heterobasidion annosum or Armillaria ostoyae in mountain pines (Pinus mugo ssp. uncinata) were investigated in the Swiss Alps. A sample of dying or recently dead mountain pine trees (≥12 cm d.b.h.) and saplings (<1.3 m height) was assessed for root pathogen infection by taking root samples followed by isolations in the laboratory. From a subsample, an additional core was taken from the butt of each tree and evaluated in the same fashion. A total of 157 dying or recently dead mountain pine trees and 184 saplings with roots infected by either of the two pathogens or which lacked infection were analyzed using logistic regression models. The main objectives were to determine the most prominent symptoms induced by the fungi (resinosis), signs of the fungi (mycelia, fruiting bodies and rhizomorphs), and tree characteristics (d.b.h./height and evidence of wounds) that would allow an easy and reliable determination of H. annosum and/or A. ostoyae infection of mountain pines in the field. Heterobasidion annosum caused both root and butt rot on mountain pine, whereas A. ostoyae was mostly restricted to the root systems of the trees sampled. The most discriminating sign for the presence of A. ostoyae infection was the presence of characteristic mycelial fans, and for H. annosum root rot the presence of H. annosum mycelia (sheets of paper‐thin mycelium and mycelial pustules). In addition, resinosis was a powerful predictor for A. ostoyae in trees. Symptoms and signs indicating A. ostoyae or H. annosum infections were more reliable for saplings than for mature trees. Armillaria rhizomorphs were not useful in detecting A. ostoyae infection and, if present, were often formed by saprophytic Armillaria species. Heterobasidion annosum fruiting bodies were rarely observed and poorly reflected the widespread occurrence of this pathogen in the mountain pine forests.     

Discoloration and associated fungi in stems of silver birch (Betula pendula Roth.) following logging damage

Study aim was to investigate discoloration and associated fungi in 50‐ to 70‐year‐old stems of Betula pendula damaged by logging. Investigated wounds (on 70 stems) were inflicted 4–18 years previously, and all of them had discoloration with mean radial spread (±SD) 2.9 ± 2.9 cm and longitudinal spread 50.3 ± 24.0 cm. Both wound area and length had a strong impact on a total length of discoloration (r = 0.665 and r = 0.745, respectively; p < 0.001), but had no influence on its spread beyond wound margins (r = ?0.035 and r = ?0.079). There was no correlation between the age of an injury and spread of the discoloration neither in vertical (r = ?0.110) nor in radial (r = ?0.280) direction. Average wound closure rate was 1.2 ± 0.5 cm year ^?1. The difference between discoloration length in stems with open and occluded injuries was insignificant (t‐test, p = 0.769). The principal fungi isolated from the wounds were ascomycetes (Epicoccum, Cadophora, Neonectria, Alternaria spp.) that were able to cause discoloration of wood with little effect on its mechanical properties and capable only for limited spread inside a stem of a living tree. In conclusion, results of the present study demonstrate that the amount of discoloured wood beyond logging wounds in B. pendula is mainly restricted to the damaged portion of a stem and that the associated loss of wood production remains low during about 10 years since the damage.     

Community of Aphyllophorales and Root Rot in Stumps of Picea abies on Clear-felled Forest Sites in Lithuania

The community of Aphyllophorales fungi in stumps of Picea abies (L.) Karst. and the occurrence of root rot caused by Heterobasidion annosum were investigated at 38 clear-felled sites in Lithuania. Fruit-bodies were recorded on 36.0% of the 3924 examined stumps. The most common were Bjerkandera adusta, Phlebiopsis gigantea, Fomitopsis pinicola, Gloeophyllum sepiarium, Stereum sanguinolentum, Trametes zonata and H. annosum. All species occurred in stumps both with and without established root rot, but B. adusta, F. pinicola, G. sepiarium, T. zonata and Trichaptum abietinum occurred less often in stumps containing root rot, while H. annosum was encountered more often. Greater numbers of fruit-bodies were found on stumps cut in summer than on those cut in winter. The fruiting became most abundant 3-4 yrs after the trees were felled. The abundance of nearly all Aphyllophorales correlated positively with the stump diameter, and on larger stumps, fruit-bodies of several different fungi were more common. The number of stumps containing H. annosum root rot in different sites varied from 9.8% to 68.8%, and was 27.6% on average. The incidence of root rot correlated neither with the age nor with the density of the felled stand, but it correlated negatively with the proportion of deciduous trees within a stand.     

Microflora of sound-looking wood in Picea abies stems

Ascocoryne spp. (A. cylichnium and A. cf. sarcoides) were found in 48 % of 262 60-year-old Picea abies stems. They were isolated with increasing frequency towards the pith from the lower 2-3 m, more often from thicker than from thinner stems. Neobulgaria premnophila was present in 10 % of the stems, more evenly distributed, and with no difference in occurrence between thicker and thinner stems. Nectria fuckeliana was situated at random in 8 % of the trees.     

Intraspecific variation in Heterobasidion annosum for growth in sapwood of Picea abies and Pinus sylvestris

Two greenhouse experiments were conducted to study intraspecific variation in growth of the root rot fungus Heterobasidion annosum in living host sapwood. In experiment 1, Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) seedlings were inoculated with H. annosum isolates, 14 each of the S-and P-intersterility groups, collected from various parts of Sweden. In pine, the P-group isolates were more virulent than the S-group isolates both in terms of infection frequency, induced mortality rate (p < 0.05), and fungal growth in sapwood (p < 0.05). In spruce, the P-group isolates were also more virulent on average, but the difference was not statistically significant. Both S and P isolates had a higher infection frequency and a significantly longer sapwood growth on spruce than on pine. The P-group caused higher mortality on pine than on spruce. The length of the lesion in the inner bark was strongly correlated with fungal growth in spruce, but not in pine where the lesions were short or absent. In experiment 2, ten Norway spruce clones were inoculated with 18 S-isolates, originating from nine live-decayed trees and from nine spore-infected stumps in a single Norway spruce stand. The objective was to test whether any selection for growth rate in sapwood was detectable among individuals of H. annosum originating either from stumps or trees. The results gave no support for such selection since no difference in sapwood growth between the two groups of isolates was found.     

Quantitative assessment of fungal colonization in Norway spruce after green pruning

In July and in October of 1978, 1979, 1980 five Picea abies stands in Baden-Württemberg, Germany were green-pruned up to a tree height level of c. 10 m. In 1993–94, 30 pruned trees and five control trees from each stand were harvested for investigation. The quality of pruning proved to be excellent because only few branch collar, bark injuries or too long branch stubs were detected. Based on isolations from more than 6000 wood specimens of c. 20 mm³ obtained from 175 trees, specific infection rates are given for different tree compartments. Wood decay fungi as well as important blue stain fungi were only rarely present. Tolerable discolourations were limited to the stub containing core of a few trees. Wood formed after pruning showed neither more fungal infections nor other related disadvantages compared with the respective increment from unpruned control trees. Nectria fuckeliana, proved to be the most abundant fungus in pruned trees especially in the branch stubs. Respective infection rates in and close to dry branches were compared. Bacteria could be found in the pruned branch stubs, however, they did not penetrate into the heartwood or sapwood of the stems. Both summer and autumn pruning involve only very low risk of wood deterioration. However, summer pruning shows some advantages with respect to lower infection rates by N. fuckeliana.     

Modelling the incidence of Heterobasidion annosum butt rots and related economic losses in alpine mixed naturally regenerated forests of northern Italy

A total of 2257 recently felled stumps were sampled from 22 mixed naturally regenerated forest stands in the Aosta Valley, western Italian Alps, and examined for Heterobasidion annosum butt rots. Disease incidence ranged from 6% to 71% depending on sites, and H. annosum accounted for 92% of the total number of diseased stumps. H. annosum incidence was significantly higher (Chi‐squared multiple comparison tests, p < 0.05) on Norway spruce (44%) than on the other tree species (silver fir = 18%, larch = 12% and Scots pine = 6%). Based on the information on the airborne inoculum composition of the fungus, all the three European species of H. annosum were present, with a variable frequency, depending on site. A partial least squares regression analysis showed that the relative abundance of Norway spruce and four variables describing the size of trees were the best predictors for the incidence of H. annosum butt rots. A model having these variables as predictors was developed (r² = 0.75; p < 0.001) and successfully validated on five additional forest stands. An estimate of the losses in yield and value of timber associated with the disease, i.e. direct losses, was also carried out in the forests included in the survey. The percentage of direct financial losses was either comparable or lower than the average level of disease incidence.     

Lesion development in stems of rough‐ and smooth‐barked Eucalyptus nitens following artificial inoculations with canker fungi

A study of lesion development in stems of Eucalyptus nitens following artificial inoculations with canker fungi was carried out on 16‐year‐old plantation trees. In a first trial cambium bark wounds on smooth‐ and rough‐barked trees were inoculated with the mycelium of nine species of canker fungi, including Endothia gyrosa. In a second trial spores or mycelium of E. gyrosa were applied directly onto undamaged or superficially wounded bark surfaces. Infection subsequent to artificial inoculation via wounding (whatever the wounding technique or type of inoculum) resulted in significantly larger external lesions (mean lesion area up to 35.6 cm² 20 months after inoculation) on smooth bark compared with those on rough bark (up to 19.0 cm²). Microscopic studies of infected rough and smooth bark suggest that, once smooth bark is compromised by wounding and artificial inoculation, the particular anatomical structure of smooth bark may offer less mechanical resistance to post‐penetration hyphal spread in comparison with rough bark. It is suggested that at a pre‐penetration stage under natural conditions spores of E. gyrosa more easily infect rough bark via cracks associated with this type of bark but not present in smooth bark.     

In vitro interactions between bacteria isolated from Sitka spruce stumps and Heterobasidion annosum

Culture medium composition affected antagonism by bacterial isolates from Sitka spruce (Picea sitchensis) stumps against Heterobasidion annosum. Fifty percent of bacterial isolates inhibited H. annosum growth on sporulation agar or yeast–dextrose–peptone agar; only 10% of isolates caused inhibition on both media. Proportions of isolates inhibiting H. annosum varied with stump age; fewer isolates from 4‐ or 6‐year‐old stumps exhibited antagonism than isolates from older or younger stumps. Fifteen isolates showing antagonism on sporulation agar were tested against H. annosum in spruce wood cubes. None of the bacterial isolates alone caused a significant weight reduction in inoculated cubes. Relative inoculation times of bacterial isolates and H. annosum had an effect on weight loss in interactions; simultaneous inoculation with isolates and H. annosum inhibited weight loss caused by H. annosum compared with bacteria‐free controls. Inoculation with bacterial isolates 10 days before H. annosum had no effect on the decay rate. In contrast, inoculation with H. annosum 10 days before bacteria increased weight loss of cubes by 200% relative to cultures lacking bacteria. The effect of a mixed bacterial inoculum on weight change in 0.2‐mm spruce wood slips co‐inoculated with H. annosum, Resinicium bicolor, Hypholoma fasciculare, Stereum sanguinolentum or Melanotus proteus differed between different fungi.     

Effects of Wheeled Cable Skidding on Residual Trees in Selective Logging in Caspian Forests

There are increasing demands on silvicultural practices to reduce the adverse impacts of harvesting. Damage to residual trees caused by ground-based skidding was assessed in stands with low [3.4 stems per hectare (sph), 14.36 m³/ha], medium (5.2 sph, 21.61 m³/ha), and high (7.1 sph, 25.95 m³/ha) harvest intensities. Skidding was conducted using a cable skidder. After the skidding operation, a field survey was conducted to collect data on all residual trees (species, dbh, height) and on tree wounds (size class, location, intensity of damage). It was hypothesized that increased harvest intensity leads to increased injury rates. The treatment with the highest harvest intensity was found to cause the highest percentage of damage and the largest stem wounds. The most common types of damage were stem wounds to the cambium layer and bark scrapes. In all three harvest intensity treatments the probability of individual tree damage decreased as skid-trail cross slope decreased and distance to skid-trail edge increased. It is concluded that harvesting intensity should be limited to 5 trees/ha during each harvesting operation to reduce extent of tree damage and thus future financial loss.     

Induced resistance of Norway spruce,variation of phenolic compounds and their effects on fungal pathogens

Three clones of Norway spruce (Picea abies) were studied for their response to mass‐inoculation with the blue‐stain fungus Ceratocystis polonica. The effect of different pretreatments (fungal inoculation and wounding) before mass‐inoculation was investigated for their possible role in an acquired resistance reaction. Pretreated trees showed enhanced resistance to the subsequent mass‐inoculation relative to control trees that received no pretreatment. Furthermore, the fungal colonization of inoculated trees was less than that of wounded trees. The phenolic content of the bark, analysed by RP‐HPLC, was compared in trees receiving different treatments. Trees inoculated with C. polonica had higher average concentration of (+)‐catechin, taxifolin and trans‐resveratrol than wounded trees. Both inoculated and wounded trees had higher average concentrations of these compounds than control trees. The effect of the phenolic extract of Norway spruce bark on the growth of the root rot fungus Heterobasidion annosum and the blue‐stain fungi C. polonica and Ophiostoma penicillatum were investigated in vitro. Heterobasidion annosum was not negatively affected, and the extracts had fungistatic effects on the blue‐stain fungi. The growth of O. penicillatum was more inhibited than the growth of the more aggressive C. polonica.     

Impact of bark wounds on sapwood in Norway spruce and silver fir

Bark wounds by damage during harvesting are a serious problem in forestry due to fungi infection and wood deterioration. This paper presents results of an investigation about the influence of the wounds on the internal structure of such injured stems. In an experiment, bark wounds were artificially created at the stem base of Norway spruce [Picea abies (L.) Karst.] and silver fir (Abies alba Mill.). 2 years later, the injured stems along with undamaged controls were cut and the trunk portion below breast height subjected to computer tomographic (CT) analysis. Analysis of the CT-images revealed a substantial impact of wounding on sapwood properties in spruce: directly adjacent to the wound surface in all examined trees, a large disturbance zone was detected affecting on average 17% of the potential sapwood area. With increasing distance from the wound, the size of this disturbance zone diminished, but was still detectable in all trees at breast height ca. 1 m above the bark wound.     

The spreading of the S type of Heterobasidion annosum from Norway spruce stumps to the subsequent tree stand

The occurrence of Heterobasidion annosum in stumps and growing trees was investigated on 15 forest sites in southern Finland where the previous tree stand had been Norway spruce (Picea abies) infected by H. annosum, and the present stand was either Scots pine (Pinus sylvestris), lodgepole pine (Pinus contorta), Siberian larch (Larix siberica), silver birch (Betula pendula) or Norway spruce 8–53 years old. Out of 712 spruce stumps investigated of the previous tree stand, 26.3% were infected by the S group and 0.3% by the P group of H. annosum. The fungus was alive and the fruit bodies were active even in stumps cut 46 years ago. In the subsequent stand, the proportion of trees with root rot increased in spruce stands and decreased in stands of other tree species. On average, one S type genet spreading from an old spruce stump had infected 3.0 trees in the following spruce stand, 0.5 trees in lodgepole pine, 0.3 trees in Siberian larch, 0.05 trees in Scots pine and 0.03 trees in silver birch stand. Although silver birch generally was highly resistant to the S type of H. annosum, infected trees were found on one site that was planted with birch of a very northern provenance.     

Butt-rot of Scots pine in Thetford Forest caused by Heterobasidion annosum: a local phenomenon

Heterobasidion annosum was found to be the main cause of decay in 50–60-year-old Scots pine in Thetford Forest in East England. On some sites, up to 15% of the trees could be suffering from H. annosum rot, with decay occasionally extending 2 m or more up the stem. Prior to this study, Scots pine had been considered as resistant to H. annosum butt-rot in Britain, except in overmature trees.     

In vitro interactions in artificial and wood‐based media between fungi colonizing stumps of Sitka spruce

Interspecific interactions between fungi that colonize stumps of Picea sitchensis in Scotland were tested in dual cultures on Norkrans agar, spruce sawdust and in autoclaved blocks cut from roots. Isolates were ranked according to competitive ability on the different media, based on their ability to overgrow competitors or to form deadlock interactions. On the defined medium, Phaeolus schweinitzii was the species most able to overgrow competitors, followed by Stereum sanguinolentum and Heterobasidion annosum; Resinicium bicolor was the least able to overgrow competitors on this medium. By contrast, R. bicolor was the most competitive on spruce sawdust medium. Deadlocking interactions were formed most often in dual cultures on Norkrans agar. Observation of hyphal interactions on Norkrans agar under the microscope identified several different response types including growth of thin hyphae compared to control cultures, hyphal coiling, vacuolation of hyphae, hyphal lysis of one competitor and deposition of crystals in the agar. Hymenomycetes caused varying amounts of decay in autoclaved root blocks. Resinicium bicolor was able to replace other species in most co‐inoculations. Stereum sanguinolentum appeared to be the least competitive species in root block inoculations, being replaced by Melanotus proteus and R. bicolor, although interactions with H. annosum varied widely. These results indicate that substrate has a marked effect on interspecific fungal interactions, with wood‐based, particularly intact woody tissues closely matching competitive behaviour displayed in the field.