Possible altitude and temperature limits on pine wilt disease: the reproduction of vector sawyer beetles (Monochamus alternatus), survival of causal nematode (Bursaphelenchus xylophilus), and occurrence of damage caused by the disease

Pine wilt disease is caused by the pine wood nematode [Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle]. In East Asia, an important vector of the nematode is Monochamus alternatus Hope. We determined the tolerance and reproductive ability of sawyer beetles and the nematode to altitude and temperature at elevations between 850 and 1,450 m on Mt. Fuji in Japan. The number of emergent adults decreased markedly along the altitudinal gradient, but the beetle could still reproduce at 1,050 m (8.2 °C annual mean temperature). Beetles with a 2-year life cycle increased rapidly in number with increasing altitude. The pine wood nematode survived through winter at all altitudes tested (850–1,450 m). The beetle population decreased between 950 (9.1 °C) and 1,150 m (8.3 °C). Therefore, the beetle population seems to be stable at 850 m (10.2 °C) and lower altitudes (higher temperatures) but cannot be maintained from 950 (9.1 °C) to 1,150 m (8.3 °C) without constant immigration of beetles from lower altitudes. The beetles could not reproduce at altitudes above 1,150 m (lower than 8.2 °C). From the mean and effective cumulative temperatures, we concluded that the beetle (and its population) can endure temperatures lower than those previously reported. Pine wilt disease also occurred at lower temperatures and higher altitudes than expected. We have summarized the principal strategies for controlling the disease at high altitudes based on these results.     

Effects of bark girdling on carbohydrate supply and resistance of loblolly pine to southern pine beetle (Dendroctonus frontalis Zimm.) attack

Importance of current photosynthate in the regulation of tree defense against the southern pine beetle (SPB),Dendroctonus frontalis Zimm. (Coleoptera: Scolytidae) was investigated in loblolly pine,Pinus taeda L. Downward translocation of carbohydrate was blocked by removing a ring of bark (girdle) at 3.5 m above ground. Beetle colonization success and tree defensive responses measured as resin flow and induced lesion formation to inoculations with the beetle-associated fungus,Ophiostoma minus (Hedge.) H. and P. Sydow., were assessed above and below girdles. We hypothesized that a decrease in a available carbohydrate would lead to a decrease in tree defense and an increase in SPB colonization success below girdles. At 2 weeks, post-girdling carbohydrates were already reduced by 50% below girdles, but no significant differences in beetle colonization success or defensive responses were measured. At 8 weeks, post-girdling starch was reduced by 93%, sucrose by 44% and resin flow by 44% below girdles. Southern pine beetle adults were more successful in colonizing areas below than above girdles. However, no significant differences were detected in the size of the lesions that formed in response to inoculated fungi. This suggests that the size of the induced lesion may not be a reliable indicator of tree resistance to bark beetle attack as previously believed, and that lesion development is not entirely dependent on available carbohydrate or related to tree defense against beetles. Cambial growth was reduced below girdles with no latewood formed below and 25 rows of latewood formed above girdles. Latewood contains much higher densities of resin ducts than earlywood. This may explain why resin flow was lower and beetles were more successful in colonizing areas of the tree below girdles. Therefore, tree defense against bark beetles may be more complex than a simple supply-and-demand relationship for carbohydrate, and changes in source-sink relationships, as influenced by the environment, may be more important than supply.     

Über die Variabilität der Brutbilder von Kiefernborkenkäfern (Coleoptera,Ipidae)

Summary Studies on the variability of galleries of pine bark beetles (Col., Ipidae) The variability of the galleries of bark beetles haven't been considered enough till now. Examples of anomalies are given and reduced to their causes. The great pine bast beetle,Myelophilus piniperda, builds the mother-gallery under the bark of stumps downwards instead of above. This can be fed back to the conditions of humidity in the stumps. The little pine bast beetle,Myelophilus minor, when attacking lying stems, often lays eggs only into the higher part of the gallery which is kept free from bore meal. Under the influence of different environment factors also other species of Hylesinini and Ipini show anomalies in building up their galleries.     

Response of bark beetles and their natural enemies to fire and fire surrogate treatments in mixed-conifer forests in western Montana

Four treatments (control, burn-only, thin-only, and thin-and-burn) were evaluated for their effects on bark beetle-caused mortality in both the short-term (one to four years) and the long-term (seven years) in mixed-conifer forests in western Montana, USA. In addition to assessing bark beetle responses to these treatments, we also measured natural enemy landing rates and resin flow of ponderosa pine (Pinus ponderosa) the season fire treatments were implemented. All bark beetles were present at low population levels (non-outbreak) for the duration of the study. Post-treatment mortality of trees due to bark beetles was lowest in the thin-only and control units and highest in the units receiving burns. Three tree-killing bark beetle species responded positively to fire treatments: Douglas-fir beetle (Dendroctonus pseudotsugae), pine engraver (Ips pini), and western pine beetle (Dendroctonus brevicomis). Red turpentine beetle (Dendroctonus valens) responded positively to fire treatments, but never caused mortality. Three fire damage variables tested (height of crown scorch, percent circumference of the tree bole scorched, or degree of ground char) were significant factors in predicting beetle attack on trees. Douglas-fir beetle and pine engraver responded rapidly to increased availability of resources (fire-damaged trees); however, successful attacks dropped rapidly once these resources were depleted. Movement to green trees by pine engraver was not observed in plots receiving fire treatments, or in thinned plots where slash supported substantial reproduction by this beetle. The fourth tree-killing beetle present at the site, the mountain pine beetle, did not exhibit responses to any treatment. Natural enemies generally arrived at trees the same time as host bark beetles. However, the landing rates of only one, Medetera spp., was affected by treatment. This predator responded positively to thinning treatments. This insect was present in very high numbers indicating a regulatory effect on beetles, at least in the short-term, in thinned stands. Resin flow decreased from June to August. However, resin flow was significantly higher in trees in August than in June in fire treatments. Increased flow in burned trees later in the season did not affect beetle attack success. Overall, responses by beetles to treatments were short-term and limited to fire-damaged trees. Expansions into green trees did not occur. This lack of spread was likely due to a combination of high tree vigor in residual stands and low background populations of bark beetles.     

太原市油松小蠹虫及其综合防控技术研究

小蠹虫是一类重要的森林害虫,多为次期性害虫。通过调查,在太原市为害油松的主要种类是松六齿小蠹、松八齿小蠹和松十二齿小蠹;成虫扬飞期分别出现在5月份、7月份、8月份、9月份,是防治的关键时期;引起小蠹虫成灾的原因除自然因素外,主要是人为因素,所以防控小蠹虫要以虫情测报为基础,以检疫和林木管护措施为主导,并辅以生物、人工、化学等综合防控措施。     

Bark beetle (Coleoptera: Scolytidae) diversity in spaced and unmanaged mature lodgepole pine (Pinaceae) in southeastern British Columbia

Variation in the number and diversity of bark beetles in spaced mature lodgepole pine stands in the East Kootenay region of British Columbia was analyzed in relation to location (site), spacing treatment and years following treatment. We analyzed the number of bark beetles and the number of bark beetle species that emerged from stumps or were captured in flight traps in the first five years following spacing. We also investigated the incidence of bark beetle attacks on the remaining trees and the mean dates of emergence from stumps and of capture in flight traps for the common species. Observations were made on three sites, each having three treatments: 4 m × 4 m spacing, 5 m × 5 m spacing, and an untreated control. The mean density of bark beetles emerged from stumps was different among sites and years but not between spacing treatments. There was no statistically significant variation in the number of bark beetle species captured in flight traps by site, spacing treatment, years, or spacing treatment and years. Significantly more bark beetles were captured in the 4 m × 4 m spacing treatment than in the control. The number of bark beetles captured was the highest in the first 2 years following treatment. Up to 26 species of bark beetles, excluding ambrosia beetles, were captured in flight barrier traps. There was no difference in species diversity by site or treatment indicating that species diversity in mature lodgepole pine is relatively stable over large areas. Of the 213 trees that sustained at least 10 attacks by bark beetles on the lower 2 m of the bole, 59.1% occurred in the spaced plots but only 18.2% of those were successful, versus 74.7% success in the infested trees in the control plots. The majority of infested trees contained Ips sp., Dendroctonus valens and D. murrayanae. Of the seven trees attacked by mountain pine beetle (D. ponderosae) only one tree was located in a spaced plot.     

Colour responses from wood,thermally modified in superheated steam and pressurized steam atmospheres

Abstract

In this study, two different methods were used to produce thermally modified wood. One was carried out in a typical kiln drying chamber using superheated steam (SS) and the other used pressurized steam in an autoclave cylinder (PS). Overall, both processes followed the same principles and the wood was not treated with any chemicals. Two wood species were studied, Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). Treatments in the autoclave were carried out under pressure using temperatures of 160°C, 170°C and 180°C. Temperatures of 190°C and 212°C were used in treatments in the chamber at normal air pressure. The colour was measured using L*C*H colour space. Results for both species showed that similar L* (lightness) can be reached at lower (20–30°C) temperatures using PS compared with SS treatment. The hue angle of PS-treated wood was smaller than that of SS-treated wood. No significant difference in C* (chroma) was detected. The difference in E value between PS- and SS-treated wood was smaller for Norway spruce than for Scots pine. The residual moisture content was about 10% higher in wood treated by the PS process compared with the SS process.     

Pine bark beetle problem in Japan,referring to the discovery of the pine wood nematode,Bursaphelenchus lignicolus (Mamiya & Kiyohara)

Heavy loss of pine trees has been occurring for several decades throughout central to southwestern districts of Japan. In spite of beetles abundantly found under bark of dead trees, entomologists were inclined to the assumption that some other agents had already infected healthy trees before beetle attack based on various findings. It has been proved recently that the causative agent was the pine wood nematode (Bursaphelenchus lignicolus) newly discovered by pathologists and its transmitter was the Japanese pine sawyer (Monochamus alternatus). Aerial application of insecticides against the sawyer is now employed as a tentative measure of control.     

Effects of impregnation and heat treatment on the physical and mechanical properties of Scots pine (Pinus sylvestris) wood

Wood modification, of which thermal modification is one of the best-known methods, offers possible improvement in wood properties without imposing undue strain on the environment. This study investigates improvement of the properties of heat-treated solid wood. Scots pine (Pinus sylvestris) was modified in two stages: impregnation with modifiers followed by heat treatment at different temperatures. The impregnation was done with water glass, melamine, silicone, and tall oil. The heat treatment was performed at the temperatures of 180°C and 212°C for three hours. The modified samples were analyzed using performance indicators and scanning electron microscope micrographs. The mechanical and physical properties were determined with water absorption, swelling, bending strength, and impact strength tests. All the modifiers penetrated better into sapwood than hardwood; however, there were significant differences in the impregnation behavior of the modifiers. As regards the effect of heat treatment, generally the moisture properties were improved and mechanical strengths impaired with increasing treatment temperature. In contrast to previous studies, the bending strength increased after melamine impregnation and mild heat treatment. It is concluded that the properties of impregnated wood can be enhanced by moderate heat treatment.     

Fungi associated with the spruce bark beetle Ips typographus in an endemic area in Norway

To investigate the fungal flora associated with the spruce bark beetle Ips typographus in an endemic area, beetles were collected during the flight period in six locations in Tr?ndelag, Norway. The beetles were inoculated into fresh Norway spruce logs, and the frequency of different species was monitored by fungal isolation from bark and wood. The most common species were Ophiostoma bicolor, O. penicillatum, O. polonicum and a previously undescribed Graphium species, the same species which were the most important associates of I. Typographus in an epidemic area in southeastern Norway. The frequency of the primary invader, O. polonicum, was, however, lower in Tr?ndelag, which may indicate that this species is less frequent in endemic areas than in epidemic areas.     

Mountain pine beetle-associated blue-stain fungi are differentially adapted to boreal temperatures

Mountain pine beetles (MPB) are the most serious pest of lodgepole pine in Canada and are likely to invade boreal jack pine forests. MPB vector three blue-stain fungi, Grosmannia clavigera, Ophiostoma montium and Leptographium longiclavatum, which contribute to beetle success. Fungal survival at extreme boreal temperatures will contribute to their success in jack pine. Growth, sporulation and survival of the three fungi at −20 to 37°C were tested in vitro. Overwintering survival of G. clavigera and O. montium was assessed in vivo. All species grew at 5–30°C, with optimal growth at 20–25°C. Grosmannia clavigera and L. longiclavatum survived at −20°C, but O. montium died. Growth of G. clavigera and L. longiclavatum was inhibited at 30°C, but O. montium grew well. Grosmannia clavigera and O. montium overwintered in living pines. These results suggest that G. clavigera and L. longiclavatum were adapted to cold boreal winters but not hot summers, with the converse true for O. montium. Temperature tolerance varied among G. clavigera isolates. British Columbian and Californian isolates grew faster at 25°C than Albertan isolates. Isolates from Alberta and Idaho/Montana grew optimally at 20°C, while British Columbian and Californian isolates grew optimally at 25°C.     

Assessing forest vulnerability and the potential distribution of pine beetles under current and future climate scenarios in the Interior West of the US

The aim of our study was to estimate forest vulnerability and potential distribution of three bark beetles (Curculionidae: Scolytinae) under current and projected climate conditions for 2020 and 2050. Our study focused on the mountain pine beetle (Dendroctonus ponderosae), western pine beetle (Dendroctonus brevicomis), and pine engraver (Ipspini). This study was conducted across eight states in the Interior West of the US covering approximately 2.2 million km² and encompassing about 95% of the Rocky Mountains in the contiguous US. Our analyses relied on aerial surveys of bark beetle outbreaks that occurred between 1991 and 2008. Occurrence points for each species were generated within polygons created from the aerial surveys. Current and projected climate scenarios were acquired from the WorldClim database and represented by 19 bioclimatic variables. We used Maxent modeling technique fit with occurrence points and current climate data to model potential beetle distributions and forest vulnerability. Three available climate models, each having two emission scenarios, were modeled independently and results averaged to produce two predictions for 2020 and two predictions for 2050 for each analysis. Environmental parameters defined by current climate models were then used to predict conditions under future climate scenarios, and changes in different species’ ranges were calculated. Our results suggested that the potential distribution for bark beetles under current climate conditions is extensive, which coincides with infestation trends observed in the last decade. Our results predicted that suitable habitats for the mountain pine beetle and pine engraver beetle will stabilize or decrease under future climate conditions, while habitat for the western pine beetle will continue to increase over time. The greatest increase in habitat area was for the western pine beetle, where one climate model predicted a 27% increase by 2050. In contrast, the predicted habitat of the mountain pine beetle from another climate model suggested a decrease in habitat areas as great as 46% by 2050. Generally, 2020 and 2050 models that tested the three climate scenarios independently had similar trends, though one climate scenario for the western pine beetle produced contrasting results. Ranges for all three species of bark beetles shifted considerably geographically suggesting that some host species may become more vulnerable to beetle attack in the future, while others may have a reduced risk over time.     

Effects of preboiling on the acidity and strength properties of heat-treated wood

Heat treatment is an alternative to the chemical treatment in wood preservation, which has been used to some extent in improving timber quality. However, reduction in strength properties has been one of the major limitations in the use of this technique and therefore investigations on the use of various pre-treatment methods are highly essential. Wood samples from Scots pine were immersed in already boiling water (100°C) for 20 min followed by 2 h of heat treatment at 160 and 200°C. The acidity and strength properties were determined by measurement of pH and static bending test, respectively. There were no significant changes in pH due to preboiling in both heat-treated and untreated wood. Similarly, preboiling did not result in any appreciable differences in strength both before heat treatment and during heat treatment at 160°C. However, for 200°C heat treatment preboiling reduced significantly the degree of strength loss as indicated by 19.4% reduction in modulus of rupture in preboiled wood compared to 26.6% reduction in unpreboiled wood. From the results of this study it is evident that preboiling has a buffering effect on wood during heat treatment and the higher the intensity of heat treatment the higher the significance of the buffering effect of pre-boiling.     

Long‐term survival and non‐vector spread of the pinewood nematode,Bursaphelenchus xylophilus,via wood chips

The pinewood nematode, Bursaphelenchus xylophilus, is the causal agent of pine wilt disease and is transmitted to new host trees by beetles of the genus Monochamus. The increasing interest in imported wood chips from North America for paper production and energy purposes and the corresponding phytosanitary risk of non‐vector transmission of B. xylophilus has been discussed since 1984, the year of the first interception of B. xylophilus in wood chips in the European Union. The long‐term survival of B. xylophilus in wood chips and its non‐vector spread from infested wood chips to non‐infested trees were studied. Pinus sylvestris logs were inoculated with a suspension of B. xylophilus to produce infested wood chips. During the long‐term storage test, B. xylophilus in P. sylvestris wood chips were examined. Four variants, including sealed and openly stored wood chips at both 15°C and 25°C, were studied. For the test of non‐vector spread, B. xylophilus ‐infested wood chips were placed on three‐ to four‐year‐old P. sylvestris saplings under different conditions. Bursaphelenchus xylophilus survived for more than 1 year at both temperatures in the sealed wood chips, which was significantly longer than for the openly stored variant at 25°C. Temperature, tree condition and wood chip location all influenced non‐vector spread through wood chips. Of the 480 trees that were in contact with infested wood chips and showed clear symptoms of pine wilt disease, B. xylophilus were extracted from 42 pines at 25°C and one pine at 15°C. The highest B. xylophilus infestation rates resulting in clear pine wilt disease symptoms (75%) were found in infested wood chips directly attached to stem‐wounded trees at 25°C. However, more variants exhibited B. xylophilus infestation at this temperature; trees with stem or root injuries plus direct contact with infested wood chips to the wounded part were primarily affected. Moreover, non‐vector spread was also detected in stem‐ and root‐injured pines without any direct contact with infested wood chips. Our results confirmed that B. xylophilus can survive for long periods in wood chips and can be transmitted from infested wood chips to damaged trees, but the likelihood of such PWN establishment should be low compared to spread through vectors. These findings must be considered in the pest risk analysis of B. xylophilus, and studies using outdoor trials should be carried out to complete this pest risk analysis.     

Effect of post treatment temperature and humidity conditions on fixation performance of CCA-C treated red pine and southern pine

introductionWaterbornepreservativesareamajorcomponentofthewood-treatingindustrybecauseoftheireaseofapplication,lowcost,andthecleanappearanceofthewoodattertreatment.Theuseofchromatedcopperarsenate(CCA)preservativesintheUSAhasgrownfroma14%shareofthewoodpreservativesmarketin1977to73%in1987(Micklewright1993).ThisismainlyduetotheincreasinguseofCCAtreatedwoodasdecksandoutdoorstructures.ThewaterbornepreservativeCCAhasbecomeoneofthemosteffectivetreatmentsforNorthAmericanwoodproduCts,usedinapplic…     

Bark beetle-caused mortality in a drought-affected ponderosa pine landscape in Arizona,USA

Extensive ponderosa pine (Pinus ponderosa Dougl. ex Laws.) mortality associated with a widespread severe drought and increased bark beetle (Coleoptera: Curculionidae, Scolytinae) populations occurred in Arizona from 2001 to 2004. A complex of Ips beetles including: the Arizona fivespined ips, Ips lecontei Swaine, the pine engraver beetle, Ips pini (Say), Ips calligraphus (Germar), Ips latidens (LeConte), Ips knausi Swaine and Ips integer (Eichhoff) were the primary bark beetle species associated with ponderosa pine mortality. In this study we examine stand conditions and physiographic factors associated with bark beetle-caused tree mortality in ponderosa pine forests across five National Forests in Arizona. A total of 633 fixed-radius plots were established across five National Forests in Arizona: Apache-Sitgreaves, Coconino, Kaibab, Prescott, and Tonto. Prior to the bark beetle outbreak, plots with mortality had higher tree and stocking compared with plots without pine mortality. Logistic regression modeling found that probability of ponderosa pine mortality caused by bark beetles was positively correlated with tree density and inversely related with elevation and tree diameter. Given the large geographical extent of this study resulting logistic models to estimate the likelihood of bark beetle attack should have wide applicability across similar ponderosa pine forests across the Southwest. This is particularly true of a model driven by tree density and elevation constructed by combining all forests. Tree mortality resulted in significant reductions in basal area, tree density, stand density index, and mean tree diameter for ponderosa pine and for all species combined in these forests. Most of the observed pine mortality was in the 10–35 cm diameter class, which comprise much of the increase in tree density over the past century as a result of fire suppression and grazing practices. Ecological implications of tree mortality are discussed.     

Crystalline structure of heat-treated Scots pine [<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.] and Uludağ fir [<Emphasis Type="Italic">Abies nordmanniana</Emphasis> (Stev.) subsp. <Emphasis Type="Italic">bornmuelleriana</Emphasis> (Mattf.)] wood

The aim of this study was to determine changes in crystallinity and crystalline unit cell type of heat-treated Scots pine (Pinus sylvestris L.) and Uludağ fir (Abies nordmanniana stev. subsp. bornmuelleriana Mattf.) wood samples by means of FT-IR spectroscopic method. Heat treatment was applied on the test samples in an oven at three different temperatures (120, 150, and 180°C) and for two different periods of time (6 and 10 h) under atmospheric pressure. It was designated that crystallinity of both Scots pine and Uludağ fir wood samples increased during heat treatment depending on the duration. However, monoclinic structure in crystalline unit cells of Scots pine and Uludağ fir wood samples converted to triclinic structure when heat treated. It was estimated that monoclinic structure was dominant in the crystalline unit cell. It was established that the crystalline structure of Scots pine wood samples was more affected by heat treatment than that of Uludağ fir wood samples.     

Influence of heating history on dynamic viscoelastic properties and dimensions of dry wood

To obtain new information about the mechanical and physical properties of dry wood in unstable states, the influence of heating history on viscoelastic properties and dimensional changes of dry wood in the radial, tangential, and longitudinal directions was studied between 100° and 200°C. Unstable states of dry wood still existed after heating at 105°C for 30 min and were modified by activated molecular motion in the first heating process to temperatures above 105°C. This phenomenon is thought to be caused by the unstable states reappearing after wetting and drying again. Dry wood components did not completely approach the stable state in the temperature range tested, because they did not entirely surpass the glass transition temperatures in most of the temperature range. In constant temperature processes at 135° and 165°C, E′ increased and E″ decreased with time regardless of the direction. This indicated that the unstable states of dry wood components were gradually modified with time at constant temperatures. On the other hand, anisotropy of dimensional change existed and dimension increased in the longitudinal direction, was unchanged in the radial direction, and decreased in the tangential direction with time at constant temperatures. Part of this report was presented at the 13th Annual Meeting of the Chubu Branch of the Japan Wood Research Society, Shizuoka, August 2003     

Pronounced fluctuations of spruce bark beetle (Scolytinae: Ips typographus) populations do not invoke genetic differentiation

The dynamics of a recent outbreak of the spruce bark beetle (Ips typographus) in Switzerland was ruled by a devastating winter storm in 1999 and the drought and heat of the summer 2003. Starting from a similar level of population sizes, estimated as the rate of infested growing stock, beetle populations increased differently in magnitude and time among different regions in Switzerland. Accordingly, we expected local or regional genetic differentiation as a result of such repeated population expansion/breakdown dynamics. We analyzed 5 nuclear microsatellites of spruce bark beetles sampled from pheromone traps at 30 locations distributed over Switzerland. Our genetic results did not indicate any sign of population differentiation, structure, isolation by distance, or recent bottlenecks. This complete lack of genetic structure suggests that spruce bark beetles are highly mobile, precluding the formation of a spatial structure at neutral molecular markers. Thus, this molecular–genetic approach does not allow us to discriminate among regional gene pools and to identify the origin of expanding beetle populations.     

Optimisation of a two-stage heat treatment process: durability aspects

Heat treatment of wood at relatively high temperatures (in the range of 150–280°C) is an effective method to improve biological durability of wood. This study was performed to investigate the effect of heat treatment process optimisation on the resistance against fungal attack, including basidiomycetes, molds and blue stain fungi. An industrially used two-stage heat treatment method under relatively mild conditions (<200°C) was used to treat the boards. Heat treatment of radiata pine sapwood revealed a clear improvement of the resistance against the brown rot fungi Coniophora puteana and Poria placenta. Increasing process temperature and/or effective process time during the first process stage, the hydro thermolysis, appeared to affect the resistance against C. puteana attack, but the effect on the resistance against P. placenta was rather limited. Heat treated radiata pine showed a limited resistance against the white rot fungus Coriolus versicolor and process variations during the hydro thermolysis stage appeared not to affect this resistance. A clear difference between the resistance of heat treated Scots pine sapwood and heartwood against fungal attack is observed. Scots pine heartwood showed a higher resistance against C. puteana and P. placenta but also against the white rot fungus C. versicolor. Similar results were obtained when heat treated birch was exposed to brown and white rot fungi. Heat treatment showed an improved resistance against C. puteana attack, especially at higher temperatures during the hydro thermolysis stage. A clear improvement of the durability was also observed after exposure to the white rot fungus C. versicolor and especially Stereum hirsutum. Increasing the process temperature or process time during the hydro thermolysis stage appeared to have a limited effect on the resistance against C. versicolor attack. Heat treated radiata pine and Norway spruce were still susceptible to mold growth on the wood surface, probably due to the formation of hemicelluloses degradation products (e.g. sugars) during heat treatment. Remarkable is the absence of blue stain fungi on heat treated wood specimen, also because the abandant blue stain fungi were observed on untreated specimen. Molecular reasons for the resistance of heat treated wood against fungal attack are discussed in detail contributing to a better understanding of heat treatment methods.