Gap dynamics in the Western Carpathian mixed beech old-growth forests affected by spruce bark beetle outbreak

Understanding how species-specific disturbances affect the dynamics of mixed forests is becoming increasingly important due to rapidly changing disturbance regimes. This study estimated the effect of Norway spruce (Picea abies (L.) Karst.) mortality on the disturbance processes in two mixed beech stands of the Western Carpathians that were affected by a bark beetle outbreak. We evaluated the size distribution, fraction of canopy and expanded gaps, the characteristics of gapmakers and the contribution of different species to gap size. The measured canopy gap fraction was <5%, and most canopy gaps were small (<100 m²). Spruce was the most abundant gapmaker, and its share among gapmakers was 3–6 times higher than its share in the canopy. We found that the increase in spruce mortality due to the outbreak resulted in a fine-scale mortality pattern. However, spruce gapmakers did not contribute much to gap area size, as shown by a weak correlation between the number of spruce gapmakers and the area of expanded gaps. Diameter distribution of living versus recently dead trees showed that beech mortality occurred disproportionately in large size classes. However, dead spruce trees were equally frequent in all diameter classes, which means beetles did not exclusively attack larger trees in these stands during the outbreak. We conclude that spruce mortality may have influenced successional processes by giving a competitive advantage to two other species that were not affected by the outbreak, provided that a high deer browsing intensity does not hinder the regeneration of new seedlings.

     

Fungal succession in sapwood of Norway spruce infested by the bark beetle Ips typographus

Fungal invasion of Norway spruce sapwood was investigated during a period of 130 weeks fol-lowing attack by the spruce bark beetle Ips typographus. Heavy beetle attack tended to overwhelm the trees quickly and no secondary resinosis was produced. Nonetheless, fungal penetration in the sapwood was initiated only slowly, although it accelerated during the fourth week after attack. Typically the leading edge of fungal penetration was a few millimeters in advance of the visible blue-stain during the sapwood colonization. Fungi invaded the sapwood in a successional pattern with the most pathogenic species Ophiostoma polonicum first, followed by other beetle-transmitted Ophiostoma and Graphium species. The later succession was probably influenced by sapwood moisture. Strong decaying white-rotters invaded near the base of the trees, where sapwood moisture remained favourable, while cf. Trichoderma viride dominated in the drier parts or the trees.     

Long-term effects on tree regeneration of soil scarification with microtopography manipulation in mixed forests of central Hokkaido,northern Japan

Natural regeneration of canopy tree species is generally poor under a selective cutting regime practised in mixed conifer–hardwood stands on Hokkaido, northern Japan, and is prevented by dense bamboo layers in the understory. To promote tree regeneration, we scarified soil in ten sites, with elevations ranging from 420 to 760 m, in 1979, with a rake-equipped bulldozer to produce three different artificial microtopographies (concave, flat, and convex). Twenty-six years after scarification, six canopy tree species (Acer mono, Abies sachalinensis, Betula ermanii, B. maximowicziana, Kalopanax pictus, and Picea jezoensis) had become well established. Abies sachalinensis and B. ermanii regenerated at all sites. Picea jezoensis was well established in high-elevation sites, whereas other hardwood tree species (A. mono, B. maximowicziana, and K. pictus) were well established at low-elevation sites. The Betula species dominated upper layers of regenerated trees, and two conifer species (A. sachalinensis and P. jezoensis) occupied lower layers. Regenerated densities of four (of six) major tree species were positively correlated with standing timber volume of mother trees, whereas those of shade-intolerant species (two Betula species and K. pictus) were negatively correlated with standing timber volume of all canopy trees. Small-seeded species (P. jezoensis and the two Betula species) had higher regeneration densities on convex sites than on other microtopographies. Adequate seed supply, convex substratum for small-seeded species, and control of light conditions for shade-intolerant species should be taken into account when planning regeneration of desirable tree species in central Hokkaido.     

Colonisation of native and exotic conifers by indigenous bark beetles (Coleoptera: Scolytinae) in France

Planting exotic conifers offers indigenous forest insects an opportunity to extend their host range and eventually to become significant pests. Knowing the ecological and evolutionary modalities driving the colonisation of exotic tree species by indigenous insects is thus of primary importance. We compared the bark beetle communities (Coleoptera: Curculionidae, Scolytinae) associated with both native and introduced conifers in France. The aim of our study was to estimate the influence of both host- and insect-related factors on the beetles’ likelihood to shift onto new hosts. We considered the influence of host origin (i.e. native vs. exotic), host tree species identity, tree bark thickness and tree taxonomic proximity, as well as insects’ host specificity. A field inventory using trap trees was carried out in two regions in France (Limousin and Jura) during two consecutive years (2006 and 2007) on three European native conifer species [Norway spruce (Picea abies); Scots pine (Pinus sylvestris) and European Silver-fir (Abies alba)] and five North American [Sitka spruce (Picea sitchensis); Eastern white pine (Pinus strobus); Grand fir (Abies grandis); Douglas fir (Pseudotsuga menziesii) and Western red cedar (Thuja plicata)]. A total of 18 indigenous and 2 exotic bark beetle species were collected. All exotic conifer species were colonised by indigenous bark beetle species and no significant difference was observed of the cumulated species richness of the latter between native and exotic tree species (13 vs. 14, P < 0.05). The ability of indigenous bark beetles to shift onto exotic conifers appeared to strongly depend on host species (significantly structuring bark beetle assemblages), the presence of phylogenetically related native conifer species and that of similar resources, in combination with insect host specificity. Host tree species status (native or exotic) also seemed to be involved, but its effect did not seem as essential as that of the previous factors. These findings are discussed in terms of adaptation, plasticity and practical aspects of forest management.     

A method for the protection of spruce stands againstIps typographus by the use of barriers of pheromone traps in north-eastern Slovakia

A method and layout of various systems of barriers of pheromone traps is described. The rationale of the method is based on the stress of spruce and the chemical communication ofIps typographus. Various systems of pheromone trap barriers were used according to the required level of protection. The method was used in two areas affected by air pollution and bark beetle outbreak. The first area was in an unnatural spruce monoculture region while the second was in a National Park. The described method led to a significant reduction of bark beetle attacks on trees along forest edges and subsequently to the stopping of movement of the zone of attacked trees due to bark beetle damage. In the case of forest stands with no reduced canopy closure, the reduction of attacks led to a dramatic decline of bark beetle outbreak. On the other hand, this method was not able to reduce the level of bark beetle attack in the interior of forest stands with a decreased level of canopy closure. This method, as part of differentiated pest management measures in one forest district, was successful without any other protection measures in the condition of natural reserves in a spruce vegetation zone.     

Difference in uprooting resistance among coniferous species planted in soils of volcanic origin

Uprooting resistance against wind force for coniferous plantations in soils of volcanic origin was studied. The difference in uprooting resistance among Abies sachalinensis, Picea jezoensis, and Larix kaempferi was discussed. The sample site was set in Chitose plantations in Hokkaido Japan, where typhoon 0418 caused fatal uprooting damage in 2004. An uproot resistance index—the ratio of the geometrical moment of area for uprooted root-plate to the moment susceptibility to wind force—was defined to quantify relative uprooting resistance against wind force. It was calculated from the dimensional measurements for the tree forms and root-plates of 100 uprooted sample trees after the typhoon attack. As a result, the uprooting resistance for Picea jezoensis, which was less damaged among the sample species, was estimated to be greater than those for the other two species.     

Removal of heavy metal ions from solutions by coniferous barks

Summary The abilities of 15 coniferous barks for removing toxic heavy metal ions were investigated. The barks considerably varied in the adsorption ability to each metal ion. Of the barks tested, high adsorption ability for heavy metal ions was found inPicea abies (Norway spruce). Equilibrium experiments usingP. jezoensis (Yezo spruce) bark showed that the adsorption of Cd²⁺ was greatly affected by the pH of solution and the initial Cd²⁺ concentration in solution. The adsorption of Cd²⁺ byP. jezoensis bark followed Freundlich isotherm in the concentration range 10–330 mg Cd²⁺/L. The continuous column experiments usingP. jezoensis bark indicated that the packing had retained 10.1–14.2 mg Cd²⁺/g adsorbent until the column broke through.     

Bark beetle (Coleoptera, Scolytidae) outbreak and system of IPM measures in an area affected by intensive forest decline connected with honey fungus (Armillaria sp.)

The character of a bark beetle outbreak, planning system, and implementation of IPM measures in a forest affected by intensive decline connected with honey fungus (Armillaria sp.) is described. It is possible to distinguish two levels of outbreak in the study area. The first level is characterized by spruce mortality connected with yellowing of spruce and presence of plant pathogens, mostly Armillaria sp. Forest stands have disperse infestations of bark beetles. Identification of infested trees and salvage cutting in time are problematic. In case of late processing of infested trees, the second level of outbreak could become manifest. The populations of bark beetle increase. Beetles could attack relatively healthy trees. The classical outbreak with forest edges and spot infestations starts. The identification of infested trees is easier. The application of pheromone trap barriers is effective. Thus, the second level of outbreak could be easily managed. The planning of IPM measures is concerned with localization of various pheromone trap systems in particular forest stands. It is based on field survey, data acquisition, estimation of swarming bark beetle population, and information of pheromone system effectiveness.     

<Emphasis Type="Italic">Bursaphelenchus mucronatus</Emphasis> (Nematoda: Aphelenchoididae) vectored by <Emphasis Type="Italic">Monochamus </Emphasis><Emphasis Type="Italic">urussovi</Emphasis> (Coleoptera: Cerambycidae) in Hokkaido,Japan

Bursaphelenchus mucronatus Mamiya et Enda has been recovered for the first time from adults of the cerambycid beetle, Monochamus urussovi (Fischer), in Hokkaido, Japan. The nematode was also recovered from the inner bark of Picea jezoensis (Siebold et Zuccarini) Carrière and Abies sachalinensis (Fr Schmidt) Masters infested with M. urussovi larvae. PCR–RFLP analysis indicated that B. mucronatus in Hokkaido is the European type.     

Types of bark beetle (Coleoptera: Scolytidae) infestation in spruce forest stands affected by air pollution, bark beetle outbreak and honey fungus (Armillaria mellea)

583 spruce stands in an area affected by air pollution and bark beetle outbreak in Eastern Slovakia were studied in 1996. According to bark beetle infestation of dominant and codominant trees, stands were classified into following types of spruce stand decline:Ips typographus-A,Ips typographus-B,Polygraphus poligraphus, I. typographus/P. poligraphus—A,I. typographus/P. poligraphus—B. The presence of attacked trees in forest edges, bark beetle spots and forest interior was the key important factor for the classification. Data from forest inventory and forest management evidence together with data on types of spruce stands decline were used in further analyses. Results shows that the distribution of forest stands classified into different types or uninfested stands is related mainly to host size and site quality. The percentage of spruce, exposition of stands and stand density showed significant effects. The mechanisms of spreading of studied bark beetle outbreak could be explained by direct effects of stress of trees caused by an abrupt increase of level of solar irradiation and by weakening of trees by the honey fungus.     

Susceptibility of ponderosa pine, Pinus ponderosa (Dougl. ex Laws.), to mountain pine beetle, Dendroctonus ponderosae Hopkins,attack in uneven-aged stands in the Black Hills of South Dakota and Wyoming USA

Mountain pine beetle, Dendroctonus ponderosae Hopkins can cause extensive tree mortality in ponderosa pine, Pinus ponderosa Dougl. ex Laws., forests in the Black Hills of South Dakota and Wyoming. Most studies that have examined stand susceptibility to mountain pine beetle have been conducted in even-aged stands. Land managers increasingly practice uneven-aged management. We established 84 clusters of four plots, one where bark beetle-caused mortality was present and three uninfested plots. For all plot trees we recorded species, tree diameter, and crown position and for ponderosa pine whether they were killed or infested by mountain pine beetle. Elevation, slope, and aspect were also recorded. We used classification trees to model the likelihood of bark beetle attack based on plot and site variables. The probability of individual tree attack within the infested plots was estimated using logistic regression. Basal area of ponderosa pine in trees ≥25.4 cm in diameter at breast height (dbh) and ponderosa pine stand density index were correlated with mountain pine beetle attack. Regression trees and linear regression indicated that the amount of observed tree mortality was associated with initial ponderosa pine basal area and ponderosa pine stand density index. Infested stands had higher total and ponderosa pine basal area, total and ponderosa pine stand density index, and ponderosa pine basal area in trees ≥25.4 cm dbh. The probability of individual tree attack within infested plots was positively correlated with tree diameter with ponderosa pine stand density index modifying the relationship. A tree of a given size was more likely to be attacked in a denser stand. We conclude that stands with higher ponderosa pine basal area in trees >25.4 cm and ponderosa pine stand density index are correlated with an increased likelihood of mountain pine beetle bark beetle attack. Information form this study will help forest managers in the identification of uneven-aged stands with a higher likelihood of bark beetle attack and expected levels of tree mortality.     

Bark beetles,fuels, fires and implications for forest management in the Intermountain West

Bark beetle-caused tree mortality in conifer forests affects the quantity and quality of forest fuels and has long been assumed to increase fire hazard and potential fire behavior. In reality, bark beetles, and their effects on fuel accumulation, and subsequent fire hazard, are poorly understood. We extensively sampled fuels in three bark beetle-affected Intermountain conifer forests and compared these data to existing research on bark beetle/fuels/fire interactions within the context of the disturbance regime. Data were collected in endemic, epidemic and post-epidemic stands of Douglas-fir, lodgepole pine and Engelmann spruce. From these data, we evaluated the influence of bark beetle-caused tree mortality on various fuels characteristics over the course of a bark beetle rotation. The data showed that changes in fuels over time create periods where the potential for high intensity and/or severe fires increases or decreases. The net result of bark beetle epidemics was a substantial change in species composition and a highly altered fuels complex. Early in epidemics there is a net increase in the amount of fine surface fuels when compared to endemic stands. In post-epidemic stands large, dead, woody fuels, and live surface fuels dominate. We then discuss potential fire behavior in bark beetle-affected conifer fuels based on actual and simulated fuels data. Results indicated that for surface fires both rates of fire spread and fireline intensities were higher in the current epidemic stands than in the endemic stands. Rates of spread and fireline intensities were higher in epidemic stands due, however, to decreased vegetative sheltering and its effect on mid-flame wind speed, rather than changes in fuels. Passive crown fires were more likely in post-epidemic stands, but active crown fires were less likely due to decreased aerial fuel continuity. We also discuss the ecological effects of extreme fire behavior. Information is presented on managing forests to reduce the impact of bark beetle outbreaks and the interplay between management, bark beetle populations, fuels and fire hazard and behavior.     

Surface temperature change of spruce forest as a result of bark beetle attack: remote sensing and GIS approach

In the 1990s, a bark beetle (Ips typographus [L.]) infection caused the decay of spruce forest (Picea abies [L.] Karst.) in the central part of the Šumava Mountains, the Czech Republic, bordering the Bavarian Forest National Park, Germany, where the bark beetle infection started in the late 1980s. Some areas were left without human intervention and, consequently, the trees around these areas were removed to stop further bark beetle outbreak. The objective of our study was the assessment of surface temperature (ST) change in spruce forest decayed under bark beetle and following clear-cutting. The change detection of ST is based on the comparison of modelled values and thermal satellite data. For this purpose, Landsat scenes from July 11th, 1987 and July 28th, 2002 were used. The models describe the dependence of ST of living spruce forest on topography. The topography effect is based on the Altitude and Hillshade index, which expresses the influence of Aspect and Slope on the relief illumination. Then the modelled ST values were extrapolated for decayed spruce forest and clear-cut areas. In order to increase model accuracy, the forest edge zones (90 m wide) were removed because of their different energy balance; then explained variability value (R ²) increased from 0.37 to 0.55. The results of comparing modelled values with satellite ST in the decayed spruce forest and clear-cut areas show an average increase of ST by 5.2 and 3.5°C, respectively. The thermal satellite data from 1987 were used for model validation. This showed that the accuracy of ST modelling using topography was sufficient, because the difference between the modelled ST with and without decayed spruce forest and clear-cut areas was at most only 0.4°C.     

A review： chemical ecology of Ips typographus （Coleoptera, Scolytidae）

Chemical ecology of the spruce bark beetle lps typographus （L.） was reviewed. The outbreak of 1.typographus in central Europe triggered extensive research on chemical ecology, Males initiate host location and produce semiochemicals which attract both males and females, A successful mass attack must first overcome the resistance of the host tree. Pioneer I. typographus evolved to use the resin flow of host trees as kairomones in host location, and synthesized semiochemicals initially to detoxify the resin. If small bark beetle populations infest healthy trees, mass attack is prevented by host resistance, Nine monoterpene alcohols were found in male hind-guts, including cis-verbenol （cV） and 2-methyl-3-buten-2-ol （MB） which are regarded as primary aggregation pheromones, and a low proportion of lpsdienol （ld） which increases attractiveness of cV and MB, Verbenone （Vn） and Ipsenol （le） are anti-aggregation pheromones, that play important roles in adjusting attack density and insect density under the bark. Non-host volatiles are repellent to L typographus, so that beetles do not waste energy boring into non-host trees. The relationship between host resistance, pheromone compounds and behavior, non-host volatiles, bioassays and mass trapping are reviewed, Results of field bioassays stressed that traps baited with specific pheromones could be used as a reasonable protection measure.     

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.     

Fungi in bark peeling wounds of Picea abies in central Sweden

A total of 210 Norway spruce trees with stem wounds resulting from bark peeling by moose (Alces alces) were examined in three 45–50-year-old stands that contained 20-30% of damaged trees. Injured stems were between 8 and 40 cm diameter at breast height (d.b.h.) and showed 1 to 23-year-old wounds. Wounds varied in size from 2 to 4815 cm². The size of injury correlated negatively with the age of the injury (r=-0.24; p=0.004), and positive correlation was established between the age of the injury and d.b.h. of the wounded tree (r=0.50; p=0.0001). Each wound was sampled once using an increment borer and fungi were isolated. Among basidiomycetes, Stereum sanguinolentum was the most common (isolated from 26.7% of the damaged stems). Other common species were Cylindrobasidium evolvens (23.8%), Amylostereum areolatum (5.2%), A. chailletii (0.5%), Heterobasidion annosum (5.2%), Peni-ophorapithya (1.4%), Sistotrema brinkmannii (1.0%). The ascomycete Nectria fuckeliana was the most common among all fungi (present in 35.7% of bark peeling wounds). The frequency of S. sanguinolentum infection correlated positively with the age of the injury (r=0.27; p=0.001) and the opposite relationship was revealed for C. evolvens (r=?0.30; p=0.0001). Furthermore, C. evolvens infection correlated positively with the wound size (r=0.30; p=0.0001) and negatively with the tree d.b.h. (r=?0.20; p=0.004). A positive correlation was found between tree d. b. h. and the occurrence in stems of H. annosum (r=0.23; p=0.001 and N. fuckeliana (r=0.23; p=0.0006). The spruce bark beetle Dendroctonus micans attacked 14.8% of wounded trees. Presence in stems of N. fuckeliana was associated significantly with the D. micans attack (r=0.190; p =0.006; χ² test: p=0.01). Except for a negative correlation between infections of S. sanguinolentum and H. annosum (r=-0.140; p=0.04), no significant relationship between fungal species was found.     

Availability of standing trees for large cavity-nesting birds in the eastern boreal forest of Québec,Canada

Large cavity-nesting birds depend on large-diameter trees for suitable nest sites. The increased spatial extent of commercial timber harvesting is modifying forest structure across the land base and may thus compromise the availability of large trees at the landscape scale. In this study, our objectives were to (1) characterize the availability of large living and dead trees in old-growth stands dominated by different tree species and surficial deposits that encompass the range of natural cover types of eastern Québec's boreal forest; (2) analyze the distribution of trees among decay-classes; and (3) compare the availability of large trees in unharvested, remnant, and harvested stands for the entire range of decay-classes. A total of 116 line transects were distributed across unharvested forests, remnant linear forests, and cutblocks in cutover areas. Unharvested forest stands (black spruce [Picea mariana], balsam fir [Abies balsamea]–black spruce, balsam fir–white spruce [Picea glauca] and balsam fir) reflected a gradient of balsam fir dominance. The remnant forests selected were isolated for 5–15 years. Analyses were performed at two diameter cut-off values. Trees with DBH ≥20 cm were considered for availability of total trees whereas trees with DBH ≥30 cm were considered for availability of large trees. Forest stands comprised high proportions of standing dead trees (33% of all stems, 8% were large dead stems). Availability of total and large standing trees increased with the dominance of balsam fir in stands. Forest stands located on thick surficial deposits showed higher densities of large dead trees for every stand type suggesting a higher productivity on those sites. Availability of stems according to decay-classes showed a dome-shaped distribution with higher densities of snags in intermediate decay stages. However, for large stems, black spruce stands showed a significantly lower availability that was consistent across all decay-classes. In linear remnant forests, pure balsam fir stands were absent. Remnant stands thus showed a much lower availability in large trees when compared with unharvested balsam fir stands. Clearcuts had the lowest densities of dead trees across sampled stands. Current even-aged management practices clearly affect availability and recruitment of large trees, therefore forest-dwelling wildlife relying on these structures for breeding is likely to be affected by large-scale harvesting in coniferous boreal forests.     

Protection of spruce from colonization by the bark beetle, Ips perturbatus, in Alaska

Field bioassays were conducted in south-central Alaska in a stand of Lutz spruce, Picea × lutzii, to determine whether a semiochemical interruptant (verbenone and trans-conophthorin) and/or a defense-inducing plant hormone (methyl jasmonate, MJ) could be used to protect individual standing trees from bark beetle attack. During two experiments (initiated in May 2004 and 2005, respectively), attacks by Ips perturbatus on standing trees were induced by using a three-component aggregation pheromone (ipsenol, cis-verbenol, and ipsdienol) and prevented by using the interruptant. In 2005, treatments from 2004 were repeated and additional treatments were evaluated by using MJ spray or injection with and without the interruptant. Aggregation began before 3 or 7 June, and attack density was monitored through 3 or 16 August. During both years, tree mortality caused by I. perturbatus was recorded twice (in August, and in May of the following year). In both experiments, attack density was greatest on trees baited with the three-component attractive pheromone, but was significantly reduced by addition of the semiochemical interruptant to trees baited with the attractant. There were no significant differences in attack density between attractant + interruptant-treated trees and unbaited trees. In 2004, mortality was highest among attractant-baited trees, whereas addition of the interruptant significantly reduced the level of initial (10 week post-treatment) and final (54 week post-treatment) mortality. In 2005, no significant reduction in attack density occurred on trees baited with the attractant when MJ was sprayed or injected. The highest initial (10.6 week post-treatment) and final (49.4 week post-treatment) mortality was observed among trees that had been injected with MJ and baited with the attractant. Mortality at the final assessment was significantly lower in all other treatment groups. As in 2004, addition of the interruptant to attractant-baited trees significantly reduced the level of final mortality compared to attractant-baited trees. MJ was not attractive or interruptive to I. perturbatus or associated bark beetles in a flight trapping study. However, MJ-treated trees (sprayed or injected) exuded copious amounts of resin on the bark surface. Anatomical analyses of felled trees from four treatment groups [Tween (solvent)-sprayed, MJ-sprayed, Tween-injected, and MJ-injected + attractant baited] showed that treatment with MJ increased the number and size of resin ducts produced following treatment. These analyses also revealed a reduction in radial growth in MJ-treated trees. Our results show that during both years, treatment with a simple, two-component interruptant system of verbenone and trans-conophthorin significantly reduced I. perturbatus attack density and tree mortality on attractant-baited trees and provided a full year of protection from bark beetle attack.     

The threshold of successful attack by Ips typographus on Picea abies: A field experiment

The spruce bark beetle, Ips typographus, was induced to attack Norway spruce by means of pheromone dispensers. The degree of attack on each tree was recorded and the trees were later categorized as surviving or dying, according to the degree of sapwood blue-staining caused by the attacks. A threshold of successful attack was observed; i.e. above a certain number of attacks the trees were successfully invaded by the beetles and their mutualistic blue-stain fungi. The height of this threshold increased with increasing tree vigour, measured as the relative increment of the sapwood cross-sectional area.     

Effects of forest restoration treatments on the abundance of bark beetles in Norway spruce forests of southern Finland

Restoration of protected areas in boreal forests frequently includes creating substantial volumes of dead wood. While this benefits a wide range of dead wood dependent invertebrate species, some of these are regarded as forest pests. Therefore, the risk of elevated levels of tree mortality in surrounding commercial forests must be considered. In a large-scale field experiment in southern Finland, we studied the effects of restoration treatments on the abundance of bark beetles within and in the vicinity of restored areas, in particular focusing on Ips typographus and Pityogenes chalcographus. The treatments applied to managed Norway spruce forests were controlled burning and partial harvesting combined with retaining 5, 30 or 60 m³/ha of cut down wood. We found that the abundance of bark beetles increased by both burning and harvesting with down wood retention, being highest where burning and harvesting had been combined. The actual volume of down wood retention had no significant effect. The effect of burning on the number of bark beetles along host tree boles was negative which suggests that burnt spruces provided a less suitable resource for bark beetles than unburnt dead spruces. The abundance of bark beetles along host trees also decreased with increasing volume of down wood retention. The abundance of P. chalographus was slightly elevated up to 50 m outside restored areas but the abundance was very low compared to that within the areas. The abundance of I. typographus was extremely low outside restored areas. We conclude that restoration treatments increase the abundance of bark beetles via increased availability of resources, but that the effect of burning is likely to be counteracted by decreased resource quality. Thus, burning might be the “safest” way to produce large quantities of dead wood. Furthermore, the fact that only few beetles were collected in adjacent areas suggests that restored areas pose little threat of serving as refugia in which bark beetle populations increase in sufficient numbers to attack live trees in adjacent forests. However, restoration actions repeated at consecutive years within a small area might enable the populations to grow to outbreak levels.