In recent decades, European temperate forests have repeatedly suffered from severe droughts. Drought‐weakened forests have often become more susceptible to pest outbreaks such as bark beetle ...infestations. Tree species diversity is expected to increase resistance to drought and pests, but evidence for a positive tree diversity effect on insect pest reduction is largely circumstantial.
Here we tested the effects of tree diversity and biogeographic origin of tree species on bark beetle infestation in a large, young tree diversity experiment, with six broadleaved and six conifer species from Europe and North America. Lower infestation risk was expected for the exotic tree species in each congeneric pair (spruce, larch and pine) and for mixtures with higher species richness and higher broadleaf proportion. Following a severe drought in summer 2018, the conifer trees were attacked by the six‐toothed spruce bark beetle Pityogenes chalcographus. Bark beetle boreholes were recorded in winter 2018/2019 on all conifer species.
Norway spruce Picea abies and European larch Larix decidua were the most infested species and thus considered main hosts of the bark beetle. For these two species, probability of infestation decreased with increasing tree diversity (although this was only significant for Larix). In contrast, Pinus, which were less infested overall, were more likely to be infested in plots with high tree diversity. Exotic trees tended to be less infested, with clearest support for enemy release found at the level of infestation intensity when considering pure conifer stands. Overall, the effects of tree diversity and tree species origin were not as strong as the effect of position within the experimental site, where higher rates of infestation were observed at the edge than in the centre.
Synthesis. Increasing tree diversity may reduce the risk of bark beetle infestation for genera prone to high infestation rates (Picea and Larix), but risk for less preferred genera (Pinus, and to some extent the exotic tree species) may increase with tree diversity due to spillover from preferred hosts. In mixed forests, the risk of infestation, even by relatively specialized insect pests, may be redistributed among tree species rather than reduced for all.
Zusammenfassung
In den letzten Jahrzehnten haben die Wälder der gemäßigten Zone Europas wiederholt unter schweren Dürreperioden gelitten. Durch Trockenheit geschwächte Wälder sind oft anfälliger für Befall mit Schädlingen wie z.B. Borkenkäfer geworden. Es wird erwartet, dass Baumartenvielfalt die Resistenz gegen Trockenheit und Schädlinge erhöht, aber bisher gibt es nur wenige Hinweise dafür, dass Baumdiversität den Befall mit Insektenschädlingen reduziert.
In dieser Studie haben wir die Auswirkungen der Baumdiversität und der biogeographischen Herkunft der Baumarten auf den Borkenkäferbefall in einem großen, jungen Baumdiversitätsexperiment mit sechs Laub‐ und sechs Nadelbaumarten aus Europa und Nordamerika getestet. Nach einer starken Trockenheit im Sommer 2018 wurden die Nadelbäume vom Kupferstecher Pityogenes chalcographus befallen. Bohrlöcher durch den Borkenkäfer wurden im Winter 2018/2019 an allen Nadelbaumarten festgestellt. Ein geringeres Befallsrisiko wurde für die exotischen Baumarten in jedem Gattungspaar (Fichte, Lärche und Kiefer) und für Mischungen mit höherem Artenreichtum und höherem Laubbaumanteil erwartet.
Die Gemeine Fichte Picea abies und Europäische Lärche Larix decidua waren die am stärksten befallenen Arten und galten somit als Hauptwirte des Borkenkäfers. Für diese beiden Arten nahm die Befallswahrscheinlichkeit mit zunehmender Baumdiversität ab (obwohl dies nur für Larix signifikant war). Im Gegensatz dazu waren Pinus, die insgesamt weniger befallen waren, in Parzellen mit hoher Baumdiversität häufiger befallen. Exotische Bäume waren tendenziell weniger befallen, wobei der deutlichste Beleg dafür auf der Ebene der Befallsintensität bei reinen Nadelbaumbeständen gefunden wurde. Insgesamt waren die Effekte der Baumvielfalt und der Baumartenherkunft nicht so stark wie der Effekt der Position innerhalb der Versuchsfläche, wo am Rand höhere Befallsraten als in der Mitte beobachtet wurden.
Synthese. Eine zunehmende Baumvielfalt kann das Risiko eines Borkenkäferbefalls für Gattungen, die für hohe Befallsraten anfällig sind (Picea und Larix), verringern, aber das Risiko für weniger bevorzugte Gattungen (Pinus und bis zu einem gewissen Grad die exotischen Baumarten) kann mit der Baumvielfalt aufgrund von spill‐over von bevorzugten Wirten zunehmen. In Mischwäldern kann das Befallsrisiko, selbst durch relativ spezialisierte Schadinsekten, eher auf die Baumarten umverteilt als für alle reduziert werden.
Increasing tree diversity may reduce the risk of bark beetle infestation for genera prone to high infestation rates (Picea and Larix), but risk for less preferred genera (Pinus, and to some extent the exotic tree species) may increase with tree diversity due to spillover from preferred hosts. In mixed forests, the risk of infestation, even by relatively specialized insect pests, may be redistributed among tree species rather than reduced for all. Aerial view forest photograph: Kyle R. Kovach.
1. Forestry has markedly changed a large proportion of the world's boreal forests, often with negative effects on biodiversity. As a result, forest restoration is increasingly implemented to ...counteract the negative effects. However, restoration measures aimed at mimicking natural disturbance regimes could simultaneously increase the risk of unwanted negative effects, such as damage by forest pest species. This study compares the effect of two restoration methods (prescribed burning and gap-cutting), on both biodiversity conservation and pest control, to provide a basis for solutions to this potential conflict. 2. Bark beetles are ideal for studying this conflict, as this group is both species-rich and contains notorious pest species. We conducted a unique, large-scale field experiment in which we compared the effect of two different restoration methods on the abundance, species richness and assemblage composition of bark beetles. In addition, we estimated uncontrolled tree mortality by the number of trees that died post-restoration. 3. Beetles were divided in two groups, primary and secondary, the former with an ability to kill growing trees. Bark beetle diversity did not differ between treatment groups prior to restoration. However, after restoration, assemblage composition and primary bark beetle abundance differed between the treatments. Furthermore, species richness was higher in burned and gap-cut stands compared to reference stands. 4. The number of trees that died post-restoration was highest on burned sites, whereas no difference was found between gap-cut and reference stands. The number of dead trees was correlated with the number of primary beetles. 5. Synthesis and applications. We demonstrate the potential for a conflict between forest restoration for biodiversity conservation and the potential risk for tree mortality caused by forest pests. This is likely to become a problem in many boreal forests; however, our results suggest that this conflict can be moderated by the choice of restoration method. The restoration method gap-cutting had a similar positive impact on bark beetle species richness as compared to the burning method, but did not as burning, increase tree mortality. Thus, in areas where there is an apparent risk for pest outbreaks, our data suggest that gap-cutting should be the chosen method to avoid an unwanted increase in tree mortality at the stand level.
Ips typographus and Pityogenes chalcographus are two sympatric Palearctic bark beetle species with wide distribution ranges. As both species are comparable in biology, life history, and habitat, ...including sharing the same host, Picea abies, they provide excellent models for applying a comparative approach in which to identify common historical patterns of population differentiation and the influence of species‐specific ecological characteristics. We analysed patterns of genetic diversity, genetic structure and demographic history of ten I. typographus and P. chalcographus populations co‐distributed across Europe using both COI and ITS2 markers. Rather than similarities, our results revealed striking differences. Ips typographus was characterised by low genetic diversity, shallow population structure and strong evidence that all extant haplogroups arose via a single Holocene population expansion event. In contrast, genetic variation and structuring were high in P. chalcographus indicating a longer and more complex evolutionary history. This was estimated to be five times older than I. typographus, beginning during the last Pleistocene glacial maximum over 100 000 years ago. Although the expansions of P. chalcographus haplogroups also date to the Holocene or just prior to its onset, we show that these occurred from at least three geographically separated glacial refugia. Overall, these results suggest that the much longer evolutionary history of P. chalcographus greatly influenced the levels of phylogeographic subdivision among lineages and may have led to the evolution of different life‐history traits which in turn have affected genetic structure and resulted in an advantage over the more aggressive I. typographus.
The North American lodgepole pine Pinus contorta has been planted on 660 000 ha in Sweden.
We compared the performance of Ips typographus and Pityogenes chalcographus in storm‐felled and standing ...pheromone‐baited trees of the historical host species Norway spruce (Picea abies) and lodgepole pine.
In the first summer after a storm, I. typographus colonized 0.2% and P. chalcographus colonized 2.4% of the storm‐felled lodgepole pines compared with 31% and 25%, respectively, of the storm‐felled Norway spruces. In the second summer 1.6% and 41.5% of the lodgepole pines were colonized by I. typographus and P. chalcographus, respectively. The reproductive success of I. typographus was five‐fold higher in Norway spruce than in lodgepole pine. Other species colonizing lodgepole pine were Ips duplicatus, Orthotomicus proximus, Orthotomicus laricis, Monochamus sutor and Pissodes pini.
The male attack densities of both bark beetle species required to overcome defences of standing pheromone‐baited trees were much higher in lodgepole pine than in Norway spruce. The reproductive success of I. typographus and P. chalcographus was approximately five‐ and 14‐fold higher, respectively, in Norway spruce than in lodgepole pine.
Larvae of the most important groups of bark beetle enemies were present in both storm‐felled and standing pheromone‐baited lodgepole pines colonized by I. typographus and P. chalcographus. In the standing trees, the densities of enemy larvae were lower in lodgepole pine than in Norway spruce, whereas the opposite was true for storm‐felled trees.
Stereoselective synthesis of methyl-(2
E
,4
Z
)-deca-2,4-dienoate, a component of sex pheromones of
Pityogenes chalcographus
and
Acanthoscelides obtectus
, was performed on the basis of Fe-catalyzed ...cross-coupling of methyl-(2
E
,4
Z
)-5-chloropenta-2,4-dienoate with
n
-pentylmagnesium bromide.
CONTEXT: Ophiostomatoid fungi can severely affect the health and economic value of Norway spruce trees (Picea abies). Although the diversity of ophiostomatoid species and their associations with ...insects have been well-investigated in central and northern Europe, little is known about the conditions in south-eastern Europe. AIM: This study aims to study the assemblages of ophiostomatoid fungi associated with three bark beetle species (Ips typographus, Ips amitinus, and Pityogenes chalcographus) that infect Norway spruce in Slovenia. METHODS: Bark beetles were sampled in four phytogeographic regions in Slovenia. The fungi found on the bark beetles were identified based on morphology, DNA sequence comparisons of ITS regions and phylogenetic analysis. The species compositions of the fungal associates of the three insect species were compared and the pairwise associations of the occurrence of the fungal species were analysed. RESULTS: Thirteen different species were found. The most commonly encountered fungal associates of the beetles were Ophiostoma bicolor, Ophiostoma brunneo-ciliatum, Grosmannia piceiperda, Ophiostoma ainoae, Ceratocystiopsis minuta, and Grosmannia penicillata. The composition of the fungal associates differed among the bark beetle species, but not among the phytogeographic regions. CONCLUSIONS: This study confirms that ophiostomatoid species are common associates of the investigated bark beetle species. Many ophiostomatoid species have strong host associations. I. typographus and P. chalcographus can act as effective vectors for O. bicolor, O. ainoae, G. piceiperda and O. brunneo-ciliatum, whereas I. amitinus often carries G. piceiperda and C. minuta in Slovenian forests.
A model is presented to predict sanitary felling of Norway spruce (
Picea abies) due to spruce bark beetles (
Ips typographus,
Pityogenes chalcographus) in Slovenia according to different climate ...change scenarios. The model incorporates 21 variables that are directly or indirectly related to the dependent variable, and that can be arranged into five groups: climate, forest, landscape, topography, and soil. The soil properties are represented by 8 variables, 4 variables define the topography, 4 describe the climate, 4 define the landscape, and one additional variable provides the quantity of Norway spruce present in the model cell. The model was developed using the M5′ model tree. The basic spatial unit of the model is 1
km
2, and the time resolution is 1 year. The model evaluation was performed by three different measures: (1) the correlation coefficient (51.9%), (2) the Theil's inequality coefficient (0.49) and (3) the modelling efficiency (0.32). Validation of the model was carried out by 10-fold cross-validation. The model tree consists of 28 linear models, and model was calculated for three different climate change scenarios extending over a period until 2100, in 10-year intervals. The model is valid for the entire area of Slovenia; however, climate change projections were made only for the Maribor region (596
km
2). The model assumes that relationships among the incorporated factors will remain unchanged under climate change, and the influence of humans was not taken into account. The structure of the model reveals the great importance of landscape variables, which proved to be positively correlated with the dependent variable. Variables that describe the water regime in the model cell were also highly correlated with the dependent variable, with evapotranspiration and parent material being of particular importance. The results of the model support the hypothesis that bark beetles do greater damage to Norway spruce artificially planted out of its native range in Slovenia, i.e., lowlands and soils rich in N, P, and K. The model calculation for climate change scenarios in the Maribor region shows an increase in sanitary felling of Norway spruce due to spruce bark beetles, for all scenarios. The model provides a path towards better understanding of the complex ecological interactions involved in bark beetle outbreaks. Potential application of the results in forest management and planning is discussed.
1 The influence of trapping site (i.e. fresh clear‐cuts) characteristics and habitat amount (i.e. area of stands that may hold breeding material) in the surrounding landscape on catches of the bark ...beetles Ips typographus (L.) and Pityogenes chalcographus (L.) in pheromone‐baited flight‐barrier monitoring traps was studied. 2 For the two species, the study investigated: (i) the extent of the variation in catches among trapping sites; (ii) the extent of this variation that can be explained by models including trapping site characteristics (clear‐cut size, percentage of spruce in the cut stand, altitude) and habitat amounts in the surrounding landscape; and (iii) the spatial scale at which beetles respond to the habitat amount in the landscape. 3 The variation in catches among trap sites was 15‐fold larger for I. typographus than for P. chalcographus. There was a positive relationship between the catches of I. typographus and (i) the percentage of the surrounding landscape covered by mature spruce forest at radii 500–4000 m and (ii) the percentage of spruce in stands cut when the clear‐cuts used as trapping sites were created. For P. chalcographus, only the second relationship could be demonstrated. 4 Thus, for monitoring of I. typographus: (i) several trapping sites per landscape are required; (ii) the amount of mature spruce forest around trapping sites needs to be considered when choosing trapping sites; and (iii) the trapping sites need to be standardized with respect to the percentage of spruce in the cut stand when fresh clear‐cuts are used. For P. chalcographus, fewer trapping sites per landscape are required and only the percentage of spruce in the cut stand needs to be considered.
This study addresses the relationships between the foliage and bark area of Norway spruce (Picea abies) branches left in the forest after managing large timber: the densities of infestation by ...Pityogenes chalcographus, Pityophthorus pityographus and Dryocoetes autographus; and the reproductive efficiency of P. chalcographus. Based on the models developed in this study, a positive correlation was found between the foliage area of spruce branches and the densities infested by P. chalcographus and D. autographus, though a higher negative correlation was found in relation to the size of the branch bark area (BA) and the infestation densities. A negative correlation for the branch BA was also found on P. pityographus. This result shows that the desiccation of branches affects the infestation densities of bark beetles. In contrast, the size of the branch BA was positively correlated with the reproductive efficiency of P. chalcographus, with higher reproductive efficiency on the branches from the outer layer of the pile than on disorderly scattered branches on the ground.
PDF
