Possibility of using three invasive non-forest tree species as an alternative source for energy production

Non-woody biomass species have high-energy potentials, which could be used for bioenergy production. Invasive species are species spreading into areas, where they are not native, consequently causing environmental and economic problems. Therefore, the present study evaluated the proximate, ultimate, chemical, and fuel characteristics of wood and charcoal of three invasive non-forest tree species in Saudi Arabia: Calotropis procera, Rhazya stricta, and Phragmites australis, which were compared with the wood of Acacia tortilis, a preferable local fuelwood. All these data were discussed to investigate the possibility of using the invasive plants for energy production. The thermal behavior of wood was analyzed using thermo-gravimetric and derivative thermo-gravimetric methods. Overall, compared with the wood of A. tortilis, the woods of R. stricta and P. australis are suitable for energy production. The charcoal produced from P. australis emitted less nitrogen (N) oxide than that of R. stricta.     

Natural durability of the culturally and historically important timber: <Emphasis Type="Italic">Erythrophleum fordii</Emphasis> wood against white-rot fungi

The natural resistance of Erythrophleum fordii Oliver wood to degradation by Phanerochaete sordida and Phanerochaete chrysosporium white-rot fungi was investigated. In this study, Fagus crenata Blume (Japanese beech) was selected as reference species. The results showed that both fungi caused less than 2% mass loss in E. fordii wood, while the degradation of beech wood produced by P. chrysosporium and P. sordida was approximately 12 and 14%, respectively. Microscopic observations revealed high structural rigidity of E. fordii timber. Hyphae were only observed in the lumen of vessels and parenchymal cells, while the fibers were not affected. The E. fordii wood fiber consisted of highly lignified thick-walled fibers with the fiber lumina almost completely closed. Two-dimensional heteronuclear single-quantum coherence nuclear magnetic resonance evaluation revealed the E. fordii wood to have a highly condensed-lignin structure that reflected by the durability classes. These unique parameters are likely to be critical for the high natural resistance of E. fordii.     

Regeneration dynamics of mixed stands of <Emphasis Type="Italic">Pinus pinaster</Emphasis> Ait. and <Emphasis Type="Italic">Pinus pinea</Emphasis> L. in Central Spain

The dynamics of mixed stands are more complex and less studied than those of monospecific stands. The objective of this work was to analyze the variables involved in seedling occurrence and seedling survival in mixed stands of Pinus pinaster and P. pinea in Mediterranean areas. From 2011 to 2016, regeneration of both species was monitored at two sites located in Central Spain. We installed 72 regeneration plots where seedling dynamics were monitored. All the trees in the study areas were measured and mapped. Additionally, we took hemispherical photographs in each regeneration plot. The average density of P. pinea seedlings over the study period was almost 20 times larger than that of P. pinaster. Our results indicate that the seedlings of both species grow under moderate light conditions. In addition, we found that the occurrence of seedlings of both species was related to the structure of the stand. P. pinea seedlings grew where the density and size of P. pinaster trees were low and where P. pinea trees provided moderately sheltered conditions, whereas the number of P. pinaster seedlings was related to under intermediate densities of P. pinaster trees. Furthermore, seedling survival was positively associated with age of the seedlings and negatively with the August average maximum temperature. The temporal continuity of mixed stands of P. pinea and P. pinaster in the study area is compromised by the observed lack of regeneration of P. pinaster.     

The effect of the G‐layer on the viscoelastic properties of tropical hardwoods

Context and aim

This study aimed to examine the effect of the tension wood G‐layer on the viscoelastic properties of wood.

Methods

Tension wood and opposite wood samples were obtained from six French Guianese tropical rainforest species (Sextonia rubra, Ocotea guyanensis, Inga alba, Tachigali melinoni, Iyranthera sagotiana and Virola michelii); the tension wood of the former three of these species had a G‐layer, whilst the tension wood from the latter three had no G‐layer. Tensile dynamic mechanical analysis (DMA) was performed on green never dried wood samples in the longitudinal direction with samples submerged in a water bath at a temperature (30°C) and frequency (1 Hz) representative of the conditions experienced by wood within a living tree. Then, DMA was repeated with samples conditioned to an air-dried state. Finally, samples were oven-dried to measure longitudinal shrinkage.

Results

Tension wood did not always have a higher longitudinal storage (elastic) modulus than opposite wood from the same tree regardless of the presence or absence of a G‐layer. For the species containing a G‐layer, tension wood had a higher damping coefficient and experienced a greater longitudinal shrinkage upon drying than opposite wood from the same species. No difference was found in damping coefficients between tension wood and opposite wood for the species that had no G‐layer.

Conclusion

It is proposed that the different molecular composition of the G-layer matrix has an influence on the viscoelasticity of wood, even if a biomechanical gain is not yet clear. This study shows that rheological properties and longitudinal shrinkage can be used to detect the presence of a G‐layer in tension wood.

     

Occurrence of <Emphasis Type="Italic">Bursaphelenchus mucronatus</Emphasis> (Nematoda; Aphelenchoididae) in France and association with <Emphasis Type="Italic">Monochamus galloprovincialis</Emphasis> (Coleoptera: Cerambycidae)

As a consequence of the recent introduction of the pine wood nematode Bursaphelenchus xylophilus in Portugal, nematodes of the genus Bursaphelenchus were looked for in various French pine forests, in trees attacked by Monochamus galloprovincialis, the vector insect of B. xylophilus, and in the insects themselves. Trap trees were felled in 12 localities distributed all over the country. Nematodes were extracted from transversal stem discs; insects emerging from the trap trees were studied. B. hellenicus, B. leoni, B. mucronatus and B. sexdentati were isolated, but not B. xylophilus. The presence of B. mucronatus and the absence of B. xylophilus were confirmed by molecular markers. B. mucronatus was isolated from several regions with an average prevalence of 19%. The infestation of M. galloprovincialis by B. mucronatus reached 26.7%. The wide distribution of B. mucronatus in France could have an effect on the extension of B. xylophilus in a case of an introduction.     

Radial growth of <Emphasis Type="Italic">Cinnamomum kanehirae</Emphasis> Hayata displays a larger temperature sensitivity in dominant than codominant trees

Key message

The radial wood growth curves of Cinnamomum kanehirae Hayata (an endangered species of subtropical Taiwan) exhibit an S shape. The dominant trees displayed a larger radial growth than the codominant trees, and their growth was more sensitive to air temperature.

Context

Knowledge of wood radial growth is important for evaluating the factors that limit tree growth performance. The relevant experiments have mostly been conducted in cold and temperate ecosystems, but rarely in subtropical ecosystems.

Aims

In this study, we aimed to construct a unified radial growth model for Cinnamomum kanehirae Hayata and to identify its sensitivity to temperature.

Methods

The wood radial increments were quantified for 3 years by either pinning or microcoring. The radial wood growth curves were modelled integratively by semiparametric regression and individually by curve fitting. The effects of tree social class, interannual and environmental factors on radial growth were analysed quantitatively.

Results

A unified S-shaped growth model for C. kanehirae was successfully constructed. By including the social class effect, the model was significantly improved. The maximum radial increment (A) was significantly correlated with the maximum growth rate (μ); both A and μ were significantly higher in dominant than in codominant trees. The time-varying radial growth rate was more sensitive to air temperature in dominant than in codominant trees.

Conclusion

Semiparametric models revealed an S-shaped growth curve of C. kanehirae and confirmed the higher temperature sensitivity of dominant trees compared to codominant trees in humid subtropical areas.

     

Analysis of tree interactions in a mixed Mediterranean pine stand using competition indices

Studying species interactions in mixed forests allows us to assess their potential benefits and adapt current silvicultural tools developed in monospecific stands to multi-specific stands. We analyzed tree interactions in a Pinus halepensis Mill. and Pinus pinea L. mixed plantation using individual tree neighborhood models and competition indices that accounted for symmetric and asymmetric competition, to analyze whether the growth of each species was better explained by symmetric or asymmetric competition. We also split the competition indices into their intra- and interspecific forms, to test for competition effects on growth change based on competitor identity. Finally, we analyzed whether P. halepensis and P. pinea trees had different growth responses to competition. When calculating competition indices, we explored how spatial information and size of competitor trees contributed to the quantification of the process. Competition measurements were optimized to more precisely describe interactions. Results showed that the inclusion of competition indices generated important improvements in growth models. The main mode of competition was symmetric, which could be related to water restrictions typical of the Mediterranean climate. Considering competitor identity did not improve the growth models, while measurement without discriminating competitors by species generated more parsimonious models. P. halepensis and P. pinea trees had similar growth responses to competition, indicating that the two species cope with competition in similar ways. However, P. pinea showed lower average growth than P. halepensis in the period analyzed. Results suggest that preventing the onset of intense interspecific competition processes could help slow down the long-term replacement of P. pinea by P. halepensis and could have benefits for silvicultural management in systems with two species that share ecological niches but are capable of generating different goods and services.     

Production of selected short-rotation wood crop species and quality of obtained biomass

Short-rotation coppice (SRC) represents an important source of wood biomass. Many uncertainties create barriers to farmers establishing SRC plantations, especially under Mediterranean climate conditions. In this study, five species and respective genotypes were analyzed. The five species were Fraxinus angustifolia, Robinia pseudoacacia, Salix alba, Populus nigra (Limatola), and Populus × euroamericana, with the genotypes of the latter being Grimminge, Vesten, Hoogvorst, Muur. For the plantations studied, two different harvesting systems were replicated: the single machine pass, or cut-and-chip (CC); and the double machine pass, for which the tree are cut first, then chipped later (chip of stored trees CS). In the CC, fresh trees were harvested and chipped by Claas Jaguar 880. In the CS, dry trees were chipped by Farmi Forest CH 260. Within the same site, in climatic conditions and low-input management, the best result in terms of biomass yield was obtained from the black poplar Limatola. Both wood typologies and harvesting systems affected the chip quality. The disk chipper, when working on dried biomass, produced lower quality chips than the other chipping device in terms of particle size. In the chips obtained, there was an increase in the number of chips classified as being “larger size” and “oversized”, and a decrease in the percentage of those classified as “accept” (45–3 mm fraction). The chips obtained from dried trees were of better energy quality compared with the same biomass obtained from the fresh trees in terms of heating value and ash content.     

Effects of <Emphasis Type="Italic">Verticillium nonalfalfae</Emphasis> on <Emphasis Type="Italic">Ailanthus altissima</Emphasis> and associated indigenous and invasive tree species in eastern Austria

The naturally occurring Verticillium nonalfalfae shows promise for biocontrol of the highly invasive Tree of Heaven (Ailanthus altissima), but might also bear a risk for non-target tree species. In this study, we conducted inoculations on potted seedlings of A. altissima as well as on eight indigenous and two invasive tree species associated with Tree of Heaven in Austria. Although vascular discolourations developed in all inoculated tree species, V. nonalfalfae was reisolated from Ailanthus and eight of the ten non-target-species, whereas typical disease symptoms and mortality only occurred on A. altissima. Results confirmed high susceptibility (S) of A. altissima to V. nonalfalfae but indicated tolerance (T) of Acer campestre, Acer pseudoplatanus and Quercus robur, possible resistance (PR) of Fraxinus excelsior, Populus nigra, Tilia cordata, Ulmus laevis and Ulmus minor and resistance (R) of Fraxinus pennsylvanica and Robinia pseudoacacia to this potential biocontrol agent. Results from seedling inoculations were confirmed by cursory field observations in Ailanthus-inoculated forest stands, where admixed A. campestre, A. pseudoplatanus, F. excelsior, Populus alba, R. pseudoacacia and U. laevis canopy trees remained asymptomatic, while mortality was induced in Ailanthus.     

Within- and between-tree variation of wood density components in <Emphasis Type="Italic">Pinus nigra</Emphasis> at six sites in Portugal

Key message

In Europe, P. nigra wood presents a density pattern of longitudinal variation with an increase from east to west. However, no latitudinal tendencies were detected. Compared to other Portuguese resinous species, P. nigra revealed higher density, identical radial growth and intra-ring heterogeneity, which presents advantages for industry purposes. The environmental factors (Sites effect) manifest more strongly in the latewood components while the Trees/Sites effect is more strongly expressed in the earlywood components.

Context

Although P. nigra Arnold is one of the most important conifers in Europe, little is known about the wood’s characteristics in the southwest European region.

Aims

Our aims are to outline a first approach to study the growth and wood quality in P. nigra in Portugal comparing to other European natural stands and other resinous species.

Methods

Inter- and intra-wood density variation of P. nigra from six Portuguese sites was studied using microdensitometry. Analysis of variance (ANOVA) was performed in three subsets: 50 common rings, core (juvenile wood) and peripheral analysis (mature wood).

Results

The average ring density was 0.588 g cm^?3, with maximum values in the north and low altitudes. Regarding growth traits, no latitudinal and altitudinal tendencies were detected. Compared to the main timber species in Portugal (P. pinaster Aiton), P. nigra showed similar radial growth, higher density but lower intra-ring density homogeneity. The Sites effect mainly influenced latewood density components, while the Trees/Sites effect primarily influenced earlywood components. The Rings effect was found to be relatively low, with a density decrease in the tree’s first years followed by an increase in the periphery. Growth traits showed a reduction from pith to bark.

Conclusion

Considering the quality (density) and growth features of the Black pine, this species could be useful for the reforestation of mountainous Southern Europe areas that are not favourable for other species.

     

Geometric morphometric analyses of leaf shapes in two sympatric Chinese oaks: <Emphasis Type="Italic">Quercus dentata</Emphasis> Thunberg <Emphasis Type="Italic">and Quercus aliena</Emphasis> Blume (Fagaceae)

Key message

Geometric morphometric analyses (GMMs) of the leaf shape can distinguish two congeneric oak species Quercus dentata Thunberg and Quercus aliena Blume in sympatric areas.

Contexts

High genetic and morphological variation in different Quercus species hinder efforts to distinguish them. In China, Q. dentata and Q. aliena are generally sympatrically distributed in warm temperate forests, and share some leaf morphological characteristics.

Aims

The aim of this study was to use the morphometric methods to discriminate these sympatric Chinese oaks preliminarily identified from molecular markers.

Methods

Three hundred sixty-seven trees of seven sympatric Q. dentata and Q. aliena populations were genetically assigned to one of the two species or hybrids using Bayesian clustering analysis based on nSSR. This grouping served as a priori classification of the trees. Shapes of 1835 leaves from the 367 trees were analyzed in terms of 13 characters (landmarks) by GMMs. Correlations between environmental and leaf morphology parameters were studied using linear regression analyses.

Results

The two species were efficiently discriminated by the leaf morphology analyses (96.9 and 95.9% of sampled Q. aliena trees and Q. dentata trees were correctly identified), while putative hybrids between the two species were found to be morphologically intermediate. Moreover, we demonstrated that the leaf morphological variations of Q. aliena, Q. dentata, and their putative hybrids are correlated with environmental factors, possibly because the variation of leaf morphology is part of the response to different habitats and environmental disturbances.

Conclusion

GMMs were able to correctly classify individuals from the two species preliminary identified as Q. dentata or Q. aliena by nSSR. The high degree of classification accuracy provided by this approach may be exploited to discriminate other problematic species and highlight its utility in plant ecology and evolution studies.

     

Response of species and stand types to snow/wind damage in a temperate secondary forest,Northeast China

Snow/wind damage is one of the important natural disturbances in forest ecosystems, especially in a montane secondary forest. However, the effects of snow/wind damage remain unclear which affects the management of these forests. Therefore, we investigated the responses of species, individual tree traits and stand structure to snow/wind damage in a montane secondary forest. Results show that, amongst the canopy trees, Betula costata exhibited the most uprooting, bending and overall damage ratio (the number of damaged stems to the total number of stems in a plot); Quercus mongolica showed the highest breakage ratio and Fraxinus mandshurica and Juglans mandshurica the least overall damage ratios. Among the subcanopy trees, Carpinus cordata, Acer mono, Acer tegmentosum and Acer pseudo-sieboldianum showed the least uprooting and breakage, and the most bending damage. A. pseudo-sieboldianum demonstrated the lowest breakage and highest bending damage ratios. These findings indicate that different species have various sensitivities to snow/wind damage. Larger trees (taller, wider crowns) tend to break and become uprooted, while smaller trees are bent or remain undamaged, suggesting that tree characteristics significantly influence the types of damage from snow and wind. Stands of Q. mongolica and B. costata had the highest damage ratios, whereas A. pseudo-sieboldianum had the lowest snapping ratio. In summary, the severity and type of snow/wind damage are related to individual tree attributes and stand-level characteristics. Therefore, selection of suitable species (e.g., shorter, smaller with deep root systems, hard wood, bending resistance and compression resistance) and appropriate thinning are recommended for planting in the montane secondary forests.     

Lipophilic extractives of the inner and outer barks from six different <Emphasis Type="Italic">Pinus</Emphasis> species grown in Indonesia

The chemical compositions of the dichloromethane extracts of inner and outer barks from six Pinus species (P. elliotii, P. oocarpa, P. caribeae, P. merkusii, P. montezumae, and P. insularis) grown in Indonesia were investigated by GC and GC–MS. Generally, the amounts of extractive contents were higher in the inner bark than in the outer bark except for P. merksuii. Fatty acids, monoterpenes, sesquiterpenes, resin acids, triterpenoids, and steroids were detected and quantified. Inner and outer barks differed not only in content of these compounds but also in their composition. Fatty acids and alcohols were the major classes of lipophilic compounds in the outer bark of P. caribeae, P. insularis, and P. montezumae. Steroids and triterpenoids were the dominant compounds identified in the inner bark of P. elliotii, P. insularis, and P. merkusii. Resin acids were the most abundant group in the inner bark of P. oocarpa whereas monoterpenes and sesquiterpenes were recorded in minor quantities in both bark layers of all species.     

Identification and characterization of fungi associated with internal wood lesions and decline disease of willow and poplar trees in Iran

During the study of fungal trunk pathogens associated with urban trees decline in Shiraz (Iran), a serious decline of willow and poplar trees was observed. Therefore, an investigation was conducted on these trees in some areas of this city during spring and summer 2012 and 2013, to determine the main fungal trunk pathogens associated with these ornamental plants. Plant materials were collected from trees exhibiting disease symptoms such as yellowing, shoot canker, shoot dieback, defoliation and internal wood necrosis and decayed wood. Fungal isolations were made from discoloured or decayed wood tissue onto 2% malt extract agar (MEA) amended with streptomycin sulphate. Nine species, Fomes fomentarius, Diplodia seriata, Lasiodiplodia theobromae, Dothiorella sarmentorum, Neoscytalidium hyalinum, Diatrype whitmanensis, Phaeoacremonium rubrigenum, P. aleophilum and P. parasiticum, were identified based on morphology and DNA sequence comparisons. Pathogenicity tests were performed on detached shoots of willow and poplar trees under greenhouse conditions. Lasiodiplodia theobromae caused the longest lesions on willow. On poplar shoots, the longest lesions were caused by P. parasiticum. Diplodia seriata produced the smallest lesions on both woody hosts. First reports from willow wood include P. parasiticum, P. rubrigenum, D. whitmanensis, L. theobromae, D. seriata and N. hyalinum, while new reports from poplar wood include P. parasiticum and Do. sarmentorum. Based on our knowledge, this is also the first report of D. whitmanensis in Iran.     

When the ground cover brings guests: is <Emphasis Type="Italic">Anaphothrips obscurus</Emphasis> a friend or a foe for the biological control of <Emphasis Type="Italic">Tetranychus urticae</Emphasis> in clementines?

Biological control of Tetranychus urticae Koch (Acari: Tetranychidae), a key pest of clementines, can be improved in this crop with the establishment of a ground cover of Festuca arundinacea Schreber (Poaceae). This cover houses an abundant and diverse community of predatory Phytoseiidae mites including Euseius stipulatus (Athias-Henriot), Neoseiulus barkeri Hughes, Neoseiulus californicus (McGregor) and Phytoseiulus persimilis Athias-Henriot and a dense population of the grass thrips Anaphothrips obscurus Müller (Thysanoptera: Thripidae) throughout the year. The aim of this study was to determine whether the presence of this thrips species could be related to the improvement in the biological control of T. urticae. Therefore, the capacity of the abovementioned phytoseiids to feed and reproduce on A. obscurus and their feeding preferences when T. urticae and A. obscurus were simultaneously offered, were analyzed. The results show that E. stipulatus, N. barkeri and N. californicus have a type II functional response when offered A. obscurus nymphs, whereas P. persimilis barely feeds on this thrips species. Furthermore, N. barkeri and N. californicus can reproduce feeding only on thrips. Regarding prey preference, the Tetranychus spp.-specialist P. persimilis preferably preyed on T. urticae, the generalists N. barkeri and E. stipulatus preferred A. obscurus, and the selective predator of tetranychid mites N. californicus showed no preference. Therefore, we hypothesize that the enhanced biological control of T. urticae observed could be related to A. obscurus becoming an alternative prey for non-specialist phytoseiids, without altering the control exerted by the T. urticae-specialist P. persimilis and likely reducing intraguild predation.     

Horizontal niche differentiation of ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) within the standing trunk of <Emphasis Type="Italic">Quercus serrata</Emphasis>

Niche differentiation, in terms of time and space, has been reported within a community of ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) in a tree trunk. Two platypodid ambrosia beetles, Platypus quercivorus (Murray) and Platypus calamus Blandford, utilize a similar height range with respect to the Quercus serrata Murray (Fagaceae) trunk. The sapwood and heartwood (i.e., wood types) are known to differ in their physical and chemical characteristics. The objective of this study was to determine the differences among ambrosia beetles, in terms of wood type preferences, in a Q. serrata tree trunk. We analyzed the horizontal distribution patterns of ambrosia beetles within two mature Q. serrata tree trunks. Platypus calamus and the other ambrosia beetles [P. quercivorus, Ambrosiodmus lewisi (Blandford), Ambrosiophilus atratus Eichhoff, and Xyleborus sp.] showed different horizontal distribution patterns within the wood. The former tended to utilize the heartwood, whereas the latter utilized the sapwood. These results suggest that the wood type can be regarded as one of the niche dimensions of ambrosia beetles in a Q. serrata trunk.     

Sequencing and quantifying plastid DNA fragments stored in sapwood and heartwood of <Emphasis Type="Italic">Torreya nucifera</Emphasis>

The selection of wood species and the styles of sculpture play key roles in the characterization of Buddhist statues. After Jianzhen, a Chinese Buddhist monk, visited Japan in the mid-eighth century, wood of the genus Torreya had been frequently used to produce single-bole statues. Establishing measures for the accurate identification of wood in the genus Torreya is effective for investigating the drastic change in the production of statues during this period. Analyzing the plastid deoxyribonucleic acid (DNA) fragments extracted from wood is considered helpful in the identification of species in the same genus. This study analyzed the sequences and residual amounts of plastid DNA fragments in the wood of Torreya nucifera. Nucleotide substitutions in the plastid DNA were clearly identified between T. nucifera and the species distributed in China, indicating that the wood of Torreya sp. can be discriminated based on the plastid DNA sequences. DNA polymorphism analyses revealed sequence diversity for the intergenic spacers on the T. nucifera plastid DNA. A series of polymerase chain reaction (PCR) analyses demonstrated that the plastid DNA fragments with a length of approximately 100 bp could be amplified from the residual DNA extracted from the T. nucifera sapwood with longer elapsed years after cutting. Therefore, an identification of wood species in the genus Torreya based on their plastid DNA is considered to be one of the most effective measures taken in the study regarding the historical changes of Buddhist statues.     

Biomass production,carbon sequestration and nutrient characteristics of 22-year-old support trees in black pepper (<Emphasis Type="Italic">Piper nigrum</Emphasis>. L) production systems in Kerala,India

Diverse kinds of fast growing multipurpose trees are traditionally grown as support trees (standards) for trailing black pepper vines in the humid tropics of India. Apart from differential black pepper yields, such trees exhibit considerable variability to accumulate biomass, carbon and nutrients. An attempt was made to assess the biomass production, carbon sequestration potential (tree + soil) and nutrient stocks of six multipurpose tree species (age: 22 years) used for trailing black pepper vines (Acacia auriculiformis, Artocarpus heterophyllus, Grevillea robusta, Macaranga peltata, Ailanthus triphysa and Casuarina equisetifolia). Results indicate that G. robusta showed the highest total biomass production (365.72 Mg ha^?1), with A. triphysa having the least value (155.13 Mg ha^?1). Biomass allocation among tissue types followed the order stemwood > roots > branchwood > twigs > leaves. Total C stocks were also highest for G. robusta (169 Mg C ha^?1), followed by A. auriculiformis (155 Mg C ha^?1). Mean annual carbon increment also followed a similar trend. Among the various tissue fractions, stemwood accounted for the highest N, P and K stocks, implying the potential for nutrient export from the site through wood harvest. All the support trees showed significantly higher soil carbon content compared to the treeless control. Soil N, P and K contents were higher under A. auriculiformis than other species. Nitrogen fixation potential, successional stage of the species, stand age and tree management practices such as lopping may modify the biomass allocation patterns and system productivity.     

Host specificity of Asian parasitoids for potential classical biological control of <Emphasis Type="Italic">Drosophila suzukii</Emphasis>

The Asian spotted wing drosophila, Drosophila suzukii, has recently become a serious pest of soft fruits in Europe. Classical biological control through the introduction of larval parasitoids from its native range in Asia is presently being considered. However, host specificity of potential biological control agents has to be determined to avoid releasing species that may have unintended non-target impacts. Larvae of six different European non-target fly species and the target D. suzukii were exposed either on diet or blueberries to three Asian larval parasitoids, Asobara japonica, Leptopilina japonica, and Ganaspis cf. brasiliensis, and one European species, Leptopilina heterotoma. Asobara japonica showed the lowest specificity, attacking and developing in all Drosophilidae. Leptopilina japonica successfully parasitized two non-target Drosophilidae, D. melanogaster and D. subobscura, with one singly progeny emerging from D. immigrans. Ganaspis cf. brasiliensis had the highest level of specificity but variations occurred between two geographical populations tested. A Japanese population was strictly specific to D. suzukii, whereas another population from China parasitized D. suzukii, D. melanogaster and sporadically D. subobscura. The European L. heterotoma successfully developed in D. melanogaster, D. subobscura and occasionally in D. immigrans, but nearly all eggs and larvae in D. suzukii were encapsulated. These results show that Ganaspis cf. brasiliensis is the species with the highest potential for biological control, but more studies are needed on its taxonomic status and the existence of biotypes or cryptic species varying in their specificity before field releases can be conducted in Europe.     

Fungal root pathogen (<Emphasis Type="Italic">Heterobasidion parviporum</Emphasis>) increases drought stress in Norway spruce stand at low elevation in the Alps

Tree-ring patterns of Picea abies (L.) Karst. both unaffected and affected by Heterobasidion parviporum were analysed in three mature stands located at different elevations in the Eastern Alps. The main objectives were (1) to clarify the role of climatic conditions on infected trees; (2) to estimate indirect volume losses due to the prolonged presence of the fungus within the wood. The low elevation site showed the highest growth decline in the last decade, whereas all infected trees at medium and high elevation showed a slow growth decline over many decades. We hypothesise that infection could be dated over 80 years at the highest site. Fungal attack made P. abies more susceptible to drought stress at low elevation site. Both infected and healthy P. abies at medium and high elevation showed similar climate–growth relationships, suggesting that the same driving environmental factors influence their growth. At low elevation, H. parviporum was seemingly more aggressive, causing a more rapid decline, decreasing the ability of host trees to cope with drought and, in some cases, inducing cambial activity to stop. P. abies at higher elevation, however, exhibited a very slow decline and no sign of increasing water stress since the influence of climate on tree growth was the same for both infected and healthy trees.