Prof. Dr. Martin Gossner

• Le volume de bois mort en Suisse a augmenté à 32 mètres cubes par hectare (m³/ha) durant la dernière décennie. L'objectif politique a ainsi été atteint dans la plupart des régions. Mais sur le Plateau, il est par endroits inférieur à 20 m³/ha.
• Ces deux valeurs ne suffisent que pour les espèces peu exigeantes. Les vieux arbres aux microhabitats très diversifiés et les gros bois morts sont encore trop rares. Des mesures s'imposent pour conserver le gros bois mort et de vieux arbres accomplissant tout leur cycle de vie.
• La demande accrue en bois pourrait menacer l'évolution positive du volume de bois mort.

• The deadwood volume across Switzerland has increased to 32 cubic metres per hectare in the past decade, meaning that this forest policy objective has been achieved in most regions. On the Plateau, however, there is less than 20 cubic metres of deadwood per hectare in some regions.
• Both values are sufficient only for species with low deadwood requirements. Old trees with a wide variety of microhabitats and large-diameter deadwood are still too scarce. Measures are needed to promote large-diameter deadwood and old trees that complete their entire life cycle.
• The growing demand for wood could jeopardise the positive trend towards higher deadwood volumes.

• Nell'ultimo decennio il volume di legno morto è salito a 32 metri cubi per ettaro a livello nazionale. Questo obiettivo di politica forestale è stato quindi raggiunto nella maggior parte delle regioni. Sull'Altipiano, invece, in alcune regioni si rilevano meno di 20 metri cubi di legno morto per ettaro.
• Entrambi i valori sono sufficienti solo per le specie con basse esigenze in termini di legno morto. Gli alberi vecchi con una grande varietà di microhabitat e il legno morto di grandi dimensioni sono ancora una rarità. Servono quindi misure per promuoverli lungo l'intero ciclo di vita.
• La crescente domanda di legno potrebbe compromettere la tendenza positiva all'aumento del volume di legno morto.

• Das Totholzvolumen hat sich in der letzten Dekade schweizweit auf 32 Kubikmeter pro Hektare erhöht.  Somit ist dieses waldpolitische Ziel in den meisten Regionen erreicht. Im Mittelland gibt es aber in gewissen Regionen weniger als 20 Kubikmeter Totholz pro Hektare.
• Beide Werte reichen nur für Arten mit niedrigen Totholzansprüchen aus. Alte Bäume mit grosser Vielfalt an Mikrohabitaten und dickes Totholz sind noch zu selten. Es besteht ein Bedarf an Massnahmen zur Förderung von dickem Totholz und alten Bäumen, die den vollständigen Lebenszyklus durchlaufen.
• Die steigende Nachfrage nach Holz könnte den positiven Trend zu höheren Totholzvolumen gefährden.

• In 2022, the proportion of forest reserves within the total forest area reached 7.3%, meaning that the Forest Policy target of 10% reserve area by 2030 was already almost three-quarters achieved.
• Natural forest reserves have a positive impact on the number and distribution of deadwood-dependent species, with the number of endangered fungi species higher in reserves than in managed forests.
• In the designation of future forest reserves, even greater consideration is to be given to the promotion of National Priority Species and Habitats and a better connected spatial distribution of reserve areas.

• Nel 2022, le riserve forestali coprivano il 7,3 per cento della superficie forestale totale; pertanto l'obiettivo di politica forestale di raggiungere il 10 per cento di riserve forestali entro il 2030 era già stato raggiunto per quasi tre quarti.
• Le riserve forestali naturali hanno effetti positivi sul numero e sulla distribuzione delle specie che dipendono
dal legno morto. Il numero di specie di funghi in pericolo nelle riserve è maggiore che nei boschi gestiti.
• In futuro, nella designazione delle riserve forestali andrà tenuto conto maggiormente dei piani cantonali per la promozione delle specie e degli ambienti prioritari a livello nazionale e di una migliore distribuzione territoriale delle superfici connesse.

• En 2022, les réserves forestières représentaient 7,3 % de la surface totale de forêt. L'objectif politique de créer 10% de surface de réserves d'ici 2030 est ainsi presque aux trois quarts atteint.
• Les réserves forestières naturelles ont une influence positive sur le nombre et la répartition des espèces tributaires du bois mort. Les champignons menacés y sont plus nombreux que dans les forêts exploitées.
• Lors de la délimitation des futures réserves forestières, il faudra encore mieux tenir compte des planifications cantonales visant à conserver les espèces et les milieux prioritaires au niveau national et d'une meilleure mise en réseau spatiale des surfaces.

• Im Jahr 2022 erreichte der Anteil der Waldreservate an der gesamten Waldfläche 7,3 %. Damit war das waldpolitische Ziel von 10 % Reservatfläche, die bis 2030 errichtet werden sollen, schon beinahe zu drei Vierteln erreicht.
• Naturwaldreservate wirken sich positiv auf die Anzahl und Verbreitung totholzabhängiger Arten aus. Die Anzahl gefährdeter Pilzarten ist in Reservaten höher als in bewirtschafteten Wäldern.
• Bei der Ausscheidung von Waldreservaten sollen in Zukunft die kantonalen Planungen für die Förderung von National Prioritären Arten und Lebensräumen
sowie eine besser vernetzte räumliche Verteilung der Flächen noch stärker berücksichtigt werden.

1. Thanasimus formicarius (L.) (Coleoptera: Cleridae) is an important bark beetle predator and can reduce bark beetle population densities of some of the most severe forest pests in Europe.
2. We analysed the population genetics and phylogeography of T. formicarius across its European range, using mitochondrial COI data from 187 individuals sampled from 23 locations. Our extensive sampling from the Fennoscandian to the Mediterranean region and from Iberia to the Middle East provides insights into the genetic structure of T. formicarius.
3. We found a high genetic diversity, revealing 119 haplotypes across the sampling range. Two main clades, an Atlantic and a Continental, were identified, suggesting the presence of at least two glacial refugia during the last ice ages.
4. An isolated population was discovered on the island of Corsica, suggesting that a limited number of individuals, probably from mainland France, may have colonized Corsica and a founder effect occurred.
5. These findings increase our understanding of the recent evolutionary history of T. formicarius, which was shaped by Pleistocene events and certain species-specific life-history traits.

Understanding how land use affects temporal stability is crucial to preserve biodiversity and ecosystem functions. Yet, the mechanistic links between land-use intensity and stability-driving mechanisms remain unclear, with functional traits likely playing a key role. Using 13 years of data from 300 sites in Germany, we tested whether and how trait-based community features mediate the effect of land-use intensity on acknowledged stability drivers (compensatory dynamics, portfolio effect, and dominant species variability), within and across plant and arthropod communities. Trait-based plant features, especially the prevalence of acquisitive strategies along the leaf-economics spectrum, were the main land-use intensity mediators within and across taxonomic and trophic levels, consistently influencing dominant species variability. Functional diversity also mediated land-use intensity effects but played a lesser role. Our analysis discloses trait-based community features as key mediators of land-use effects on stability drivers, emphasizing the need to consider multi-trophic functional interactions to better understand complex ecosystem dynamics.

1. Windthrow disturbance is an important driver of arthropod diversity in forests. In the past, studies have mainly focused on the first years after disturbance, and there are hardly any data on arthropod trajectories in windthrows and on salvage logging effects over decades.
2. We sampled arthropods of different functional groups on 16 permanent plots following two windstorms (Vivian and Lothar) in coniferous and broadleaf forests at different elevations in Central Europe over two decades. Flight interception and pitfall traps were operated during the entire growing seasons in three habitat types per site: unsalvaged windthrow, salvaged windthrow and control forest.
3. In total, 524,115 individuals from 1666 arthropod species were identified, of which more than 90% occurred in windthrows, including 40%–53% species exclusively found in windthros. Over the two decades, saproxylics, herbivores, pollinators, predators and endangered species showed significantly higher species numbers and abundances in windthrows than in control forests, where only 6% exclusive species occurred.
4. Arthropod communities in windthrows showed distinct dynamics during the two decades. Their species numbers and abundances peaked in the first 3 years, coined by saproxylic species, such as bark beetles, and by pollinating hoverflies. While abundances declined rapidly, species numbers remained elevated for two decades. Arthropod similarity between windthrows and forests (indicating resilience) increased with time but depended on elevation and forest type. After 20 years, it reached an average of 50% in lowland broadleaf forests, but only 30% in high-elevation spruce forests, indicating lower resilience.
5. Salvage logging had no significant effect on overall species numbers but altered species composition. More than 10% exclusive species were found in salvaged and up to 20% in unsalvaged windthrows, with the latter supporting more endangered species, particularly towards the second decade.
6. Synthesis and applications. Our study shows that windthrow causes an initial boost of arthropod diversity. While abundances thereafter rapidly decline, species numbers remain at relatively high levels during at least two decades. Unsalvaged windthrows are an indispensable resource for endangered species, particularly in later wood decay stages.

1. How biodiversity underpins ecosystem resistance (i.e. ability to withstand environmental perturbations) and recovery (i.e. ability to return to a pre-perturbation state), and thus, stability under extreme climatic events is a timely question in ecology. To date, most studies have focussed on the role of taxonomic diversity, neglecting how community functional composition and diversity beget stability under exceptional climatic conditions. In addition, land use potentially modulates how biodiversity and ecosystem functions respond to extreme climatic conditions.
2. Using an 11-year time-series of plant biomass from 150 permanent grassland plots spanning a gradient of land-use intensity, we examined how taxonomic and functional components of biodiversity affected resistance and recovery of biomass under extreme drought.
3. The association between biodiversity, land use and biomass varied across years, especially in the driest years. Species-rich or functionally diverse communities (associated with low land-use intensity) buffered extreme droughts better, while species-poor communities or those dominated by fast-growing species (associated with high land-use intensity) had higher recovery capabilities after a moderate-to-extreme drought.
4. Synthesis. Our results show that plant community functional and taxonomic components determine grasslands resistance and recovery under moderate-to-extreme drought. In turn, this points to the importance of designing landscapes with both extensively and intensively managed grasslands. Functionally or taxonomically rich communities (favoured under low land-use intensity) would preserve biomass under extreme droughts, whereas species-poor or fast-growing communities (favoured by high land-use intensity) would restore biomass after extreme droughts.

Recent losses in the abundance and diversity of arthropods have been documented in many regions and ecosystems. In grasslands, such insect declines are largely attributed to land use, including modern machinery and mowing regimes. However, the effects of different mowing techniques on arthropods remain poorly understood. Using 11 years of data from 111 agricultural grassland plots across Germany, we analyzed the influence of various grassland management variables on the abundance and abundance-accounted species richness of four arthropod orders: Araneae, Coleoptera, Hemiptera, and Orthoptera. The analysis focused on detailed mowing information, for example, days after mowing and mower type, and compared their effect with other aspects of grassland management, that is, rolling, leveling, fertilization, and grazing. We found strong negative effects of mowing on all four arthropod orders, with arthropod abundance being lowest directly after mowing and steadily increasing to three to seven times the abundance after 100 days post-mowing. Likewise, Hemiptera and Coleoptera species richness was 30% higher 100 days after mowing. Mower width showed a positive effect on Orthoptera abundance, but not on the other arthropods. Arthropod abundance and Coleoptera species richness were lowest when a mulcher was used compared to rotary or bar mowers. In addition to mowing, intensive grazing negatively affected Orthoptera abundance but not the other orders. Mowing represents a highly disturbing and iterative stressor with negative effects on arthropod abundance and diversity, likely contributed by mowing-induced mortality and habitat alteration. While modifications of mowing techniques such as mower type or mowing height and width may help to reduce the negative impact of mowing on arthropods, our results show that mowing itself has the most substantial negative effect. Based on our results, we suggest that reduced mowing frequency, omission of mowing in parts of the grassland (refuges), or extensive grazing instead of mowing have the greatest potential to promote arthropod populations.

Urban trees are of high importance for healthy urban ecosystems. However, some trees are invasive plants that may ‘escape’ from urban areas into natural environments. Furthermore, invasive forest pests often arrive and establish in urban environments before they spread to forest ecosystems. Therefore, knowledge of tree species composition in urban areas is important for the biosecurity of cities and surrounding forests. Despite this, urban tree inventories often lack information on trees on private properties. To assess the potential role of urban areas as a source of invasive trees as well as invasive pests of trees, we compared the species composition of urban trees in public and private spaces in several Swiss cities and in tree nurseries (henceforth: ‘nurseries’) in Switzerland. We analysed the various data sets we compiled regarding invasive tree species, and examined how many trees are potential hosts for invasive quarantine pests of trees. We found no statistically significant difference in tree species composition in public and private urban areas, but the proportion of non-native trees was higher in private than in public spaces. Tree species available in nurseries and those present in cities were not significantly different, with larger urban tree inventories having a greater overlap with the species available in nurseries. Five of eight tree species considered invasive whose sale was banned since September 2024 were still on sale ten months before the ban came into force. All eight tree species were present in urban tree inventories. Importantly, between 91 % and 97 % of all urban trees in public and private spaces were suitable hosts for at least one quarantine forest pest. Given the pivotal role that urban trees play for the health of urban and peri-urban ecosystems, knowledge of tree species composition is essential from a biosecurity perspective. Our findings suggest that the combination of public urban tree inventories and trees available from nurseries can provide an estimate of the composition of private urban trees and can be useful for invasive species monitoring.

• Extreme droughts can have long-lasting effects on forest community dynamics and species interactions. Yet, our understanding of how drought legacy modulates ecological relationships is just unfolding. We tested the hypothesis that leaf chemistry and herbivory show long-term responses to premature defoliation caused by an extreme drought event in European beech (Fagus sylvatica L.).
• For two consecutive years after the extreme European summer drought in 2018, we collected leaves from the upper and lower canopy of adjacently growing drought-stressed and unstressed trees. Leaf chemistry was analyzed and leaf damage by different herbivore-feeding guilds was quantified.
• We found that drought had lasting impacts on leaf nutrients and on specialized metabolomic profiles. However, drought did not affect the primary metabolome. Drought-related phytochemical changes affected damage of leaf-chewing herbivores whereas damage caused by other herbivore-feeding guilds was largely unaffected. Drought legacy effects on phytochemistry and herbivory were often weaker than between-year or between-canopy strata variability.
• Our findings suggest that a single extreme drought event bears the potential to long-lastingly affect tree–herbivore interactions. Drought legacy effects likely become more important in modulating tree–herbivore interactions since drought frequency and severity are projected to globally increase in the coming decades.

Sommerdürren können die Interaktionen zwischen Bäumen und Insekten kurzfristig stark verändern. Wie Dürreeffekte aber auch Jahre später noch auf Baum-Insekten-Interaktionen nachwirken können, zeigen Analysen, die am SwissForestLab Science Day 2023 präsentiert wurden.

Qua o là sta amo ün tal eroe plain fideltà sün seis post, cun büst sfrattamà, e stenda il bratsch our da spelm e grava, sco üna sgür pronta pel cumbat, o ch'el sta ingramüschà sco ün vegliet cha la burasca da la vita ha fat sgobar sün sias crotschas.

The emerald ash borer (EAB), Agrilus planipennis, is a woodboring beetle native to East Asia. It is highly invasive in North America, where it causes large-scale dieback of American ash species, Fraxinus spp. EAB is also invasive in Western Russia and Ukraine, and it continues to spread towards Central and Western Europe where all three native ash species are susceptible. Biological control approaches offer sustainable solutions to control invasive pests. In North America, four Asian parasitoid species that have coevolved with EAB have been introduced to control the pest. In Europe, many species of the genus Agrilus occur, and it is likely that at least some of their parasitoids will adopt EAB as a host as it spreads across the continent. However, parasitoids of Agrilus spp., are very poorly known in Europe because of the difficulty of studying the parasitoid complex of these solitary wood boring insects. In this review, we provide a literature overview of studies and records of European parasitoids of Agrilus spp. to provide a basis for future studies on the emerging parasitoid complex of EAB in Europe. Parasitoid records were found for 24 European species of Agrilus. Sixty-four parasitoid species were recorded, mostly larval parasitoids. However, it is likely that several of them are erroneous host-parasitoid associations or misidentifications, and the biology of most species and their role in the population dynamics of their hosts has been poorly studied. It is recommended to conduct pre-emptive studies on these parasitoids and their suitability as potential biological control organisms with EAB.

Rising temperatures are leading to increased prevalence of warm-affinity species in ecosystems, known as thermophilisation. However, factors influencing variation in thermophilisation rates among taxa and ecosystems, particularly freshwater communities with high diversity and high population decline, remain unclear. We analysed compositional change over time in 7123 freshwater and 6201 terrestrial, mostly temperate communities from multiple taxonomic groups. Overall, temperature change was positively linked to thermophilisation in both realms. Extirpated species had lower thermal affinities in terrestrial communities but higher affinities in freshwater communities compared to those persisting over time. Temperature change’s impact on thermophilisation varied with community body size, thermal niche breadth, species richness and baseline temperature; these interactive effects were idiosyncratic in the direction and magnitude of their impacts on thermophilisation, both across realms and taxonomic groups. While our findings emphasise the challenges in predicting the consequences of temperature change across communities, conservation strategies should consider these variable responses when attempting to mitigate climate-induced biodiversity loss.

Deadwood provides habitat for fungi and serves diverse ecological functions in forests. We already have profound knowledge of fungal assembly processes, physiological and enzymatic activities, and resulting physico-chemical changes during deadwood decay. However, in situ detection and identification methods, fungal origins, and a mechanistic understanding of the main lignocellulolytic enzymes are lacking. This study used metaproteomics to detect the main extracellular lignocellulolytic enzymes in 12 tree species in a temperate forest that have decomposed for 8 ½ years. Mainly white-rot (and few brown-rot) Basidiomycota were identified as the main wood decomposers, with Armillaria as the dominant genus; additionally, several soft-rot xylariaceous Ascomycota were identified. The key enzymes involved in lignocellulolysis included manganese peroxidase, peroxide-producing alcohol oxidases, laccase, diverse glycoside hydrolases (cellulase, glucosidase, xylanase), esterases, and lytic polysaccharide monooxygenases. The fungal community and enzyme composition differed among the 12 tree species. Ascomycota species were more prevalent in angiosperm logs than in gymnosperm logs. Regarding lignocellulolysis as a function, the extracellular enzyme toolbox acted simultaneously and was interrelated (e.g. peroxidases and peroxide-producing enzymes were strongly correlated), highly functionally redundant, and present in all logs. In summary, our in situ study provides comprehensive and detailed insight into the enzymatic machinery of wood-inhabiting fungi in temperate tree species. These findings will allow us to relate changes in environmental factors to lignocellulolysis as an ecosystem function in the future.