Dr. Beat Wermelinger

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.

Ohne das unsichtbare Wirken von Insekten, die im Holz leben, würde der Wald nicht existieren – zumindest nicht so, wie wir ihn kennen. Sie haben sich auf verschiedene Baumarten und Holzzersetzungsstadien spezialisiert und sind unverzichtbar für ein funktionierendes Ökosystem. Gleichzeitig ist ein vielfältiges Angebot an Totholz lebenswichtig für die Insektenarten, die ausschliesslich in totem Holz vorkommen.

Trichoferus campestris (Faldermann, 1835), a new element of the fauna of Switzerland (Coleoptera, Cerambycidae). - First records of the longhorn beetle Trichoferus campestris in Switzerland are documented and details of these discoveries are reported. Several records concern larvae in wood packaging material and two adult beetles were found in the wild near the city of Zurich in 2019 and 2022. In 2022, several adults were observed in an urban district of the city of Geneva.

Die Bockkäferart Trichoferus campestris (Faldermann, 1835) wird als neues Element der Schweizer Fauna gemeldet und die Fundumstände werden mitgeteilt. Mehrere Larven wurden in Verpackungsholz gefunden und zwei adulte Käfer 2019 und 2022 im Freiland in der Nähe von Zürich. Im Jahr 2022 wurden in der Stadt Genf mehrere Adulttiere gefunden.

Trichoferus campestris (Faldermann, 1835), une nouvelle espèce pour la faune de Suisse (Coleoptera, Cerambycidae). - Le longicorne Trichoferus campestris (Faldermann) est signalé comme nouvelle espèce de la faune suisse. Les circonstances de sa découverte dans différents sites sont décrites. Plusieurs larves ont été trouvées dans du bois d’emballage puis deux Coléoptères adultes ont été collectés en milieu naturel dans deux stations près de Zurich en 2019 et 2022. Finalement, plusieurs adultes ont été observés dans une zone urbaine de Genève en 2022.

Understanding natural disturbance regimes and their impacts is crucial in designing ecosystem management strategies. However, disturbances do not always occur in isolation; the occurrence of one disturbance influences the likelihood or the effect of another. In this chapter, we illustrate the importance of disturbance interactions by focusing on a subset of interactions present in different parts of the boreal forest. The selected interactions include insects and wind, insects and fire, and wind and fire. The potential consequences of climate change on these interactions are also discussed.

Dieser Beitrag gibt eine Darstellung von bereits beobachteten und künftig zu erwartenden Auswirkungen der sich verändernden Klimabedingungen auf die Biologie und Lebensweise von Insekten. Anhand von Beispielen aus der europäischen Forschung und mit einem Schwerpunkt auf in der Schweiz heimischen Waldinsekten werden die wichtigsten, typischerweise für Insekten in terrestrischen Ökosystemen geltenden Effekte dargestellt.

Der Eichenprozessionsspinner ist ein in Europa heimischer Schmetterling, der sich hauptsächlich auf Eichen entwickelt. In der Schweiz konzentriert sich seine Verbreitung auf Regionen in der West- und Nordwestschweiz sowie auf die Alpensüdseite. Nach dem Schlupf ernähren sich seine in geselligen Verbänden lebenden Raupen von Eichenblättern und können bei grossen Populationsdichten zur völligen Entlaubung der befallenen Bäume führen. Besondere Aufmerksamkeit wird dem Eichenprozessionsspinner zuteil, weil die Brennhaare seiner Raupen bei Menschen und Tieren allergische Reaktionen auslösen können.

La processionnaire du chêne est un papillon européen qui se développe principalement sur les chênes. En Suisse, son aire de répartition comprend essentiellement les régions de Suisse occidentale et du Nord-Ouest ainsi que le Sud des Alpes. Après leur éclosion, les chenilles sociales vivent en groupes, se nourrissent de feuilles de chênes et peuvent causer des défoliations totales lorsque leurs populations se densifient. La processionnaire du chêne retient particulièrement l’attention, car les poils urticants de la chenille peuvent provoquer des réactions allergiques chez l’homme et l’animal.

The oak processionary moth is a moth native to Europe that develops mainly on oak trees. In Switzerland, it is mainly found in western and north-western regions, and on the southern side of the Alps. After hatching, its caterpillars feed in gregarious clusters on the leaves of oak trees, and large populations can lead to the complete defoliation of infested trees. The oak processionary moth attracts particular attention because the urticating (stinging) hairs of its caterpillars can cause allergic reactions in humans and animals.

Street lights are important light sources that contribute to artificial light at night (ALAN). To date, ecological impacts of individual LED properties (color temperature, dimmability) have been studied, while interactions between light properties or aspects of luminaire design have not been addressed. However, the design of luminaires can influence ALAN impacts as the shape determines the spatial distribution of light and its visibility in the environment. This may cause amplifying or mitigating effects. We assessed the relative individual and interacting effects of two LED luminaire designs and three LED color temperatures (1750 K, 3000 K, 4000 K) on nocturnal insect abundance, bat foraging and feeding activity. We considered a standard LED luminaire shape with focused light emission and a luminaire shape with a diffusor to scatter the light spatially, leading to increased visibility of the light in the environment. During 104 nights, we trapped 51263 nocturnal insects of which 97% were caught at lights and 3% at dark sites. For bats, up to 44.8% fewer acoustic signals were recorded at dark sites. We caught 31% insects at LEDs with1750 K, 34% and 35% at 3000 K and 4000 K, respectively. Thus, color temperatures of 1750 K proved less detrimental than 3000/4000 K. Effects of luminaire shape led to an increase (16%) of trapped insects for luminaires with diffusors compared to the standard shape. In addition, luminaires with diffusors amplified the effects of LED color (+12% insects at 1750 K/3000 K; +25.6% at 4000 K). In contrast, bat foraging activity was independent of the light treatments while bat feeding activity was increased by 21.5% at standard luminaire shapes. Likely, intense straylight at diffused lights negatively affects the target-focused echolocation by deterring the bats. We concluded that ecological impacts of luminaire shape are an important, yet underestimated variable in light-pollution impact research.

Climate change exposes ecosystems to strong and rapid changes in their environmental boundary conditions mainly due to the altered temperature and precipitation patterns. It is still poorly understood how fast interlinked ecosystem processes respond to altered environmental conditions, if these responses occur gradually or suddenly when thresholds are exceeded, and if the patterns of the responses will reach a stable state. We conducted an irrigation experiment in the Pfynwald, Switzerland from 2003–2018. A naturally dry Scots pine (Pinus sylvestris L.) forest was irrigated with amounts that doubled natural precipitation, thus releasing the forest stand from water limitation. The aim of this study was to provide a quantitative understanding on how different traits and functions of individual trees and the whole ecosystem responded to increased water availability, and how the patterns and magnitudes of these responses developed over time. We found that the response magnitude, the temporal trajectory of responses, and the length of initial lag period prior to significant response largely varied across traits. We detected rapid and stronger responses from aboveground tree traits (e.g., tree-ring width, needle length, and crown transparency) compared to belowground tree traits (e.g., fine-root biomass). The altered aboveground traits during the initial years of irrigation increased the water demand and trees adjusted by increasing root biomass during the later years of irrigation, resulting in an increased survival rate of Scots pine trees in irrigated plots. The irrigation also stimulated ecosystem-level foliar decomposition rate, fungal fruit body biomass, and regeneration abundances of broadleaved tree species. However, irrigation did not promote the regeneration of Scots pine trees, which are reported to be vulnerable to extreme droughts. Our results provide extensive evidence that tree- and ecosystem-level responses were pervasive across a number of traits on long-term temporal scales. However, after reaching a peak, the magnitude of these responses either decreased or reached a new stable state, providing important insights into how resource alterations could change the system functioning and its boundary conditions.

Disturbances alter biodiversity via their specific characteristics, including severity and extent in the landscape, which act at different temporal and spatial scales. Biodiversity response to disturbance also depends on the community characteristics and habitat requirements of species. Untangling the mechanistic interplay of these factors has guided disturbance ecology for decades, generating mixed scientific evidence of biodiversity responses to disturbance. Understanding the impact of natural disturbances on biodiversity is increasingly important due to human-induced changes in natural disturbance regimes. In many areas, major natural forest disturbances, such as wildfires, windstorms, and insect outbreaks, are becoming more frequent, intense, severe, and widespread due to climate change and land-use change. Conversely, the suppression of natural disturbances threatens disturbance-dependent biota. Using a meta-analytic approach, we analysed a global data set (with most sampling concentrated in temperate and boreal secondary forests) of species assemblages of 26 taxonomic groups, including plants, animals, and fungi collected from forests affected by wildfires, windstorms, and insect outbreaks. The overall effect of natural disturbances on α-diversity did not differ significantly from zero, but some taxonomic groups responded positively to disturbance, while others tended to respond negatively. Disturbance was beneficial for taxonomic groups preferring conditions associated with open canopies (e.g. hymenopterans and hoverflies), whereas ground-dwelling groups and/or groups typically associated with shady conditions (e.g. epigeic lichens and mycorrhizal fungi) were more likely to be negatively impacted by disturbance. Across all taxonomic groups, the highest α-diversity in disturbed forest patches occurred under moderate disturbance severity, i.e. with approximately 55% of trees killed by disturbance. We further extended our meta-analysis by applying a unified diversity concept based on Hill numbers to estimate α-diversity changes in different taxonomic groups across a gradient of disturbance severity measured at the stand scale and incorporating other disturbance features. We found that disturbance severity negatively affected diversity for Hill number q = 0 but not for q = 1 and q = 2, indicating that diversity–disturbance relationships are shaped by species relative abundances. Our synthesis of α-diversity was extended by a synthesis of disturbance-induced change in species assemblages, and revealed that disturbance changes the β-diversity of multiple taxonomic groups, including some groups that were not affected at the α-diversity level (birds and woody plants). Finally, we used mixed rarefaction/extrapolation to estimate biodiversity change as a function of the proportion of forests that were disturbed, i.e. the disturbance extent measured at the landscape scale. The comparison of intact and naturally disturbed forests revealed that both types of forests provide habitat for unique species assemblages, whereas species diversity in the mixture of disturbed and undisturbed forests peaked at intermediate values of disturbance extent in the simulated landscape. Hence, the relationship between α-diversity and disturbance severity in disturbed forest stands was strikingly similar to the relationship between species richness and disturbance extent in a landscape consisting of both disturbed and undisturbed forest habitats. This result suggests that both moderate disturbance severity and moderate disturbance extent support the highest levels of biodiversity in contemporary forest landscapes.

Bark beetles are important components of the natural dynamics of coniferous forests. In Europe, the European spruce bark beetle (Ips typographus) in particular has the potential to cause extensive infestations and thus can act as an ecological disturbance. After disturbances such as windthrow or drought, this beetle can increase its population density to such an extent that it is able to successfully colonize vigorous trees. The further development of mass infestations of living trees mainly depends on temperature and the susceptibility of the host trees. From an ecological viewpoint, bark beetles contribute to the natural dynamics of forest ecosystems and create valuable new habitats for many organisms. Socio-economically, however, bark beetle outbreaks often lead to extensive damage.

In den letzten Jahren war «der Borkenkäfer» wieder in aller Munde. Vielen Leuten ist aber nicht bewusst, dass es mehr als nur eine Borkenkäferart gibt. Allein in der Schweiz sind 112 Arten bekannt, weltweit sogar über 6000. Allen mitteleuropäischen Arten gemeinsam ist, dass sie sich in holzigem Substrat entwickeln.

Les scolytes font régulièrement parler d'eux lorsqu'ils pullulent et qu’ils entraînent le dépérissement d'arbres à grande échelle. Leur pullulation ne se fait toutefois pas sans obstacle. Environ 300 espèces différentes d'ennemis naturels les tiennent en échec, coléoptères prédateurs et guêpes parasitoïdes notamment. La plupart vivent - à l'image de leur proie - de façon discrète sous l'écorce et y régulent les populations de coléoptères.

De schorskevers komen regelmatig te sprake wanneer ze welig tieren en leiden tot het afsterven van bomen op grote schaal. Bij hun voortwoekeren komen ze echter toch wel wat hindernissen tegen. Ze hebben ongeveer 300 verschillende soorten natuurlijke vijanden die hen proberen te dwarsbomen, met name roofkevers en sluipwespen. De meesten van hen leven, net zoals hun prooi, discreet onder de schors en reguleren er de populatie aan kevers.
De belangrijkste natuurlijke vijanden van schorskevers worden in dit artikel besproken.

Gegen 300 verschiedene Arten, vor allem räuberische Käfer und parasitische Wespen, sind als natürliche Feinde des Buchdruckers bekannt. Die meisten leben – wie ihre Beute – unauffällig unter der Baumrinde und ernähren sich dort von Borkenkäferbrut. Sie spielen bei der Regulation von Borkenkäfern eine wichtige Rolle.

Üblicherweise werden Borkenkäfer vor allem als Schädlinge wahrgenommen. Tatsächlich können einige Borkenkäferarten in Jahren von Massenvermehrungen wichtige vom Menschen erwartete Waldleistungen wie Holzproduktion, Schutz vor Naturgefahren oder Erholung massiv beeinträchtigen. Borkenkäfer erfüllen aber auch wichtige Funktionen im Ökosystem.

Aim: Red wood ants (Formica rufa group) mitigate invertebrate pest outbreaks, alter invertebrate communities, and contribute to nutrient cycling. The IUCN lists these insects as near threatened. We investigated whether disturbances of Red Wood Ant (RWA) forest habitats related to recreation, infrastructure, and forest management were associated with RWA occurrence. We also investigated the habitat associations of this group.
Location: Switzerland.
Methods: We trained random forest models to predict RWA occurrence using data from 6,341 plots distributed throughout Swiss forests. Our explanatory variables included descriptions of vegetation, terrain, climate and human disturbance of the forest. A model trained using all of these variables (Model 1) was compared to another trained using all of these variables except those describing human disturbance (Model 2). We compared the abilities of these models to differentiate between RWA presences and absences using areas under receiver operator curves (AUC). The nature of the associations between the probability of RWA occurrence predicted by Model 1 and the explanatory variables that made the greatest contributions to the AUC of this model were investigated using individual conditional expectation plots.
Results: No significant difference in AUC was detected between Models 1 and 2. RWA occurrence was positively associated with elevation, conifers, canopy gaps, ground cover vegetation and solar insolation while negatively associated with air temperature and a soil wetness index.
Main conclusions: The distribution of RWA within Swiss forests appeared unassociated with the human disturbances we investigated. To conserve RWA in Switzerland, we recommend the conservation of forests with high proportions of conifers, particularly those at high elevations. We also recommend forest management that promotes ground cover vegetation and open canopy structures. The negative associations between RWA occurrence and temperatures raise concerns for the prospects of RWA in the context of predicted climate warming.

Deux projets distincts d'inventaire de Coléoptères saproxyliques ont permis la découverte d'Aesalus scarabaeoides en Suisse en 2019 et ainsi confirmé sa présence, documentée jusqu'alors par une seule donnée datant de près de 50 ans.

Der Kurzschröter Aesalus scarabaeoides wurde 2019 anlässlich zweier Monitoringprojekte für Totholzkäfer in der Schweiz gefunden. Damit wurde diese Art in der Schweiz bestätigt, da bisher nur ein fast 50 Jahre alter Fund dokumentiert war.

Droughts and other rapid changes in abiotic environmental conditions can predispose trees to damage by pest insects and pathogens. For survival of coniferous trees, functional resin-based defences are essential, and it is important to know how they react to changes in environmental conditions at various time scales.
We studied the effects of differing water availabilities on resin-based defences in mature Scots pine (Pinus sylvestris) trees in a naturally drought-prone forest within a long-term irrigation experiment. Our objectives were to understand the effects of long-term drought on carbon allocation to resin production and to analyse its influence on resin flow and pressure in comparison to the shorter-term effects of seasonal drought. We tracked carbon allocation to resin after ¹³C-pulse labelling experiment in late summer 2017 and compared the observed resin dynamics between drought-exposed control trees and irrigated trees from June to August during the dry hot summer of 2018.
Dry control trees showed higher allocation of labelled carbon to resin than irrigated trees. Resin pressure was higher in dry control than in irrigated trees with similar water potentials, and resin flow in June was higher in dry control than in irrigated trees with similar crown transparency. Yet, resin pressures of dry control trees in particular decreased with decreasing water availability from June to August. Resin flow was little affected by short-term changes in water availability and mostly associated with crown transparency. We suggest that because of differing timescales of direct drought effects and changes in allocation patterns, dry conditions may support resin-based defences in the long term, but a drought period decreases resin pressure in the short term.