Spatiotemporal dynamics of forest geometrid outbreaks

We highlight recent developments and avenues for advancement, which can improve insight into the causes of changes in the spatiotemporal dynamics of forest Geometridea moth species (hereafter ‘geometrids’). Some forest geometrids possess fundamental biological traits, which make them particularly liable to outbreak range expansions and host shifts mitigated by climate change. Indeed, recently observed changes in geometrid spatiotemporal dynamics represent both new research opportunities and challenges for empirically testing drivers of intra- and interspecific spatial synchrony, including the role of trophic interactions and biological traits (e.g. dispersal ability). We advocate that the emerging field of near-term ecological forecasting holds promise for studies of the spatiotemporal dynamics of forest geometrids and could be tailored to give both accurate predictions at managementrelevant timescales and new insights into the mechanisms that underlie spatiotemporal population dynamics

A pioneering pest: the winter moth (Operophtera brumata) is expanding its outbreak range into Low Arctic shrub tundra

Climate warming allows generalist boreal consumers to expand into Arctic ecosystems. We present experimental and observational field data showing that a generalist boreal insect pest—the winter moth (Operophtera brumata Linnaeus, 1758)—is expanding its outbreak range out of the northern boreal mountain birch forest in northeast Fennoscandia and into the adjacent Low Arctic shrub tundra. This is the first documented example of an outbreaking boreal insect pest expanding into a tundra ecosystem. The expansion has coincided with a long-term advancing trend in the expected hatching date of moth eggs in spring for the study region. We show that the winter moth can complete development on Low Arctic willows and that the density of winter moth larvae in willow thickets is unrelated to the amount of mountain birch (the main host plant in northern boreal forest) in the thickets. However, we also demonstrate that larval densities on willows show a regional-scale spatial decline when moving away from the birch forest and into the shrub tundra. Continued monitoring is needed to establish whether the outbreaks will spread farther into the tundra. The expansion of outbreaking boreal pests into the tundra could alter conventional expectations of increasing vegetation productivity and shrubification in tundra ecosystems. Le réchauffement climatique permet aux consommateurs boréaux généralistes de s’étendre aux écosystèmes arctiques. Les auteurs présentent des données expérimentales et d’observation sur le terrain montrant qu’un insecte nuisible boréal généraliste — l’arpenteuse tardive (Operophtera brumata Linnaeus, 1758) — est en train d’étendre son aire de répartition boréale-nordique hors de la forêt de bouleaux de montagne du nord-est de la Fennoscandie et dans la toundra arbustive aride adjacente du Bas-Arctique. Il s’agit du premier exemple documenté d’un insecte nuisible boréal en pullulation dans un écosystème de toundra. Cette expansion a coïncidé avec une tendance à long terme à l’avancement de la date d’éclosion prévue des œufs d’arpenteuse au printemps dans la région étudiée. Les auteurs montrent que l’arpenteuse tardive peut achever son développement sur les saules du Bas-Arctique et que la densité des larves de l’arpenteuse tardive dans les fourrés de saules n’est pas liée à la quantité de bouleau de montagne (l’hôte principal dans la forêt boréale nordique) dans les fourrés. Cependant, ils démontrent également que les densités de larves sur les saules montrent un déclin spatial à l’échelle régionale lorsque l’on s’éloigne de la forêt de bouleaux et que l’on entre dans la toundra arbustive. Une surveillance continue est nécessaire pour déterminer si les pullulations s’étendront plus loin dans la toundra. L’expansion des ravageurs boréaux dans la toundra pourrait modifier les attentes conventionnelles d’une augmentation de la productivité de la végétation et de l’arbustification dans les écosystèmes de la toundra

The state of health of Norwegian forests. Results from the national forest damage monitoring 2017

Source at http://hdl.handle.net/11250/2559230Skogens helsetilstand påvirkes i stor grad av klima og værforhold, enten direkte ved tørke, frost og vind, eller indirekte ved at klimaet påvirker omfanget av soppsykdommer og insektangrep. Klimaendringene og den forventede økningen i klimarelaterte skogskader gir store utfordringer for forvaltningen av framtidas skogressurser. Det samme gjør invaderende skadegjørere, både allerede etablerte arter og nye som kan komme til Norge i nær framtid. Denne rapporten presenterer resultater fra skogskadeovervåkingen i Norge i 2017 og trender over tid for følgende temaer...Forest health is to a large extent affected by climate and weather conditions, either directly by e.g. drought, frost and wind, or indirectly when climatic conditions influence the occurrence and abundance of pests and diseases. Climate change and the expected increase in abiotic damage are a challenge to the management of future forest resources. The same is true for invasive damage agents, both species which are already established and species which can possibly migrate to Norway in the future. This report presents results from the Norwegian forest damage monitoring in 2017 and trends over time for..

Skogens helsetilstand i Norge. Resultater fra skogskadeovervåkingen i 2020

Skogens helsetilstand påvirkes i stor grad av klima og værforhold, enten direkte ved tørke, frost og vind, eller indirekte ved at klimaet påvirker omfanget av soppsykdommer og insektangrep. Klimaendringene og den forventede økningen i klimarelaterte skogskader gir store utfordringer for forvaltningen av framtidas skogressurser. Det samme gjør invaderende skadegjørere, både allerede etablerte arter og nye som kan komme til Norge i nær framtid. I denne rapporten presenteres resultater fra skogskadeovervåkingen i Norge i 2020 og trender over tid

Skogens helsetilstand i Norge. Resultater fra skogskadeovervåkingen i 2022

Skogens helsetilstand påvirkes i stor grad av klima og værforhold, enten direkte ved tørke, frost og vind, eller indirekte ved at klimaet påvirker omfanget av soppsykdommer og insektangrep. Klimaendringene og den forventede økningen i klimarelaterte skogskader gir store utfordringer for forvaltningen av framtidas skogressurser. Det samme gjør invaderende skadegjørere, både allerede etablerte arter og nye som kan komme til Norge i nær framtid. I denne rapporten presenteres resultater fra skogskadeovervåkingen i Norge i 2022 og trender over tid for følgende temaer: (i) Landsrepresentativ skogovervåking; (ii) Intensiv skogovervåking; (iii) Overvåking av bjørkemålere i Troms og Finnmark; (iv) Barkbilleovervåkingen; (v) Furuvednematode; (vi) Askeskuddsyke; (vii) Andre spesielle skogskader i 2022

Cyclically outbreaking geometrid moths in sub-arctic mountain birch forest: the organization and impacts of their interactions with animal communities

In sub-arctic mountain birch forest in northern Fennoscandia, the 2 geometrid moth species Epirrita autumnata (autumnal moth) and Operophtera brumata (winter moth) show high-amplitude population cycles with regular 10-year periodicity. During some population peaks, moth populations attain outbreak densities and cause region-wide defoliation and mortality of mountain birch. The severity and duration of moth outbreaks presently appears to be increasing, owing to climate-driven range-expansions of both native and novel (see below) moth species in the system. The causal mechanisms of moth population cycles have been widely studied, with research focusing on the role of parasitoids during the last decade. This research has focused on total parasitism rates and has paid little attention to parasitoid community organization and its consequences for the functionality of parasitoid communities. Study I – III of this PhD project addressed this knowledge gap for larval parasitoids, which have received more attention than other parasitoid guilds in the research on parasitism the birch-moth system. Study I explored the possibility of stochastic extinction-recolonization dynamics – induced by fluctuations in moth host populations – as a driver of the spatial distribution patterns of different larval parasitoid species. The study documented large-scale spatial segregation in the prevalence of different parasitoid species in O. brumata, which may have resulted from stochastic extinction-recolonization processes. However, the alternative explanation that the observed patterns were caused by spatial gradients in habitat characteristics could not be rejected. Further, the study found that the magnitude of total larval parasitism rates at a given location was independent of which parasitoid species was locally dominant. Study II mapped out the phenology of attack of the larval parasitoid species of O. brumata. The study showed that the attacks of different parasitoid species followed each other in a successional manner throughout the larval season, so that all larval instars were attacked by at least 1 parasitoid species. The study argued that this phenological diversity within the larval parasitoid guild would reduce the probability of climate-induced phenological mismatches between larvae and many parasitoid species within a single season, hence buffering total larval parasitism rates against stochastic climatic variation. Study III compared larval parasitoid species richness and prevalence rates among E. autumnata, O. brumata and Agriopis aurantiaria (scarce umber moth). E. autumnata is native species to the mountain birch forest, while O. brumata and A. aurantiaria invaded this system by range-expansion approximately a century and 15 years ago, respectively. The study found that E. autumnata and O. brumata hosted similar numbers of larval parasitoid species in the mountain birch system, while the larval parasitoid guild of A. aurantiaria was strongly species-impoverished compared to the 2 other moth species. Based on this, the study argued that invasive moth species take at least a century to acquire a larval parasitoid guild with native levels of species richness in the mountain birch forest. Total larval parasitism rates were similar among all 3 moth species, suggesting that invasive geometrid moths do not enjoy release from larval parasitism in the mountain birch forest, despite having species-impoverished larval parasitoid guilds. Taken together, study I – III pointed towards high levels of functional redundancy among larval parasitoid species in the birch-moth system. This could act to stabilize total larval parasitism rates in space and time. The studies also highlighted that it is necessary to resolve numerous uncertainties surrounding parasitoid taxonomy in order to make further progress in parasitoid community ecology in this system. While the causes of moth population cycles and outbreaks have been intensively studied, comparatively little attention has been paid to the ecological consequences of moth outbreaks. Some of the most serious knowledge gaps relate to the consequences of outbreak-induced forest damage for animal communities in the mountain birch ecosystem. Study IV and V addressed this issue by investigating the short-term responses of saproxylic (i.e. associated with dead wood) beetles and passerine birds, respectively, to an outbreak that had caused widespread mortality of birch forest 3 – 5 years before the outset of the studies. Study IV showed that the proportion of obligate saproxylic species in the beetle community was only about 10 % higher in damaged than undamaged birch forest. The study thereby indicated that saproxylic beetles have limited ability to respond numerically to the enormous amounts of dead wood that are generated by moth outbreaks. Climatic constraints on beetle activity and diversity in my sub-arctic study region, and species-specific preferences for dead wood in certain stages of decay, were suggested as explanations for the weak response of the saproxylic beetle community. The study raised the possibility that saproxylic beetles, owing to weak numerical responses, may play a minor role in wood decomposition in the immediate aftermath of moth outbreaks. This highlighted that there is need to learn more about the role of microbial wood-decomposer communities after outbreaks. The results of study V mirrored those of study IV, by indicating a weak response of bird communities to outbreak-induced forest damage. In 1 of my 2 main study areas (Kirkenes), the total abundance of birds was roughly 25 % lower in damaged than undamaged forest. Bird species-richness showed an even smaller reduction in damaged forest. Meanwhile, in the other study area (Tana), there were no consistent differences in bird abundance or richness between damaged and undamaged forest. The observed reduction in bird abundance in damaged forest in Kirkenes was mainly driven by the Willow warbler (Phylloscopus trochilus); a foliage gleaning species which may have suffered loss of foraging habitat due to outbreak-induced mortality of trees. By documenting a weak response to forest damage in the studied bird community, study V suggested that this community has a high degree of resistance to the habitat disturbance caused by outbreaks. This may be explained by the fact that many of the studied bird species are habitat generalists. It was also suggested that bird populations in the outbreak area might have been maintained by surviving trees and by standing birch trunks, which could serve to maintain the vertical structure of the forest habitat. Study IV and V were limited in their conclusions by their short-term time perspectives. Thus, both studies highlighted the need for more long-term research on the responses of animal communities to outbreak-induced forest damage in the mountain birch ecosystem

Populasjonssykluser hos bjørkemålere – små dyr med enorme svingninger

Fjellbjørkemåler og liten frostmåler er to nattsommerfugler som har sykliske populasjonssvingninger i fjellbjørkeskogen i Skandinavia. Populasjonstopper kommer med omtrent ti års mellomrom, og tettheten av målere i toppår kan være flere tusen ganger høyere enn i bunnår. Selv om syklusene er godt beskrevet ved hjelp av lange tidsserier er årsaken til svingningene dårlig forstått. Antibeitestoffer hos bjørka blir ofte fremholdt som årsaken til syklusene i media, selv om denne hypotesen har svært begrenset støtte i forskningsresultater. Sykliske svingninger i solflekkaktivitet har også blitt forkastet som årsak til målersyklusene. Naturlige fienders rolle i syklusene er fortsatt omdiskutert på grunn av sprikende forskningsresultater. Målersyklusene spiller uansett en viktig rolle i fjellbjørkeksogen, da målerne er mat for mange andre arter og kan forårsake alvorlige skader på skogen i toppår

Environmental conditions alter successional trajectories on an ephemeral resource: a field experiment with beetles in dead wood

Successional processes can be observed for many organisms and resources, but most studies of succession have focused on plants. A general framework has been proposed, advocating that successional patterns in species turnover are predominantly driven by competition, dispersal or abiotic limitation, and that the patterning of species accumulation over time gives clues to which process is most influential in a given system. We applied this framework to succession in communities of wood-living beetles, utilizing ephemeral resources in the form of 60 experimentally created dead aspen high stumps. High stumps were created at sun-exposed sites (high ambient temperature; favourable abiotic conditions) and shaded sites (low ambient temperature; abiotically limiting conditions). The sites were intermixed, ensuring similar dispersal opportunities. Beetle species richness and abundance were monitored with flight interception traps over four consecutive years. Consistent with predictions from the tested framework, several beetle functional groups accumulated species more slowly at the unfavourable shaded sites than at the favourable exposed sites. Species richness at the exposed sites increased rapidly to a plateau, consistent with a limiting effect of competition on community development. Similar results were obtained for beetle abundance and community structure. Part of the variance in beetle community structure was jointly explained by habitat and fungal community composition, suggesting that differences in the composition and developmental rate of fungal communities in the two habitats contributed to the observed patterns. Targeted experimental studies are now required to decisively establish what processes underlie the contrasting successional trajectories in the two environments.publishedVersio

Resistance of a sub-arctic bird community to severe forest damage caused by geometrid moth outbreaks

Outbreaks by geometrid moths periodically cause mass mortality of trees and state changes in understorey vegetation in sub-arctic mountain birch forest in northern Scandinavia. In order to assess the short-term impacts of such disturbance on forest bird communities, we took bird censuses in forest where almost all birch trees had been killed by moth outbreaks 2–4 years before the study and in undamaged forest. The study was repeated in two locations (Kirkenes and Tana) with contrasting forest structure and fragmentation. Using a hierarchical community model, we show that the total abundance of birds in Kirkenes was only about 25 % lower in damaged than undamaged forest and that species richness differed even less between the two forest types. Meanwhile, neither bird abundance nor species richness differed between damaged and undamaged forest in Tana. The observed patterns in abundance were mainly driven by a few very common species. Only a single species showed indication of being more abundant in damaged forest. Thus, our findings indicate that bird communities in sub-arctic mountain birch forest have a high degree of resistance to forest damage caused by moth outbreaks. We suggest that bird populations in outbreak-affected forest may be maintained by surviving trees and by standing dead tree trunks, which help maintain the vertical structure of the forest habitat. The fact that many of the studied bird species are habitat generalists may also explain their apparently weak responses to the damage caused by the outbreak. Our results do not point towards forest damage caused by moth outbreaks as a major driver of change in bird communities in the study system, although more long-term research is needed to substantiate this conclusion

Environmental conditions alter successional trajectories on an ephemeral resource: a field experiment with beetles in dead wood

Successional processes can be observed for many organisms and resources, but most studies of succession have focused on plants. A general framework has been proposed, advocating that successional patterns in species turnover are predominantly driven by competition, dispersal or abiotic limitation, and that the patterning of species accumulation over time gives clues to which process is most influential in a given system. We applied this framework to succession in communities of wood-living beetles, utilizing ephemeral resources in the form of 60 experimentally created dead aspen high stumps. High stumps were created at sun-exposed sites (high ambient temperature; favourable abiotic conditions) and shaded sites (low ambient temperature; abiotically limiting conditions). The sites were intermixed, ensuring similar dispersal opportunities. Beetle species richness and abundance were monitored with flight interception traps over four consecutive years. Consistent with predictions from the tested framework, several beetle functional groups accumulated species more slowly at the unfavourable shaded sites than at the favourable exposed sites. Species richness at the exposed sites increased rapidly to a plateau, consistent with a limiting effect of competition on community development. Similar results were obtained for beetle abundance and community structure. Part of the variance in beetle community structure was jointly explained by habitat and fungal community composition, suggesting that differences in the composition and developmental rate of fungal communities in the two habitats contributed to the observed patterns. Targeted experimental studies are now required to decisively establish what processes underlie the contrasting successional trajectories in the two environments