The arthropod complex associated with Ips typograpfius (L.) (Coleoptera, Scolytidae): species composition, phenology, and impact on bark beetle productivity

The biology of forest arthropods associated with the bark beetle lps typographus and the impact of these associates on bark beetle productivity were investigated in the field. Arthropods were allowed access to spruce bolts for different lengths of time, 0, 1, 4, and 8 weeks, following onset of attack by lps typograplus, after which time the bolts were moved to a nonforested area and caged. Arthropods were collected as they emerged from the bolts in autumn and the following spring. At least 32 arthropod species were collected, of which 17 are known to feed on bark beetle brood. The longer the exposure period the more bark beetle enemies and the fewer lps typographus emerged. Natural enemies were estimated to have reduced bark beetle productivity by 83%. Arrival and emergence patterns and relative impact on bark beetle productivity of different species are discussed

Coarse woody debris legacies and their dynamics in retained forest patches

Retaining trees in small patches at final harvest is a common forest conservation measure to maintain structural and biological diversity through the young forest phase. Long-term studies of coarse woody debris (CWD, breast height diameter ≥ 10 cm) changes in retention patches remain uncommon, especially in relation to different types of patches with varying tree species composition, ground moisture, size, shape, and exposure. In the present study we re-inventoried CWD three times (1–3, 5–7 and 18–20 years after harvesting) in 60 small tree retention patches (0.03–0.54 ha) of six commonly created retention patch types, in central boreal Sweden. Most retention patch types, despite being very small (3 ha−1 and buffer zones to rocky outcrop the highest average volume of 32 m3 ha−1, when summarised over the whole study period. Very few patch-level environmental variables (except type) related to the amount of CWD in retention patches; only the retained living tree volume of patches during creation was clearly positively correlated with higher post-harvest CWD volumes. Patch characteristics such as size and shape index did not relate to the CWD volumes in retention patches, and patch exposure only related to higher CWD volumes within the first 1–3 years after harvest. Retention patches generally supported a variety of living trees, CWD volumes and qualities over time. Several retention patch types; such as free-standing coniferous and deciduous patches, rocky outcrop buffers, wet forest patches and buffers to water, supported average CWD volumes between 19–41 m3 ha−1 after 18–20 years, under remaining canopy cover. Our findings challenge the traditional management principles aimed at minimizing severe windthrow and CWD input (i.e., creating larger patches (>0.5–1 ha), choosing topographically sheltered areas, selecting specific tree species and ground conditions). However, our study was too small in scale to investigate multiple within-patch-type interacting environmental variables. Future larger-scale studies over extended time periods are needed to disentangle such interactions for the dynamics of CWD and associated biodiversity in retention patches

Release of retained oaks in Norway spruce plantations. A 10-year perspective on oak vitality, spruce wood production and ground vegetation

This study explores the decade-long effects of release cutting around old retained oaks (Quercus robur L.) in a Norway spruce (Picea abies L. Karst) stand that was 33 year old when thinned. The impacts on both nature conservation values and spruce wood production were evaluated in a randomized block design. To release oaks from competition, stems of Norway spruce were cut around 33 oaks, in three different treatments: high release (HR), medium release (MR) and no release (NR). Trees within a circular sample plot (15 m radius from the oak) were measured at time of treatment and 10 years after. The treatment effects on stand development, oak vitality and understory vegetation were evaluated after ten years, using tree diameter, height measurements, oak crown and tree structure estimates as well as ground vegetation surveys. Release cutting did not impact spruce production within the sample plot, and given that there were no other obvious sources of spruce suppression in the stand, we speculate that release cutting has little to no impact at the stand scale. Oak crowns in the control plots (NR) became smaller after ten years, while the crowns expanded and colonized the gap in the release treatments. Simultaneously, the amount of dead wood in the crown increased among oaks in the control treatment, indicating dieback. Cover and species richness of vascular plants in the understory were significantly higher in the HR and MR treatments compared to NR. These results suggest that the creation of relatively wide gaps (greater than 2 m) around retained oak crowns is one efficient approach to maintain their conservation values in a spruce dominated stand on a longer time frame. This will allow oaks to expand their crowns, increase their vitality and increase species richness and diversity of plants under the canopy. The economic loss of creating large gaps instead of no gaps may be negligible since the overall spruce production was not affected within 15 m of each oak

Density of dispersal sources affects to what extent restored habitat is used: A case study on a red-listed wood-dependent beetle

When restoring habitats, an important question is whether the spatial distribution of habitat affects its contribution to biodiversity conservation. In Sweden, high-cut stumps are routinely created at forestry operations. By counting the number of exit holes of a red-listed beetle, Peltis grossa, we assessed occurrence, colonisations and extinctions per high-cut stump and beetle density per clear-cut. We found a threshold, at which the form of the relationship between density of the beetle and density of high-cut stumps per clear-cut changes abruptly. The beetle density was considerably higher where the density of high-cut stumps exceeded 4.5 per hectare. Such thresholds can be explained by colonisation-extinction processes. Observed colonisation-extinction dynamics were consistent with metapopulation theory. For instance, there was a positive relationship between colonisation rate and a connectivity measure that considered beetle abundance and distance for each high-cut stump in the surrounding area. However, the relationship disappeared when using a connectivity measure solely based on the distance of the high-cut stumps. The observed threshold implies that P. grossa benefits from aggregating the same total number of created high-cut stumps into fewer clear-cuts. This is because the total area with a density of high-cut stumps exceeding the threshold increases, and this expands the number and size of dispersal sources. Therefore, P. grossa and other species that reveal thresholds in their distribution patterns, are favoured when conservation measures are more spatially aggregated than what is resulting from current Swedish policy

Granbarkborren och dess fienders övervintring i stående träd vintern 2021/2022

Granbarkborren övervintrar antingen i barken i de träd de har utvecklats i, eller i förnan kring stambasen av träden. Tidigare studier visar att knappt hälften av barkborrarna övervintrar under bark i dödade träd i Småland, medan i norra Svealand och Norrland så är denna andel betydligt lägre. Den lägre andelen i norr är sannolikt en anpassning till de kallare vintrarna där barkborrarna riskerar att frysa ihjäl om de inte lämnar träden. Det har tidigare saknats data på andelen övervintrande granbarkborrar i bark för stora delar av Svealand.I denna studie togs barkprover från träd inom 10 områden från södra Götaland till mellersta Norrland. Som en indikator på hur kärvt vinterklimatet är användes odlingszon, enligt Riksförbundet Svensk Trädgård. Målet var att undersöka variationen mellan träd och områden i andelen granbarkborrar som övervintrar i barken samt vilka faktorer som kan förklara denna variation. Detta är viktigt att veta när man bedömer bekämpningseffekten av att avverka angripna träd under vintern. Dessutom undersöktes tätheten av granbarkborrar och deras fiender på olika höjder av trädet för att därmed kunna uppskatta hur barkprovtagning på standardhöjden 4 m avspeglar insektstätheter i hela trädet. På varje träd (n=134) togs ett barkprov på 4 m höjd. Ytterligare två barkprover togs på cirka vart tredje träd (n=48), på 37,5 procent och 62,5 procent av trädets totala höjd.I medeltal övervintrade 53 procent av granbarkborrarna i bark vid 4 m höjd. Andelen övervintrande granbarkborrar i bark avtog längs stammen från 4 m och uppåt och det uppskattade medelvärdet per träd var, 43 procent, det vill säga 10 procentenheter lägre än vad barkprovet vid 4 m visade. Det fanns tydliga skillnader för flera andra variabler mellan barkprover på olika höjd. Antal producerade granbarkborrar per m2, granbarkborrens förökningskvot samt tätheten av styltflugelarver sjönk med ökande höjd. Tätheten av parasitstekellarver och kokonger var högre längre upp på stammen än vid 4 m. Mer än 40 procent av variationen i andelen övervintrande granbarkborrar i bark vid 4 m kunde förklaras av fyra variabler. Den klart viktigaste variabeln var barktjocklek som ensam förklarade 23 procent av variationen. Ju tjockare bark desto högre andel övervintrande i bark. Träd med bruna kronor (indikation på tidigt angrepp) hade lägre andel övervintrande granbarkborrar än träd som fortfarande hade en del gröna barr (sena angrepp). Träd i kanter (nästan en hyggeskant) hade lägre andel övervintrande granbarkborrar i bark än träd inne i bestånd. Träd i odlingszon VI och VII (norra Värmland och Jämtland) hade lägre andel övervintrande granbarkborrar än träd i odlingszoner II-IV (Götaland och södra och mellersta Svealand). Det fanns inte några skillnader i andelen övervintrande granbarkborrar i bark mellan odlingszonerna II, III och IV där nuvarande utbrott av granbarkborre pågår

Naturhänsyn vid avverkning

En ny typ av naturvård har de senaste decennierna införts i svenskt skogsbruk. Vid alla skogsbruksåtgärder, och framförallt vid slutavverkning, måste hänsyn tas till den biologiska mångfalden. Det kan ske genom att medvetet välja ut och lämna enskilda träd och trädgrupper, att spara döda träd eller att skapa ny död ved med till exempel högstubbar. Hänsynen är angiven i skogsvårdslagen, men är också central inom ett certifierat skogsbruk, enligt såväl FSC som PEFC. Vad betyder naturhänsynen för de djur och växter som lever i skogen och kan man göra den ännu bättre? Vad säger egentligen forskningen? Inom forskningsprogrammet ”Smart Hänsyn” har vi försökt svara på dessa frågor genom att sammanfatta cirka 120 vetenskapligt granskade studier om naturhänsyn i norra Europa (Sverige, Norge, Finland och Baltikum). Vi har valt att begränsa oss till detta geografiska område eftersom länderna har likartade naturförhållanden och skogsbrukssätt. Urvalet är också begränsat till studier av naturhänsyn i det praktiska skogsbruket, och framför allt effekterna av hänsyn vid slutavverkning. En del stora, internationella översikter har också inkluderats. Baserat på studierna har vi gjort synteser över olika teman: kantzoner,hänsynsytor, högstubbar, död ved, asp, kostnadseffektivitet och internationella kunskapsöversikter. Syftet har varit att förmedla den stora kunskap som finns samlad inom forskningen till de som planerar och utför naturhänsyn i praktiken, till beslutsfattare på olika nivåer och till de som är allmänt intresserade av skog och miljö

Natural versus National boundaries

Applying biogeographical insights to the regulation of production forestry and the determination of forest reserve strategies is expected to increase the effectiveness of biodiversity conservation actions. Here, we assess the extent to which such applications take place. By using Sweden as a case study, we demonstrate fundamental differences among biogeographical regions in natural patterns and processes, past land-use, and anthropogenic impacts that need to be better incorporated into strategic conservation planning and decisions. Furthermore, assessment of specific forestry regulations and biogeographical variation in a number of other countries/provinces embracing boreal and temperate biomes also indicate that natural boundaries are insufficiently considered in forest management policies. We suggest that a substantial potential exists to better align conservation priorities with biogeographical characteristics. To illustrate the application of such an approach, we present a decision support model on how forest conservation policies that rest on natural boundaries and ecological processes can be developed

Research on retention forestry in Northern Europe

Retention approaches in forest management are today common in several North European countries, integrated into the clearcutting practice as a way to promote biodiversity and maintain ecosystem functions. Individual green trees and retention patches (tree groups) are retained at final harvest, and deadwood is left at site or created. Here, we review research on retention in Sweden, Finland, Norway, the Baltic States, and NW Russia, with special focus on biodiversity. Following the first publication in 1994, about 180 peer-reviewed articles have been published. We present results from a systematic search of the retention literature, separated into the following topics: buffer zones, retention patches, high stumps, other types of deadwood, European aspen Populus tremula, and cost-efficiency. Russian literature is synthesized separately since studies from this region have so far almost exclusively been published in the Russian language. Furthermore, we describe six ongoing large-scale, replicated experiments with varying retention levels, five in Finland and one in Sweden, and summarize their main results. Among main conclusions for practice from the literature and experiments are that retention patches as large as 0.5 ha and 10-m-wide buffers to watercourses are not enough to maintain pre-harvest species composition but survival of forest species is still larger than on conventional clearcuts. Deadwood on clearcuts may present important habitats to saproxylic species, including rare and red-listed ones and a prioritization of tree species per stand is recommended. We identify several important future research directions including switch of focus towards the landscape as well as the species population level. Surveys in parts of European Russia where retention has been unintentionally implemented already for a century would indicate possible future trajectories of biodiversity and their drivers in other regions of Northern Europe. A stronger link to ecological theory would help in study designs and in the formulation of predicted outcomes.202

Trilemma of Nordic–Baltic Forestry—How to Implement UN Sustainable Development Goals

Forests are the dominant land cover in Nordic–Baltic countries, and forestry, the management of forests for improved ecosystem-service (ES) delivery, is an important contributor to sustainability. Forests and forestry support multiple United Nations Sustainability Goals (UN SDGs) and a number of EU policies, and can address conflicting environmental goals. Forests provide multiple ecosystem services and natural solutions, including wood and fibre production, food, clear and clean water and air, animal and plant habitats, soil formation, aesthetics, and cultural and social services. Carbon sequestered by growing trees is a key factor in the envisaged transition from a fossil-based to a biobased economy. Here, we highlight the possibilities of forest-based solutions to mitigate current and emerging societal challenges. We discuss forestry effects on forest ecosystems,focusing on the optimisation of ES delivery and the fulfilment of UN SDGs while counteracting unwanted effects. In particular, we highlight the trilemma of (i) increasing wood production to substitute raw fossil materials, (ii) increasing forest carbon storage capacity, and (iii) improving forest biodiversity and other ES delivery