Jan Weslien

Substrate requirements of red-listed saproxylic invertebrates in Sweden

To evaluate which qualities of dead wood have the highest conservational value for invertebrates, substrate requirements were recorded for all 542 saproxylic (wood-living) red-listed invertebrates in Sweden. Preferred qualities of dead trees were described for each species in seven category variables: tree species, stage of decay, type of main stem, coarseness of stem, part of tree, light preference and microhabitat. For each quality we quantified the number of red-listed insect species using it and the number that are specific to the quality. The number of species associated with different tree genera ranged from five to 202. Species-rich genera had a higher proportion of monophagous species. To what extent different tree genera have faunas complementary to each other was also analysed. As the wood decays, the host range broadens and the flora of decay fungi will probably take over as the most important factor determining the saproxylic fauna. Because there are many different types of rot required by different invertebrates, an abundance of similar looking dead trees, logs and snags are probably needed. Some 59% of the invertebrate species can live in sun-exposed sites. Most of these are favoured when the forest burns and at least 29 of them are more strongly associated with fires. For the former category, leaving dead wood on clear cuts should be an effective way to increase the amount of breeding substrate. However, some species, especially those living in the last successional stages, are dependent on shaded sites. Hollow tree trunks are another important microhabitat; 64 of the 107 species living there are specialists. To maintain all saproxylic species we need a diversity of substrate types and management methods. Our data can help to decide how to optimize the conservation measures taken during forest operations.

Felled or standing retained wood—it makes a difference for saproxylic beetles

High stumps are often retained at clear cuttings to increase the abundance of habitat patches for saproxylic (wood living) insects. However, these high stumps constitutes a very uniform dead wood habitat which probably supports only a part of the saproxylic fauna. Therefore, we compared the saproxylic fauna of high spruce stumps with the fauna of long and short felled boles of spruce. We also investigated the associations between insect species and polypore fungi growing in the wood. All wood units were created at the same occasion on a clear cut in SW Sweden. The dominating species of bark beetles and longhorn beetles were surveyed in the first year after the cutting. Four years later, the fauna was sampled again by sifting bark samples and all species found were determined. In total we recorded six species early in the succession and 43 four years later. Two species were red-listed. Three out of five statistically tested early successional species had significant associations with some of the wood types, while the corresponding figures later in the succession were six of 15. Three of the 15 species in the late succession were also significantly associated with the presence of fruiting bodies of the polypore fungus Fomitopsis pinicola. We concluded that retaining felled wood in addition to high stumps may provide an important means of diversifying the dead wood substrates, which may in turn increase the number of saproxylic species on a site.

Saproxylic beetles in high stumps of spruce: Fungal flora important for determining the species composition

In most Swedish felling operations high stumps are created from living trees to increase the amounts of dead wood in the forest. The fauna of saproxylic beetles and aradid bugs (Heteroptera) in spruce (Picea abies) high stumps were studied to determine which characteristics (diameter, height, amount of bark and fungal flora) had the strongest influence on the species composition. The practical aim was to see whether it is possible to increase the biodiversity values by management recommendations. The high stumps (n=59) were situated in the middle boreal zone in Sweden and were 6 years old. The insects were sampled by sieving 0.25 m2 bark on each stump In total, 803 saproxylic beetles and Aradus bugs were found, representing 42 different species, five of which were red-listed. The most important factor for determining the beetle community was the presence or absence of two polyporous fungi, Fomitopsis pinicola and Trichaptum abietinum. Other factors were much less important, indicating that it is difficult to influence the stumps’ biodiversity values significantly simply by selecting trees of certain diameters or optimizing cutting heights.

Long-term priority effects among insects and fungi colonizing decaying wood

1. Priority effects have been hypothesized to have long-lasting impact on community structure in natural ecosystems. Long-term studies of priority effects in natural ecosystems are however sparse, especially in terrestrial ecosystems. 2. Wood decay is a slow process involving a high diversity of insect and fungus species. Species interactions that drive change in communities of insects and fungi during wood decay are poorly understood because of a lack of sufficient long-term studies. 3. In this paper, we followed the colonization and succession of wood-living insects and fungi on cut trees during 15 years, from tree death and onwards, in a boreal forest landscape. We test the long-term priority effects hypothesis that the identity and abundance of species that colonize first affect the colonization success of later-arriving species. We also hypothesize that species interact in both facilitative and inhibitory ways, which ultimately affect habitat quality for a red-listed late-succession beetle species. 4. Possible causal associations between species were explored by path analysis. The results indicate that one bark beetle species, Hylurgops palliatus, and one wood-borer species, Monochamus sutor, which colonized the wood during the first year after cutting, influenced the occurrence of a rare, wood-living beetle, Peltis grossa, that started to emerge from the stumps about 10 years later. The positive effects of Hylurgops palliatus and negative effects of M. sutor were largely mediated through the wood-decaying fungus species Fomitopsis pinicola. 5. The study shows that variable priority effects may have long-lasting impact on community assembly in decaying wood. The study also exemplifies new possibilities for managing populations of threatened species by exploring links between early, well-understood species guilds and late, more poorly understood species guilds.

Estimating risks for spruce bark beetle (Ips typographus (L.)) damage using pheromone‐baited traps and trees

The risk for damage associated with spruce bark beetle attacks on living trees was estimated in 12 forest districts in the Nordic countries during three years. Pheromone‐baited traps and trees were used. Five groups of three traps were deployed annually on fresh spruce clear‐fellings in each district. The mean catches within districts and years ranged from 950 to 46000 beetles per trap group. The standard error averaged 15 % of the mean catch. One tree was baited annually at each of five other sites in each district. The mean number of trees colonized by Ips typographus in each district and year ranged from 0 to 5 per site. The standard error was high, averaging 44% of the mean. Inventories of tree mortality within the districts yielded values ranging from 0 to 150 killed trees per km of spruce forest edge. There was a strong linear correlation between mean catches in traps and log‐transformed tree mortality (r=0.82). The correlation between colonization success at tree‐baiting sites and tree mortality wa...

Influence of Stem Diameter on the Survival and Growth of Containerized Norway Spruce Seedlings Attacked by Pine Weevils (Hylobius spp.)

Pine weevils (Hylobius spp.) feeding on stem bark of young conifer seedlings pose a serious threat to forest regeneration-planting programmes in Nordic countries. This study was designed to determine the threshold diameter for planted, untreated containerized seedlings, above which pine weevils cause little or no damage. The effects of sublethal weevil damage on seedling growth were also assessed. In total, 5320 containerized spruce seedlings were planted on scarified and unscarified plots on three sites in southern Sweden. Seedlings in six size classes, which differed with regard to age (1.5-3.5 yrs) and cultivation density (28-446 seedlings m 2) were grown using the Combicell system. None of the seedlings was treated with insecticides, except for those in the smallest class, where both untreated and treated seedlings were used. Inspections were made periodically during the first 3 yrs and after both 5 and 7 yrs. A statistically significant relationship was found between seedling losses due to pine weevil attack and seedling stem-base diameter at the time of planting out, on both scarified and unscarified plots. For seedlings with a stem-base diameter of around 10 mm, mortality due to pine weevil attack on scarified plots was low enough to be considered negligible. This threshold diameter was several millimetres greater for seedlings planted on unscarified plots. An analysis of the relationship between the extent of weevil damage and seedling growth rate showed that among surviving seedlings, those that grew fast tended to show low levels of damage. On unscarified plots, the mortality rate amongst seedlings treated once with a permethrin insecticide was only one-third that of untreated seedlings. On scarified plots, the corresponding difference was somewhat smaller. Repeated insecticide treatment resulted in a pronounced reduction in seedling mortality on the unscarified plots, whereas the effect was weaker on scarified plots.

Interactions within and between species at different densities of the bark beetle Ips typographus and its predator Thanasimus formicarius

Interactions between the bark beetle Ips typographus and one of its predators, Thanasimus formicarius, were investigated in caged spruce logs containing both species in eight different density combinations. Productively (offspring per female) of Ips was adversely affected by high Ips gallery density as well as high Thanasimus density. Thanasimus productivity was enhanced by high Ips gallery density but negatively affected by high Thanasimus density. Ips productivity and Thanasimus developmental rate differed between tree individuals, probably owing to tree-related differences in phloem thickness. Relative predator-caused Ips mortality was ca 20% higher at high gallery density (ca 300 egg galeries per m 2 ) than at low gallery density (ca 100 egg galleries per m 2 ), indicating that mortality was density dependent

Attacks by bark- and wood-boring Coleoptera on mechanically created high stumps of Norway spruce in the two years following cutting

Abstract Attacks of bark- and wood-boring beetles on mechanically created high stumps of Norway spruce, Picea abies L. (Karst.), were studied in the provinces of Dalarna (Grangarde area) and Uppland (Fageron) in central Sweden. The experiment included a total of 362 stumps in the Grangarde area as well as 48 stumps and 18 logs at Fageron. Most inspections were conducted in the first and second autumns following the cuttings made to create the stumps. All stumps were attacked by at least one species during the two-year period, and for almost all of them (95%) the initial attacks occurred in the first summer. The most frequently encountered species on the stumps were the scolytids Ips typographus (L.), Pityogenes chalcographus (L.), Hylurgops palliatus (Gyll.), Orthotomicus spp., Trypodendron lineatum (Oliv.), Dryocoetes sp. and Polygraphus poligraphus (L.), and the cerambycids Tetropium spp. and Monochamus sutor (L.). Both the time of cutting and stump diameter influenced beetle colonisation. I. typographus was not found in autumn-cut stumps, while Orthotomicus spp. was found more frequently in autumn-cut stumps than in spring-cut stumps. There was a positive relationship between I. typographus occupancy and stump diameter, while negative relationships were found between stump diameter and H. palliatus and T. lineatum occupancy. Most stumps (ca. 80%) were attacked by more than one bark- and wood-boring species in the first summer. The proportion of stumps attacked was significantly higher than the proportion of logs attacked for P. poligraphus, T. lineatum and Tetropium spp., whereas the opposite was true for I. typographus. The percentage of bark area utilised by I. typographus was significantly higher in logs than in stumps.

Tree killing by Ips typographus (Coleoptera: Scolytidae) at stand edges with and without colonized felled spruce trees

Abstract 1 To maintain biodiversity in managed spruce forests in Sweden more wind‐felled trees must be retained. However, there is concern among forest owners that this may result in higher tree mortality caused by the spruce bark beetle, Ips typographus (L.) (Col. Scolytidae).

Conservation goals and the relative importance of costs and benefits in reserve selection.

Including both economic costs and biological benefits of sites in systematic reserve selection greatly increases cost-efficiency. Nevertheless, limited funding generally forces conservation planners to choose which data to focus the most resources on; therefore, the relative importance of different types of data must be carefully assessed. We investigated the relative importance of including information about costs and benefits for 3 different commonly used conservation goals: 2 in which biological benefits were measured per site (species number and conservation value scores) and 1 in which benefits were measured on the basis of site complementarity (total species number in the reserve network). For each goal, we used site-selection models with data on benefits only, costs only, and benefits and costs together, and we compared the efficiency of each model. Costs were more important to include than benefits for the goals in which benefits were measured per site. By contrast, for the complementarity-based goal, benefits were more important to include. To understand this pattern, we compared the variability in benefits and in costs for each goal. By comparing the best and the worst possible selection of sites with regard to costs alone and benefits alone for each conservation goal, we introduced a simple and consistent variability measure that is applicable to all kinds of reserve-selection situations. In our study, benefit variability depended strongly on how the conservation goal was formulated and was largest for the complementarity-based conservation goal. We argue that from a cost-efficiency point of view, most resources should be spent on collecting the most variable type of data for the conservation goal at hand.