Patterns of terricolous and field layer invertebrates along a boreal mire-forest gradient

In a study area ca. 5 km N of Umeå, Sweden, we tested the relationship between abundance and biomass of terricolous and field layer invertebrate taxa along a light gradient (consisting of four different forest habitats of boreal coniferous forests, each represented by one stand). In 1984, five sampling locations, each having 6 pitfall traps and 3 sweep-net samples, were randomly allocated in each stand. In total, 4879 terricolous invertebrates with a biomass of 63 490 mg and 1894 field-layer invertebrates with a biomass of 17 143 mg were caught. Mean values for each sampling location were used to analyse the pattern of invertebrate groups along the gradient using Spearman rank correlation (n = 20). There was a decrease in both abundance and biomass from shaded to sunny forests of Diptera (both terricolous and field layer), Hymenoptera (terricolous), Collembola (field layer) and Lepidoptera larvae (field layer), and for the abundance of terricolous Coleoptera and field layer Hymenoptera. An increase in both abundance and biomass from shaded to sunny forests was found for terricolous Collembola, Homoptera and Acari, and the abundance of terricolous Formicidae and Coleoptera larvae, and the biomass of field layer Hymenoptera larvae and total invertebrates. Diptera, Coleoptera and, especially, Lepidoptera larvae have earlier been shown to be important prey for several bird species breeding in the boreal forest and the high number and biomass of these taxa in the shaded forest habitats may indicate that preserving buffer zones and fragments of wet, shaded forest, currently done in forest management at final felling, is a good strategy

Comparison of invertebrate abundance and biomass between a clear-cut stand and four stands under tree cover in Swedish boreal coniferous forests

This study assesses differences between a seven-year old clear-cut and four forest habitats as regards abundance and biomass of different invertebrate taxa - important for habitat quality for insectivorous birds. Forest types studied were pine bog, spruce mire, mesic spruce and pine heath forest. Data were collected in the second half of June 1984 (to coincide with the peak feeding demands of many nestling birds). Results indicate that the clear-cut differed more from the tree covered habitats with respect to the field layer fauna than with respect to the terricolous fauna. Compared to the forest habitats, the clear -cut was characterized by a higher abundance and biomass of sap-suckers (Hemiptera: Homoptera and Heteroptera) but a lower abundance and biomass of leaf-eating herbivorous larvae (Hymenoptera: Symphyta and Lepidoptera) in the field layer. The difference with respect to leaf-eating larvae was probably caused by low abundance of larvae food plants in the clear-cut. This may be an important ecological difference because these larvae can be an important food source for insectivorous birds

Effects of clear-cutting and selective felling in Swedish Boreal coniferous forest: response of invertebrate taxa eaten by birds

Our aim was to analyse the short-term effects (0-4 years) of selective felling and clear-cutting on the food resources of insectivorous birds. Literature data on bird diets showed that herbivorous larvae (Lepidoptera and Hymenoptera: Symphyta) and spiders (Araneae) were used by 81 and 50%, respectively, of 16 bird species breeding in the Swedish boreal coniferous forest. A field study comparing selective fellings, clear-cuttings and uncut controls showed considerable effects of clear-cutting on both terricolous and field layer invertebrates. Clear-cuttings had significantly lower abundance and biomass, and a different composition of herbivorous larvae and spiders, as well as a lower total biomass of invertebrates in the field layer than controls. Drastic changes of abiotic factors (like increased temperature range) following clear-cutting may directly affect the occurrence of invertebrates. However, indirect effects (like increased sun exposure, affecting food plant quality for herbivorous larvae) are probably also responsible. Selective fellings did not differ from controls in the occurrence of herbivorous larvae and spiders. Therefore, over the four-year term of our study, selective felling seems to provide birds with conditions similar to uncut forest for invertebrates used by birds

Forestry effects on a boreal ground beetle community in spring: Selective logging and clear-cutting compared

To compare the effects of two tree harvesting methods (clear-cutting and single tree selection felling), spring-occurring ground beetles (Carabidae) were studied by pitfall trapping in northern Sweden. Species abundance, total abundance and Hill's diversity indices were used to compare the ground beetle community in clear-cuts to selectively-logged and to uncut control forests. In addition, to highlight the importance of site replication when evaluating a spatially-variable ecosystem like the boreal forest, we consider how our conclusions might have differed with and without site replication. Results from the two analyses differed considerably, highlighting the importance of site replication in studies offorestry effects in order to increase confidence in the conclusions. Overall, no significant harvest effects were found on the ground beetle community except for a significantly higher abundance of the open habitat species P. assimilis in clear-cuts than in uncut control forests. Our results thus do not support suggestions of an increase in diversity following clear-cutting, but are consistent with previous findings regarding increased abundances of open habitat species and no changes in abundance of forest generalists in clear-cuts. In general, the carabid community in the selection loggings resembled that in the uncut control forest, indicating a low effect of this harvesting method. Based on our analysis, we suggest that future studies of forestry impacts on invertebrates attempt to increase the number of sites evaluated rather than increase the number of samples from a given area

Changes in species richness and composition of boreal waterbird communities : a comparison between two time periods 25 years apart

Global measures of biodiversity indicate consistent decline, but trends reported for local communities are more varied. Therefore, we need better understanding of mechanisms that drive changes in diversity of local communities and of differences in temporal trends between components of local diversity, such as species richness and species turnover rate. Freshwater ecosystems are vulnerable to multiple stressors, and severe impacts on their biodiversity have been documented. We studied species richness and composition of local boreal waterbird communities in 1990/1991 and 2016 at 58 lakes distributed over six regions in Finland and Sweden. The study lakes represented not only local trophic gradients but also a latitudinal gradient in the boreal biome. While species richness tended to be lower in 2016 than in 1990/1991, species turnover was relatively high. Within foraging guilds, local species richness of diving ducks and surface feeding waterbirds decreased, whereas that of large herbivores increased. The number of species gained in local communities was higher in lakes with rich vegetation than in lakes with sparse vegetation. Conservation of boreal freshwater ecosystems would benefit from recognizing that large-scale environmental changes can affect local diversity via processes operating at finer scales.Peer reviewe