Otso Suominen

Effects of mammalian herbivores on revegetation of disturbed areas in the forest-tundra ecotone in northern Fennoscandia

Herbivores influence the structure of plant communities in arctic-alpine ecosystems. However, little is known of the effect of herbivores on plant colonisation following disturbance, and on its variability depending on the identity of herbivores and the characteristics of the habitats. To quantify the role of large and small vertebrate herbivores, we established exclosures of two different mesh sizes around disturbed subplots in forest and nearby tundra habitats in four contrasting locations in the forest-tundra ecotone in northernmost Sweden and Norway. The study revealed that herbivores influenced the abundance but not the species composition of regenerating vegetation. Gaps were colonised by the dominant species in the surrounding vegetation. The only exception to this expectation was Empetrum nigrum, which failed to colonise gaps even though it dominated undisturbed vegetation. Significant effects of herbivory were only detected when both small and large herbivores were excluded. Herbivores decreased the abundance of three of the most common species Vaccinium myrtillus, Vaccinium vitis idaea, and Deschampsia flexuosa. The effect of herbivory on the abundance of these three species did not differ between habitats and locations. However, the composition of the regenerating vegetation differed between habitats and locations. The disturbance treatment increased the species richness on the scale of plots, habitats, and sites. However, on the scale of whole locations, all species found in disturbed areas were also found in undisturbed areas, suggesting that the natural disturbance regime in arctic landscapes is high enough to sustain colonising species.

Effects of pollution on land snail abundance, size and diversity as resources for pied flycatcher, Ficedula hypoleuca.

Passerine birds need extra calcium during their breeding for developing egg shells and proper growth of nestling skeleton. Land snails are an important calcium source for many passerines and human-induced changes in snail populations may pose a severe problem for breeding birds. We studied from the birds viewpoint how air pollution affects the shell mass, abundance and diversity of land snail communities along a pollution gradient of a copper smelter. We sampled remnant snail shells from the nests of an insectivorous passerine, the pied flycatcher, Ficedula hypoleuca, to find out how the availability of land snails varies along the pollution gradient. The total snail shell mass increased towards the pollution source but declined abruptly in the vicinity of the smelter. This spatial variation in shell mass was evident also within a single snail species and could not be wholly explained by spatially varying snail numbers or species composition. Instead, the total shell mass was related to their shell size, individuals being largest at the moderately polluted areas. Smaller shell size suggests inferior growth of snails in the most heavily polluted area. Our study shows that pollution affects the diversity, abundance (available shell mass) and individual quality of land snails, posing reproductive problems for birds that rely on snails as calcium sources during breeding. There are probably both direct pollution-related (heavy metal and calcium levels) and indirect (habitat change) effects behind the observed changes in snail populations.

Simulated Moose (Alces alces L.) Browsing Increases Accumulation of Secondary Metabolites in Bilberry (Vaccinium myrtillus L.) Along Gradients of Habitat Productivity and Solar Radiation

We have addressed the impact of moose (Alces alces L.) on accumulation of secondary metabolites, lignin, and nitrogen in bilberry (Vaccinium myrtillus L.) along gradients of habitat productivity and solar radiation. The study was conducted within a long-term research project on direct and indirect impacts of moose on the ecosystem. In the experiment, browsing, defecation, and urination corresponding to four different moose densities were simulated for eight years before bilberry tissue was collected and analyzed. Some quantitatively dominant flavonoids were affected by the simulated moose browsing and by habitat productivity and light. The content of flavonoids increased with increasing moose density and light, and decreased with increasing habitat productivity. The higher concentration of secondary metabolites in bilberry from nutrient-poor sites may have resulted from the increased photosynthesis relative to growth, which facilitated secondary metabolism. The higher concentration of secondary metabolites in plants subjected to simulated moose- herbivory might have been caused in part by loss of biomass. In addition, in areas with high biomass loss, i.e., high moose density, a more open canopy was created and more solar radiation could have induced secondary metabolism.

Role of climate and herbivory on native and alien conifer seedling recruitment at and above the Fennoscandian tree line

Questions: We investigated the importance of climate and herbivory on native and alien conifer colonization of the birch-dominated Fennoscandian tree line by addressing the following questions: (a) ...

Publisher Correction to: Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome

The above mentioned article was originally scheduled for publication in the special issue on Ecology of Tundra Arthropods with guest editors Toke T. Høye . Lauren E. Culler. Erroneously, the article was published in Polar Biology, Volume 40, Issue 11, November, 2017. The publisher sincerely apologizes to the guest editors and the authors for the inconvenience caused.