Siri Lie Olsen

Increasing Vascular Plant Richness on 13 High Mountain Summits in Southern Norway since the Early 1970s

Abstract We describe changes in vascular plant richness on 13 high mountain summits based on a historical study performed approximately 40 years ago. A summit is defined as the uppermost 30 m of the mountain tops. The altitudes of the summits range from 1512 to 1814 m. Data from neighboring climatologic stations showed higher mean values for July temperature (+0.7 °C) and January temperature (+1.5 °C), and mean annual precipitation had increased from 714 to 764.7 mm (7.1%) for the period from 1970 until 2009 compared with average data for the normal period (1961–1990). The total “top flora” had during this period increased by 19 taxa. On average, the increase in taxa richness was 18.9 ± 8.4 per summit, representing an average increase of 90.2%. Woody species had an average upward movement of 7.3 m during the study period. The ongoing upward shift of common, ubiquitous alpine species has resulted in a floristic homogenization of the mountain summits, and thus increasing α-diversity was accompanied by decreasing β-diversity. The use of recorded plants as temperature indicators showed that average summer temperatures had increased by approximately 1.3 °C during this period. Several of the newly established species indicate that the climate has become more humid. We assume that the recorded floristic changes are the result of ongoing climatic changes.

From facilitation to competition: temperature-driven shift in dominant plant interactions affects population dynamics in seminatural grasslands.

Biotic interactions are often ignored in assessments of climate change impacts. However, climate-related changes in species interactions, often mediated through increased dominance of certain species or functional groups, may have important implications for how species respond to climate warming and altered precipitation patterns. We examined how a dominant plant functional group affected the population dynamics of four co-occurring forb species by experimentally removing graminoids in seminatural grasslands. Specifically, we explored how the interaction between dominants and subordinates varied with climate by replicating the removal experiment across a climate grid consisting of 12 field sites spanning broad-scale temperature and precipitation gradients in southern Norway. Biotic interactions affected population growth rates of all study species, and the net outcome of interactions between dominants and subordinates switched from facilitation to competition with increasing temperature along the temperature gradient. The impacts of competitive interactions on subordinates in the warmer sites could primarily be attributed to reduced plant survival. Whereas the response to dominant removal varied with temperature, there was no overall effect of precipitation on the balance between competition and facilitation. Our findings suggest that global warming may increase the relative importance of competitive interactions in seminatural grasslands across a wide range of precipitation levels, thereby favouring highly competitive dominant species over subordinate species. As a result, seminatural grasslands may become increasingly dependent on disturbance (i.e. traditional management such as grazing and mowing) to maintain viable populations of subordinate species and thereby biodiversity under future climates. Our study highlights the importance of population-level studies replicated under different climatic conditions for understanding the underlying mechanisms of climate change impacts on plants.

Influence of Two N-Fixing Legumes on Plant Community Properties and Soil Nutrient Levels in an Alpine Ecosystem

Abstract Low nitrogen (N) supply is a limiting factor for plant growth in most terrestrial ecosystems. N-fixing legumes therefore have the potential to facilitate surrounding vegetation by increasing soil N levels. This effect should be especially pronounced in low-productivity habitats where ambient soil N levels are low, such as in alpine areas. We examined whether plant species composition, community diversity measures, and soil N levels differed with and without the presence of two alpine legumes, Oxytropis lapponica (Wahlenb.) Gay and Astragalus alpinus L., in a Dryas octopetala heath at Finse, Norway. Species composition and richness differed between plots with and without Oxytropis in one of two study sites, as other plant species were positively associated with the legume. None of the measured community properties differed between plots with and without the presence of Astragalus. The contrasting influence of the two legume species corresponds to our findings of higher soil N levels below Oxytropis, but not Astragalus. Differences in microhabitat N levels may explain why only Oxytropis acts as a facilitator. By affecting local species composition Oxytropis increases spatial heterogeneity, which may increase total species richness of the ecosystem.

Restoration of peatland by spontaneous revegetation after road construction

Questions Spontaneous re-vegetation from indigenous soil was used as a restoration method of peatlands degraded during road construction in northern Norway. We examined how plant community properties responded to the restoration, and which environmental factors affected the restoration success. Location Restored peatlands along roadsides at E10, the mainland connection to the Lofoten islands in Northern Norway. Methods The restored area originally consisted of poor to intermediate Sphagnum dominated natural peatlands. Restoration consisted of stripping and stockpiling of the topmost (30 cm) peat. The peat was stored for 1-2 years before redistribution with no further hydrological management. We conducted first time analyses of plant community properties 8 and 9 years after restoration. We recorded vegetation and environmental variables in 108 plots distributed between 18 transects running from the road edge over the restored area to the undisturbed peatland. Undisturbed peatland was used as target for successful restoration. We used canonical correspondence analysis (CCA) and ANOVA to test the effect of restoration on species composition and richness. Results The ordination showed that species composition still differed significantly between restored and undisturbed plots, indicating incomplete restoration after 8 and 9 years. Soil moisture, pH, slope and microtopography were the most important environmental factors for species composition. Polytrichum mosses had a high percentage cover in restored (30%) compared to undisturbed control plots (1%). Linear regression showed that peatland species decreased in abundance with increasing depth of Polytrichum cushions. Conclusion The low soil moisture level in the restored areas is most likely limiting the establishment of Sphagnum mosses, considered as key species of the typical peatland environment. Thus, the restoration method studied here must be improved to increase the soil moisture by rising the water table or reduce drainage. This should be done by reducing storage time of the peat before redistribution, and minimizing slopes and heterogeneity of the microtopography of the restored area. This article is protected by copyright. All rights reserved.