Christian Pedersen

Research Scientist

(+47) 974 34 123
christian.pedersen@nibio.no

Place
Ås O43

Visiting address
Oluf Thesens vei 43, 1433 Ås

Biography

I hold a Ph.D. in ecology and I am generally interested in the factors that shape population and community dynamics. I have worked for many years in arctic and alpine areas where my focus has been herbivore-plant interactions in relation to climate change. Currently my work focus on how land use and land use change in the agricultural landscape affect biodiversity, population dynamics and community composition using birds and plants as indicators. Main responsibilities include management of and reporting from the Norwegian monitoring program for agricultural landscapes, with particular focus on the development and use of indicators of biodiversity.

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Abstract

Biodiversity is declining globally in response to multiple human stressors, including climate forcing. Nonetheless, local diversity trends are inconsistent in some taxa, obscuring contributions of local processes to global patterns. Arctic tundra diversity, including plants, fungi, and lichens, declined during a 15-year experiment that combined warming with exclusion of large herbivores known to influence tundra vegetation composition. Tundra diversity declined regardless of experimental treatment, as background growing season temperatures rose with sea ice loss. However, diversity declined slower with large herbivores than without them. This difference was associated with an increase in effective diversity of large herbivores as formerly abundant caribou declined and muskoxen increased. Efforts that promote herbivore diversity, such as rewilding, may help mitigate impacts of warming on tundra diversity.

Abstract

Aim Grasslands of varying land-use intensity and history were studied to describe and test species richness and compositional patterns and their relationships with the physical environment, land cover of the surrounding landscape, patch geometry, and grazing. Location The mainland of Norway. Methods We utilized data from the Norwegian Monitoring Programme for Agricultural Landscapes, which recorded vascular plants from 569 plots, placed within 97 monitoring squares systematically distributed throughout agricultural land on the Norwegian mainland. We identified four grassland types: (i) moderately fertilized, moist meadows; (ii) overgrown agricultural land; (iii) cultivated pastures and disturbed ground; and (iv) natural/unfertilized and outfield pastures. Results Soil moisture and grazing measures were found to be important in explaining species compositional variation in all grassland types. Richness patterns were best explained by complex and differing combinations of environmental indicators. Nevertheless, negative (nitrogen and light level) or unimodal (pH) responses were similar across grassland types. Vegetation plots adjacent to areas historically and/or currently dominated by mires, forests, or pastures, as well as abandoned and overgrown grasslands, had a slightly higher species richness. Larger grasslands surrounding the vegetation plots had slightly less species than smaller grasslands. Conclusions This study demonstrates that data from a national monitoring programme on agricultural grasslands can be used for plant ecological research. The results indicate that climate-change-related shifts along moisture and nutrient gradients (increases) may alter both species composition and species richness in the studied grasslands. It is likely that large and contiguous managed (grass)land might affect areas perceived as remnants, probably caused by the transformation to homogeneous (agri)cultural landscapes reducing edge zones, which in turn may threaten the species pool and richness. The importance of land use and land-cover composition should be considered when planning management actions in extensively used high-latitude grasslands.

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Abstract

Ecological rarity, characterized by low abundance or limited distribution, is typical of most species, yet our understanding of what factors contribute to the persistence of rare species remains limited. Consequently, little is also known about whether rare species might respond differently than common species to direct (e.g., abiotic) and indirect (e.g., biotic) effects of climate change. We investigated the effects of warming and exclusion of large herbivores on 14 tundra taxa, three of which were common and 11 of which were rare, at an inland, low-arctic study site near Kangerlussuaq, Greenland. Across all taxa, pooled commonness was reduced by experimental warming, and more strongly under herbivore exclusion than under herbivory. However, taxon-specific analyses revealed that although warming elicited variable effects on commonness, herbivore exclusion disproportionately reduced the commonness of rare taxa. Over the 15-year duration of the experiment, we also observed trends in commonness and rarity under all treatments through time. Sitewide commonness increased for two common taxa, the deciduous shrubs Betula nana and Salix glauca, and declined in six other taxa, all of which were rare. Rates of increase or decline in commonness (i.e., temporal trends over the duration of the experiment) were strongly related to baseline commonness of taxa early in the experiment under all treatments except warming with grazing. Hence, commonness itself may be a strong predictor of species’ responses to climate change in the arctic tundra biome, but large herbivores may mediate such responses in rare taxa, perhaps facilitating their persistence.

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Abstract

Aims Understanding fine-grain diversity patterns across large spatial extents is fundamental for macroecological research and biodiversity conservation. Using the GrassPlot database, we provide benchmarks of fine-grain richness values of Palaearctic open habitats for vascular plants, bryophytes, lichens and complete vegetation (i.e., the sum of the former three groups). Location Palaearctic biogeographic realm. Methods We used 126,524 plots of eight standard grain sizes from the GrassPlot database: 0.0001, 0.001, 0.01, 0.1, 1, 10, 100 and 1,000 m2 and calculated the mean richness and standard deviations, as well as maximum, minimum, median, and first and third quartiles for each combination of grain size, taxonomic group, biome, region, vegetation type and phytosociological class. Results Patterns of plant diversity in vegetation types and biomes differ across grain sizes and taxonomic groups. Overall, secondary (mostly semi-natural) grasslands and natural grasslands are the richest vegetation type. The open-access file ”GrassPlot Diversity Benchmarks” and the web tool “GrassPlot Diversity Explorer” are now available online (https://edgg.org/databases/GrasslandDiversityExplorer) and provide more insights into species richness patterns in the Palaearctic open habitats. Conclusions The GrassPlot Diversity Benchmarks provide high-quality data on species richness in open habitat types across the Palaearctic. These benchmark data can be used in vegetation ecology, macroecology, biodiversity conservation and data quality checking. While the amount of data in the underlying GrassPlot database and their spatial coverage are smaller than in other extensive vegetation-plot databases, species recordings in GrassPlot are on average more complete, making it a valuable complementary data source in macroecology.

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A major challenge in predicting species’ distributional responses to climate change involves resolving interactions between abiotic and biotic factors in structuring ecological communities. This challenge reflects the classical conceptualization of species’ regional distributions as simultaneously constrained by climatic conditions, while by necessity emerging from local biotic interactions. A ubiquitous pattern in nature illustrates this dichotomy: potentially competing species covary positively at large scales but negatively at local scales. Recent theory poses a resolution to this conundrum by predicting roles of both abiotic and biotic factors in covariation of species at both scales, but empirical tests have lagged such developments. We conducted a 15-y warming and herbivore-exclusion experiment to investigate drivers of opposing patterns of covariation between two codominant arctic shrub species at large and local scales. Climatic conditions and biotic exploitation mediated both positive covariation between these species at the landscape scale and negative covariation between them locally. Furthermore, covariation between the two species conferred resilience in ecosystem carbon uptake. This study thus lends empirical support to developing theoretical solutions to a long-standing ecological puzzle, while highlighting its relevance to understanding community compositional responses to climate change.

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This report describes the development of a novel model & digital map system for visualising diverse ecosystem services at national scale in Norway. Denne rapporten beskriver utviklingen av en ny metode og en digital kartløsning for å visualisere ulike økosystemtjenester på nasjonal skala i Norge.

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Abstract: GrassPlot is a collaborative vegetation-plot database organised by the Eurasian Dry Grassland Group (EDGG) and listed in the Global Index of Vegetation-Plot Databases (GIVD ID EU-00-003). Following a previous Long Database Report (Dengler et al. 2018, Phyto-coenologia 48, 331–347), we provide here the first update on content and functionality of GrassPlot. The current version (GrassPlot v. 2.00) contains a total of 190,673 plots of different grain sizes across 28,171 independent plots, with 4,654 nested-plot series including at least four grain sizes. The database has improved its content as well as its functionality, including addition and harmonization of header data (land use, information on nestedness, structure and ecology) and preparation of species composition data. Currently, GrassPlot data are intensively used for broad-scale analyses of different aspects of alpha and beta diversity in grassland ecosystems.

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Aim Species–area relationships (SARs) are fundamental scaling laws in ecology although their shape is still disputed. At larger areas, power laws best represent SARs. Yet, it remains unclear whether SARs follow other shapes at finer spatial grains in continuous vegetation. We asked which function describes SARs best at small grains and explored how sampling methodology or the environment influence SAR shape. Location Palaearctic grasslands and other non‐forested habitats. Taxa Vascular plants, bryophytes and lichens. Methods We used the GrassPlot database, containing standardized vegetation‐plot data from vascular plants, bryophytes and lichens spanning a wide range of grassland types throughout the Palaearctic and including 2,057 nested‐plot series with at least seven grain sizes ranging from 1 cm2 to 1,024 m2. Using nonlinear regression, we assessed the appropriateness of different SAR functions (power, power quadratic, power breakpoint, logarithmic, Michaelis–Menten). Based on AICc, we tested whether the ranking of functions differed among taxonomic groups, methodological settings, biomes or vegetation types. Results The power function was the most suitable function across the studied taxonomic groups. The superiority of this function increased from lichens to bryophytes to vascular plants to all three taxonomic groups together. The sampling method was highly influential as rooted presence sampling decreased the performance of the power function. By contrast, biome and vegetation type had practically no influence on the superiority of the power law. Main conclusions We conclude that SARs of sessile organisms at smaller spatial grains are best approximated by a power function. This coincides with several other comprehensive studies of SARs at different grain sizes and for different taxa, thus supporting the general appropriateness of the power function for modelling species diversity over a wide range of grain sizes. The poor performance of the Michaelis–Menten function demonstrates that richness within plant communities generally does not approach any saturation, thus calling into question the concept of minimal area.

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We report an observation of a flightless fledgling Lapland longspur (Calcarius lapponicus (Linnaeus, 1758)) at a long-term study site near Kangerlussuaq, Greenland, in late July 2018. Based on our observations of longspur nests at the site dating back to 1993, we estimate that the fledgling observed in 2018 may have originated from a nest initiated 12–37 d later than nesting in previous years. Onset of spring in 2018 was late, but comparable with other years in which longspur nests were observed a full calendar month earlier than in 2018. An analysis including multiple candidate predictor variables revealed a strong negative association between estimated longspur nest initiation dates and mean May temperature, as well as a weaker association with the length of the annual period of vegetation green up at the site. Given the limitations of our data, however, we are unable to assign causality to the 2018 observation, and cannot rule out other possibilities, such as that it may have resulted from a second clutch.

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The decline in farmland birds observed throughout Europe during recent decades has attracted much attention. Agricultural intensification or land abandonment are commonly forwarded as key drivers. Several countries have established agri-environmental schemes (AES) to counter these negative trends among farmland birds. This paper reports a study of the relationship between land use and bird species in the agricultural landscape of Norway. The main objective was to investigate the effect of spatial heterogeneity and diversity of land use on total richness and abundance of farmland birds at a national level. Monitoring the distribution and abundance of birds is part of the Norwegian monitoring programme for agricultural landscapes. The monitoring programme is based on mapping of 1 × 1 km squares distributed across the entire agricultural landscape. Within these squares permanent observation points are established for bird monitoring. Detailed interpretation of aerial photographs provides the land classification. We tested the relationship between landscape metrics at different levels of land type detail and species richness and abundance of farmland and non-farmland birds. There was a positive relationship between species richness and abundance of farmland birds and agricultural area. For non-farmland birds the relationship was negative. Spatial heterogeneity of land use was a significant positive factor for both farmland and non-farmland species. High land type diversity was positive for farmland bird richness, but negative for abundance. Non-farmland bird richness was not affected by land type diversity, but abundance had a negative response. The results presented in this paper highlight the importance of a spatial heterogeneous landscape. However, we also found that land type diversity could negatively affect the abundance of both farmland and non-farmland birds. Our findings suggest a need for different management approaches depending on whether the aim is increased species richness or abundance. Achieving both aims with the same means might be difficult. We thus suggest a need for land use analyses before proper management strategies can be implemented.

Abstract

Background & Aim: Land-use regimes and their changes, as well as landscape heterogeneity are key determinants of the distribution and composition of species in cultural landscapes. In European agricultural landscapes, habitat loss due to both abandonment and intensification of agriculture fields are major causes for the decline of species diversity. Landscapes that are diverse in habitats and species are important to maintain basic ecosystem functions and services as, for instance, pollination or habitat preservation. In Norway, semi-natural species-rich habitats, such as agricultural grasslands, often occur in mosaics with forests and crop fields. This research studies key information for design of conservation plans focused on these habitats, addressing how landscape structure and land-use history affect the distribution, richness and composition of species in species-rich grasslands across geographical regions. Material & Methods: We recorded vegetation (species occurrence and cover) in agricultural grasslands with varying intensity and type of use from 569 plots of 8 x 8 m size systematically distributed throughout Norway (from 64 to 78 °N latitude). To identify the most important driving factors of species diversity and composition we explored the combined effects of historic and current land-use and the spatial landscape configuration of nearby land cover types (e.g. minimum distance to or area of neighbouring wetland, forest, cultivated land) taking into account the effects of grazing, elevation, and moisture conditions. Non-metrical multidimensional scaling (NMDS) was applied to identify the most important drivers of species composition. We used Generalized Additive Mixed Models to test the relationship of these drivers with patterns in species richness. Main results & Interpretations: NMDS revealed species composition to be explained most by the distance to surface cultivated land and transportation corridors (r=0.905, p<0.001 and r=-0.982, p<0.001; 1. NMDS axis) as well as shape of the patch in which the vegetation plot is embedded (patch shape) and grazing intensity (r=0.988, p<0.001 and r=-0.952, p<0.001; 2. NMDS axis). Observed patterns in species richness were statistically significantly linked to the combined effects of elevation, grazing intensity, historical land-use, patch shape, distance to transportation corridors and forest, and area of nearest wetland. Our results demonstrate the importance of a variety of factors influencing the species composition and richness in Norwegian grasslands. We found that both the landscape element harbouring the observed plot and also the surrounding landscape structure and intensity of land-use are important determinants of species diversity. The fact that distance to more intensively managed agricultural land is one of the strongest explanatory facts signals how effects of agricultural management practices reaches outside the field itself and into adjacent landscape elements. This suggests that the entire landscape needs to be taken into consideration when management of a particular habitat patch is planned.

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Interspecific interaction among sympatric ungulates is important in management and conservation. We investigated behavioral interference between sympatric wild or semidomestic reindeer (Rangifer tarandus tarandus) and sheep (Ovis aries) in two field studies and one enclosure experiment. For free-ranging wild and semidomestic reindeer, interference between the two species increased with decreasing distances, occurring only at less than 200 m and 30 m, for wild and semidomestic reindeer, respectively, and neither species consistently dominated the other. In a controlled, duplicated experiment we tested interference and confrontations at the feeding patch level among semidomestic reindeer and sheep within 40 × 50 m enclosures. When new reindeer or sheep were introduced into enclosures already occupied by reindeer, new reindeer resulted in significantly more interference and confrontations among individuals compared to new sheep; i.e., intraspecific interference was more prevalent than interspecific interference at equal densities. For all study areas, confrontations decreased with time after “first encounter,” indicating cohabituation. A sympatric use of pastures was not visually disruptive for recorded grazing behavior for either species.

Abstract

As in many countries throughout Europe, there has been a polarisation within the agricultural landscape of Norway during the last decades. On the one hand there is an increasing trend of intensified use of favourable areas, while on the otherhand there is an increase in the amount of land abandonment of extensively managed or marginal areas (Fjellstad Dramstad 1999, Robinson Sutherland 2002, Haines-Younget al. 2003). Among the main impact factors for biodiversity in agricultural landscapes are increased amount of built-up areas, intensification of agriculture and land abandonment. But different land use practices has been shown to have differential effects on biodiversity (Haines-Young 2009). Finding the relationships between land use practices and effects on biodiversity are fundamental to understand the links between people and their environment and development of sustainable agriculture ....