Pattern and process in Norwegian upland grasslands: an integrated ecological approach.

In this thesis I examine community patterns and the effects of disturbances on these patterns within successional subalpine grasslands at summer farms in Norway. On a broad scale, I investigate how environment, land-use history, and spatial variability affect vegetation patterns within and between farms. On a fine scale, I investigate the effect of the creation and revegetation of bare-ground gaps along a secondary successional sequence. Finally, I investigate seed germination responses in subalpine grassland plants, and relate these to the potential for establishment in semi-natural grasslands during succession. The study is based on field data and seed collections from 19 summer farms in two valleys in western and eastern Norway. The data originate from observational field studies via field experiments to phytotron germination trials, and the biological responses monitored range from floristic composition via field recruitment to the timing of germination in individual seeds. The temporal scales and resolutions range from snapshot studies via day-to-day monitoring of germination and four-year field experiments to 40-year chronosequences. The data are analysed using different univariate and multivariate statistical procedures. Three major findings emerge from the study. (1) Disturbance, at scales ranging from the disturbance regimes of entire summer farms via gradients in disturbance intensity within landscapes to fine-scale gaps in a closed vegetation sward, exert considerable influence on the composition and functional traits of species at these various scales. Rare species increased in relative abundance in gaps. (2) The dynamics within fine-scale disturbances, and the responses of individual species to disturbance, change along a secondary successional sequence. This indicates that the processes operating at broad and fine spatial and temporal scales are not independent. (3) The secondary successions, gap revegetation, and regeneration from sown seeds in the field, were slow relative to seminatural vegetation elsewhere. (4) The seeds from subalpine populations of 11 species had consistently high temperature thresholds for germination relative to species from lowland grasslands in Norway and elsewhere. Together, these findings suggest that summer farm grasslands share some common characteristics with semi-natural vegetation elsewhere, but that they also have their own particularities. These may be related to climatic constraints. This study contributes to the knowledge of these systems by demonstrating that land-use changes have had, and will continue to have, dramatic effects on the vegetation and flora of subalpine semi-natural landscapes. The slow secondary successional rates in the mountains may explain why upland semi-natural vegetation is regarded as less immediately threatened than its lowland counterparts

Distinguishing the roles of dispersal in diversity maintenance and in diversity limitation

In recent years, a considerable research effort has gone into studying how dispersal might affect the diversity of local communities. While this general topic has received attention from theoretical and empirical ecologists alike, the research focus has differed between the two groups; theoretical ecologists have explored the role of dispersal in the maintenance of diversity within local communities, whereas empirical ecologists have sought to quantify the role of dispersal in limiting local diversity. In this paper we argue that, because the underlying causal relationship between dispersal and diversity is empirically unknown (e.g., flat, linear, and humped relationships have been suggested), there is no necessary relationship between the dispersal-maintained and the dispersal-limited component of diversity. In order to test and parameterize theoretical models we therefore need to develop a empirical approaches that allow us to quantify not only the dispersal-limited but also the dispersal-maintained component of diversity

Evolutionary rescue as a mechanism allowing a clonal grass to adapt to novel climates

Filing gaps in our understanding of species' abilities to adapt to novel climates is a key challenge for predicting future range shifts and biodiversity loss. Key knowledge gaps are related to the potential for evolutionary rescue in response to climate, especially in long-lived clonally reproducing species. We illustrate a novel approach to assess the potential for evolutionary rescue using a combination of reciprocal transplant experiment in the field to assess performance under a changing climate and independent growth chamber assays to assess growth- and physiology-related plant trait maxima and plasticities of the same clones. We use a clonal grass, Festuca rubra, as a model species. We propagated individual clones and used them in a transplant experiment across broad-scale temperature and precipitation gradients, simulating the projected direction of climate change in the region. Independent information on trait maxima and plasticities of the same clones was obtained by cultivating them in four growth chambers representing climate extremes. Plant survival was affected by interaction between plant traits and climate change, with both trait plasticities and maxima being important for adaptation to novel climates. Key traits include plasticity in extravaginal ramets, aboveground biomass, and osmotic potential. The direction of selection in response to a given climatic change detected in this study mostly contradicted the natural trait clines indicating that short-term selection pressure as identified here does not match long-term selection outcomes. Long-lived clonal species exposed to different climatic changes are subjected to consistent selection pressures on key traits, a necessary condition for adaptation to novel conditions. This points to evolutionary rescue as an important mechanism for dealing with climate change in these species. Our experimental approach may be applied also in other model systems broadening our understanding of evolutionary rescue. Such knowledge cannot be easily deduced from observing the existing field clines.publishedVersio

Coastal heathland vegetation is surprisingly resistant to experimental drought across successional stages and latitude

In the last decade, several major dwarf-shrub dieback events have occurred in northern European coastal heathlands. These dieback events occur after extended periods with sub-zero temperatures under snow-free conditions and clear skies, suggesting that coastal heathlands have low resistance to winter drought. As climate projections forecast increased drought frequency, intensity, and duration, coastal heathlands are likely to experience more such diebacks in the future. There are, however, few empirical studies of drought impacts and responses on plant communities in humid oceanic ecosystems. We established a drought experiment with two distinct levels of intensified drought to identify responses and thresholds of drought resistance in coastal heathland vegetation. We repeated the experiment in two regions, separated by five degrees latitude, to represent different bioclimatic conditions within the coastal heathlands' wide latitudinal range in Europe. As coastal heathlands are semi-natural habitats managed by prescribed fire, and we repeated the experiment across three post-fire successional phases within each region. Plant community structure, annual primary production, and primary and secondary growth of the dominant dwarf-shrub Calluna vulgaris varied between climate regions. To our surprise, these wide-ranging vegetation- and plant-level response variables were largely unaffected by the drought treatments. Consequently, our results suggest that northern, coastal heathland vegetation is relatively resistant to substantial intensification in drought. This experiment represents the world's wettest (2200 mm year−1) and northernmost (65°8'N) drought experiment to date, thus filling important knowledge gaps on ecological drought responses in high-precipitation and high-latitude ecosystems across multiple phases of plant community succession.publishedVersio

Restoring heathlands after afforestation on two islands in western Norway

The ongoing loss of red-listed coastal heathlands is a threat to biodiversity and cultural heritage legacies throughout the Atlantic coastal regions of Europe. It is possible to restore degraded and afforested heathlands, but restoration interventions are often labour-intensive and costly, and the outcome of specific restoration actions are not well documented. We assess the efficiency of restoring coastal heathlands through natural succession (i.e. ‘passive restoration') after removal of Sitka spruce Picea sitchensis (Bong.) Carr. plantations. The study was replicated on two neighbouring islands in a nature reserve in Western Norway. Low-intensity free-range sheep grazing was implemented as part of the reserve management plan. Furthermore, we tested the effect of leaving the clear-felled woody material as chips on site, this being a cost-efficient strategy on islands. Succession was monitored 1, 2, 4/5 and 8 years after clear-felling, and revegetation of vascular plants and bryophytes was compared to target heathland vegetation. Surprisingly, we found different successional trajectories on the two islands. Species composition on one island approached target heathland vegetation during succession, but not on the other. Wood chips reduced species richness and slowed the restoration process, but these negative effects were only short-term (<8 years). Differences in seed bank composition and soil conditions due to land use may explain the deviating successional trajectories on the two islands. We also found that management actions beyond clear-felling and introducing sheep grazing are necessary due to the rapid seed regeneration of the Sitka spruce.publishedVersio

Reducing Wooden Structure and Wildland-Urban Interface Fire Disaster Risk through Dynamic Risk Assessment and Management

In recent years, severe and deadly wildland-urban interface (WUI) fires have resulted in an increased focus on this particular risk to humans and property, especially in Canada, USA, Australia, and countries in the Mediterranean area. Also, in areas not previously accustomed to wildfires, such as boreal areas in Sweden, Norway, and in the Arctic, WUI fires have recently resulted in increasing concern. January 2014, the most severe wooden town fire in Norway since 1923 raged through Lærdalsøyri. Ten days later, a wildfire raged through the scattered populated community of Flatanger and destroyed even more structures. These fires came as a surprise to the fire brigades and the public. We describe and analyze a proposed way forward for exploring if and how this increasing fire incidence can be linked to concomitant changes in climate, land-use, and habitat management; and then aim at developing new dynamic adaptive fire risk assessment and management tools. We use coastal Norway as an example and focus on temporal changes in fire risk in wooden structure settlements and in the Norwegian Calluna vulgaris L. dominated WUI. In this interface, the fire risk is now increasing due to a combination of land-use changes, resulting in large areas of early successional vegetation with an accumulation of biomass, and the interactive effects of climatic changes resulting in increased drought risk. We propose a novel bow-tie framework to explore fire risk and preventive measures at various timescales (years, months, weeks, hours) as a conceptual model for exploring risk contributing factors and possibilities for risk management. Ignition is the top event of the bow-tie which has the potential development towards a fire disaster as a worst case outcome. The bow-tie framework includes factors such as changes in the built environment and natural habitat fuel moisture content due to the weather conditions, WUI fuel accumulation, possibly improved ecosystem management, contribution by civic prescribed burner groups, relevant fire risk modeling, and risk communication to the fire brigades and the public. We propose an interdisciplinary research agenda for developing this framework and improving the current risk understanding, risk communication, and risk management. This research agenda will represent important contributions in paving the road for fire disaster prevention in Norway, and may provide a model for other systems and regions.publishedVersio

Temperature, precipitation and biotic interactions as determinants of tree seedling recruitment across the tree line ecotone

Seedling recruitment is a critical life history stage for trees, and successful recruitment is tightly linked to both abiotic factors and biotic interactions. In order to better understand how tree species’ distributions may change in response to anticipated climate change, more knowledge of the effects of complex climate and biotic interactions is needed. We conducted a seed-sowing experiment to investigate how temperature, precipitation and biotic interactions impact recruitment of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) seedlings in southern Norway. Seeds were sown into intact vegetation and experimentally created gaps. To study the combined effects of temperature and precipitation, the experiment was replicated across 12 sites, spanning a natural climate gradient from boreal to alpine and from sub-continental to oceanic. Seedling emergence and survival were assessed 12 and 16 months after sowing, respectively, and aboveground biomass and height were determined at the end of the experiment. Interestingly, very few seedlings were detected in the boreal sites, and the highest number of seedlings emerged and established in the alpine sites, indicating that low temperature did not limit seedling recruitment. Site precipitation had an overall positive effect on seedling recruitment, especially at intermediate precipitation levels. Seedling emergence, establishment and biomass were higher in gap plots compared to intact vegetation at all temperature levels. These results suggest that biotic interactions in the form of competition may be more important than temperature as a limiting factor for tree seedling recruitment in the sub- and low-alpine zone of southern Norway.acceptedVersio

Massive structural and compositional changes over two decades in forest fragments near Kampala, Uganda

Private forests harbor considerable biodiversity, however, they are under greater threat than reserved areas, particularly from urbanization, agriculture, and intense exploitation for timber and fuel wood. The extent to which they may act as habitats for biodiversity and how level of protection impacts trends in biodiversity and forest structure over time remain underresearched. We contribute to filling this research gap by resampling a unique data set, a detailed survey from 1990 of 22 forests fragments of different ownership status and level of protection near Kampala, Uganda. Eleven of the 22 fragments were lost over 20 years, and six of the remnants reduced in size. Forest structure and composition also showed dramatic changes, with six of the remnant fragments showing high temporal species turnover. Species richness increased in four of the remaining forests over the resample period. Forest ownership affected the fate of the forests, with higher loss in privately owned forests. Our study demonstrates that ownership affects the fate of forest fragments, with private forests having both higher rates of area loss, and of structural and compositional change within the remaining fragments. Still, the private forests contribute to the total forest area, and they harbor biodiversity including IUCN “vulnerable” and “endangered” species. This indicates the conservation value of the fragments and suggests that they should be taken into account in forest conservation and restoration.publishedVersio

Germination and seedling growth of Calluna vulgaris is sensitive to regional climate, heathland succession, and drought

The coastal heathlands of Northwest Europe are highly valued cultural landscapes, that are critically endangered due to land use and climatic changes, such as increased frequency and severity of drought events. Our study is the first to assess how the germination and early seedling growth of Calluna vulgaris respond to drought. In a factorial design field experiment, we exposed maternal plants to three in-situ drought treatments (control, 60%, 90% roof coverage), across three successional stages after fire (pioneer, building, mature), and two regions (60°N, 65°N). Seeds from 540 plants within the experiment were, weighed, and exposed to five water potentials, ranging from −0.25 to −1.7 MPa, in a growth chamber experiment. We recorded germination (percentage, rate), seedling growth (above- vs. belowground allocation), and seedling functional traits (specific leaf area [SLA], specific root length [SRL]). Overall variation in germination between regions, successional stages, and maternal drought treatments was largely mediated by variation in seed mass. Plants from the northernmost region had higher seed mass and germination percentages. This is indicative of higher investment in seeds, likely linked to the populations' absence of vegetative root sprouting. Seeds from the mature successional stage germinated to lower final percentages than those from earlier successional stages, especially when the maternal plants had been exposed to drought (60% and 90% roof coverage). Exposure to reduced water availability decreased germination percentage and increased the time to 50% germination. Seedlings fully developed in the range −0.25 to −0.7 MPa, with increased root:shoot and lower SRL during reduced water availability, suggesting a resource-conservative response to drought during the early stages of development. Our results thus suggest a sensitivity to drought during the germination and seedling life-history stages that may reduce Calluna's ability to re-establish from seeds as the incidence and severity of droughts are projected to increase under future climates.publishedVersio

Cooperative learning goes online: teaching and learning intervention in a digital environment impacts psychosocial outcomes in biology students

Identifying evidence-based teaching and learning strategies that can ease teacher challenges and mitigate student concerns in digital settings becomes increasingly important. In this intervention study we compared the effect of digital cooperative learning (CL) and digital lectures on a range of psychosocial outcomes, specifically students’ sense of belonging, science confidence, perceived generic skills, and loneliness, among a Norwegian sample of undergraduate biology students (n = 71). Employing a one-group pretest/posttest quasi-experimental design with a double pretest and follow-up, we found that students’ scores on psychosocial outcomes improved significantly following digital CL compared to digital lectures. Further, the effect sizes suggest that the effect of CL on psychosocial outcomes in digital settings is at least as substantial as in physical settings.publishedVersio