Southwestern Norway Research Articles

Agricultural Development in the Context of the 6th Century Crisis – A Synthesis of Plant-Macrofossil Data from Southwestern Norway

ABSTRACT The transition between the Early and Late Iron Age in Southwestern Norway, around AD 550, is a transformative time when the archaeological material displays major changes and the number of finds and settlement sites decreases significantly. This period coincides with the 6th century crisis when volcanic cooling and subsequent plague pandemic caused famine, demographic decline and disruption in Europe. Recent research suggests harsh conditions for crop cultivation in southwestern Norway, with up to 3.5° C lower temperatures. This paper synthesizes plant macrofossil data and radiocarbon dates from 20 settlement sites to explore agricultural development from AD 400–1050 and to investigate whether the crisis influenced the agricultural practices and strategies. Reduced settlement activity is suggsted from the time of the cooling. The plant macrofossil compilation shows a focus on barley and oat cultivation , but a decrease in oats in favour of barley is seen from AD 550 forward. Rye was temporarily introduced in the 7th century. An indicated increased focus on animal husbandry is most prominent from the late Merovingian Period (AD 650–800). A comparison between sites based on their main crop suggests that sites with a high ratio of oats relative to barley had a lower chance of surviving the crisis. .

Топонимические и фольклорные корни «Пряди о Сельторире»

Selþórir, or Þórir the Seal, Grímsson, descended from the nobility of southwestern Norway, is one of the most famous first settlers of the Western Quarter of Iceland. A þáttr about him (original manuscripts caption “Frá Selþori”) is included in the second part of the medieval Icelandic historical work “The Book of the Settlements” (Landnámabók). The þáttr speaks not only of Þórir receiving a nickname, but also reveals the meanings of toponyms included in his possessions. As in many other þættir of the Landnámabók, in the one we are studying there are motives for predicting the place of a future settlement (in our case, the prediction is merman) and irrational determination of the place of settlement (in this þáttr with the help of a horse). However, the rich concentration of supernatural beings (not only the merman, but also the troll and the helper horse act in the þáttr) and events (predictions, posthumous “going uphill”) distinguishes it from a number of other þættir of the Landnámabók. At the same time, discrepancies in the editions of the Landnámabók (they are few in relation to the entire volume of the þáttr, but they are significant and reflect the rethinking of the text by the authors of the earlier editions) reveal the desire of the author of the Hauksbók edition, Haukr Erlendsson, to level the folklore component. It is also noteworthy that the folklore elements present in the þáttr can be attributed to fairly common Western Scandinavian motifs. Tracing the Celtic influence on the images of characters and plot twists, in our opinion, looks like a stretch. In addition, most of the plots of the þáttr are toponymic legends. Within the framework of this single þáttr, the meanings of five Icelandic toponyms are revealed at once: Grímsey (“Grim’s Island”), Skálmarnes (“Skalm’s Ness”), Skálmarkelda (“Skalm’s Well”), Rauðamel (“Red Sandbank”), Borgarhraun (“Wilderness of Castle”) and Þórisberg (“Þórir’s Mount”). Thus, it turns out that the Selþórisþáttr is present in the Landnámabók as a toponymic tradition, most likely of oral origin.

Comments to the paper “A 10Be chronology of the Esmark Moraine and Lysefjorden region, southwestern Norway: Evidence for coeval glacier resurgence in both polar hemispheres during the Antarctic Cold Reversal” by Aron E. Putnam, George H. Denton and Joerg M. Schaefer

Comments to the paper “A 10Be chronology of the Esmark Moraine and Lysefjorden region, southwestern Norway: Evidence for coeval glacier resurgence in both polar hemispheres during the Antarctic Cold Reversal” by Aron E. Putnam, George H. Denton and Joerg M. Schaefer

Marine Geophysical Survey of a Medieval Shipwreck in Shallow Waters Using an Autonomous Surface Vehicle: A Case Study from Avaldsnes, Norway

This study demonstrates the successful use of a single-channel chirp system mounted on an Autonomous Surface Vehicle (ASV) for detecting and mapping a partly buried medieval ship found in water approximately one meter (m) deep in a dynamic, intertidal environment at Avaldsnes, south-western Norway. The ASV's fast mobilization and access to areas otherwise difficult to reach, makes it an efficient, low-cost, and non-invasive platform for examining the seafloor and subsurface with high-resolution seismic data, acquired in a dense grid. Line spacing of 0.25 m allowed for the generation of a detailed 3D data cube, enabling effective interpretation of both acoustic vertical sections and horizontal amplitude maps. This approach empowered accurate identification of the outline of the wooden hull and provided information about ship dimensions and maximum burial depth. Structural elements observed in the geophysical datasets, including the keelson, raiders, and maststep, corroborates with findings from previous diving investigations and photogrammetry documentation. Moreover, the geophysical survey offers valuable additional knowledge of the buried ship remains, revealing a slight tilt of the keel and a substantial object buried in close proximity to the stern, probably the rudder or another wreck-related artefact.

Configuration of the Scandinavian Ice Sheet in southwestern Norway during the Younger Dryas

The extent of the Scandinavian Ice Sheet in southwestern Norway is precisely located during the well-characterized Younger Dryas re-advance. However, the thickness of the ice sheet is less well constrained inland from the terminal position. Some exceptions include lateral moraines traced inland and up to 1000 m a.s.l. along Hardangerfjorden. Here, we apply 10Be dating in two areas: (1) bedrock and boulders in the high-relief landscapes near the Younger Dryas margin around the Bergen urban area, and (2) boulders from an upland 1600 m a.s.l. much farther (120 km) inland. We find that coastal summits ranging from ~400 to ~680 m a.s.l. and located only ~10–15 km up-flow from the ice margin, were covered by the Scandinavian Ice Sheet during the Younger Dryas. The scatter in the 10Be age population of 22 boulder samples is best explained by isotopic inheritance owing to inefficient subglacial erosion during the foregoing glaciation. Most of the 11 bedrock samples also exhibit inheritance, pointing to the source of inheritance in boulders and implying inefficient subglacial erosion during the last glaciation even in valley-bottoms near Bergen. Regional glacial striae compilations suggest that ice flow during maximum Younger Dryas ice-sheet configurations was for the most part cross-valley, with potentially low basal slip rates. Five new 10Be ages from the inland site help to constrain ice height far inland. We combine these new results with prior information to generate a cross profile of the Younger Dryas ice sheet in southern Norway.

An early set of clasps from Østabø in Sandeid, south-western Norway

An early set of clasps from Østabø in Sandeid, south-western Norway

A 10Be chronology of the Esmark Moraine and Lysefjorden region, southwestern Norway: Evidence for coeval glacier resurgence in both polar hemispheres during the Antarctic Cold Reversal

From 10Be surface-exposure dating we make the case that classic late-glacial moraines in southwestern Norway, including the iconic Esmark moraine, and in the Southern Hemisphere middle latitudes, including the iconic Birch Hill moraine of the Southern Alps of New Zealand, were constructed coevally within dating uncertainties. This finding of simultaneous glacier resurgence in the two polar hemispheres carries the implication that the millennial-scale climate reversal of the last deglaciation was global and required a change in the energy budget of the earth's climate system.

Twenty years of catchment monitoring highlights the predominant role of long-term phosphorus balances and soil phosphorus status in affecting phosphorus loss in livestock-intensive regions

Livestock husbandry has raised enormous environmental concerns around the world, including water quality issues. Yet there is a need to document long-term water quality trends in livestock-intensive regions and reveal the drivers for the trends based on detailed catchment monitoring. Here, we assessed the concentration and load trends of dissolved reactive phosphorus (DRP) in streamwater of a livestock-intensive catchment in southwestern Norway, based on continuous flow measurements and flow-proportional composite water sampling. Precipitation and catchment-level soil P balance were monitored to examine the drivers. At the field level, moreover, the relationship between soil P balance and soil test P (measured using the ammonium lactate extraction method, P-AL) was assessed. Results showed that on average of 20 years 95 % of the P was applied to the catchment during March–August, when 40 % of annual precipitation and 25 % of annual discharge occurred. The low runoff helped reduce P loss following P applications. However, flow-weighted annual mean DRP concentration significantly increased with increasingly cumulative soil P surplus (R2 = 0.55, p = 0.0002). With a mean annual P surplus of 8.8 kg ha−1, the annual mean DRP concentration (range: 49–140 μg L−1; mean: 80 μg L−1) and annual DRP load (range: 0.35–1.46 kg ha−1; mean: 0.65 kg ha−1) significantly increased over the 20-year monitoring period (p = 0.001 and 0.0003, respectively). At the field level, P-AL concentrations were positively correlated with soil P balances (R2 = 0.48, p < 0.0001), confirming the long-term impact of P balances on the risks of P loss. The study highlights the predominant role of long-term P balances in affecting DRP loss in livestock-intensive regions through the effect on soil test P.

Citizen science reveals the first occurrence of the greater white-toothed shrew Crocidura russula in Fennoscandia

Abstract The occurrence of the non-native, greater white-toothed shrew Crocidura russula in the Stavanger area in Southwestern Norway was brought to our attention by two records from the public (from 2012 and 2017). A citizen-science project, based on targeted media-calls between 2017 and 2019, resulted in 78 reported observations. A correct species identity, using photographs and collected specimen, was confirmed for 103 observations from 68 unique localities. Many of the sightings resulted directly from the media calls, but several were made both years before and after (ranging from 2012 to 2021). The minimum area of occurrence was 60 km long and 20 km wide and is characterised by one of the mildest climates in Norway. No clear expansion pattern was evident from the data, though an introduction between 2000 and 2010 seems likely. As only a few other shrew species were reported by the public, it is possible that the white-toothed shrew has outcompeted native shrews in the area. However, this could be biased by the nature of the media call or the commensal lifestyle of the shrew. Media calls beyond the area of occurrence did not result in any reports of the species. The introduction route and origin of the present population remain unclear.

How long and how frequent is sufficient? Long time study (2003-2022) of variation in occurrence, species richness and fructification of grassland-fungi in a semi-natural grassland in South-Western Norway

The semi natural grassland described in this paper, Hovaneset in Stord municipality, South-Western Norway, has been examined for grassland fungi for 20 years, from 2003 until today (2022). This has resulted in the discovery of 92 different species after a total of 180 visits to the locality. Change in the frequency of survey to approximately a weekly visit during the seasons from 2010 resulted in a large increase in species diversity, also of red-listed species. During these last 13 years of survey, the total number of species more than doubled, and the number of red-listed species more than tripled, which clearly shows the huge effect in changing the frequency of visits to a visit once a week during the season. The survey also clearly shows that the number of finds during a visit varies greatly from year to year and from week to week. In an optimal year for grassland fungi, around 70% of the species that grow there can be found in a weekly survey throughout the season, while a less good year gives a maximum of 40% finds. The survey also shows that the time of visit in a particular year is decisive for how many species are found in one visit. In an optimal year for grassland fungi, at the best possible match with time of survey, you can find up to 50% of the species growing there in one visit, but more likely it will be around 35%. It therefore shows very clearly that visits during the whole season is necessary to get hold on all fungi growing here. The survey also shows that many grassland fungi have very irregular fructification from one year to the other, which particularly applies to species within the genera Clavaria and Entoloma. Only ten species were found each year during the survey, most of which were waxcaps (Hygrocybe s.l.), while 14 species were only found in one of the years of survey. The time of fruiting also seems to have changed during the 20 years the survey has been ongoing. The week with the highest number of species recorded in 2021/22 is approximately 3-4 weeks later than it was in 2013/14. This is particularly clear for the genus Entoloma, which normally has an early and limited fruiting period.

Near‐surface temperatures and potential for frost weathering in blockfields in Norway and Svalbard

AbstractBlockfields remain enigmatic regarding their origin, internal structure, surface processes, and glaciological implications. In Scandinavia, blockfields are found on high‐elevation, low‐relief mountains (plateaus) across the Arctic and Subarctic. In this study, we present a 1D numerical model that uses near‐surface temperatures measured between summer 2018 and summer 2020 to calculate frost‐cracking intensities (FCI) within the ground column in three different blockfields in Norway and Svalbard. Eighty‐nine miniature temperature loggers were distributed on Tron Mountain (1650 m a.s.l.) in Alvdal, Gamlemsveten (780 m a.s.l.) near Ålesund in southwestern Norway and on Platåberget (460 m a.s.l.) near Longyearbyen, Svalbard. We modelled FCI by scaling the time spent in the frost cracking window (between −3 and −8°C) with the temperature gradient and a penalty function for distance to available water. At Tron and Gamlemsveten, ground temperatures never reached the frost cracking window at one third of our sites due to insulation by a thick snow cover in depressions and on the lee sides of summits. The highest FCI (0.05–0.4 K m) are obtained where the subsurface consists of boulders and stones in a matrix of relatively fine sediment (sand, silt, gravel). In contrast, very low FCI (0.003–0.02 K m) were modelled for blocky layers with large air‐filled pores because of the low water availability. On Platåberget, all sensors reached the frost‐cracking window during the annual temperature cycle, but FCI are extremely low (0.0004–0.15 K m) as water availability is limited due to (i) permafrost and (ii) near‐surface temperatures remaining below the frost‐cracking window for 3/4 of the year. This indicates that boulder‐rich blockfields with air‐filled hollows are preserved in very cold climates, whereas warmer, maritime settings with higher availability of fine interstitial material place blockfields in the fast lane for frost weathering.

UAV magnetics over the Bjerkreim-Sokndal Intrusion, Rogaland, Norway: A first look

The Bjerkreim-Sokndal layered intrusion in Rogaland Anorthosite Province in southwestern Norway has been the focus of decades of research due to its complex geology, the presence of prominent remanent magnetic anomalies, and current economic interest in critical minerals. In 2021, collaborative geophysical fieldwork was conducted by the Norwegian University of Science and Technology and Helmholtz Institute Freiberg for Resource Technology. Despite challenging environmental conditions, more than 100 line-km of magnetic data were collected by a custom multirotor unmanned aerial vehicle (UAV) along the eastern margin of the Bjerkreim lobe of the Bjerkreim-Sokndal Intrusion. Data collection was focused over two areas. The first is an area in the south near the prominent Heskestad magnetic anomaly that is associated with large reversed magnetic remanence in a magnetite-ilmenite-gabbronorite unit. The second is an area in the north near Lake Teksevatnet that hosts mineralized zones and the Lauvneset magnetic anomaly. Initial analysis of the UAV-acquired magnetic data shows additional details on the geologic contacts of key units, especially where in-situ measurements are difficult to collect. UAV surveys help in the construction of an anomaly's geometry through incremental source-sensor separations at various flight altitudes above ground. The UAV data set is an intermediate step between ground and airborne surveys for multiscale interpretation and potentially extreme magnetic scales (from microscopic to planetary).

“They gotta understand why”: Teachers’ professional perceptions regarding the stimulation of academic motivation in upper secondary school

In recognition of the need for more research on teachers’ perceptions of motivational work in the classroom, this study explores upper secondary school teachers’ perceptions of how to stimulate academic motivation among their students at a school in southwestern Norway. The data were gathered in three steps. The school’s primary teachers (n = 33) were interviewed by teacher champions (n = 17), that is, teachers that were team leaders for each of the school’s educational departments that were given a specific role in the research in terms of initial data collection. This was followed by two extended focus groups with the teacher champions and member checks for each group. The data were subjected to conventional content analyses using NVivo 12. Then, a focus group was carried out with teacher coordinators (n = 11) aiming to refine preliminary findings. Summative content analyses were carried out, followed by deductive category application. The findings indicate that teachers perceive class management and strategies for supporting students’ learning processes as well as key students as crucial for academic motivation. “Three motivational strategies” were developed. However, feedback and differentiated learning tasks, which are central aspects of motivational theories, received less emphasis. Further in-depth studies exploring concrete approaches to and the evaluating of using strategies for stimulating academic motivation are required.

Den mystiske og anvendelige skålgropa – skålgroper i Rogaland knyttet til ferdsel, knutepunkter og kultsteder i landskapet&amp;nbsp;

Approximately 110 rock art sites and more than 100 decorated slabs/stones are known from Rogaland County, southwestern Norway. This article looks at cupmarks and their relationship to travelling routes and nodal points along the coast, waterways, and inland pathways, with a focus on dating, context and placement within the wider landscape. The primary group is located in the maritime zone and along fjord systems. These sites are related to known Bronze Age and Iron Age sailing routes, probably related to interregional exchange networks. The second group, along inland pathways, dates to the Iron Age and comprises two distributions. The northernmost group is related to summer farms and constitutes the southern fringe of a larger body of cupmark sites related to sub-alpine regions in Sogn and Hardanger. The southernmost group is found within the Dalane anorthosite and heathland and is associated with nodal points and along pathways leading to ritual places of worship.

Association of CSF Glucocerebrosidase Activity With the Risk of Incident Dementia in Patients With Parkinson Disease.

Variations in the glucocerebrosidase gene (GBA) are common risk factors for Parkinson disease (PD) and dementia in PD (PDD) and cause a reduction in the activity of the lysosomal enzyme glucocerebrosidase (GCase). It is anticipated that GCase dysfunction might contribute to a more malignant disease course and predict cognitive impairment in PD, although evidence is lacking. We aimed to discover whether CSF GCase activity is altered in newly diagnosed patients with PD and associated with future development of dementia. Patients with PD were participants of the ongoing population-based longitudinal ParkWest study in Southwestern Norway and were followed prospectively for up to 10 years. CSF was collected at diagnosis, and GBA carrier status was obtained. Control samples were from persons without neurodegenerative disorders. GCase activity was measured using a validated assay. PD dementia diagnosis was set according to the Movement Disorder Society criteria, and parametric accelerated failure time models were applied to analyze the association of GCase activity with dementia-free survival. This study enrolled 117 patients with PD (mean age 67.2 years, including 12 GBA non-synonymous variant carriers) and 50 control participants (mean age 64 years). At the time of diagnosis, GCase activity was reduced in patients with PD with (mean ± SD, 0.92 ± 0.40 mU/mg, n = 12) or without GBA variations (1.00 ± 0.37 mU/mg, n = 105) compared with controls (1.20 ± 0.35, n = 50). GCase activity at the time of diagnosis was lower in patients with PD who developed dementia within 10 years (0.85 ± 0.27 mU/mg, n = 41) than in those who did not (1.07 ± 0.40 mU/mg, n = 76, p = 0.001). A 0.1-unit reduction in baseline GCase activity was associated with a faster development of PDD (hazard ratio 1.15, 95% CI 1.03-1.28, p = 0.014). The association of early CSF GCase activity with long-term progression to PD dementia will have important implications for the design of clinical trials for GCase targeting therapies and patient management. This study provides Class III evidence that reduced CSF GCase activity at the time of PD diagnosis is associated with an increased risk for later development of PDD.

High-Frequency Responses of the Blue Mussel (Mytilus edulis) Feeding and Ingestion Rates to Natural Diets

The feeding activity of bivalves is understood to change in response to a suite of environmental conditions, including food quantity and quality. It has been hypothesized that, by varying feeding rates in response to the available diet, bivalves may be able to maintain relatively stable ingestion rates, allowing them to have constant energy uptake despite changes in food availability. The purpose of this study was to determine if the blue mussel Mytilus edulis responds to fluctuations in natural diets by changing feeding rates to maintain constant ingestion rates. Three four-day experiments were conducted to measure pumping and ingestion rates in response to natural fluctuations in food concentration (chlorophyll a). Experiments were conducted in a flow-through system over the spring season in south-western Norway. Pumping and ingestion rates were measured with high temporal resolution (every 20 min), which permitted the observation of the intra- and interindividual variability of feeding rates. Results show pumping rates varying within individuals over 4 days, and some individuals pumping on average at high rates (~5 Lh−1), and some at low (~1 Lh−1), despite being held in similar conditions. The pumping rate was generally not related to changes in food availability, and population-level ingestion rates increased with increasing food availability. These results suggest that, for this population of M. edulis, feeding rates may not vary with the available diet to produce constant ingestion over time.

Multiscale lineament analysis and permeability heterogeneity of fractured crystalline basement blocks

Abstract. The multiscale analysis of lineament patterns helps define the geometric scaling laws and the relationships between outcrop- and regional-scale structures in a fracture network. Here, we present a novel analytical and statistical workflow to analyze the geometrical and spatial organization properties of the Rolvsnes granodiorite lineament (fracture) network in the crystalline basement of southwestern Norway (Bømlo Island). The network shows a scale-invariant spatial distribution described by a fractal dimension D≈1.51, with lineament lengths distributed following a general scaling power law (exponent α=1.88). However, orientation-dependent analyses show that the identified sets vary their relative abundance and spatial organization and occupancy with scale, defining a hierarchical network. Lineament length, density, and intensity distributions of each set follow power-law scaling laws characterized by their own exponents. Thus, our multiscale, orientation-dependent statistical approach can aid in the identification of the hierarchical structure of the fracture network, quantifying the spatial heterogeneity of lineament sets and their related regional- vs. local-scale relevance. These results, integrated with field petrophysical analyses of fracture lineaments, can effectively improve the detail and accuracy of permeability prediction of heterogeneously fractured media. Our results also show how the geological and geometrical properties of the fracture network and analytical biases affect the results of multiscale analyses and how they must be critically assessed before extrapolating the conclusions to any other similar case study of fractured crystalline basement blocks.

Life cycle assessment of tomato production for different production strategies in Norway

The availability of fresh vegetables grown in greenhouses under controlled conditions throughout the year has given rise to concerns about their impact on the environment. In high latitude countries such as Norway, greenhouse vegetable production requires large amounts of energy for heat and light, especially during the winter. The use of renewable energy such as hydroelectricity and its effect on the environment has not been well documented. Neither has the effect of different production strategies on the environment been studied to a large extent. We conducted a life cycle assessment (LCA) of greenhouse tomato production for mid-March to mid-October (seasonal production), 20th January to 20th November (extended seasonal) production, and year-round production including the processes from raw material extraction to farm gate. Three production seasons and six greenhouse designs were included, at one location in southwestern and one in northern Norway. The SimaPro software was used to calculate the environmental impact. Across the three production seasons, the lowest global warming (GW) potential (600 g CO2-eq per 1 kg tomatoes) was observed during year-round production in southwestern Norway for the design NDSFMLLED + LED, while the highest GW potential (3100 g CO2-eq per 1 kg tomatoes) was observed during seasonal production in northern Norway for the design NS. The choice of artificial lighting (HPS (High Pressure Sodium) or LED (Light Emitting Diodes)), heating system and the production season was found to have had a considerable effect on the environmental impact. Moreover, there was a significant reduction in most of the impact categories including GW potential, terrestrial acidification, and fossil resource scarcity from seasonal to year-round production. Overall, year-round production in southwestern Norway had the lowest environmental impact of the evaluated production types. Heating of the greenhouse using natural gas and electricity was the biggest contributor to most of the impact categories. The use of an electric heat pump and LED lights during extended seasonal and year-round production both decreased the environmental impact. However, while replacing natural gas with electricity resulted in decreased GW potential, it increased the ecotoxicity potential.

Lake sediments from southern Norway capture Holocene variations in flood seasonality

Owing to the combined impact of human encroachment and global climate change, river flood hazards have increased around the world. Over the past decades, rapid warming has augmented atmospheric moisture fluxes. The resulting intensification of the hydrological cycle, as evident from instrumental records, is linked to more frequent and severe flooding. However, this observational baseline is too short to adequately assess long-term flood variability under different climate conditions. Geological archives can fill this critical knowledge gap by providing long-term (millennia) empirical constraints on the magnitude and frequency of floods. To reconstruct the frequency of flood events over the last >8000 years, this study investigated the Holocene lacustrine sediments from Lake Lygne in southwestern Norway. The precipitation in this area is sourced from the North Atlantic Ocean and transported by the prevalent westerly winds. As such, reconstructions of flood frequency variability may shed light on past moisture flux and flood generating weather systems in this part of northwestern Europe. We applied a multiproxy approach to robustly fingerprint the flood sediment signatures using multiple independent lines of evidence. This approach included analysing the sediments using X-ray fluorescence (XRF), computed tomography (CT scanning), and magnetic susceptibility (MS). We identified two types of event beds that differed significantly from background sedimentation throughout the sedimentary archive, which we interpreted as river flood deposits: one type is minerogenic and coarse silt-dominated; the other is a composite of minerogenic sediments and macrofossils. By comparing the sediment record with instrumental water discharge data from the last 100 years, we argue that these differing flood signals represent two flood regimes: rainfall-triggered floods during autumn and snowmelt-triggered floods during spring. Conducting a rate of change (RoC) analysis, we found significant millennial- and centennial-scale variability in the frequency of flood events. Moreover, comparing our findings with palaeoclimate reconstructions in the North Atlantic region, we found that the warmer than present early-mid-Holocene was dominated by extreme precipitation-triggered floods, shifting towards more snowmelt-triggered floods in the late Holocene.

Assessment of the TREELIM model in predicting present treeline along a longitudinal continentality-maritimity gradient in south-western Norway

ABSTRACT Treelines driven by climatic conditions are characteristic of alpine areas. This study assesses the degree of accuracy with which the TREELIM model predicts present treeline elevation along a regional continentality-maritimity gradient in southwest Norway. The study area consists of 15 sites chosen along this gradient, wherein observed treelines range from nearly sea level to over 1200 m a.s.l. The TREELIM model calculates treeline position based solely on meteorological parameters obtained from gridded climate datasets. The model assumes that tree growth occurs if the length of the growing season (LGS) exceeds a minimum duration and the seasonal mean temperature (SMT) does not fall below a certain value. Six different scenarios were developed in order to determine the effects of changing precipitation and drought within TREELIM. Within these scenarios, three different SMTs were used in order to model the treeline position. Model performance was evaluated by comparing resultant treeline elevation with observed values. Results of experiments using lapse rate-based temperature input data were compared to those using the gridded climate data. Statistical analysis determined that the lapse rate-based temperature scenario removing drought constraints and using a SMT of 6.4°C gave the most accurate prediction of treeline position, and a relatively uniform growing season ranging from 110 to 128 days. Precipitation and snow cover do not significantly affect treeline elevation. The results suggest that TREELIM accurately predicts the treeline in most cases, but is less suited in areas with steeply varying topography.