Sites In Central Sweden Research Articles

Freeze-thaw effects on pore space and hydraulic properties of compacted soil and potential consequences with climate change

Freezing and thawing affect the pore-space structure in agricultural soils with implications for soil hydraulic properties and water flow. Previous studies have focused on the upper few centimeters of the tilled topsoil, where most freeze-thaw (FT) cycles occur, even though deeper soil layers are also subject to freezing and thawing in cold climates. Thus, little is known about how freezing and thawing affect untilled soil layers, which often show high bulk densities that restrict vertical water movement. Furthermore, it remains unclear how shifts in FT patterns with climate change may change the pore-space structure and water flow through these soil layers. Here we investigated the effects of freezing and thawing on X-ray imaged pore-space characteristics, water retention and near-saturated hydraulic conductivity (K) in untilled soil directly below plough depth. Intact cores were sampled at two sites in central Sweden under the same long-term reduced tillage management. The two soils, a silt loam and a silty clay loam, were subjected to three FT scenarios in a laboratory environment intended to represent FT patterns that are considered likely under current and future winter conditions for this region. The latter scenario was characterised by more FT cycles and a lower freezing temperature. Freezing and thawing increased K in the near-saturated range in both soils, which we attribute to observed small (<0.01 mm3 mm−3) increases in the volume of pores of diameters close to the X-ray resolution limit. Concomitant increases in pore network connectivity and critical pore diameter, especially in the denser silty clay loam soil, probably contributed to this increase in K. The water retention data suggested that changes in pore-space characteristics below X-ray resolution also occurred in both soils. Furthermore, our results indicate that both soils may show higher drainage rates due to shifts in FT patterns in the future, although longer-term changes in pore-space structure with an increasing number of FT cycles would mostly be limited to soils with relatively high clay contents. These soils are often more compacted below plough depth and, thus, benefits from improvements in soil structure such as improved root growth and plant water supply are also expected to be larger.

Forest edge effects on moss growth are amplified by drought.

Forest fragmentation increases the amount of edges in the landscape. Differences in wind, radiation, and vegetation structure create edge-to-interior gradients in forest microclimate, and these gradients are likely to be more pronounced during droughts and heatwaves. Although the effects of climate extremes on edge influences have potentially strong and long-lasting impacts on forest understory biodiversity, they are not well understood and are not often considered in management and landscape planning. Here we used a novel method of retrospectively quantifying growth to assess biologically relevant edge influences likely caused by microclimate using Hylocomium splendens, a moss with annual segments. We examined how spatio-temporal variation in drought across 3 years and 46 sites in central Sweden, affected the depth and magnitude of edge influences. We also investigated whether edge effects during drought were influenced by differences in forest structure. Edge effects were almost twice as strong in the drought year compared to the non-drought years, but we did not find clear evidence that they penetrated deeper into the forest in the drought year. Edge influences were also greater in areas that had fewer days with rain during the drought year. Higher levels of forest canopy cover and tree height buffered the magnitude of edge influence in times of drought. Our results demonstrate that edge effects are amplified by drought, suggesting that fragmentation effects are aggravated when droughts become more frequent and severe. Our results suggest that dense edges and buffer zones with high canopy cover can be important ways to mitigate negative drought impacts in forest edges.

Trap catch data are poor predictors of damage caused by pine weevil (Hylobius abietis) to conifer seedlings

Damage to planted conifer seedlings caused by the pine weevil Hylobius abietis (L.) is a severe and persistent threat to successful forest regeneration in Europe. Various countermeasures are available, which vary in effectiveness, costs and environmental impact, but none are ideal for all situations. Therefore, there is strong interest in robust assessments of damage risks, as they would enable more cost-effective and environmentally friendly forest pest management. It has been suggested that numbers of adult pine weevils caught in host-odour baited traps placed in regeneration sites may be valuable in such risk assessments. However, published studies provide at most weak support for the hypothesis that trap catch data provide adequate predictions of damage. Therefore, we conducted a two-year field study, designed to determine the relationship between weevil trap catch and subsequent damage at 10 regeneration sites in central Sweden. Site factors that might influence pine weevil feeding on seedlings were recorded and used as explanatory variables in the analysis. Stoniness was the only site factor identified as having a significant effect; damage mainly increased with increases in stoniness. No significant correlation was detected between damage to planted conifer seedlings and numbers of pine weevils trapped in the same locations. We suggest that this lack of correlation between weevil numbers and damage is due to planted seedlings only constituting a minor part of the weeviĺs food intake and considerable between-site variation in availability of food sources other than seedlings. Therefore, assessment of pine weevil numbers appears unlikely to be useful for predicting damage risk at specific regeneration sites.

Food Ethics, Domestication and Togetherness - A Close-up Study of the Relation of Horse and Dog to Man in the Bronze Age Settlement of Apalle

This paper deals with the attitude to the horse and the dog at a later Bronze Age site in central Sweden. Three different phenomena of social practise are linked together: the deposition of bones, slaughter marks on bones, and pictorial representation in rock-carvings and on artefacts. Two chronological phases at the settlement are compared in order to see if they display changes, regarding the three different phenomena, over time.

Differences in growth and areal production between Norway spruce (Picea abies L. Karst) regeneration material representing different levels of genetic improvement

Six groups of Norway spruce (Picea abies L. Karst) plants with varying levels of genetic gain and unimproved local provenances were compared in four realised gain trials at four sites in central Sweden. The groups were planted separately in experimental plots and compared in terms of survival rate and height 4 years after planting, as well as survival rate, height, diameter and areal volume production 13–16 years after planting. The genetically improved groups all produced higher volumes than the unimproved local provenances, and the clonal bulk of 23 full-sib families’ volume production per unit area was 56% higher than that of local provenances. The genetic groups followed expected levels of genetic gain, except for individual clones (which varied substantially in performance) and full-sib families. There were greater relative differences between local provenances and genetic groups in areal volume production 13–16 years after planting than in height at 4 years after planting. The results confirm that growth of improved genetic groups is largely consistent with expected values of realized genetic gain. They also indicate that clonal mixes rather than one or a few clones should be deployed in clonal forestry. The comparison of early measured height with areal production showed that early height measurements are good indicators of realized genetic gain and differences in areal production are greater than early differences in height.

Composition, isotopic fingerprint and source attribution of nitrate deposition from rain and fog at a Sub-Arctic Mountain site in Central Sweden (Mt Åreskutan)

While dry and rain deposition of nitrate (NO3−) and ammonium (NH4+) are regularly assessed, fog deposition is often overlooked. This work assesses summer fog events contribution to nitrogen deposition and availability for forest ecosystems. Rain and fog samples were collected at Mt Åreskutan, Sweden, during CAEsAR (Cloud and Aerosol Characterization Experiment), in 2014. NH4+ + NO3− represent (31 ± 25) % of total rain ion amount, and (31 ± 42) % in fog. Based on ion concentrations and the nitrate stable isotope signatures δ(15N) and δ(18O), it was possible to detect the plume generated by the Västmanland forest fire; NOx emissions from oil rigs and Kola Peninsula; and the plume of Bardarbunga volcano, Iceland. Scavenging of ions by fog was more efficient than by rain. Rain NH4+ and NO3− deposition was (26 ± 36) μmol m−2 d−1 and (23 ± 27) μmol m−2 d−1, respectively. Fog NH4+ and NO3− contributed (77 ± 80) % to total wet deposition of these species. Upscaling rain deposition fluxes to 1 year gave an inorganic nitrogen deposition of (18 ± 16) mmol m−2 a−1 ((252 ± 224) mg m−2 a−1 N equivalents), whereas fog deposition was estimated as (59 ± 47) mmol m−2 a−1 ((826 ± 658) mg m−2 a−1 N equivalents). Annual fog deposition was four times higher than previously reported for the area which only considered rain deposition. However, great uncertainty on the calculation of fog deposition need to be bear in mind. These findings suggest that fog should be considered in deposition estimates of inorganic nitrogen and major ions. If fog deposition is not accounted for, ion wet deposition may be greatly underestimated. Further sampling of wet and dry deposition is important for understanding the influence of nitrogen deposition on forest and vegetation development, as well as soil major ion loads.

Ecosystem C and N dynamics affected by a modified spring barley trait with increased nitrogen use - a simulation case study

ABSTRACTTo what extent might a crop with increased plant N uptake efficiency and/or N demand increase plant biomass and soil carbon storage, decrease N leaching, and reduce the need for N fertilisation? This was assessed for a fertilised sandy loam site in central Sweden cultivated with spring barley for a four year period using a process based crop and soil simulation model (SOILN) calibrated to fit observations of field experiments with non-modified crops. Crop properties were changed in accordance with previous model applications to other crops with higher N uptake and utilisation efficiencies, to resemble potential effects of breeding. For the modified crops a doubling of daily uptake efficiency of soil mineral N and/or increase of radiation use efficiency by 30%, increased plant biomass by 3%–30%, decreased N leaching by 1%–30% and increased soil organic carbon (SOC) content by 1–12 g C m−2 year−1. The larger changes were mainly due to increased uptake efficiency. Fertilisation of the modified spring barley crop could be reduced while still producing the same plant biomass as the non-modified crop. The plant biomass to N leaching ratio of the modified crops increased. The simulated changes in plant biomass and SOC were sensitive to weather conditions suggesting that in situ experiments would need to cover a large range of weather conditions to evaluate the performance of new crop traits under climatic variability. The study suggests a strong need that field experiments are accompanied with model applications, when exploring the potential of the modified crops under variable conditions.

Lek site defines annual spatial use of male Black Grouse (Tetrao tetrix)

Adultmale Black Grouse (Tetrao tetrix) are assumed to use the same lek throughout their life-span and juveniles are rarely observed settling far from their natal areas. Here we report results on a study of lek site fidelity in male Black Grouse using mark-recapture, radio- telemetry, and lek observations between 1984 and 1992. Data were collected at two sites in central Sweden with six and two leks, respectively. A total of 306 Black Grouse (230 full-grown adult and juvenile males, and 76 chicks) were captured and tagged.We found that all recaptured males tagged as chicks (n = 7) were caught on the lek closest to their initial capture site. Twenty-six percent (n = 59) of individuals ringed as full-grown were recaptured at least once in the subsequent springs. Fewer individuals attended leks during themating period than the premating period (t(15) = 3.06,P= 0.008). Juvenilemales were closer to the lek in the premating period (95% confidence interval = 0.45–0.65 km) than in the mating period (0.73–1.13 km), in contrast to adults, which were closer to leks in themating period (0.44–0.61 km) than the premating period (0.80–0.95 km). Inter-lek movement probability of the birds was 15%(n = 9) in the study area. Male Black Grouse remain close to their lek all year round and their recruitment is local. This indicates that leks consist of well-defined local populations, which have limited interactions with other leks.

Chemical composition and source analysis of carbonaceous aerosol particles at a mountaintop site in central Sweden

The chemical composition of atmospheric particulate matter at Mt. Åreskutan, a mountaintop site in central Sweden, was analysed with a focus on its carbonaceous content. Filter samples taken during the Cloud and Aerosol Experiment at Åre (CAEsAR 2014) were analysed by means of a thermo-optical method and ion chromatography. Additionally, the particle light absorption and particle number size distribution measurements for the entire campaign were added to the analysis. Mean airborne concentrations of organic and elemental carbon during CAEsAR 2014 were OC = 0.85 0.80 g m and EC = 0.06 0.06 g m, respectively. Elemental to organic carbon ratios varied between EC/OC = 0.02 and 0.19. During the study a large wildfire occurred in Västmanland, Sweden, with the plume reaching our study site. This led to significant increases in OC and EC concentrations (OC = 3.04 0.03 g m and EC = 0.24 0.00 g m). The mean mass-specific absorption coefficient observed during the campaign was = 9.17.3 mg (at wavelength = 637 nm). In comparison to similarly remote European sites, Mt. Åreskutan experienced significantly lower carbonaceous aerosol loadings with a clear dominance of organic carbon. A mass closure study revealed a missing chemical mass fraction that likely originated from mineral dust. Potential regional source contributions of the carbonaceous aerosol were investigated using modelled air mass back trajectories. This source apportionment pointed to a correlation between high EC concentrations and air originating from continental Europe. Particles rich in organic carbon most often arrived from highly vegetated continental areas. However, marine regions were also a source of these aerosol particles. The source contributions derived during this study were compared to emission inventories of an Earth system model. This comparison highlighted a lack of OC and EC point-sources in the model’s emission inventory which could potentially lead to an underestimation of the carbonaceous aerosol reaching Mt. Åreskutan in the simulation of this Earth system model.

Restoration of semi-natural grasslands, a success for phytophagous beetles (Curculionidae)

Semi-natural pastures have rich plant and animal communities of high conservation value which depend on extensive management. As the area of such land decreases, abandoned semi-natural grasslands have been restored to re-establish biodiversity. Restoration schemes, which include thinning of woody plants and reintroduction of grazing, are mainly designed according to the responses of well-studied groups (such as vascular plants and birds). Weevils (Curculionidae) are a very diverse phytophagous beetle family. Here, we evaluated the restoration success of pastures for weevils (Curculionidae), by comparing their species diversity in abandoned, restored, and continuously grazed semi-natural pastures on 24 sites in central Sweden. Weevils were sampled by sweep-netting. We recorded 3019 weevil individuals belonging to 104 species. There was no statistically significant difference in species numbers between the pasture management treatments. However, weevil species composition of abandoned pastures differed from those in restored and continuously managed pastures, but there was no significant difference in community composition between restored and continuously grazed pastures. The abandoned sites tended to be dominated by polyphagous species, whereas the grazed sites contained more monophagous and oligophagous species. The number of weevil species was positively related to understory vegetation height and connectivity to other semi-natural grasslands and negatively related to the cover of trees and shrubs in the pastures. We conclude that restoration of abandoned semi-natural pastures is a good approach to restore weevil communities. To maintain a species rich weevil community, pastures should be managed to be relatively open, but still have patches of tall field-layer vegetation. Restoration and conservation measures should primarily be targeted on regions and landscapes where a high proportion of semi-natural grassland still remains.

Methane exchange in a boreal forest estimated by gradient method

Forests are generally considered to be net sinks of atmospheric methane (CH4) because of oxidation by methanotrophic bacteria in well-aerated forests soils. However, emissions from wet forest soils, and sometimes canopy fluxes, are often neglected when quantifying the CH4 budget of a forest. We used a modified Bowen ratio method and combined eddy covariance and gradient methods to estimate net CH4 exchange at a boreal forest site in central Sweden. Results indicate that the site is a net source of CH4. This is in contrast to soil, branch and leaf chamber measurements of uptake of CH4. Wetter soils within the footprint of the canopy are thought to be responsible for the discrepancy. We found no evidence for canopy emissions per se. However, the diel pattern of the CH4 exchange with minimum emissions at daytime correlated well with gross primary production, which supports an uptake in the canopy. More distant source areas could also contribute to the diel pattern; their contribution might be greater at night during stable boundary layer conditions.

Impact of site-preparation on soil-surface CO&lt;sub&gt;2&lt;/sub&gt; fluxes and litter decomposition in a clear-cut in Sweden

Boreal forest soil contains significant amounts of organic carbon. Soil disturbance, caused for example by site preparation or stump extraction, may increase decomposition and thus lead to higher CO emissions, contributing to global warming. The aim of this study was to quantify responses of soil-surface CO fluxes (R) and litter (needle and root) decomposition rates following various kinds of soil disturbance commonly caused by mechanical site preparation and stump harvest. For this purpose four treatments were applied in a clear-cut site in central Sweden: i) removal of the humus layer and top 2 cm of mineral soil, ii) placement of a humus layer and 2 cm of mineral soil upside down on top of undisturbed soil, forming a double humus layer buried under mineral soil, iii) heavy mixing of the humus layer and mineral soil, and iv) no disturbance (control). R measurements were acquired with a portable respiration system during two growing seasons. To assess the treatments’ effects on litter decomposition rates, needles or coarse roots (Ø = 6 mm) were incubated in litterbags at positions they would be located after the treatments (buried, or on top of the soil). The results indicate that site preparation-simulating treatments have no effect or may significantly reduce, rather than increase, CO emissions during the following two years. They also show that buried litter decomposes more rapidly than litter on the surface, but in other respects the treatments have little effect on litter decomposition rates.22ss2

Indicators for soil organic matter quality in no-till soils under perennial crops in Central Sweden

Assessing the organic C (Corg) sequestration in no-till soils under perennial crops requires molecular-level quality indicators. Therefore, we investigated the quality of soil organic matter (SOM) in the topsoil under Salix viminalis L. and Lolium perenne L. at two test sites in Central Sweden. The willow S. viminalis (clone 78021) was grown in short rotation coppice, and the grass L. perenne in an adjacent meadow for 17 (site Ultuna) and 15 years (site Enköping), respectively. The concentrations of aliphatic lipids, determined by gas chromatography/mass spectrometry (GC/MS), as well as the molecular composition and thermal stability of the bulk SOM, determined by pyrolysis-field ionization mass spectrometry (Py-FIMS), were tested as indicators for the crop-specific SOM quality. Larger Corg concentrations (factor 1.4) in the topsoil (site Ultuna) under S. viminalis than under L.perenne corresponded to higher concentrations of summed aliphatic lipids (factor 1.6), mainly saturated n-alkanoic acids (factor 2.1) and n-alkanols (factor 1.5) in the GC/MS-analyses. Moreover, in the willow stand (site Ultuna) at soil depth of 0–10cm disproportionally higher concentrations of saturated n-alkanoic acids (C17–C36) (factor 2.4) and n-alkanes (C21–C36) (factor 2.6) indicated a preferential sequestration of aliphatic C because the bulk Corg concentrations were only larger by factor 1.4. This crop-specific impact on SOM at soil depth of 0–10cm was proven for both test sites. Furthermore, the Py-FIMS showed larger abundances of thermally stabile alkylaromatics (factor 1.4), and non-peptidic N-containing compounds (factor 1.3) in the S. viminalis plot (site Enköping), which supported a crop-specific Corg-sequestration of these compounds. Thus, in summary, accumulations in extracted long C-chain aliphatic lipids and the thermal stability of some substance classes indicated that the Corg sequestration by no-till may be more distinct in soils under S. viminalis than under L. perenne.

Short-term effects of thinning, clear-cutting and stump harvesting on methane exchange in a boreal forest

Abstract. Forest management practices can alter soil conditions, affecting the consumption and production processes that control soil methane (CH4) exchange. We studied the short-term effects of thinning, clear-cutting and stump harvesting on the CH4 exchange between soil and atmosphere at a boreal forest site in central Sweden, using an undisturbed plot as the control. Chambers in combination with a high-precision laser gas analyser were used for continuous measurements. Both the undisturbed plot and the thinned plot were net sinks of CH4, whereas the clear-cut plot and the stump harvested plot were net CH4 sources. The CH4 uptake at the thinned plot was reduced in comparison to the undisturbed plot. The shift from sink to source at the clear-cut and stump harvested plots was probably due to a rise in the water table and an increase in soil moisture, leading to lower gas diffusivity and more reduced conditions, which favour CH4 production by archea. Reduced evapotranspiration after harvesting leads to wetter soils, decreased CH4 consumption and increased CH4 production, and should be accounted for in the CH4 budget of managed forests.

Impact of Nitrogen Fertilization to Short-Rotation Willow Coppice Plantations Grown in Sweden on Yield and Economy

A fertilization trial was carried out in established short-rotation willow coppice (SRWC) plantations of two bred varieties of willow (Salix spp.; "Tora" and "Jorr") at five sites in central Sweden between 2008 and 2010. Mineral nitrogen was applied at four different rates: No fertilization (Control), 160 kg nitrogen ha−1 as a single dose after harvest (Economy), 60–100–60 kg nitrogen ha−1 in year 1–2–3 (Normal), and 160 kg nitrogen ha−1 year−1 in years 1–3 (Intensive), using a randomized block design with four replicates. The yield response (biomass increase per kg fertilizer nitrogen) was 65, 67 and 46 kg kg−1 in the Economy, Normal and Intensive treatments, respectively. The results from the fertilization trial were used for economic calculations of different fertilization strategies given varying costs for fertilization and marginal value of the increased yield (price received for wood chips minus the costs for harvest and transportation of wood chips to a district heating plant). Comparative calculations were made based on data from a previous fertilization trial during the first cutting cycle of old, non-bred varieties. The calculations showed positive net present values of fertilizing bred willow varieties given a realistic fertilization response and a price for wood chips close to the market price for forestry-based wood chips in Sweden.

High resolution seismic imaging at the planned tunnel entrance to the Forsmark repository for spent nuclear fuel, central Sweden

The Swedish Nuclear Waste Management Company (SKB) plans to build a repository for storage of high‐level radioactive spent nuclear fuel at the Forsmark site in central Sweden at a depth of about 470 m. The planned repository will cover an area of about 3.6 km2 at this depth. Prior to beginning excavation and tunneling, some detailed geophysical surveys are being performed at the planned site. One of these was a refraction seismic survey to determine depth to bedrock in the vicinity of the planned access ramp. Two lines, each about 300 m long and spaced about 35 m apart, were acquired in August 2011. Since the bedrock topography is known to be highly variable, a close receiver (2 m) and source (6 m) spacing was required to map it. This close spacing allowed the data also to be treated as reflection seismic data and some adjustments to the acquisition procedure were made in the field with this in mind to aid in the later processing. The main adjustment was that seismic data were recorded on all geophone stations simultaneously. That is, as shots were fired along one line, data were recorded along both that line and the other one. Likewise, when shots were fired along the other line, data were recorded along that line and the first line. This adjustment allowed semi‐3D coverage between the lines. Results from first break traveltime tomography along the lines indicate a depth to bedrock that is greater than that found from geotechnical observations along the lines. This discrepancy is attributed to the uppermost bedrock being highly fractured and having a velocity significantly below that expected from the intact bedrock deeper down. Reflection seismic processing of the data shows a reflection at about 20 ms (about 60 m). The reflection is interpreted to have a gentle northwesterly dip component to it. Comparison with core data in the area suggests that the reflection is from a thin (a few metres thick) fracture zone, although none of the boreholes actually penetrate the reflector where it is mapped by the seismic data. This fracture zone may be part of a larger fracture zone mapped by core drilling further to the east. The newly mapped reflector may be crossed by the ramp when excavation begins. Further seismic surveying towards the west is required to verify if this will be the case.

Simulated transformation of even-aged Norway spruce stands to multi-layered forests: an experiment to explore the potential of tree size differentiation

The study investigated the possibility to transform normal young Norway spruce (Picea abies (L.) Karst) forests to develop more heterogeneous stand structures, aiming for multi-layered forest in the long run. On three sites in central and south Sweden, 60 per cent of stand basal area was removed by thinning mainly medium-sized trees and leaving the smallest and the largest trees. Over the next 50 years, future stand development was simulated using a single-tree growth model. Simulations were run with and without ingrowth. An additional ingrowth scenario after soil preparation was tested. Basal area was kept between 10 and 20 m2 ha−1 during simulations. Projected stem wood production for the next 50 years was one-third lower compared with conventional thinning regimes. After 50 years, a multi-layered forest structure was indicated for the boreal sites in central Sweden, but not for the site in south Sweden.

Atmospheric methane removal by boreal plants

Several studies have proposed aerobic methane (CH4) emissions by plants. If confirmed, these findings would further increase the imbalance in the global CH4 budget which today underestimates CH4sinks. Oxidation by OH‐radicals in the troposphere is the major identified sink followed by smaller contribution from stratospheric loss and oxidation by methano‐ and methylotrophic bacteria in soils. This study directly investigated CH4 exchange by plants in their natural environment. At a forest site in central Sweden, in situ branch chamber measurements were used to study plant ambient CH4 exchange by spruce (Picea abies), birch (Betula pubescens), rowan (Sorbus aucuparia) and pine (Pinus sylvestris). The results show a net uptake of CH4 by all the studied plants, which might be of importance for the methane budget.

Pilgrimstad revisited - a multi-proxy reconstruction of Early/Middle Weichselian climate and environment at a key site in central Sweden

The site Pilgrimstad in central Sweden has often been cited as a key locality for discussions of ice-free/ice-covered intervals during the Early and Middle Weichselian. Multi-proxy investigations of a recently excavated section at Pilgrimstad now provide a revised picture of the climatic and environmental development between similar to 80 and 36 ka ago. The combination of sedimentology, geochemistry, OSL and 14C dating, and macrofossil, siliceous microfossil and chironomid analyses shows: (i) a lower succession of glaciofluvial/fluvial, lacustrine and glaciolacustrine sediments; (ii) an upper lacustrine sediment sequence; and (iii) Last Glacial Maximum till cover. Microfossils in the upper lacustrine sediments are initially characteristic for oligo- to mesotrophic lakes, and macrofossils indicate arctic/sub-arctic environments and mean July temperatures > 8 degrees C. These conditions were, however, followed by a return to a low-nutrient lake and a cold and dry climate. The sequence contains several hiatuses, as shown by the often sharp contacts between individual units, which suggests that ice-free intervals alternated with possible ice advances during certain parts of the Early and Middle Weichselian.

The effect of past changes in inter‐annual temperature variability on tree distribution limits

AbstractAim The northern limits of temperate broadleaved species in Fennoscanndia are controlled by their requirements for summer warmth for successful regeneration and growth as well as by the detrimental effects of winter cold on plant tissue. However, occurrences of meteorological conditions with detrimental effects on individual species are rare events rather than a reflection of average conditions. We explore the effect of changes in inter‐annual temperature variability on the abundances of the tree species Tilia cordata, Quercus robur and Ulmus glabra near their distribution limits using a process‐based model of ecosystem dynamics.Location A site in central Sweden and a site in southern Finland were used as examples for the ecotone between boreal and temperate forests in Fennoscandia. The Finnish site was selected because of the availability of varve‐thickness data.Methods The dynamic vegetation model LPJ‐GUESS was run with four scenarios of inter‐annual temperature forcing for the last 10,000 years. In one scenario the variability in the thickness of summer and winter varves from the annually laminated lake in Finland was used as a proxy for past inter‐annual temperature variability. Two scenarios were devised to explore systematically the effect of stepwise changes in the variance and shape parameter of a probability distribution. All variability scenarios were run both with and without the long‐term trend in Holocene temperature change predicted by an atmospheric general circulation model.Results Directional changes in inter‐annual temperature variability have significant effects on simulated tree distribution limits through time. Variations in inter‐annual temperature variability alone are shown to alter vegetation composition by magnitudes similar to the magnitude of changes driven by variation in mean temperatures.Main conclusions The varve data indicate that inter‐annual climate variability has changed in the past. The model results show that past changes in species abundance can be explained by changes in the inter‐annual variability of climate parameters as well as by mean climate. Because inter‐annual climatic variability is predicted to change in the future, this component of climate change should be taken into account both when making projections of future plant distributions and when interpreting vegetation history.