Arvid Odland

Local temperatures inferred from plant communities suggest strong spatial buffering of climate warming across Northern Europe

Recent studies from mountainous areas of small spatial extent (<2500 km(2) ) suggest that fine-grained thermal variability over tens or hundreds of metres exceeds much of the climate warming expected for the coming decades. Such variability in temperature provides buffering to mitigate climate-change impacts. Is this local spatial buffering restricted to topographically complex terrains? To answer this, we here study fine-grained thermal variability across a 2500-km wide latitudinal gradient in Northern Europe encompassing a large array of topographic complexities. We first combined plant community data, Ellenberg temperature indicator values, locally measured temperatures (LmT) and globally interpolated temperatures (GiT) in a modelling framework to infer biologically relevant temperature conditions from plant assemblages within <1000-m(2) units (community-inferred temperatures: CiT). We then assessed: (1) CiT range (thermal variability) within 1-km(2) units; (2) the relationship between CiT range and topographically and geographically derived predictors at 1-km resolution; and (3) whether spatial turnover in CiT is greater than spatial turnover in GiT within 100-km(2) units. Ellenberg temperature indicator values in combination with plant assemblages explained 46-72% of variation in LmT and 92-96% of variation in GiT during the growing season (June, July, August). Growing-season CiT range within 1-km(2) units peaked at 60-65°N and increased with terrain roughness, averaging 1.97 °C (SD = 0.84 °C) and 2.68 °C (SD = 1.26 °C) within the flattest and roughest units respectively. Complex interactions between topography-related variables and latitude explained 35% of variation in growing-season CiT range when accounting for sampling effort and residual spatial autocorrelation. Spatial turnover in growing-season CiT within 100-km(2) units was, on average, 1.8 times greater (0.32 °C km(-1) ) than spatial turnover in growing-season GiT (0.18 °C km(-1) ). We conclude that thermal variability within 1-km(2) units strongly increases local spatial buffering of future climate warming across Northern Europe, even in the flattest terrains.

Thirteen years of wetland vegetation succession following a permanent drawdown, Myrkdalen Lake, Norway

Myrkdalen Lake in Western Norway was subjected to a 1.4 mdrawdown in June 1987. Plant establishment and vegetation succession on theexposed sediments of a fluvial delta plain was monitored through 2000. Theinvestigated area extended from the original Equisetumfluviatile zone to the new lake edge. The substrate was homogeneousand consisted mainly of minerogenous fluvial sediments. Vegetation data weresampled within continuous quadrats along transects perpendicular to the shore,and they dropped 93 cm in elevation. Detrended CorrespondenceAnalysis and Canonical Correspondence Analysis confirmed that “time sincedrawdown” and “elevation of the quadrats” appeared to be ofnearly equal importance in explaining succession. Plant establishment was rapidon the exposed sediments due to a seed bank and to rapid invasion of plants.Thesuccession includes both floristic change as a function of time and a spatialseparation in relation to the water level. The species succession was marked bya growth form progression: mosses and annuals →non-clonal perennials→clonal perennials. After one month, the annual Subulariaaquatica and small acrocarpous mosses dominated the site. Dominancethen shifted to Deschampsia cespitosa, Juncus filiformis, Blasiapusilla and Polytrichum commune. Subsequentlythere was an increase of Carex vesicaria in the lower zoneand Calamagrostis purpurea in the upper zone,while Phalaris arundinacea was common over most of theelevational gradient. Equisetum declined where it haddominated before drawdown, but it expanded gradually towards the new shoreline.The vegetation remained dynamic after 13 years and it is not considered to beinequilibrium with the new environmental gradient yet. However, annual changesmeasured by DCA scores have slowed and two vegetation zones have developed. Themajor vegetational differences along the elevational gradient can be explainedby the height of the mean June water limit. This example of species turnover inspace and time may be a model for other successions that occur along a stronggradient.

Outbreaks by canopy-feeding geometrid moth cause state-dependent shifts in understorey plant communities

The increased spread of insect outbreaks is among the most severe impacts of climate warming predicted for northern boreal forest ecosystems. Compound disturbances by insect herbivores can cause sharp transitions between vegetation states with implications for ecosystem productivity and climate feedbacks. By analysing vegetation plots prior to and immediately after a severe and widespread outbreak by geometrid moths in the birch forest-tundra ecotone, we document a shift in forest understorey community composition in response to the moth outbreak. Prior to the moth outbreak, the plots divided into two oligotrophic and one eutrophic plant community. The moth outbreak caused a vegetation state shift in the two oligotrophic communities, but only minor changes in the eutrophic community. In the spatially most widespread communities, oligotrophic dwarf shrub birch forest, dominance by the allelopathic dwarf shrub Empetrum nigrum ssp. hermaphroditum, was effectively broken and replaced by a community dominated by the graminoid Avenella flexuosa, in a manner qualitatively similar to the effect of wild fires in E. nigrum communities in coniferous boreal forest further south. As dominance by E. nigrum is associated with retrogressive succession the observed vegetation state shift has widespread implications for ecosystem productivity on a regional scale. Our findings reveal that the impact of moth outbreaks on the northern boreal birch forest system is highly initial-state dependent, and that the widespread oligotrophic communities have a low resistance to such disturbances. This provides a case for the notion that climate impacts on arctic and northern boreal vegetation may take place most abruptly when conveyed by changed dynamics of irruptive herbivores.

Development of vegetation in created wetlands in western Norway.

Abstract The Myrkdalen lake, western Norway was subjected to a permanent 1.4 m drawdown in June 1987. After the drawdown, channels and artificial islands were constructed within the exposed floodplain system. Two permanent transects were established within this man-made environment, and these have been analyzed annually until 1995. The quadrats lie all on the same type of substrate, are at different elevations in relation to the water-level. This paper describes vegetation development on these newly created islands. The investigation shows major vegetational changes during the eight year period. Two main processes have taken place, vegetation zonation and primary succession. The first year after the construction, most of the created sites had a similar floristic composition, regardless of elevation. Major dominants during the first three years (e.g., Subularia aquatica, Marchantia polymorpha, Blasia pusilla, and numerous acrocarpous mosses) disappeared or were greatly reduced, and they were gradually replaced by species which were climax species in the wetland communities before the drawdown (e.g., Carex rostrata, C. vesicaria, Phalaris arundinacea, Salix nigricans). The main vegetational change occurred between the third and the fourth year. After three years characteristic vegetation zones were differentiated, with aquatic plants and helophytes in the lowermost parts, and willow shrubs in the uppermost parts of the islands

Oligotrophic and mesotrophic vegetation in southern Scandinavian mountains. Gradients in species and community distribution extracted by numerical analyses of earlier published vegetation descriptions

Fennoscandian mountain vegetation and its ecology has been a field of intensive research for more than a century, and the main aims of the studies have in most cases been to perform regional vegetation descriptions with subsequent phytosociological classifications. The main patterns in species distribution and vegetation composition along important ecological gradients are therefore well known, but so far no generally accepted classification of mountain vegetation has been reached. The present study is based on a compilation of 306 oligotrophic and mesotrophic communities (with data from more than 2200 stands and 4800 relevés) from the Scandinavian mountains. The sampling unit used here is the described plant communities, and an importance value (IV) is calculated for all species (taxa) based on their frequency and mean cover. The main aims were: (1) to quantify similarities and dissimilarities between earlier described mountain vegetation communities by use of numerical methods, (2) to discuss the results in relation to earlier proposed classifications of Scandinavian mountain vegetation, and (3) to interprete the main gradients in the data. DCA axis 1 (5.04 SD units long with an eigenvalue of 0.60) was interpreted to represent a complex gradient with increasing length of snow cover, soil moisture and altitude. DCA axis 2 describes a complex gradient in soil thickness, soil moisture and altitude. Eighteen groups of communities were separated by TWINSPAN, and these are discussed in relation to earlier classifications. Most of these groups have some overlap in the ordination diagram, indicating that the communities make a continuum. Along the main gradient, three community clusters could be separated: (1) communities dominated by lichens and ericaceous species; (2) fern-, graminoidand Salix herbacea-dominated communities; and (3) extreme moss-dominated snow beds.

Seasonal variation in the frequency of abnormal anaphases and mitotic index values in wild populations of herb-Paris (Paris quadrifolia L., Trilliaceae): implications for genetic monitoring

The main aim of our study was to investigate seasonal variation in the frequency of abnormal anaphases and mitotic index values in wild populations of herb-Paris (Paris quadrifolia L., Trilliaceae). Plant material was collected in the year 2000 in Norway and in the year 2001 in Lithuania. There was statistically significant variation in the mitotic index values (chi(2)=1087.9, d.f.=16, P<0.0001) with the highest values during the active growth period in May and the lowest values at the end of vegetation period in September. Seasonal variation in the frequency of abnormal anaphases was statistically significant as well (chi(2)=28.23, d.f.=16, P=0.0297). The most frequent type of anaphase abnormality was vagrant chromosomes (64.2%) followed by bridges (28.6%), fragments (3.6%), sticky chromosomes (2.4%) and multipolar anaphases (1.2%). During the fieldwork, quite deep late frosts occurred. Mitotic index was lower in the plants collected immediately after the frosts or 1 week later than in the plants sampled before the frosts (52+/-13 and 123+/-15, respectively, P=0.0014). On the contrary, frequency of abnormal anaphases was statistically significantly elevated (P=0.0082) in plants after the frosts (6.35+/-1.54%) when compared to plants before the frosts (2.49+/-0.56%). Our results clearly indicated significant variation in the mitotic index values and frequency of abnormal anaphases in the wild populations of herb-Paris during the growth season. This variation may be related to the physiological conditions of the analysed plants as well as to certain ecological factors.

Patterns in the secondary succession of a Carex vesicaria L. wetland following a permanent drawdown

The Myrkdalen Lake, western Norway, was subjected to a ca. 1.4 m permanent drawdown in June 1987. This left the original wetland vegetation belts “hanging” over the new water level. One year after the drawdown, a permanent transect with contiguous 1.0m × 0.5 m quadrats was established through a Carex vesicariawetland belt, and was analysed annually through 2001. The transect was 17 m long and included the lower part of a Phalaris arundinaceavegetation and the upper part of an Equisetum fluviatile vegetation. All quadrats were located on the same type of substrate and extended through a 65-cm difference in elevation. During the study period, the transect was completely inundated for only 6 days. A secondary succession was initiated immediately after the drawdown. The main trend was a gradual decreased cover of C. vesicaria and an increase particularly in the cover of P. arundinaceaand Calamagrostis purpurea. Regression analyses indicated that variation in the cover of the different species could be expressed as linear, quadratic, or exponential functions of the number of years since drawdown. Parallel with the decreased abundance of C. vesicaria, there was a linear decrease in the number of its fertile shoots. Very low numbers of flowering shoots were found after the mean cover of P. arundinaceaexceeded the cover of C. vesicaria. The study indicates that the drawdown resulted in a hydrological regime that was not optimal for C. vesicaria. Despite this, a clonal wetland sedge may obviously survive a major drawdown for more than 14 years.

Differences in richness of vascular plants, mosses, and liverworts in southern Norwegian alpine vegetation

Background: Theories regarding patterns of species richness often focus on single factors such as stress, productivity and disturbance, but these have recently been challenged. Vascular plant species richness is also frequently used as a surrogate for richness in other species groups, but species richness relationships have rarely been studied in alpine areas. Aims: To establish the relationship between environmental variables and species richness of vascular plants, mosses and liverworts, and to identify common patterns across these different groups. Methods: A stratified random sampling procedure was followed to select sample plots (4 m2) from ecologically different homogeneous alpine vegetation stands. The data were analysed by Pearsson correlation analysis, regression analysis, stepwise regression analysis, principal correlation analysis (PCA), and redundancy analysis (RDA). Results: 210 vascular plants, 152 mosses and 89 liverworts were identified from 304 plots. Humped (quadratic) responses were found for some species groups only in relation to date of snowmelt and total vascular plant cover. Vascular plant and moss richness were strongly positively correlated with soil richness. Conclusions: Richness of vascular plants and mosses, and mosses and liverworts, may be used as surrogates for one another in the alpine vegetation plots studied, but vascular plant richness cannot be used as a surrogate for liverwort richness.

Effect of latitude and mountain height on the timberline (Betula pubescens ssp. czerpanovii) elevation along the central Scandinavian mountain range

Previously published isoline maps of Fennoscandian timberlines show that their highest elevations lie in the high mountain areas in central south Norway and from there the limits decrease in all directions. These maps are assumed to show differences in “climatic forest limits”, but the isoline patterns indicate that factors other than climate may be decisive in most of the area. Possibly the effects of ‘massenerhebung’ and the “summit syndrome” may locally have major effects on the timberline elevation. The main aim of the present study is to quantify the effect of latitude and mountain height on the regional variation of mountain birch timberline elevation. The study is a statistical analysis of previous published data on the timberline elevation and nearby mountain height. Selection of the study sites has been stratified to the Scandinavian mountain range (the Scandes) from 58 to 71 o N where the timberlines reach their highest elevations. The data indicates that only the high mountain massifs in S Norway and N Sweden are sufficiently high to allow birch forests to reach their potential elevations. Stepwise regression shows that latitude explains 70.9% while both latitude and mountain explain together 89.0% of the timberline variation. Where the mountains are low (approximately 1000 m higher than the measured local timberlines) effects of the summit syndrome will lower the timberline elevation substantially and climatically determined timberlines will probably not have been reached. This indicates that models of future timberlines and thereby the alpine area extent in a warmer world may result in unrealistic conclusions without taking account of local mountain heights.

Relationships between vegetation, air and soil temperatures on Norwegian mountain summits

ABSTRACT Geographic variations in air and soil temperatures are dependent on several biotic and abiotic factors. Air temperature has mostly been used to characterize thermal conditions for plant life, and studies of bioclimatic gradients. From a biological point of view, it is also essential to know to what extent soil temperature is coupled with air temperature. In this study, we have quantified the deviations between soil and air temperatures along gradients in latitude, altitude, and possible effects of the vegetation. Sixteen different temperature variables were estimated from 49 vegetation plots on 19 mountain summits along the high mountain range in Norway, ranging from 230 to 1780 m a.s.l., and from 59°N to 71°N. Soil and air temperature variables were estimated from the study plots during one year. All air and soil temperature variables were significantly correlated, but the rate of explanation was mostly relatively low (37.0–60.0%), except during the growing season. Start of the growing season, determined by air or soil temperatures, could deviate by 38 days mainly due to effects of frozen soils. Vegetation composition, especially the lichen cover, had a major impact on soil temperature, Dwarf shrub cover increased significantly with increasing July temperature. Lichen abundance and degree of soil frost were strongly correlated, and explained a major part of the variation in soil temperatures. The study indicates that air temperature is generally a poor proxy for soil temperature in cold areas, except during July.