Summary 0 A dwarf shrub heath in subarctic Sweden was subjected to factorial manipulation of air temperature\ water and nutrient supply for 4 years[ The responses of the vegetation to the perturbations were then assessed by point intercept "quadrat# analy! sis followed by determination of above!ground biomass[ 1 Nineteen vascular and 12 non!vascular species "or species groups# were recorded and the most dramatic response was that of the grass Calama`rostis lapponica to nutrient addition\ with abundance being stimulated by a factor of more than 07 compared with plots not subjected to nutrient addition[ Calama`rostis lapponica did not show any signi_cant responses to temperature or water alone but there was a synergistic interaction between all three variables[ 2 The abundance of the dominant dwarf shrubs "Empetrum hermaphroditum\ Vac! cinium vitis!idaea\ V[ myrtillus and V[ uli`inosum# was una}ected by the perturbations but elevated temperature stimulated the biomass of V[ uli`inosum by 014) and total shrub biomass by 05)[ The low ratio of current year|s growth to standing biomass may have concealed other responses of the dwarf shrub group to the perturbations[ 3 The response of the non!vascular~ora to the perturbations was either neutral or negative\ with lichens showing the most dramatic responses[ Lichen biomass on temperature! and nutrient!amended plots was 45) and 07)\ respectively\ of that on unperturbed plots[ Nutrients also exerted a negative e}ect on the biomass of bryophy! tes\ and the combined biomass of lichens and bryophytes on nutrient!treated plots was almost a third of that on plots which did not receive additional nutrients[ 4 Total above!ground biomass was not a}ected by the perturbations but the total number of interceptions determined by point quadrat analysis was greater on the elevated temperature and nutrient!treated plots[ Point quadrat analysis also revealed an accumulation of litter and standing dead material in response to the nutrient and temperature perturbations\ both singly and in combination\ suggesting a faster turnover of plant material[ 5 Both temperature and nutrients increased canopy height and also interacted syn! ergistically such that together they resulted in a mean canopy height of 03[8 cm compared with 7[9 cm in plots subjected to neither perturbation[ 6 Nutrient addition lowered species richness by 06[6)\ mainly through its impact on the mosses and lichens[ 7 In general\ nutrient addition elicited the greatest response\ followed by temperature\ with water exerting little measurable in~uence[ There were a number of important interactions that were often synergistic\ and some involved water[ 8 Species| responses were highly individualistic and changes in the community were mediated through the response of a small number of key species already present in the community\ with no invasion of new species[ In the short term at least\~oristic diversity may decline as understorey species become less abundant and immigration by new species is inhibited by the dominance of clonal a...

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Mass loss, together with nitrogen and carbon loss, from above‐ground material and roots of Festuca vivipara were followed for 13 months in a high Arctic polar semi‐desert and a low Arctic tree‐line dwarf shrub heath. Festuca vivipara for the study was obtained from plants cultivated at two different CO2 concentrations (350 and 500 μL L–1) in controlled environment chambers in the UK. Each of the four resource types (shoots or roots from plants grown in elevated or ambient CO2 concentrations) was subsequently placed in an experiment simulating aspects of environmental change in each Arctic ecosystem. Air, litter and soil temperatures were increased using open‐topped polythene tents at both sites, and a 58% increase in summer precipitation was simulated at the high Arctic site. Mass loss was greatest at the low Arctic site, and from the shoot material, rather than the roots. Shoots grown under an elevated CO2 concentration decomposed more slowly at the high Arctic site, and more quickly at the low Arctic one, than shoots grown at ambient CO2. After 13 months, greater amounts of C and N remained in above‐ground litter from plants grown under elevated, rather than ambient, CO2 at the polar semi‐desert site, although lower amounts of C remained in elevated CO2 litter at the low Arctic ecosystem. In the high Arctic, roots grown in the 500 μL L–1 CO2 concentration decomposed significantly more slowly than below‐ground material derived from the ambient CO2 chambers. Elevated CO2 concentrations significantly increased the inital C:N ratio, % soluble carbohydrates and α‐cellulose content, and significantly decreased the inital N content, of the above‐ground material compared to that derived from the ambient treatment. Initially, the C:N ratio and percentage N were similar in both sets of roots derived from the two different CO2 treatments, but soluble carbohydrate and α‐cellulose concentrations were higher, and percentage lignin lower, in the elevated CO2 treatments.The tent treatments significantly retarded shoot decomposition in both ecosystems, probably because of lower litter bag moisture contents, although the additional precipitation treatment had no effect on mass loss from the above‐ground material. The results suggest that neither additional summer precipitation (up to 58%), nor soil temperature increase of 1 °C, which may occur by the end of the next century as an effect of a predicted 4 °C rise in air temperature, had an appreciable effect on root decomposition in the short term in a high Arctic soil. However, at the low Arctic site, greater root decomposition, and a lower pool of root N remaining, were observed where soil temperature was increased by 2 °C in response to a 4 °C rise in air temperature. These results suggest that decomposition below‐ground in this ecosystem would increase as an effect of predicted climate change. These data also show that there is a difference in the initial results of decomposition processes between the two Arctic ecosystems in response to simulated environmental change.

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Many general circulation models (GCMs) predict that high latitude environments will experience substantial warming over the next 100 years, which will be particularly pronounced during the winter months. Precipitation is also expected to increase but there is uncertainty as to the amount and spatial variation. The flora and fauna of the arctic and subarctic regions, together with indigenous people, such as the Saami, are particularly vunerable to rising temperatures and changing precipitation. Mean monthly temperature and precipitation data were examined for the last 100 years for northern Finland. These data were further analysed for the first and second half of the 20th century. There was no discernible warming trend between 1876 and 1993, but a significant annual warming (r=0.344, ρ<0.05) occurred in the period 1901–1945, together with a significant summer warming (r=0.381, ρ<0.05). Warming has occurred consistently in May and June over the last 100 years and there appears to be a current (i.e. post 1990) annual trend, mostly due to winter warming. The greatest temperature anomaly increase for the period 1901–1945 was in the winter months (+0.72°C). The degree of temperature variation in the winter is greater than in the summer and has risen from 3.98°C for December in the period 1901–1945 to 4.37°C in the period 1946–1990. This is attributed to the recent high variability in the North Atlantic Oscillation (NAO) Index. Annual precipitation has increased significantly during the period 1880–1993. The period 1946–1990 was wetter than 1901–1945, with greater variability particularly in the summer months, which contribute most to the annual precipitation in Lapland. Copyright © 2000 Royal Meteorological Society