| 1. |
- Antonsson, Henrik, 1976, et al.
(författare)
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Nurse plant effect of the cushion plant Silene acaulis (L.) Jacq. in an alpine environment in the subarctic Scandes, Sweden
- 2009
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Ingår i: Plant Ecology & Diversity. - : Informa UK Limited. - 1755-0874 .- 1755-1668. ; 2:1, s. 17-25
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Tidskriftsartikel (refereegranskat)abstract
- Background: Facilitation plays important roles in the structuring of plant communities and several studies have found that it tends to increase with environmental severity in alpine plant communities. In addition, cushion plants have been shown to act as nurse plants, moderating extreme environmental conditions, and providing resources for other species, with substantial effects on local plant diversity. Aims: This study addresses the nurse plant effects of Silene acaulis – a common, circumpolar alpine plant species with a compact cushion-forming growth form – along an altitude transect in the mid- to high-alpine zones in northern Sweden. Methods: The numbers of species in paired S. acaulis cushions and identical-sized control plots along an altitude transect between 1150 m and 1450 m above sea level were compared, and differences in species composition were analysed. Results: At altitudes above c. 1280 m, but not at lower altitudes, more species were found inside the cushions than in their paired control plots. Species composition was similar inside cushions and in control plots. Conclusions: Our results suggest that S. acaulis acts as a nurse plant at altitudes higher than a certain threshold (c. 1280 m at the investigated site). It appears to play an important role in creating focal points for local vascular plant diversity in highalpine environments, where vegetation is open and occurs in small patches. Keywords: facilitation; plant-to-plant interactions; Silene acaulis; species richness; stress
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| 2. |
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| 3. |
- Beylich, Achim A., et al.
(författare)
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Selection of critical key test catchments
- 2007
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Ingår i: In: Beylich AA and Warburton J, eds. Analysis of Source-to-Sink-Fluxes and Sediment Budgets in Changing High-Latitude and High-Altitude Cold Environments: SEDIFLUX Manual, First Edition.. - Trondheim : Geological Survey of Norway.
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Björk, Robert G., 1974, et al.
(författare)
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A Climate Change aspect on root dynamics and nitrogen partitioning in a tundra landscape
- 2005
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Ingår i: Sediment budgets and rates of sediment transfer across cold environments in Europe. 3rd Workshop of the ESF Network SEDIFLUX, Durham, UK, 15 – 19 December 2005..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Arctic Climate Impact Assessment (ACIA) recently reported that Arctic is rapidly changing due to Climate Change. Likewise, the mountains of Europe are going to experience large shifts in plant composition and 41-56% of the alpine species might be on the edge of extinction according to the 1st synthesis of the Global Observation Research Initiative in Alpine Environments (GLORIA). Although the tundra ecosystems are subjected to dramatical changes as a result of Climate Change, there is little knowledge of the effect on root dynamics and its implication on the nitrifying and denitrifying microbial community. Here, we compare nitrification enzyme activity (NEA) and denitrification enzyme activity (DEA) rates along an altitudinal gradient with the effects of climatic warming using Open Top Chambers (OTCs) in consideration with root dynamics and architecture. This study was conducted at Latnjajaure Field Station (LFS) located in the midalpine region in northern Sweden. LFS is the Swedish field site for the International Tundra Experiment (ITEX), established in 1993. This gives an opportunity to investigate long-term effects of climatic warming by OTCs and an altitudinal gradient (1000m to 1365m), both within a very small geographical range. The OTCs used at LFS increases the soil surface temperature by approximately 1.5ºC whereas air temperatures normally falls with 0.6ºC with every hundred meter of increased altitude. To analyse the NEA and DEA we used an anaerobic incubation technique, based on acetylene inhibition technique, resulting in N2O as the only end product, which then were analysed by gas chromatography. Soil cores were additionally sampled in the OTCs to study the effects of climatic warming on the root system. The specific root length, root length density and root biomass were determined for the different root fractions. The results from NEA and DEA contradict each other. The gradient study show decreased NEA and DEA rates with falling altitude, whereas the warming experiment show a slight non significant increase due to the temperature enhancement by OTCs. The preliminary results from the root sampling indicate that there is a plant community specific response in root architecture, which has an output on root biomass and particularly in the fraction of fine roots, although, climatic warming did not have any significant affect on the root biomass. The fact that altitudinal temperature decline did not reduce NEA and DEA rates might in part be explained of the variables measured here, although they are not conclusive.
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| 5. |
- Björk, Robert G., 1974, et al.
(författare)
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Biocomplexity and biogeochemical cycling in terrestrial ecosystems
- 2008
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Ingår i: 1st Workshop and planning meeting ‘Winter processes in arctic tundra ecosystems’, Longyearbyen, Svalbard, 9-11 June 2008..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The activities concerted within Tellus are aiming at adding essential knowledge to the system scale aspects of fluxes and transformation of carbon (C) in the terrestrial domain. The systems studied are the Arctic, the alpine area of the Scandes, and organic soils in southern Sweden (including both forest and agricultural systems). The main research sites are Skogaryd, in the boreal forest, and Latnjajaure Field Station in the western Abisko Mountains. The overall aim with the present work at Skogaryd is to increase our fundamental understanding of process involved in cycling of C and nitrogen (N) in forest ecosystems, and generate high quality data on C/N cycle from drained forested organic soils using micrometeorological methods, laser and automatic chambers techniques. Skogaryd is also included in NitroEurope, an EU project focusing on modelling and up-scaling of greenhouse gas fluxes, and is incorporated in two interdisciplinary research centres at University of Gothenburg, Tellus (http://www.tellus.science.gu.se/english/) and Gothenburg Atmospheric Science Centre (GAC; http://www.chalmers.se/gmv/gac-en/). Furthermore, our research group has been instrumental in the establishment of the International Tundra Experiment (ITEX) network by Professor Ulf Molau who chaired ITEX 1992-1996 and Latnjajaure Field Station have been a master site within the network since 1992. As an outcome, much of the research in Latnjajaure during the 90ies was focused plant responsiveness to global change. However, since 2002 the research has expanded and projects are now running that are dealing with snow-vegetation-soil interactions. Recently, a collaboration with Dr. Elisabeth J. Cooper, of the University Centre in Svalbard (UNIS), and Prof. Bo Elberling, University of Copenhagen, was initiated focusing on winter soil respiration and comparing sub-arctic and high-arctic trace gas fluxes. Currently, we have these projects running in tundra ecosystems: 1.Climate-related changes in tundra ecosystems – An IPY project (PIs Björk and Molau with others). 2.Temporal pattern of CO2, CH4 and N2O fluxes and soil microbial structure in snow-covered ecosystems (PIs Björk, Elberling, Klemedtsson, and Cooper). 3.The responsiveness of tundra ecosystems to warming: linking above- and below-ground components (PI Björk). There is also a project under evaluation by the Swedish Research Council, which are entitled ‘The fate of carbon in high-arctic tundra ecosystems under changing snow cover conditions’. The research questions that we want to address within this winter ecology network are 1) to increase our understand of the C dynamics (thus explicitly linking ecosystem C sequestration pattern and soil microbial dynamics) in tundra ecosystems, and, particularly, (2) to improve the winter resolution of carbon dioxide (and other greenhouse gases) effluxes to the atmosphere. Furthermore, (3) to understand the influence of changing snow cover, both in depth and duration, for the C dynamics in tundra ecosystems.
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| 6. |
- Björk, Robert G., 1974, et al.
(författare)
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Can present melt-out patterns identify snowbed plant species vulnerable to climate change?
- 2005
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Ingår i: Second International Conference on Arctic Research Planning – ICARP II, Copenhagen, Denmark, 10 – 12 November 2005..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Snowbeds form in topographic depressions which accumulate high amounts of snow during the winter months and the final snowmelt does not occur until late in the growing season. Many species preferentially grow in snowbed habitats and some of these are even limited to habitats in which winter snow accumulates. In connection with the Global Warming forecast, snowbed ecosystems of alpine Europe are regarded as particularly vulnerable in IPCC’s 2001 assessment report. This study is running at Latnjajaure Field Station, in northern Swedish Lapland, where four snowbed plant communi¬ties are studied. The snowbeds are of the “moderate type”, which means that they are melting out before the end of July, and they are situated in both heath and meadow sites. In this study we try to identify vulnerable plant species by the use of snow dynamics and plant community structure. Snowbed plant communi¬ties have high abundances of bryophytes along with high bryophyte diversity, 55 identified bryophytes within the snowbeds. The dominant bryophytes (e.g. Kiaeria stakei, Polytrichastrum sexangulare, Sanionia nivalis, Anthelia juratzkana, Scapania obcordata) are also snowbed specialist. The preliminary results show that earlier melt-out day will increase the vascular plant cover by 0.8 percent per day as well as increase in lichen cover by 0.5 percent per day. Bryophytes will suffer the most by decreasing in abundance by 1.7 percent per day of earlier melt-out day. Although, the response among bryophyte species is not uniform with Kiaeria stakei having the large decrease followed by Anthelia juratzkana, whereas Polytrichastrum sexangulare does not respond at all. There is also interaction among bryophyte species.
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| 7. |
- Björk, Robert G., 1974, et al.
(författare)
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Ecology of Alpine Snowbeds and the Impact of Global Change
- 2007
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Ingår i: Arctic, Antarctic, and Alpine Research. ; 39:1
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Recension (övrigt vetenskapligt/konstnärligt)abstract
- The ecosystems of alpine snowbed habitats are reviewed with emphasis on ecosystem functioning and capability to adapt to current and predicted global change. Snowbeds form in topographic depressions that accumulate large amounts of snow during the winter months, and the final snowmelt does not occur until late in the growing season. Many species preferentially grow in snowbed habitats and some of these are even restricted to these habitats. In this review we identify several ecosystem services which snowbeds provide to the alpine landscape. For instance, snowbeds provide a steady water and nutrient supply to adjacent plant communities and offer newly emerged high-quality food for herbivores late in the growing season. We also propose that alpine snowbeds are much more productive than earlier thought, especially when the very short growing season and often high grazing pressure are taken fully into account. Furthermore, we propose that bryophytes and graminoids (grasses, sedges, and rushes) probably will be most negatively impacted by global change, and the snowbed plant communities will be invaded by species from adjacent plant communities, especially by shrubs and boreal species. As snowbed plants have special growth conditions, their sensitivity and ability to respond rapidly to changes in annual snowfall patterns make snowbed communities particularly vulnerable in a warmer climate, and thereby sensitive indicators of global change
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| 8. |
- Björk, Robert G., 1974, et al.
(författare)
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Effect of reduced below-ground C sequestration on greenhouse gas fluxes within dry tundra ecosystems along an altitudinal gradient
- 2008
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Ingår i: Mountain soils under a changing climate and land-use, Birmensdorf, Switzerland, 6–8 March 2008..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- It has been suggested that global climate change will have a great impact on arctic and alpine areas, affecting the carbon and nitrogen dynamics in these ecosystems. Temperature are widely thought to be the main limiting factors for plants and microorganisms in these tundra ecosystem, and warming the soil in high latitude tundra have been shown to change trace gas (CO2, CH4, and N2O) exchange rates and increase N availability. However, little attention has been paid, to date, to variations in trace gas fluxes with altitude, although it is a key determinant of temperature and should therefore be strongly correlated with these fluxes if temperature is the main variable affecting these processes. The objectives of this study were, therefore, to measure growing season variation in carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes from heath plant communities along an altitudinal gradient ranging from mid alpine (~950 m a.s.l) to high alpine (~1,365 m a.s.l) zones within an alpine tundra landscape in the subarctic region of Sweden. Furthermore, by reducing the C supply to the root system and mycorrhizal fungi (achieved by clipping the above-ground plant parts) we wanted to decrease the rhizosphere priming effect and thereby change the C sequestration pattern within the ecosystem to be able to separate heterotrophic and root respiration. The study was conducted on the slopes of Mt. Latnjatjårro (1,447 m; 68°21’N, 18°31’E), near Latnjajaure Field Station, 16 km west of Abisko in Northern Sweden. Flux measurements of CO2 were analysed using a portable infra red gas analyser (IRGA) based on the SBA-4 OEM CO2 Analyzer (PP System). Fluxes of CH4 and N2O were sampled using a closed chamber system, where chambers were placed at collars, which were gently pressed into the ground. Air from the chamber was circulated into a headspace bottle and analysed by gas chromatograph. A two-step incubation technique was also used to determine Nitrification Enzyme Activity (NEA) for analysing nitrification in acid soils with low activities, and for Denitrification Enzyme Activity (DEA) an anaerobic incubation technique, based on acetylene inhibition of the N2O-reductase, was used. Preliminary, our results show a decrease in average growing season CO2 efflux with altitude, but not constantly, and although soil temperature in general decreased with altitude there were no perfect fit between soil temperature and average growing season CO2 efflux. Furthermore, the clipping of the above-ground plant parts reduced the CO2 efflux at all altitudes, except at 1,225 m a.s.l., and in August the reduction in CO2 efflux was largest at 950 m a.s.l. (231 mg CO2 m-2 h-1) and decreased with altitude (to 33 mg CO2 m-2 h-1 at 1,365 m a.s.l). However, the proportion of the reduced CO2 efflux, corresponding to root respiration, was relatively constant with altitude (28-43% of total respiration), except at 1,365 m a.s.l where the root respiration only contributed with 12%. The fluxes of CH4 and N2O was very low with poor resolution of the fluxes due to many samples had a flux lower than the limit of detection for the gas chromatograph, thus no particularly pattern was discerned. However, to try to improve the resolution along the altitudinal gradient the NEA and DEA was used and give a potential measure on the nitrification and denitrification rates, which goes back to the actual populations of nitrifiers and denitrifiers in the soil. The results shows that there were a substantial increases with altitude in the activities of nitrifying and denitrifying microbes, this is contrary to expectations and the average growing season CO2 efflux if the decline in mean annual temperature with altitude is the main driver for nitrification and denitrification. Thus, our results are just indicative for the complex interaction that may occur along altitudinal gradients. But, clearly, there is a need for further studies to assess the effects of altitude and temperature on carbon and nitrogen dynamics in high alpine and arctic ecosystems across wide altitudinal ranges.
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| 9. |
- Björk, Robert G., 1974, et al.
(författare)
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Effect of reduced below-ground C sequestration on greenhouse gas fluxes within dry tundra ecosystems along an altitudinal gradient
- 2008
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Ingår i: The 15th ITEX workshop, Reykjavik, Iceland, 9–12 October 2008..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- It has been suggested that global climate change will have a great impact on arctic and alpine areas, affecting the carbon and nitrogen dynamics in these ecosystems. Temperature is widely thought to be the main limiting factor for plants and microorganisms in these tundra ecosystems, and warming the soil in high latitude tundra has been shown to change trace gas (CO2, CH4, and N2O) exchange rates and increase N availability. However, little attention has been paid, to date, to variations in trace gas fluxes with altitude, although altitude is a key determinant of temperature and should therefore be strongly correlated with these fluxes if temperature is a major variable affecting these processes. The objectives of this study were, therefore, to measure growing season variation in carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes from heath plant communities along an altitudinal gradient ranging from mid alpine (~950 m a.s.l) to high alpine (~1,365 m a.s.l) zones within an alpine tundra landscape in the subarctic region of Sweden. Furthermore, by reducing the C supply to the root system and mycorrhizal fungi (achieved by clipping the above-ground plant parts) we wanted to decrease the rhizosphere priming effect and thereby change the C sequestration pattern within the ecosystem to be able to separate heterotrophic and autotrophic respiration. The study was conducted on the slopes of Mt. Latnjatjårro (1,447 m a.s.l.; 68°21’N, 18°31’E), near Latnjajaure Field Station, 16 km west of Abisko in Northern Sweden. Flux measurements of CO2 were analysed using a portable infra red gas analyser (IRGA) based on the SBA-4 OEM CO2 Analyzer (PP System). Fluxes of CH4 and N2O were sampled using a closed chamber system, where chambers were placed on collars, which were gently pressed into the ground. Air from the chamber was circulated into a headspace bottle and analysed by gas chromatograph. A two-step incubation technique was also used to determine Nitrification Enzyme Activity (NEA) for analysing nitrification in acid soils with low activities, and for Denitrification Enzyme Activity (DEA) an anaerobic incubation technique, based on acetylene inhibition of the N2O-reductase, was used. Our results show a decrease in average growing season CO2 efflux with altitude, but not consistently, and although soil temperature in general decreased with altitude there was only a loose association between soil temperature and average growing season CO2 efflux. Furthermore, the clipping of the above-ground plant parts reduced the CO2 efflux at all altitudes, except at 1,225 m a.s.l., and in August the reduction in CO2 efflux was largest at 950 m a.s.l. (231 mg CO2 m-2 h-1) and decreased with altitude (to 33 mg CO2 m-2 h-1 at 1,365 m a.s.l.). However, the proportion of the reduced CO2 efflux, corresponding to autotrophic respiration, was relatively constant with altitude (28-43% of total respiration), except at 1,365 m a.s.l. where the autotrophic respiration only contributed 12%. The fluxes of CH4 and N2O were very low, and resolution was constrained by the large number of samples with apparent fluxes below the limit of detection for the gas chromatograph, thus no particular pattern could be identified. However, to try to improve the resolution along the altitudinal gradient, the NEA and DEA were used, and give a potential measure of the nitrification and denitrification rates, which goes back to the actual populations of nitrifiers and denitrifiers in the soil. The results show that there were a substantial increases with altitude in the activities of nitrifying and denitrifying microbes; this is contrary to expectations and the average growing season CO2 efflux if the decline in mean annual temperature with altitude is the main driver for nitrification and denitrification. Thus, our results are indicative of the complex interaction that may occur along altitudinal gradients. But, clearly, there is a need for further studies to assess the effects of altitude and temperature on carbon and nitrogen dynamics in high alpine and arctic ecosystems across wide altitudinal ranges.
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| 10. |
- Björk, Robert G., 1974, et al.
(författare)
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ITEX at Latnjajaure
- 2007
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Ingår i: The 14th ITEX workshop, Falls Creek, Victoria, Australia, 2–6 February 2007..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- ITEX and ITEX-related research at Latnjajaure in northern Swedish Lapland has been quite diverse during the past few years, with most emphasis at the ecosystem and landscape scales. The basic warming experiment with open-top chambers and control plots is still running in a variety of ecosystems since 1993. During 2006, a re-inventory of OTCs and controls in Eriophorum vaginatum (cottongrass) dominated tussock tundra at the outlet of the lake showed significant changes since the last point-framing in 1995, not only in the OTCs but also in the control plots. No species were lost but dominance relationships among species had changed dramatically. The underlying permafrost had degraded substantially; it was continuous here in the early 1990ies but could not be detected in 2006. Already in 2003, a geo-radar transect showed no indication of remaining permafrost at the site (Else Kohlstrup et al., Uppsala University). The ecosystem had undergone a clear desiccation, and formerly water-filled boulder pits were now invaded by moss-dominated pioneer vegetation. The cottongrass tussocks had become less dense and more "fluffy" and had gradually been invaded by lingonberry (Vaccinium vitis-idaea), the most expansive species in the community. The effect size was about twice as high in OTCs as in controls. The cottongrass tussock tundra is one of a handful of vegetation types pointed out as particularly sensitive to Climate Change, based on the listing in IPCC's Third Assessment Report 2001. Our team is undertaking a longer-term project including four of these systems, i.e., snowbeds, tussock tundra, high alpine fellfields, and mesic alpine heath (being invaded by mountain birch). A helicopter inventory of possible sites for tussock tundra in the region in August 2005 revealed a total stock of ca 2 km2 in Sweden (compared with the circum-arctic total of 336,000 km2). As a further outcome of the project on indicator ecosystems, new project, Alpine Cliff Ecology (ACE) was initiated at Latnjajaure in 2006 (see separate presentation). In the snowbed project, initiated in 2002, four snowbed plant communi¬ties are studied. The snowbeds are of the “moderate" class (melting out before the end of July), and they are situated in both heath and meadow sites. Our current studies encompass plant community scale to landscape scale, and include, e.g., monitoring of snow dynamics, microbial and plant community structure in fertilized and control plots, lemming population dynamics, nitrogen and debris deposition, and soil processes (for microbial studies see separate abstract/presentation). Interestingly, our preliminary data suggests that the plant community structure does not change due to fertilization. In 2004 we sampled the OTCs, established in 1993, in dry meadow and dry heath for root morphology characteristics, root biomass distribution, and microbial activity. This study shows that tundra plants may respond to climate change by increasing their specific root length (SRL; m gDM-1) and specific root area (SRA; m2 kgDM -1), whilst the microbial activity may remain unaffected. Furthermore, this study suggests that there might be incorporation of C in tundra soils partly as a result of increased turnover of the finer roots produced within the OTCs. However, the response across plant communities is not consistent. The "Meeting of Litters" experiment headed by Hans Cornelissen, Vrije Universiteit Amsterdam (Holland) was finalized in 2004, with a multi-authored paper in review at present. The project focused on comparative decomposition studies on litter samples from a large number of ITEX sites gathered at two experimental outdoor facilities in Sweden: Latnjajaure (mid alpine) and Abisko (sub-alpine). Other international within-ITEX activities at Latnja include a field research campaign by Catharine Copass Thompson and Carrie McCalley from the Marine Biological Laboratory, Woods Hole, and Robert Bell and Kerry Dinsmore from the University of Edinburgh. They visited the Latnjajaure Field Station between August 2 and August 9, 2004. Their research in the Abisko area entailed linking measurements of carbon fluxes to the Normalized Difference Vegetation Index (NDVI), an index of greenness which can be measured on multiple scales, including from satellites. The goal for the 2004 summer was to cover as many different kinds of vegetation types in the region as possible, given the constraints of their sampling protocol. The up-scaling to the landscape level was manifested by the final publication of the GIS-based vegetation map over the Latnjajaure catchment (12 km2, 1 m2 pixel resolution) by Lindblad et al. (Pirineos 161: 3-32, 2006). This work is part of Karin Lindblad's Ph.D. thesis for her dissertation 26 January 2007.
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