Synergies and trade-offs between provisioning and climate-regulating ecosystem services in reindeer herding ecosystems

Reindeer (Rangifer tarandus) pastoralism utilizes vast boreo-arctic taiga and tundra as grazing land. Highly fluctuating population sizes pose major challenges to the economy and livelihood of indigenous herder communities. In this study we investigated the effect of population fluctuations on core provisioning and regulating ecosystem services in two Sámi reindeer herding districts with contrasting fluctuation trends. We compared 50-year long time series on herd size, meat production, forage productivity, carbon footprint, and CO2-equivalence metrics for surface albedo change based on the radiative forcing concept. Our results show, for both districts, that the economic benefits from the provisioning services were higher than the costs from the regulating services. Still, there were major contrasts; the district with moderate and stable reindeer density gained nearly the double on provisioning services per unit area. The costs from increasing heat absorption due to reduction in surface albedo caused by replacement of high-reflective lichens with low-reflective woody plants, was 10.5 times higher per unit area in the district with large fluctuations. Overall, the net economic benefits per unit area were 237 % higher in the district with stable reindeer density. These results demonstrate that it is possible to minimize trade-offs between economic benefits from reindeer herding locally and global economic costs in terms of climate-regulating services by minimizing fluctuations in herds that are managed at sustainable densities.

The northernmost hyperspectral FLoX sensor dataset for monitoring of high-Arctic tundra vegetation phenology and Sun-Induced Fluorescence (SIF)

A hyperspectral field sensor (FloX) was installed in Adventdalen (Svalbard, Norway) in 2019 as part of the Svalbard Integrated Arctic Earth Observing System (SIOS) for monitoring vegetation phenology and Sun-Induced Chlorophyll Fluorescence (SIF) of high-Arctic tundra. This northernmost hyperspectral sensor is located within the footprint of a tower for long-term eddy covariance flux measurements and is an integral part of an automatic environmental monitoring system on Svalbard (AsMovEn), which is also a part of SIOS. One of the measurements that this hyperspectral instrument can capture is SIF, which serves as a proxy of gross primary production (GPP) and carbon flux rates. This paper presents an overview of the data collection and processing, and the 4-year (2019-2021) datasets in processed format are available at: https://thredds.met.no/thredds/catalog/arcticdata/infranor/NINA-FLOX/raw/catalog.html associated with https://doi.org/10.21343/ZDM7-JD72 under a CC-BY-4.0 license. Results obtained from the first three years in operation showed interannual variation in SIF and other spectral vegetation indices including MERIS Terrestrial Chlorophyll Index (MTCI), EVI and NDVI. Synergistic uses of the measurements from this northernmost hyperspectral FLoX sensor, in conjunction with other monitoring systems, will advance our understanding of how tundra vegetation responds to changing climate and the resulting implications on carbon and energy balance.

Sub-arctic mosses and lichens show idiosyncratic responses to combinations of winter heatwaves, freezing and nitrogen deposition

Arctic ecosystems are increasingly exposed to extreme climatic events throughout the year, which can affect species performance. Cryptogams (bryophytes and lichens) provide important ecosystem services in polar ecosystems but may be physiologically affected or killed by extreme events. Through field and laboratory manipulations, we compared physiological responses of seven dominant sub-Arctic cryptogams (three bryophytes, four lichens) to single events and factorial combinations of mid-winter heatwave (6°C for 7 days), re-freezing, snow removal and summer nitrogen addition. We aimed to identify which mosses and lichens are vulnerable to these abiotic extremes and if combinations would exacerbate physiological responses. Combinations of extremes resulted in stronger species responses but included idiosyncratic species-specific responses. Species that remained dormant during winter (March), irrespective of extremes, showed little physiological response during summer (August). However, winter physiological activity, and response to winter extremes, was not consistently associated with summer physiological impacts. Winter extremes affect cryptogam physiology, but summer responses appear mild, and lichens affect the photobiont more than the mycobiont. Accounting for Arctic cryptogam response to multiple climatic extremes in ecosystem functioning and modelling will require a better understanding of their winter eco-physiology and repair capabilities.

Identifying climate thresholds for dominant natural vegetation types at the global scale using machine learning: Average climate versus extremes

The global distribution of vegetation is largely determined by climatic conditions and feeds back into the climate system. To predict future vegetation changes in response to climate change, it is crucial to identify and understand key patterns and processes that couple vegetation and climate. Dynamic global vegetation models (DGVMs) have been widely applied to describe the distribution of vegetation types and their future dynamics in response to climate change. As a process-based approach, it partly relies on hard-coded climate thresholds to constrain the distribution of vegetation. What thresholds to implement in DGVMs and how to replace them with more process-based descriptions remain among the major challenges. In this study, we employ machine learning using decision trees to extract large-scale relationships between the global distribution of vegetation and climatic characteristics from remotely sensed vegetation and climate data. We analyse how the dominant vegetation types are linked to climate extremes as compared to seasonally or annually averaged climatic conditions. The results show that climate extremes allow us to describe the distribution and eco-climatological space of the vegetation types more accurately than the averaged climate variables, especially those types which occupy small territories in a relatively homogeneous ecological space. Future predicted vegetation changes using both climate extremes and averaged climate variables are less prominent than that predicted by averaged climate variables and are in better agreement with those of DGVMs, further indicating the importance of climate extremes in determining geographic distributions of different vegetation types. We found that the temperature thresholds for vegetation types (e.g. grass and open shrubland) in cold environments vary with moisture conditions. The coldest daily maximum temperature (extreme cold day) is particularly important for separating many different vegetation types. These findings highlight the need for a more explicit representation of the impacts of climate extremes on vegetation in DGVMs.

Global maps of soil temperature

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0-5 and 5-15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications.

Springtime grazing by Arctic-breeding geese reduces first- and second-harvest yields on sub-Arctic agricultural grasslands

Large population increases of Arctic-breeding waterfowls over recent decades have intensified the conflict with agricultural interests in both Eurasia and North America. In the spring-staging region Vesterålen in sub-Arctic Norway, sheep, dairy and meat farmers have reported reduced agricultural grassland yields due to pink-footed geese Anser brachyrhynchus and barnacle geese Branta leucopsis that rest and forage in the region for 3-4 weeks in spring on their way to their breeding grounds on Svalbard. Here, we report from an experimental exclosure design where goose access to plots at three grassland fields in Vesterålen was prevented. The experiment was conducted over 3 years between 2012 and 2014. Goose abundance varied greatly between fields and years as a function of variable spring weather and forage quantity, facilitating evaluation of longer-term impacts under contrasting grazing intensities. First and second harvest yields across fields and years were 20% and 19% higher in exclosures than in plots open for grazing, while total yields (sum of first and second harvests) were on average 27% higher. Within-year effects on harvest yields varied substantially, primarily due to highly contrasting sward development during the spring-staging periods. Cool weather (2012) led to slow sward development and little or no effects on harvest yields, warmer weather (2013) resulted in generally large effects, while variable weather (2014) led to treatment effects varying across fields, with one field experiencing 61% higher yields in exclosures while there were no significant impacts on first-harvest yields at the two other fields. Goose grazing did not increase dry weight-based proportions of weeds. Overall, the farmers' reports on yield-loss due to goose grazing were confirmed, although impacts varied substantially between years. A novel finding is that second-harvest yields were also reduced. For the most affected farmers, it is unlikely that the current subsidy scheme is sufficient to cover all the their losses.

Arctic browning: Impacts of extreme climatic events on heathland ecosystem CO2 fluxes

Extreme climatic events are among the drivers of recent declines in plant biomass and productivity observed across Arctic ecosystems, known as "Arctic browning." These events can cause landscape-scale vegetation damage and so are likely to have major impacts on ecosystem CO2 balance. However, there is little understanding of the impacts on CO2 fluxes, especially across the growing season. Furthermore, while widespread shoot mortality is commonly observed with browning events, recent observations show that shoot stress responses are also common, and manifest as high levels of persistent anthocyanin pigmentation. Whether or how this response impacts ecosystem CO2 fluxes is not known. To address these research needs, a growing season assessment of browning impacts following frost drought and extreme winter warming (both extreme climatic events) on the key ecosystem CO2 fluxes Net Ecosystem Exchange (NEE), Gross Primary Productivity (GPP), ecosystem respiration (Reco ) and soil respiration (Rsoil ) was carried out in widespread sub-Arctic dwarf shrub heathland, incorporating both mortality and stress responses. Browning (mortality and stress responses combined) caused considerable site-level reductions in GPP and NEE (of up to 44%), with greatest impacts occurring at early and late season. Furthermore, impacts on CO2 fluxes associated with stress often equalled or exceeded those resulting from vegetation mortality. This demonstrates that extreme events can have major impacts on ecosystem CO2 balance, considerably reducing the carbon sink capacity of the ecosystem, even where vegetation is not killed. Structural Equation Modelling and additional measurements, including decomposition rates and leaf respiration, provided further insight into mechanisms underlying impacts of mortality and stress on CO2 fluxes. The scale of reductions in ecosystem CO2 uptake highlights the need for a process-based understanding of Arctic browning in order to predict how vegetation and CO2 balance will respond to continuing climate change.

Impact of Multiple Ecological Stressors on a Sub-Arctic Ecosystem: No Interaction Between Extreme Winter Warming Events, Nitrogen Addition and Grazing

Climate change is one of many ongoing human-induced environmental changes, but few studies consider interactive effects between multiple anthropogenic disturbances. In coastal sub-arctic heathland, we quantified the impact of a factorial design simulating extreme winter warming (WW) events (7 days at 6-7°C) combined with episodic summer nitrogen (+N) depositions (5 kg N ha-1) on plant winter physiology, plant community composition and ecosystem CO2 fluxes of an Empetrum nigrum dominated heathland during 3 consecutive years in northern Norway. We expected that the +N would exacerbate any stress effects caused by the WW treatment. During WW events, ecosystem respiration doubled, leaf respiration declined (-58%), efficiency of Photosystem II (Fv/Fm) increased (between 26 and 88%), while cell membrane fatty acids showed strong compositional changes as a result of the warming and freezing. In particular, longer fatty acid chains increased as a result of WW events, and eicosadienoic acid (C20:2) was lower when plants were exposed to the combination of WW and +N. A larval outbreak of geometrid moths (Epirrita autumnata and Operophtera brumata) following the first WW led to a near-complete leaf defoliation of the dominant dwarf shrubs E. nigrum (-87%) and Vaccinium myrtillus (-81%) across all experimental plots. Leaf emergence timing, plant biomass or composition, NDVI and growing season ecosystem CO2 fluxes were unresponsive to the WW and +N treatments. The limited plant community response reflected the relative mild winter freezing temperatures (-6.6°C to -11.8°C) recorded after the WW events, and that the grazing pressure probably overshadowed any potential treatment effects. The grazing pressure and WW both induce damage to the evergreen shrubs and their combination should therefore be even stronger. In addition, +N could have exacerbated the impact of both extreme events, but the ecosystem responses did not support this. Therefore, our results indicate that these sub-arctic Empetrum-dominated ecosystems are highly resilient and that their responses may be limited to the event with the strongest impact.

Using moss and lichens in biomonitoring of heavy-metal contamination of forest areas in southern and north-eastern Poland

In the years 2014-2016 biomonitoring studies were conducted in the forest areas of south and north-eastern Poland: the Karkonosze Mountains, the Beskidy Mountains, the Borecka Forest, the Knyszyńska Forest and the Białowieska Forest. This study used epigeic moss Pleurozium schreberi and epiphytic lichens Hypogymnia physodes. Samples were collected in spring, summer and autumn. Approximately 500 samples of moss and lichens were collected for the study. In the samples, Mn, Ni, Cu, Zn, Cd, Hg and Pb concentrations were determined. Based on the obtained results, the studied areas were ranked by extent of heavy-metal deposition: Beskidy > Karkonosze Mountains > forests of north-eastern Poland. Some seasonal changes in concentrations of metals accumulated in moss and lichens were also indicated. There was observed, i.a., an increase in Cd concentration at the beginning of the growing season, which may be related to low emissions during the heating season. Analysis of the surface distribution of deposition of metals in the studied areas showed a significant contribution of nearby territorial emissions and unidentified local emission sources. The contribution of distant emission to Zn, Hg and Pb deposition levels in the Karkonosze and Beskidy region was also indicated.

Contrasting survival and physiological responses of sub-Arctic plant types to extreme winter warming and nitrogen

MAIN CONCLUSION

Evergreen plants are more vulnerable than grasses and birch to snow and temperature variability in the sub-Arctic. Most Arctic climate impact studies focus on single factors, such as summer warming, while ecosystems are exposed to changes in all seasons. Through a combination of field and laboratory manipulations, we compared physiological and growth responses of dominant sub-Arctic plant types to midwinter warming events (6 °C for 7 days) in combination with freezing, simulated snow thaw and nitrogen additions. We aimed to identify if different plant types showed consistent physiological, cellular, growth and mortality responses to these abiotic stressors. Evergreen dwarf shrubs and tree seedlings showed higher mortality (40-100%) following extreme winter warming events than Betula pubescens tree seedlings and grasses (0-27%). All species had growth reductions following exposure to - 20 °C, but not all species suffered from - 10 °C irrespective of other treatments. Winter warming followed by - 20 °C resulted in the greatest mortality and was strongest among evergreen plants. Snow removal reduced the biomass for most species and this was exacerbated by subsequent freezing. Nitrogen increased the growth of B. pubescens and grasses, but not the evergreens, and interaction effects with the warming, freezing and snow treatments were minor and few. Physiological activity during the winter warming and freezing treatments was inconsistent with growth and mortality rates across the plants types. However, changes in the membrane fatty acids were associated with reduced mortality of grasses. Sub-Arctic plant communities may become dominated by grasses and deciduous plants if winter snowpack diminishes and plants are exposed to greater temperature variability in the near future.

Understanding the drivers of extensive plant damage in boreal and Arctic ecosystems: Insights from field surveys in the aftermath of damage

The exact cause of population dieback in nature is often challenging to identify retrospectively. Plant research in northern regions has in recent decades been largely focussed on the opposite trend, namely increasing populations and higher productivity. However, a recent unexpected decline in remotely-sensed estimates of terrestrial Arctic primary productivity suggests that warmer northern lands do not necessarily result in higher productivity. As large-scale plant dieback may become more frequent at high northern latitudes with increasing frequency of extreme events, understanding the drivers of plant dieback is especially urgent. Here, we report on recent extensive damage to dominant, short, perennial heath and tundra plant populations in boreal and Arctic Norway, and assess the potential drivers of this damage. In the High-Arctic archipelago of Svalbard, we recorded that 8-50% of Cassiope tetragona and Dryas octopetala shoots were dead, and that the ratios of dead shoots increased from 2014 to 2015. In boreal Norway, 38-63% of Calluna vulgaris shoots were dead, while Vaccinium myrtillus had damage to 91% of shoots in forested sites, but was healthy in non-forested sites. Analyses of numerous sources of environmental information clearly point towards a winter climate-related reason for damage to three of these four species. In Svalbard, the winters of 2011/12 and 2014/15 were documented to be unusually severe, i.e. insulation from ambient temperature fluctuation by snow was largely absent, and ground-ice enforced additional stress. In boreal Norway, the 2013/14 winter had a long period with very little snow combined with extremely low precipitation rates, something which resulted in frost drought of uncovered Calluna plants. However, extensive outbreaks of a leaf-defoliating geometrid moth were identified as the driver of Vaccinium mortality. These results suggest that weather and biotic extreme events potentially have strong impacts on the vegetation state of northern lands.

Combining modelling tools to evaluate a goose management scheme

Many goose species feed on agricultural land, and with growing goose numbers, conflicts with agriculture are increasing. One possible solution is to designate refuge areas where farmers are paid to leave geese undisturbed. Here, we present a generic modelling tool that can be used to designate the best locations for refuges and to gauge the area needed to accommodate the geese. With a species distribution model, locations are ranked according to goose suitability. The size of the area to be designated as refuge can be chosen by including more or less suitable locations. A resource depletion model is then used to estimate whether enough resources are available within the designated refuge to accommodate all geese, taking into account the dynamics of food resources, including depletion by geese. We illustrate this with the management scheme for pink-footed goose Anser brachyrhynchus implemented in Norway. Here, all geese can be accommodated, but damage levels appear to depend on weather, land use and refuge size.

Changing Arctic snow cover: A review of recent developments and assessment of future needs for observations, modelling, and impacts

Snow is a critically important and rapidly changing feature of the Arctic. However, snow-cover and snowpack conditions change through time pose challenges for measuring and prediction of snow. Plausible scenarios of how Arctic snow cover will respond to changing Arctic climate are important for impact assessments and adaptation strategies. Although much progress has been made in understanding and predicting snow-cover changes and their multiple consequences, many uncertainties remain. In this paper, we review advances in snow monitoring and modelling, and the impact of snow changes on ecosystems and society in Arctic regions. Interdisciplinary activities are required to resolve the current limitations on measuring and modelling snow characteristics through the cold season and at different spatial scales to assure human well-being, economic stability, and improve the ability to predict manage and adapt to natural hazards in the Arctic region.

Evolution of complex symbiotic relationships in a morphologically derived family of lichen-forming fungi

We studied the evolutionary history of the Parmeliaceae (Lecanoromycetes, Ascomycota), one of the largest families of lichen-forming fungi with complex and variable morphologies, also including several lichenicolous fungi. We assembled a six-locus data set including nuclear, mitochondrial and low-copy protein-coding genes from 293 operational taxonomic units (OTUs). The lichenicolous lifestyle originated independently three times in lichenized ancestors within Parmeliaceae, and a new generic name is introduced for one of these fungi. In all cases, the independent origins occurred c. 24 million yr ago. Further, we show that the Paleocene, Eocene and Oligocene were key periods when diversification of major lineages within Parmeliaceae occurred, with subsequent radiations occurring primarily during the Oligocene and Miocene. Our phylogenetic hypothesis supports the independent origin of lichenicolous fungi associated with climatic shifts at the Oligocene-Miocene boundary. Moreover, diversification bursts at different times may be crucial factors driving the diversification of Parmeliaceae. Additionally, our study provides novel insight into evolutionary relationships in this large and diverse family of lichen-forming ascomycetes.

Climatic and biotic extreme events moderate long-term responses of above- and belowground sub-Arctic heathland communities to climate change

Climate change impacts are not uniform across the Arctic region because interacting factors causes large variations in local ecosystem change. Extreme climatic events and population cycles of herbivores occur simultaneously against a background of gradual climate warming trends and can redirect ecosystem change along routes that are difficult to predict. Here, we present the results from sub-Arctic heath vegetation and its belowground micro-arthropod community in response to the two main drivers of vegetation damage in this region: extreme winter warming events and subsequent outbreaks of the defoliating autumnal moth caterpillar (Epirrita autumnata). Evergreen dwarf shrub biomass decreased (30%) following extreme winter warming events and again by moth caterpillar grazing. Deciduous shrubs that were previously exposed to an extreme winter warming event were not affected by the moth caterpillar grazing, while those that were not exposed to warming events (control plots) showed reduced (23%) biomass from grazing. Cryptogam cover increased irrespective of grazing or winter warming events. Micro-arthropods declined (46%) following winter warming but did not respond to changes in plant community. Extreme winter warming and caterpillar grazing suppressed the CO2 fluxes of the ecosystem. Evergreen dwarf shrubs are disadvantaged in a future sub-Arctic with more stochastic climatic and biotic events. Given that summer warming may further benefit deciduous over evergreen shrubs, event and trend climate change may both act against evergreen shrubs and the ecosystem functions they provide. This is of particular concern given that Arctic heath vegetation is typically dominated by evergreen shrubs. Other components of the vegetation showed variable responses to abiotic and biotic events, and their interaction indicates that sub-Arctic vegetation response to multiple pressures is not easy to predict from single-factor responses. Therefore, while biotic and climatic events may have clear impacts, more work is needed to understand their net effect on Arctic ecosystems.

Ecosystem change and stability over multiple decades in the Swedish subarctic: complex processes and multiple drivers

The subarctic environment of northernmost Sweden has changed over the past century, particularly elements of climate and cryosphere. This paper presents a unique geo-referenced record of environmental and ecosystem observations from the area since 1913. Abiotic changes have been substantial. Vegetation changes include not only increases in growth and range extension but also counterintuitive decreases, and stability: all three possible responses. Changes in species composition within the major plant communities have ranged between almost no changes to almost a 50 per cent increase in the number of species. Changes in plant species abundance also vary with particularly large increases in trees and shrubs (up to 600%). There has been an increase in abundance of aspen and large changes in other plant communities responding to wetland area increases resulting from permafrost thaw. Populations of herbivores have responded to varying management practices and climate regimes, particularly changing snow conditions. While it is difficult to generalize and scale-up the site-specific changes in ecosystems, this very site-specificity, combined with projections of change, is of immediate relevance to local stakeholders who need to adapt to new opportunities and to respond to challenges. Furthermore, the relatively small area and its unique datasets are a microcosm of the complexity of Arctic landscapes in transition that remains to be documented.

Ecosystem response to climatic change: the importance of the cold season

Winter climate and snow cover are the important drivers of plant community development in polar regions. However, the impacts of changing winter climate and associated changes in snow regime have received much less attention than changes during summer. Here, we synthesize the results from studies on the impacts of extreme winter weather events on polar heathland and lichen communities. Dwarf shrubs, mosses and soil arthropods were negatively impacted by extreme warming events while lichens showed variable responses to changes in extreme winter weather events. Snow mould formation underneath the snow may contribute to spatial heterogeneity in plant growth, arthropod communities and carbon cycling. Winter snow cover and depth will drive the reported impacts of winter climate change and add to spatial patterns in vegetation heterogeneity. The challenges ahead lie in obtaining better predictions on the snow patterns across the landscape and how these will be altered due to winter climate change.

Impacts of extreme winter warming events on plant physiology in a sub-Arctic heath community

Insulation provided by snow cover and tolerance of freezing by physiological acclimation allows Arctic plants to survive cold winter temperatures. However, both the protection mechanisms may be lost with winter climate change, especially during extreme winter warming events where loss of snow cover from snow melt results in exposure of plants to warm temperatures and then returning extreme cold in the absence of insulating snow. These events cause considerable damage to Arctic plants, but physiological responses behind such damage remain unknown. Here, we report simulations of extreme winter warming events using infrared heating lamps and soil warming cables in a sub-Arctic heathland. During these events, we measured maximum quantum yield of photosystem II (PSII), photosynthesis, respiration, bud swelling and associated bud carbohydrate changes and lipid peroxidation to identify physiological responses during and after the winter warming events in three dwarf shrub species: Empetrum hermaphroditum, Vaccinium vitis-idaea and Vaccinium myrtillus. Winter warming increased maximum quantum yield of PSII, and photosynthesis was initiated for E. hermaphroditum and V. vitis-idaea. Bud swelling, bud carbohydrate decreases and lipid peroxidation were largest for E. hermaphroditum, whereas V. myrtillus and V. vitis-idaea showed no or less strong responses. Increased physiological activity and bud swelling suggest that sub-Arctic plants can initiate spring-like development in response to a short winter warming event. Lipid peroxidation suggests that plants experience increased winter stress. The observed differences between species in physiological responses are broadly consistent with interspecific differences in damage seen in previous studies, with E. hermaphroditum and V. myrtillus tending to be most sensitive. This suggests that initiation of spring-like development may be a major driver in the damage caused by winter warming events that are predicted to become more frequent in some regions of the Arctic and that may ultimately drive plant community shifts.

Ice encapsulation protects rather than disturbs the freezing lichen

Arctic and alpine terricolous lichens are adapted to harsh environments and are tolerant to extremely low temperatures when metabolically inactive. However, there are reports indicating that freezing can be lethal to metabolically active lichens. With a projected warmer and more unstable climate, winter precipitation at high latitudes will fall more frequently as rain, causing snowmelt and encapsulating terricolous lichens in ice or exposing them to large temperature fluctuations. Lichens are a major winter food source for reindeer in most parts of the circumpolar region. A laboratory experiment tested how three hydrated reindeer forage lichen species covered by snow, encapsulated in ice, or uncovered responded to storage at freezing temperatures and subsequent warming. Photosynthetic performance (maximal fluorescence of dark-adapted samples and net photosynthetic rates) was significantly lower in lichens not insulated by snow or ice, whereas there were few differences between the snow and ice treatments. It is suggested that snow and ice provide sufficiently moist environments to improve extracellular and reduce intracellular ice nucleation activity. Ice encapsulation, which is often lethal to vascular plants, did not have any negative effects on the studied lichens. The results indicate that complete snow and ice melt followed by refreezing can be detrimental to terricolous lichen ecosystems. Reduced lichen biomass will have a negative effect both on reindeer winter survival and the indigenous peoples who herd reindeer.

Seasonal trends in usnic acid concentrations of Arctic, alpine and Patagonian populations of the lichen Flavocetraria nivalis

The widespread secondary metabolite usnic acid, a dibenzofuran derivative, is the principal acetone-soluble compound in the lichen Flavocetraria nivalis. Seasonal variation in concentrations were studied in four populations of this lichen, three from Arctic-alpine habitats in the Northern Hemisphere, and one from Patagonian heathland in the Southern Hemisphere. Usnic acid is produced in large amounts, making up between 4% and 8% of thallus dry weight. Large seasonal variation is seen, with a trend towards peak levels in late spring and early summer, and generally low levels during autumn and winter. However, at an Arctic steppe in Central West Greenland, remarkably high levels were also detected during late autumn and early winter. Comparisons with environmental data using model selection procedures show that usnic acid levels of three of the populations are positively correlated with time of season, as measured by the proximity in time to nearest summer solstice, solar radiation levels, and temperature conditions. All these three variables are intercorrelated, thus indicating the same overall trend. For the three driest sites, precipitation rates are included in the models that best explain the variation in usnic acid. However, the explanatory powers of the models are generally low, partly due to high variation between thalli growing together and sampled at the same time. This is the first attempt to compare statistically seasonal variation in usnic acid concentrations and environmental variables, and thus also the first time it is shown that the concentration in various populations of the same lichen species shows different types of correlation with seasonal climatic changes.

Long-term impacts of simulated climatic change on secondary metabolism, thallus structure and nitrogen fixation activity in two cyanolichens from the Arctic

• Although the most pronounced effects of stratospheric ozone depletion and climate warming probably will occur in polar regions, arctic lichens have not been much studied in relation to climate change. • Samples of two arctic cyanolichens of the genus Peltigera, exposed in situ to ambient and enhanced UV-B radiation and ambient and increased temperatures, were collected in 2001, 5 yr after the establishment of the experimental set-up. Thallus dimensions and size, coverage of soralia, nitrogen fixation activity and levels of UV-C-absorbing substances were measured. • Warming had pronounced positive effects on the tridepsides methyl gyrophorate and gyrophoric acid, and unidentified trace substances. However, the combination of enhanced UV-B and increased temperatures did not lead to higher than control levels. Warming reduced coverage of soralia. There were no significant treatment effects on thallus size, dimensions and nitrogen fixation activity. • UV-B radiation did not to have any adverse effects. The accumulation of tridepsides with warming may be related to increased activity of pathogenic microorganisms or insect herbivores.

Effects of ultraviolet radiation and PAR on the content of usnic and divaricatic acids in two arctic-alpine lichens

The fruticose lichen Flavocetraria nivalis and the crustose lichen Ophioparma ventosa, both common in light-exposed arctic-alpine environments, were exposed to ultraviolet radiation (UVR) in growth chambers for 30 days. Treatment with visible light (PAR) served as control. Both species accumulate the UV-absorbing phenolic compound usnic acid in the upper cortex. The latter species also synthesises several UV-absorbing medullary compounds, among them divaricatic acid. The effects of treatment with UVR on the synthesis of these two compounds were investigated by analysing the compounds quantitatively by RP-HPLC. UV-exposed thallus tips of F. nivalis contained higher concentrations of usnic acid than those not grown under UVR. Both treatments had a positive effect on the synthesis of usnic acid in O. ventosa. An additional experiment with O. ventosa was performed by first storing samples in a low-light habitat for 1 year to obtain near-zero levels of phenolics, and thereby exposing the samples to UVR and PAR for 90 days. A rapid resynthesis of usnic acid was observed for both treatments. The amounts of divaricatic acid were highly variable in all groups, and were not correlated with usnic acid concentrations or treatments. A comparison of O. ventosa from three different habitat types showed that the highest usnic acid amounts were found in the habitat with the highest levels of solar radiation. Results indicate that the induction of usnic acid production by UVR depends on the species studied, and on how well acclimatised the lichen samples are to solar radiation before they are exposed to supplementary UVR. In lichens with an already well-developed internal screening capacity, like the population of F. nivalis, enhanced UVR need not induce further accumulation of usnic acid, but removal of UVR may induce a biodegradation of usnic acid. Results also indicate that PAR is just as important as UVR for triggering the resynthesis of usnic acid in shade-adapted lichens. Divaricatic acid seems to be of low importance for the UV-screening properties of O. ventosa.

Association between pretransplant interferon-alpha and outcome after unrelated donor marrow transplantation for chronic myelogenous leukemia in chronic phase

Treatment options for patients diagnosed with chronic myelogenous leukemia (CML) in chronic phase (CP) who lack a suitable related donor for marrow transplantation include hydroxyurea, interferon-alpha (IFN-alpha), or transplantation from an unrelated donor (URD). Most studies support the view that treatment with IFN-alpha results in prolonged survival compared with hydroxyurea therapy. Some patients are offered URD transplantation as a second-line treatment; however, the impact of pretransplant IFN-alpha on the outcome of URD transplantation is uncertain. To address this question, we evaluated the effect of pretransplant IFN-alpha therapy in 184 patients undergoing URD transplantation for CML in CP at a single center. Of the 184 patients, 114 did not receive IFN-alpha, whereas 22, 23, and 25 patients received IFN-alpha for, respectively, 1 to 5, 6 to 12, and more than 12 months before transplant. Pretransplant IFN-alpha therapy administered for > or = 6 months was associated with an increased risk of severe (grades III-IV) acute graft-versus-host disease (GVHD; relative risk [RR], 3.0; 95% confidence interval [CI], 1.4 to 6.2; P = .004) and mortality (RR, 2. 1; 95% CI, 1.3 to 3.5; P = .003) relative to less than 6 months or no IFN-alpha therapy. Increased mortality occurred between 100 and 365 days after transplant (P = .005), was limited to patients with severe acute GVHD, and was due to chronic GVHD refractory to immunosuppressive therapy. Other variables associated with mortality included HLA-DRB1 or DQB1 (but not HLA-A or B) mismatched donors, age greater than 50 years, weight > or = 110% of ideal body weight, and the absence of cytomegalovirus (CMV) or fungal prophylaxis. For patients treated with IFN-alpha for less than 6 months before transplant, who were < or = 50 years of age, received a HLA-A, B, DRB1, and DQB1 matched URD transplant, and received CMV and fungal prophylaxis after transplant (n = 48), survival was 87% +/- 5% at 5 years. These data provide a rationale for immediate transplantation in preference to extended treatment with IFN-alpha when the patient is < or = 50 years of age and has an HLA-compatible unrelated volunteer donor.

Transplantation of marrow cells from unrelated donors for treatment of high-risk acute leukemia: the effect of leukemic burden, donor HLA-matching, and marrow cell dose

Transplantation of hematopoietic stem cells from an HLA-compatible unrelated volunteer is an option for patients with acute leukemia lacking a family match. However, criteria for patient and donor selection and the most effective transplant procedures, including the number of hematopoietic cells, remain to be defined. We tested factors influencing outcome of 174 patients with primary acute leukemia receiving non-T-cell depleted marrow from unrelated donors. Median patient age was 20 years (range, 0.5 to 54 years). A multivariable analysis found that leukemia in remission at the time of transplantation was associated with improved leukemia-free survival (relative risk [RR] of treatment failure: 0.5, confidence interval [CI]: 0.3 to 0.7), and presence of blasts in the peripheral blood, as opposed to marrow involvement only or isolated extramedullary relapse, was associated with impaired outcome (RR of treatment failure: 2.5, CI: 1.7 to 5.0). The use of donors with a limited HLA-mismatch was associated with decreased leukemic relapse (RR: 0.5, CI: 0.3 to 0.9) but no improvement in leukemia-free survival compared with HLA-matched unrelated donors. Transplantation of a marrow cell dose above the median value of 3.65 x 10(8)/kg was associated with faster neutrophil (RR: 1.5, CI: 1.1 to 2.0) and platelet (RR: 4.5, CI: 2.7 to 7.5) engraftment, and decreased incidence of severe acute graft-versus-host disease (RR: 0.6, CI: 0.4 to 0.9). In patients transplanted in remission, the use of a marrow cell dose above the median translated into less nonleukemic death (RR: 0.2, CI: 0.1 to 0.4) and better leukemia-free survival (RR of treatment failure: 0.3, CI: 0.2 to 0.6). Transplant in remission with a high dose of marrow cells was associated with the best outcome in both children and adults.

Hepatosplenic candidiasis--a contraindication to marrow transplantation?

To determine whether a prior history of hepatosplenic candidiasis resulted in increased Candida-associated morbidity and mortality after marrow transplant, 15 consecutive patients with biopsy-proven hepatosplenic candidiasis were observed prospectively. All patients received amphotericin B before transplant. Amphotericin B was continued at a dose of 0.5 mg/kg/day from conditioning through marrow engraftment, at which time it was discontinued if computerized tomography (CT) evidence of disease was stable or improved. Patients were observed for progression of candidiasis for the first 100 days after transplant. The amount and duration of antifungal therapy received before transplant varied widely. The majority of patients (73%) had persistently abnormal CT scans before transplant. After transplant, 3 of 15 died (20%) with evidence of fungal disease, although fungal species differed from those diagnosed pretransplant, compared with a historical mortality rate of 90% in posttransplant patients with documented hepatosplenic candida. Comparison CT scans obtained before and after transplant showed improvement in 9 of 15 (60%), complete resolution in 2 of 15 (13%), and none showed progression. We conclude that hepatosplenic candidiasis is not an absolute contraindication to marrow transplant when patients receive amphotericin B therapy before transplant and continue therapy until engraftment is established.