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  • 1. Anthony, Kenneth R. N.
    et al.
    Marshall, Paul A.
    Abdulla, Ameer
    Beeden, Roger
    Bergh, Chris
    Black, Ryan
    Eakin, C. Mark
    Game, Edward T.
    Gooch, Margaret
    Graham, Nicholas A. J.
    Green, Alison
    Heron, Scott F.
    van Hooidonk, Ruben
    Knowland, Cheryl
    Mangubhai, Sangeeta
    Marshall, Nadine
    Maynard, Jeffrey A.
    McGinnity, Peter
    McLeod, Elizabeth
    Mumby, Peter. J.
    Nyström, Magnus
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Obura, David
    Oliver, Jamie
    Possingham, Hugh P.
    Pressey, Robert L.
    Rowlands, Gwilym P.
    Tamelander, Jerker
    Wachenfeld, David
    Wear, Stephanie
    Operationalizing resilience for adaptive coral reef management under global environmental change2015In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 21, no 1, p. 48-61Article, review/survey (Refereed)
    Abstract [en]

    Cumulative pressures from global climate and ocean change combined with multiple regional and local-scale stressors pose fundamental challenges to coral reef managers worldwide. Understanding how cumulative stressors affect coral reef vulnerability is critical for successful reef conservation now and in the future. In this review, we present the case that strategically managing for increased ecological resilience (capacity for stress resistance and recovery) can reduce coral reef vulnerability (risk of net decline) up to a point. Specifically, we propose an operational framework for identifying effective management levers to enhance resilience and support management decisions that reduce reef vulnerability. Building on a system understanding of biological and ecological processes that drive resilience of coral reefs in different environmental and socio-economic settings, we present an Adaptive Resilience-Based management (ARBM) framework and suggest a set of guidelines for how and where resilience can be enhanced via management interventions. We argue that press-type stressors (pollution, sedimentation, overfishing, ocean warming and acidification) are key threats to coral reef resilience by affecting processes underpinning resistance and recovery, while pulse-type (acute) stressors (e.g. storms, bleaching events, crown-of-thorns starfish outbreaks) increase the demand for resilience. We apply the framework to a set of example problems for Caribbean and Indo-Pacific reefs. A combined strategy of active risk reduction and resilience support is needed, informed by key management objectives, knowledge of reef ecosystem processes and consideration of environmental and social drivers. As climate change and ocean acidification erode the resilience and increase the vulnerability of coral reefs globally, successful adaptive management of coral reefs will become increasingly difficult. Given limited resources, on-the-ground solutions are likely to focus increasingly on actions that support resilience at finer spatial scales, and that are tightly linked to ecosystem goods and services.

  • 2. Cloern, James E.
    et al.
    Abreu, Paulo C.
    Carstensen, Jacob
    Chauvaud, Laurent
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Grall, Jacques
    Greening, Holly
    Johansson, John Olov Roger
    Kahru, Mati
    Sherwood, Edward T.
    Xu, Jie
    Yin, Kedong
    Human activities and climate variability drive fast-paced change across the world's estuarine-coastal ecosystems2016In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 22, no 2, p. 513-529Article, review/survey (Refereed)
    Abstract [en]

    Time series of environmental measurements are essential for detecting, measuring and understanding changes in the Earth system and its biological communities. Observational series have accumulated over the past 2-5 decades from measurements across the world's estuaries, bays, lagoons, inland seas and shelf waters influenced by runoff. We synthesize information contained in these time series to develop a global view of changes occurring in marine systems influenced by connectivity to land. Our review is organized around four themes: (i) human activities as drivers of change; (ii) variability of the climate system as a driver of change; (iii) successes, disappointments and challenges of managing change at the sea-land interface; and (iv) discoveries made from observations over time. Multidecadal time series reveal that many of the world's estuarine-coastal ecosystems are in a continuing state of change, and the pace of change is faster than we could have imagined a decade ago. Some have been transformed into novel ecosystems with habitats, biogeochemistry and biological communities outside the natural range of variability. Change takes many forms including linear and nonlinear trends, abrupt state changes and oscillations. The challenge of managing change is daunting in the coastal zone where diverse human pressures are concentrated and intersect with different responses to climate variability over land and over ocean basins. The pace of change in estuarine-coastal ecosystems will likely accelerate as the human population and economies continue to grow and as global climate change accelerates. Wise stewardship of the resources upon which we depend is critically dependent upon a continuing flow of information from observations to measure, understand and anticipate future changes along the world's coastlines.

  • 3. Dainese, Matteo
    et al.
    Isaac, Nick J. B.
    Powney, Gary D.
    Bommarco, Riccardo
    Öckinger, Erik
    Kuussaari, Mikko
    Pöyry, Juha
    Benton, Tim G.
    Gabriel, Doreen
    Hodgson, Jenny A.
    Kunin, William E.
    Lindborg, Regina
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Sait, Steven M.
    Marini, Lorenzo
    Landscape simplification weakens the association between terrestrial producer and consumer diversity in Europe2017In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 23, no 8, p. 3040-3051Article in journal (Refereed)
    Abstract [en]

    Land-use change is one of the primary drivers of species loss, yet little is known about its effect on other components of biodiversity that may be at risk. Here, we ask whether, and to what extent, landscape simplification, measured as the percentage of arable land in the landscape, disrupts the functional and phylogenetic association between primary producers and consumers. Across seven European regions, we inferred the potential associations (functional and phylogenetic) between host plants and butterflies in 561 seminatural grasslands. Local plant diversity showed a strong bottom-up effect on butterfly diversity in the most complex landscapes, but this effect disappeared in simple landscapes. The functional associations between plant and butterflies are, therefore, the results of processes that act not only locally but are also dependent on the surrounding landscape context. Similarly, landscape simplification reduced the phylogenetic congruence among host plants and butterflies indicating that closely related butterflies become more generalist in the resources used. These processes occurred without any detectable change in species richness of plants or butterflies along the gradient of arable land. The structural properties of ecosystems are experiencing substantial erosion, with potentially pervasive effects on ecosystem functions and future evolutionary trajectories. Loss of interacting species might trigger cascading extinction events and reduce the stability of trophic interactions, as well as influence the longer term resilience of ecosystem functions. This underscores a growing realization that species richness is a crude and insensitive metric and that both functional and phylogenetic associations, measured across multiple trophic levels, are likely to provide additional and deeper insights into the resilience of ecosystems and the functions they provide.

  • 4. De Frenne, Pieter
    et al.
    Brunet, Jorg
    Shevtsova, Anna
    Kolb, Annette
    Graae, Bente J.
    Chabrerie, Olivier
    Cousins, Sara Ao
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Decocq, Guillaume
    De Schrijver, An
    Diekmann, Martin
    Gruwez, Robert
    Heinken, Thilo
    Hermy, Martin
    Nilsson, Christer
    Stanton, Sharon
    Tack, Wesley
    Willaert, Justin
    Verheyen, Kris
    Temperature effects on forest herbs assessed by warming and transplant experiments along a latitudinal gradient2011In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 17, no 10, p. 3240-3253Article in journal (Refereed)
    Abstract [en]

    Slow-colonizing forest understorey plants are probably not able to rapidly adjust their distribution range following large-scale climate change. Therefore, the acclimation potential to climate change within their actual occupied habitats will likely be key for their short-and long-term persistence. We combined transplant experiments along a latitudinal gradient with open-top chambers to assess the effects of temperature on phenology, growth and reproductive performance of multiple populations of slow-colonizing understorey plants, using the spring flowering geophytic forb Anemone nemorosa and the early summer flowering grass Milium effusum as study species. In both species, emergence time and start of flowering clearly advanced with increasing temperatures. Vegetative growth (plant height, aboveground biomass) and reproductive success (seed mass, seed germination and germinable seed output) of A. nemorosa benefited from higher temperatures. Climate warming may thus increase future competitive ability and colonization rates of this species. Apart from the effects on phenology, growth and reproductive performance of M. effusum generally decreased when transplanted southwards (e. g., plant size and number of individuals decreased towards the south) and was probably more limited by light availability in the south. Specific leaf area of both species increased when transplanted southwards, but decreased with open-top chamber installation in A. nemorosa. In general, individuals of both species transplanted at the home site performed best, suggesting local adaptation. We conclude that contrasting understorey plants may display divergent plasticity in response to changing temperatures which may alter future understorey community dynamics.

  • 5. D'Orangeville, Loic
    et al.
    Maxwell, Justin
    Kneeshaw, Daniel
    Pederson, Neil
    Duchesne, Louis
    Logan, Travis
    Houle, Daniel
    Arseneault, Dominique
    Beier, Colin M.
    Bishop, Daniel A.
    Druckenbrod, Daniel
    Fraver, Shawn
    Girard, Francois
    Halman, Joshua
    Hansen, Chris
    Hart, Justin L.
    Hartmann, Henrik
    Kaye, Margot
    Leblanc, David
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Ouimet, Rock
    Rayback, Shelly
    Rollinson, Christine R.
    Phillips, Richard P.
    Drought timing and local climate determine the sensitivity of eastern temperate forests to drought2018In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, no 6, p. 2339-2351Article in journal (Refereed)
    Abstract [en]

    Projected changes in temperature and drought regime are likely to reduce carbon (C) storage in forests, thereby amplifying rates of climate change. While such reductions are often presumed to be greatest in semi-arid forests that experience widespread tree mortality, the consequences of drought may also be important in temperate mesic forests of Eastern North America (ENA) if tree growth is significantly curtailed by drought. Investigations of the environmental conditions that determine drought sensitivity are critically needed to accurately predict ecosystem feedbacks to climate change. We matched site factors with the growth responses to drought of 10,753 trees across mesic forests of ENA, representing 24 species and 346 stands, to determine the broad-scale drivers of drought sensitivity for the dominant trees in ENA. Here we show that two factors-the timing of drought, and the atmospheric demand for water (i.e., local potential evapotranspiration; PET)-are stronger drivers of drought sensitivity than soil and stand characteristics. Droughtinduced reductions in tree growth were greatest when the droughts occurred during early-season peaks in radial growth, especially for trees growing in the warmest, driest regions (i.e., highest PET). Further, mean species trait values (rooting depth and psi(50)) were poor predictors of drought sensitivity, as intraspecific variation in sensitivity was equal to or greater than interspecific variation in 17 of 24 species. From a general circulation model ensemble, we find that future increases in earlyseason PET may exacerbate these effects, and potentially offset gains in C uptake and storage in ENA owing to other global change factors.

  • 6. Frank, Dorothe A.
    et al.
    Reichstein, Markus
    Bahn, Michael
    Thonicke, Kirsten
    Frank, David
    Mahecha, Miguel D.
    Smith, Pete
    Van der Velde, Marijn
    Vicca, Sara
    Babst, Flurin
    Beer, Christian
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Max Planck Institute for Biogeochemistry, Jena, Germany.
    Buchmann, Nina
    Canadell, Josep G.
    Ciais, Philippe
    Cramer, Wolfgang
    Ibrom, Andreas
    Miglietta, Franco
    Poulter, Ben
    Rammig, Anja
    Seneviratne, Sonia I.
    Walz, Ariane
    Wattenbach, Martin
    Zavala, Miguel A.
    Zscheischler, Jakob
    Effects of climate extremes on the terrestrial carbon cycle: concepts, processes and potential future impacts2015In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 21, no 8, p. 2861-2880Article, review/survey (Refereed)
    Abstract [en]

    Extreme droughts, heat waves, frosts, precipitation, wind storms and other climate extremes may impact the structure, composition and functioning of terrestrial ecosystems, and thus carbon cycling and its feedbacks to the climate system. Yet, the interconnected avenues through which climate extremes drive ecological and physiological processes and alter the carbon balance are poorly understood. Here, we review the literature on carbon cycle relevant responses of ecosystems to extreme climatic events. Given that impacts of climate extremes are considered disturbances, we assume the respective general disturbance-induced mechanisms and processes to also operate in an extreme context. The paucity of well-defined studies currently renders a quantitative meta-analysis impossible, but permits us to develop a deductive framework for identifying the main mechanisms (and coupling thereof) through which climate extremes may act on the carbon cycle. We find that ecosystem responses can exceed the duration of the climate impacts via lagged effects on the carbon cycle. The expected regional impacts of future climate extremes will depend on changes in the probability and severity of their occurrence, on the compound effects and timing of different climate extremes, and on the vulnerability of each land-cover type modulated by management. Although processes and sensitivities differ among biomes, based on expert opinion, we expect forests to exhibit the largest net effect of extremes due to their large carbon pools and fluxes, potentially large indirect and lagged impacts, and long recovery time to regain previous stocks. At the global scale, we presume that droughts have the strongest and most widespread effects on terrestrial carbon cycling. Comparing impacts of climate extremes identified via remote sensing vs. ground-based observational case studies reveals that many regions in the (sub-)tropics are understudied. Hence, regional investigations are needed to allow a global upscaling of the impacts of climate extremes on global carbon-climate feedbacks.

  • 7. Gentsch, Norman
    et al.
    Wild, Birgit
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. University of Vienna, Austria; Austrian Polar Research Institute, Austria.
    Mikutta, Robert
    Capek, Petr
    Diakova, Katka
    Schrumpf, Marion
    Turner, Stephanie
    Minnich, Cynthia
    Schaarschmidt, Frank
    Shibistova, Olga
    Schnecker, Joerg
    Urich, Tim
    Gittel, Antje
    Santruckova, Hana
    Barta, Jiri
    Lashchinskiy, Nikolay
    Fuss, Roland
    Richter, Andreas
    Guggenberger, Georg
    Temperature response of permafrost soil carbon is attenuated by mineral protection2018In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, no 8, p. 3401-3415Article in journal (Refereed)
    Abstract [en]

    Climate change in Arctic ecosystems fosters permafrost thaw and makes massive amounts of ancient soil organic carbon (OC) available to microbial breakdown. However, fractions of the organic matter (OM) may be protected from rapid decomposition by their association with minerals. Little is known about the effects of mineral-organic associations (MOA) on the microbial accessibility of OM in permafrost soils and it is not clear which factors control its temperature sensitivity. In order to investigate if and how permafrost soil OC turnover is affected by mineral controls, the heavy fraction (HF) representing mostly MOA was obtained by density fractionation from 27 permafrost soil profiles of the Siberian Arctic. In parallel laboratory incubations, the unfractionated soils (bulk) and their HF were comparatively incubated for 175 days at 5 and 15 degrees C. The HF was equivalent to 70 +/- 9% of the bulk CO2 respiration as compared to a share of 63 +/- 1% of bulk OC that was stored in the HF. Significant reduction of OC mineralization was found in all treatments with increasing OC content of the HF (HF-OC), clay-size minerals and Fe or Al oxyhydroxides. Temperature sensitivity (Q10) decreased with increasing soil depth from 2.4 to 1.4 in the bulk soil and from 2.9 to 1.5 in the HF. A concurrent increase in the metal-to-HF-OC ratios with soil depth suggests a stronger bonding of OM to minerals in the subsoil. There, the younger C-14 signature in CO2 than that of the OC indicates a preferential decomposition of the more recent OM and the existence of a MOA fraction with limited access of OM to decomposers. These results indicate strong mineral controls on the decomposability of OM after permafrost thaw and on its temperature sensitivity. Thus, we here provide evidence that OM temperature sensitivity can be attenuated by MOA in permafrost soils.

  • 8.
    Greiser, Caroline
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Meineri, Eric
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. CNRS, France; IRD, France; IMBE, France; Aix Marseille University, France; University of Avignon, France.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hiding from the climate: Characterizing microrefugia for boreal forest understory species2020In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486Article in journal (Refereed)
    Abstract [en]

    Climate warming is likely to shift the range margins of species poleward, but fine-scale temperature differences near the ground (microclimates) may modify these range shifts. For example, cold-adapted species may survive in microrefugia when the climate gets warmer. However, it is still largely unknown to what extent cold microclimates govern the local persistence of populations at their warm range margin. We located 99 microrefugia, defined as sites with edge populations of 12 widespread boreal forest understory species (vascular plants, mosses, liverworts and lichens) in an area of ca. 24,000 km(2) along the species' southern range margin in central Sweden. Within each population, a logger measured temperature eight times per day during one full year. Using univariate and multivariate analyses, we examined the differences of the populations' microclimates with the mean and range of microclimates in the landscape, and identified the typical climate, vegetation and topographic features of these habitats. Comparison sites were drawn from another logger data set (n = 110), and from high-resolution microclimate maps. The microrefugia were mainly places characterized by lower summer and autumn maximum temperatures, late snow melt dates and high climate stability. Microrefugia also had higher forest basal area and lower solar radiation in spring and autumn than the landscape average. Although there were common trends across northern species in how microrefugia differed from the landscape average, there were also interspecific differences and some species contributed more than others to the overall results. Our findings provide biologically meaningful criteria to locate and spatially predict potential climate microrefugia in the boreal forest. This opens up the opportunity to protect valuable sites, and adapt forest management, for example, by keeping old-growth forests at topographically shaded sites. These measures may help to mitigate the loss of genetic and species diversity caused by rear-edge contractions in a warmer climate.

  • 9.
    Griffiths, Jennifer R.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Kadin, Martina
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Nascimento, Francisco J. A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Tamelander, Tobias
    Törnroos, Anna
    Bonaglia, Stefano
    Stockholm University, Faculty of Science, Department of Geological Sciences. Lund University, Sweden.
    Bonsdorff, Erik
    Brüchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gårdmark, Anna
    Järnström, Marie
    Kotta, Jonne
    Lindegren, Martin
    Nordström, Marie C.
    Norkko, Alf
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. University of Helsinki, Finland.
    Olsson, Jens
    Weigel, Benjamin
    Zydelis, Ramunas
    Blenckner, Thorsten
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Niiranen, Susa
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Winder, Monika
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    The importance of benthic-pelagic coupling for marine ecosystem functioning in a changing world2017In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 23, no 6, p. 2179-2196Article, review/survey (Refereed)
    Abstract [en]

    Benthic-pelagic coupling is manifested as the exchange of energy, mass, or nutrients between benthic and pelagic habitats. It plays a prominent role in aquatic ecosystems, and it is crucial to functions from nutrient cycling to energy transfer in food webs. Coastal and estuarine ecosystem structure and function are strongly affected by anthropogenic pressures; however, there are large gaps in our understanding of the responses of inorganic nutrient and organic matter fluxes between benthic habitats and the water column. We illustrate the varied nature of physical and biological benthic-pelagic coupling processes and their potential sensitivity to three anthropogenic pressures - climate change, nutrient loading, and fishing - using the Baltic Sea as a case study and summarize current knowledge on the exchange of inorganic nutrients and organic material between habitats. Traditionally measured benthic-pelagic coupling processes (e.g., nutrient exchange and sedimentation of organic material) are to some extent quantifiable, but the magnitude and variability of biological processes are rarely assessed, preventing quantitative comparisons. Changing oxygen conditions will continue to have widespread effects on the processes that govern inorganic and organic matter exchange among habitats while climate change and nutrient load reductions may have large effects on organic matter sedimentation. Many biological processes (predation, bioturbation) are expected to be sensitive to anthropogenic drivers, but the outcomes for ecosystem function are largely unknown. We emphasize how improved empirical and experimental understanding of benthic-pelagic coupling processes and their variability are necessary to inform models that can quantify the feedbacks among processes and ecosystem responses to a changing world.

  • 10. Harden, Jennifer W.
    et al.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography. Stanford University, USA.
    Ahlström, Anders
    Blankinship, Joseph C.
    Bond-Lamberty, Ben
    Lawrence, Corey R.
    Loisel, Julie
    Malhotra, Avni
    Jackson, Robert B.
    Ogle, Stephen
    Phillips, Claire
    Ryals, Rebecca
    Todd-Brown, Katherine
    Vargas, Rodrigo
    Vergara, Sintana E.
    Cotrufo, M. Francesca
    Keiluweit, Marco
    Heckman, Katherine A.
    Crow, Susan E.
    Silver, Whendee L.
    DeLonge, Marcia
    Nave, Lucas E.
    Networking our science to characterize the state, vulnerabilities, and management opportunities of soil organic matter2018In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, no 2, p. e705-e718Article in journal (Refereed)
    Abstract [en]

    Soil organic matter (SOM) supports the Earth's ability to sustain terrestrial ecosystems, provide food and fiber, and retains the largest pool of actively cycling carbon. Over 75% of the soil organic carbon (SOC) in the top meter of soil is directly affected by human land use. Large land areas have lost SOC as a result of land use practices, yet there are compensatory opportunities to enhance productivity and SOC storage in degraded lands through improved management practices. Large areas with and without intentional management are also being subjected to rapid changes in climate, making many SOC stocks vulnerable to losses by decomposition or disturbance. In order to quantify potential SOC losses or sequestration at field, regional, and global scales, measurements for detecting changes in SOC are needed. Such measurements and soil-management best practices should be based on well established and emerging scientific understanding of processes of C stabilization and destabilization over various timescales, soil types, and spatial scales. As newly engaged members of the International Soil Carbon Network, we have identified gaps in data, modeling, and communication that underscore the need for an open, shared network to frame and guide the study of SOM and SOC and their management for sustained production and climate regulation.

  • 11. Hillebrand, Helmut
    et al.
    Soininen, Janne
    Snoeijs, Pauline
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Warming leads to higher species turnover in a coastal ecosystem2010In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 16, no 4, p. 1181-1193Article in journal (Refereed)
    Abstract [en]

    The responses of ecological communities and ecosystems to increased rates of environmental change will be strongly influenced by variation in the diversity of community composition. Yet, our understanding of how diversity is affected by rising temperatures is inconclusive and mainly based on indirect evidence or short-term experiments. In our study, we analyse the diversity and species turnover of benthic epilithic communities within the thermal flume of a nuclear power plant at the Swedish coast. This flume covers the range of predicted future temperature rises. Species composition was significantly different between control sites and sites with higher temperatures. We found that temperature had little effect on the number of species in three functional groups (macroinvertebrates, benthic diatoms, and macrophytes, which here comprise multicellular algae and macroscopic colonies of unicellular algae and cyanobacteria), neither at single sampling dates nor summed for the entire observation year. However, species turnover significantly increased with increasing temperature for diatoms, macrophytes and invertebrates. Different temperature regimes resulted in significantly different species composition and indicator species. Thus, increasing temperatures in the thermal flume increased temporal beta-diversity and decreased compositional stability of communities, although observed richness did not change at any point in time. We highlight the need to investigate the consequences of such declines in compositional stability for functional stability of ecosystem processes.

  • 12.
    Humborg, Cristoph
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Mörth, Carl Magnus
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Sundbom, Marcus
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Borg, Hans
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Blenckner, Thorsten
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Giesler, R.
    Ittekkot, V.
    CO2 supersaturation along the aquatic conduit in Swedish watersheds as constrained by terrestrial respiration, aquatic respiration and weathering2010In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 6, no 7, p. 1966-1978Article in journal (Refereed)
    Abstract [en]

    We tested the hypothesis that CO2 supersaturation along the aquatic conduit over Sweden can be explained by processes other than aquatic respiration. A first generalized-additive model (GAM) analysis evaluating the relationships between single water chemistry variables and pCO(2) in lakes and streams revealed that water chemistry variables typical for groundwater input, e.g., dissolved silicate (DSi) and Mg2+ had explanatory power similar to total organic carbon (TOC). Further GAM analyses on various lake size classes and stream orders corroborated the slightly higher explanatory power for DSi in lakes and Mg2+ for streams compared with TOC. Both DSi and TOC explained 22-46% of the pCO(2) variability in various lake classes (0.01-> 100 km2) and Mg2+ and TOC explained 11-41% of the pCO(2) variability in the various stream orders. This suggests that aquatic pCO(2) has a strong groundwater signature. Terrestrial respiration is a significant source of the observed supersaturation and we may assume that both terrestrial respiration and aquatic respiration contributed equally to pCO(2) efflux. pCO(2) and TOC concentrations decreased with lake size suggesting that the longer water residence time allow greater equilibration of CO2 with the atmosphere and in-lake mineralization of TOC. For streams, we observed a decreasing trend in pCO(2) with stream orders between 3 and 6. We calculated the total CO2 efflux from all Swedish lakes and streams to be 2.58 Tg C yr-1. Our analyses also demonstrated that 0.70 Tg C yr-1 are exported to the ocean by Swedish watersheds as HCO3- and CO(3)2- of which about 0.56 Tg C yr-1 is also a residual from terrestrial respiration and constitute a long-term sink for atmospheric CO2. Taking all dissolved inorganic carbon (DIC) fluxes along the aquatic conduit into account will lower the estimated net ecosystem C exchange (NEE) by 2.02 Tg C yr-1, which corresponds to 10% of the NEE in Sweden.

  • 13.
    Johansson, Maria U.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Frisk, Carl A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Nemomissa, Sileshi
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Disturbance from traditional fire management in subalpine heathlands increases Afro-alpine plant resilience to climate change2018In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, no 7, p. 2952-2964Article in journal (Refereed)
    Abstract [en]

    Species are often controlled by biotic factors such as competition at the warm edge of their distribution range. Disturbances at the treeline, disrupting competitive dominance, may thus enable alpine species to utilize lower altitudes. We searched for evidence for range expansion in grazed, fire-managed Ethiopian subalpine Erica heathlands across a 25-year chronosequence. We examined vascular plant composition in 48 plots (5x5m) across an altitudinal range of 3,465-3,711m.a.s.l. and analyzed how community composition changed in relation to increasing competition over time (using a Shade index based on Erica shrub height and cover) and altitude. Species habitats and altitudinal ranges were derived from literature. Time since fire explained more variation (r(2)=.41) in species composition than altitude did (r(2)=.32) in an NMDS analysis. Community-weighted altitudinal optima for species in a plot decreased strongly with increasing shade (GLM, Standardized Regression Coefficient SRC=-.41, p=.003), but increased only weakly with altitude (SRC=.26, p=.054). In other words, young stands were dominated by species with higher altitudinal optima than old stands. Forest species richness increased with Log Shade index (SRC=.12, p=.008), but was unaffected by altitude (SRC=-.07, p=.13). However, richness of alpine and heathland species was not highest in plots with lowest Shade index, but displayed a unimodal pattern with an initial increase, followed by a decrease when shading increased (altitude was not significant). Our results indicate that disturbance from the traditional patch burning increases the available habitat for less competitive high-altitude plants and prevents tree line ascent. Therefore, maintaining, but regulating, the traditional land use increases the Afro-alpine flora's resilience to global warming. However, this system is threatened by a new REDD+ program attempting to increase carbon storage via fire suppression. This study highlights the importance of understanding traditional management regimes for biodiversity conservation in cultural landscapes in an era of global change.

  • 14.
    Johansson, T.
    et al.
    Lund Univ.
    Malmer, N.
    Lund Univ.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Friborg, T.
    Copenhagen Univ.
    Åkerman, J.A.
    Lund Univ.
    Mastepanov, M.
    Lund Univ.
    Christensen, T.R.
    Lund Univ.
    Decadal vegetation changes in a northern peatland, greenhouse gas fluxes and net radiative forcing.2006In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 12, no 12, p. 2352-2369Article in journal (Refereed)
    Abstract [en]

    Thawing permafrost in the sub-Arctic has implications for the physical stability and biological dynamics of peatland ecosystems. This study provides an analysis of how permafrost thawing and subsequent vegetation changes in a sub-Arctic Swedish mire have changed the net exchange of greenhouse gases, carbon dioxide (CO<sub>2</sub>) and CH<sub>4</sub> over the past three decades. Images of the mire (ca. 17 ha) and surroundings taken with film sensitive in the visible and the near infrared portion of the spectrum, [i.e. colour infrared (CIR) aerial photographs from 1970 and 2000] were used. The results show that during this period the area covered by hummock vegetation decreased by more than 11% and became replaced by wet-growing plant communities. The overall net uptake of C in the vegetation and the release of C by heterotrophic respiration might have increased resulting in increases in both the growing season atmospheric CO<sub>2</sub> sink function with about 16% and the CH<sub>4</sub> emissions with 22%. Calculating the flux as CO<sub>2</sub> equivalents show that the mire in 2000 has a 47% greater radiative forcing on the atmosphere using a 100-year time horizon. Northern peatlands in areas with thawing sporadic or discontinuous permafrost are likely to act as larger greenhouse gas sources over the growing season today than a few decades ago because of increased CH<sub>4</sub> emissions.

  • 15. Järveoja, Järvi
    et al.
    Nilsson, Mats B.
    Gažovič, Michal
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Peichl, Matthias
    Partitioning of the net CO2 exchange using an automated chamber system reveals plant phenology as key control of production and respiration fluxes in a boreal peatland2018In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, no 8, p. 3436-3451Article in journal (Refereed)
    Abstract [en]

    The net ecosystem CO2 exchange (NEE) drives the carbon (C) sink-source strength of northern peatlands. Since NEE represents a balance between various production and respiration fluxes, accurate predictions of its response to global changes require an in depth understanding of these underlying processes. Currently, however, detailed information of the temporal dynamics as well as the separate biotic and abiotic controls of the NEE component fluxes is lacking in peatland ecosystems. In this study, we address this knowledge gap by using an automated chamber system established across natural and trenching/vegetation removal plots to partition NEE into its production (i.e., gross and net primary production; GPP and NPP) and respiration (i.e., ecosystem, heterotrophic and autotrophic respiration; ER, Rh and Ra) fluxes in a boreal peatland in northern Sweden. Our results showed that daily NEE patterns were driven by GPP while variations in ER were governed by Ra rather than Rh. Moreover, we observed pronounced seasonal shifts in the Ra/Rh and above/belowground NPP ratios throughout the main phenological phases. Generalized linear model analysis revealed that the greenness index derived from digital images (as a proxy for plant phenology) was the strongest control of NEE, GPP and NPP while explaining considerable fractions also in the variations of ER and Ra. In addition, our data exposed greater temperature sensitivity of NPP compared to Rh resulting in enhanced C sequestration with increasing temperature. Overall, our study suggests that the temporal patterns in NEE and its component fluxes are tightly coupled to vegetation dynamics in boreal peatlands and thus challenges previous studies that commonly identify abiotic factors as key drivers. These findings further emphasize the need for integrating detailed information on plant phenology into process-based models to improve predictions of global change impacts on the peatland C cycle.

  • 16. Kokfelt, U.
    et al.
    Rosén, P.
    Schoning, K.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Christensen, T. R.
    Förster, J.
    Karlsson, J.
    Reuss, N.
    Rundgren, M.
    Callaghan, T. V.
    Jonasson, C.
    Hammarlund, D.
    Ecosystem responses to increased precipitation and permafrost decay in subarctic Sweden inferred from peat and lake sediments2009In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 15, no 7, p. 1652-1663Article in journal (Refereed)
    Abstract [en]

    Recent accelerated decay of discontinuous permafrost at the Stordalen Mire in northern Sweden has been attributed to increased temperature and snow depth, and has caused expansion of wet minerotrophic areas leading to significant changes in carbon cycling in the mire. In order to track these changes through time and evaluate potential forcing mechanisms, this paper analyses a peat succession and a lake sediment sequence from within the mire, providing a record for the last 100 years, and compares these with monitored climate and active layer thickness data. The peat core was analysed for testate amoebae to reconstruct changes in peatland surface moisture conditions and water table fluctuations. The lake sediment core was analysed by near infrared spectroscopy to infer changes in the total organic carbon (TOC) concentration of the lake-water, and changes in delta C-13 and C, N and delta N-15 to track changes in the dissolved inorganic carbon (DIC) pool and the influence of diagenetic effects on sediment organic matter, respectively. Results showed that major shifts towards increased peat surface moisture and TOC concentration of the lake-water occurred around 1980, one to two decades earlier than a temperature driven increase in active layer thickness. Comparison with monitored temperature and precipitation from a nearby climate station indicates that this change in peat surface moisture is related to June-September (JJAS) precipitation and that the increase in lake-water TOC concentration reflects an increase in total annual precipitation. A significant depletion in C-13 of sediment organic matter in the early 1980s probably reflects the effect of a single or a few consecutive years with anomalously high summer precipitation, resulting in elevated DIC content of the lake water, predominantly originating from increased export and subsequent respiration of organic carbon from the mire. Based on these results, it was not possible to link proxy data obtained on peat and lake-sediment records directly to permafrost decay. Instead our data indicate that increased precipitation and anomalously high rainfall during summers had a significant impact on the mire and the adjacent lake ecosystem. We therefore propose that effects of increased precipitation should be considered when evaluating potential forcing mechanisms of recent changes in carbon cycling in the subarctic.

  • 17.
    Lagerholm, Vendela K.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Swedish Museum of Natural History, Sweden.
    Sandoval-Castellanos, Edson
    Stockholm University, Faculty of Science, Department of Zoology. Swedish Museum of Natural History, Sweden; Universidad Nacional Autónoma de México, México.
    Vaniscotte, Amelie
    Potapova, Olga R.
    Tomek, Teresa
    Bochenski, Zbigniew M.
    Shepherd, Paul
    Barton, Nick
    Van Dyck, Marie-Claire
    Miller, Rebecca
    Höglund, Jacob
    Yoccoz, Nigel G.
    Dalén, Love
    Stewart, John R.
    Range shifts or extinction? Ancient DNA and distribution modelling reveal past and future responses to climate warming in cold-adapted birds2017In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 23, no 4, p. 1425-1435Article in journal (Refereed)
    Abstract [en]

    Global warming is predicted to cause substantial habitat rearrangements, with the most severe effects expected to occur in high-latitude biomes. However, one major uncertainty is whether species will be able to shift their ranges to keep pace with climate-driven environmental changes. Many recent studies on mammals have shown that past range contractions have been associated with local extinctions rather than survival by habitat tracking. Here, we have used an interdisciplinary approach that combines ancient DNA techniques, coalescent simulations and species distribution modelling, to investigate how two common cold-adapted bird species, willow and rock ptarmigan (Lagopus lagopus and Lagopus muta), respond to long-term climate warming. Contrary to previous findings in mammals, we demonstrate a genetic continuity in Europe over the last 20 millennia. Results from back-casted species distribution models suggest that this continuity may have been facilitated by uninterrupted habitat availability and potentially also the greater dispersal ability of birds. However, our predictions show that in the near future, some isolated regions will have little suitable habitat left, implying a future decrease in local populations at a scale unprecedented since the last glacial maximum.

  • 18. Lastra, Mariano
    et al.
    López, Jesús
    Rodil, Iván F.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. University of Helsinki, Finland.
    Warming intensify CO2 flux and nutrient release from algal wrack subsidies on sandy beaches2018In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, no 8, p. 3766-3779Article in journal (Refereed)
    Abstract [en]

    Algal wrack subsidies underpin most of the food web structure of exposed sandy beaches and are responsible of important biogeochemical processes that link marine and terrestrial ecosystems. The response in decomposition of algal wrack deposits to global warming has not been studied in ocean-exposed sandy beaches to date. With this aim, passive open top chambers (OTCs) were used to increase soil temperature within the range predicted by the IPCC for western Europe (between 0.5 and 1.5 degrees C), following the hypothesis that the biogeochemical processing of macroalgal wrack subsidies would accelerate in response to temperature increase. The effect of temperature manipulation on three target substrates: fresh and aged macroalgae, and bare sand, was tested. Results indicated that a small warming (< 0.5 degrees C) affected the wrack decomposition process through traceable increases in soil respiration through CO2 flux, inorganic nutrients within the interstitial environment (N and P), sediment organic contents measured through the amount of proteins and microbial pool through the total soil DNA. The different responses of soil variables in the studied substrates indicated that the decomposition stage of stranded macroalgae influences the biogeochemical processing of organic matter in sandy beaches. Thus, CO2 fluxes, releases of organic and inorganic nutrients and microbial activity intensify in aged wrack deposits. Our results predict that expected global warming will increase the release of inorganic nutrients to the coastal ocean by 30% for the N (21 Gg/year) and 5.9% for P (14 Gg/year); that increase for the flow of C to the atmosphere as CO2 was estimated in 8.2% (523 Gg/year). This study confirms the key role of sandy beaches in recycling ocean-derived organic matter, highlighting their sensitivity to a changing scenario of global warming that predicts significant increases in temperature over the next few decades.

  • 19. Lenoir, Jonathan
    et al.
    Graae, Bente Jessen
    Aarrestad, Per Arild
    Alsos, Inger Greve
    Armbruster, W. Scott
    Austrheim, Gunnar
    Bergendorff, Claes
    Birks, H. John B.
    Brathen, Kari Anne
    Brunet, Jorg
    Bruun, Hans Henrik
    Dahlberg, Carl Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Decocq, Guillaume
    Diekmann, Martin
    Dynesius, Mats
    Ejrnaes, Rasmus
    Grytnes, John-Arvid
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Botany.
    Klanderud, Kari
    Luoto, Miska
    Milbau, Ann
    Moora, Mari
    Nygaard, Bettina
    Odland, Arvid
    Ravolainen, Virve Tuulia
    Reinhardt, Stefanie
    Sandvik, Sylvi Marlen
    Schei, Fride Hoistad
    Speed, James David Mervyn
    Tveraabak, Liv Unn
    Vandvik, Vigdis
    Velle, Liv Guri
    Virtanen, Risto
    Zobel, Martin
    Svenning, Jens-Christian
    Local temperatures inferred from plant communities suggest strong spatial buffering of climate warming across Northern Europe2013In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 19, no 5, p. 1470-1481Article in journal (Refereed)
    Abstract [en]

    Recent studies from mountainous areas of small spatial extent (<2500km2) 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-m2 units (community-inferred temperatures: CiT). We then assessed: (1) CiT range (thermal variability) within 1-km2 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-km2 units. Ellenberg temperature indicator values in combination with plant assemblages explained 4672% of variation in LmT and 9296% of variation in GiT during the growing season (June, July, August). Growing-season CiT range within 1-km2 units peaked at 6065 degrees N and increased with terrain roughness, averaging 1.97 degrees C (SD=0.84 degrees C) and 2.68 degrees C (SD=1.26 degrees 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-km2 units was, on average, 1.8 times greater (0.32 degrees Ckm1) than spatial turnover in growing-season GiT (0.18 degrees Ckm1). We conclude that thermal variability within 1-km2 units strongly increases local spatial buffering of future climate warming across Northern Europe, even in the flattest terrains.

  • 20. Lichtenberg, Elinor M.
    et al.
    Kennedy, Christina M.
    Kremen, Claire
    Batáry, Péter
    Berendse, Frank
    Bommarco, Riccardo
    Bosque-Pérez, Nilsa A.
    Carvalheiro, Luísa G.
    Snyder, William E.
    Williams, Neal M.
    Winfree, Rachael
    Klatt, Björn K.
    Åström, Sandra
    Benjamin, Faye
    Brittain, Claire
    Chaplin-Kramer, Rebecca
    Clough, Yann
    Danforth, Bryan
    Diekötter, Tim
    Eigenbrode, Sanford D.
    Ekroos, Johan
    Elle, Elizabeth
    Freitas, Breno M.
    Fukuda, Yuki
    Gaines-Day, Hannah R.
    Grab, Heather
    Gratton, Claudio
    Holzschuh, Andrea
    Isaacs, Rufus
    Isaia, Marco
    Jha, Shalene
    Jonason, Dennis
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Jones, Vincent P.
    Klein, Alexandra-Maria
    Krauss, Jochen
    Letourneau, Deborah K.
    Macfadyen, Sarina
    Mallinger, Rachel E.
    Martin, Emily A.
    Martinez, Eliana
    Memmott, Jane
    Morandin, Lora
    Neame, Lisa
    Otieno, Mark
    Park, Mia G.
    Pfiffner, Lukas
    Pocock, Michael J. O.
    Ponce, Carlos
    Potts, Simon G.
    Poveda, Katja
    Ramos, Mariangie
    Rosenheim, Jay A.
    Rundlöf, Maj
    Sardiñas, Hillary
    Saunders, Manu E.
    Schon, Nicole L.
    Sciligo, Amber R.
    Sidhu, C. Sheena
    Steffan-Dewenter, Ingolf
    Tscharntke, Teja
    Veselý, Milan
    Weisser, Wolfgang W.
    Wilson, Julianna K.
    Crowder, David W.
    A global synthesis of the effects of diversified farming systems on arthropod diversity within fields and across agricultural landscapes2017In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 23, no 11, p. 4946-4957Article in journal (Refereed)
    Abstract [en]

    Agricultural intensification is a leading cause of global biodiversity loss, which can reduce the provisioning of ecosystem services in managed ecosystems. Organic farming and plant diversification are farm management schemes that may mitigate potential ecological harm by increasing species richness and boosting related ecosystem services to agroecosystems. What remains unclear is the extent to which farm management schemes affect biodiversity components other than species richness, and whether impacts differ across spatial scales and landscape contexts. Using a global metadataset, we quantified the effects of organic farming and plant diversification on abundance, local diversity (communities within fields), and regional diversity (communities across fields) of arthropod pollinators, predators, herbivores, and detritivores. Both organic farming and higher in-field plant diversity enhanced arthropod abundance, particularly for rare taxa. This resulted in increased richness but decreased evenness. While these responses were stronger at local relative to regional scales, richness and abundance increased at both scales, and richness on farms embedded in complex relative to simple landscapes. Overall, both organic farming and in-field plant diversification exerted the strongest effects on pollinators and predators, suggesting these management schemes can facilitate ecosystem service providers without augmenting herbivore (pest) populations. Our results suggest that organic farming and plant diversification promote diverse arthropod metacommunities that may provide temporal and spatial stability of ecosystem service provisioning. Conserving diverse plant and arthropod communities in farming systems therefore requires sustainable practices that operate both within fields and across landscapes.

  • 21. Lindegren, Martin
    et al.
    Blenckner, Thorsten
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Stenseth, Nils C.
    Nutrient reduction and climate change cause a potential shift from pelagic to benthic pathways in a eutrophic marine ecosystem2012In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 18, no 12, p. 3491-3503Article in journal (Refereed)
    Abstract [en]

    The degree to which marine ecosystems may support the pelagic or benthic food chain has been shown to vary across natural and anthropogenic gradients for e.g., in temperature and nutrient availability. Moreover, such external forcing may not only affect the flux of organic matter but could trigger large and abrupt changes, i.e., trophic cascades and ecological regime shifts, which once having occurred may prove potentially irreversible. In this study, we investigate the state and regulatory pathways of the Kattegat; a eutrophied and heavily exploited marine ecosystem, specifically testing for the occurrence of regime shifts and the relative importance of multiple drivers, e.g., climate change, eutrophication and commercial fishing on ecosystem dynamics and trophic pathways. Using multivariate statistics and nonlinear regression on a comprehensive data set, covering abiotic factors and biotic variables across all trophic levels, we here propose a potential regime shift from pelagic to benthic regulatory pathways; a possible first sign of recovery from eutrophication likely triggered by drastic nutrient reductions (involving both nitrogen and phosphorus), in combination with climate-driven changes in local environmental conditions (e.g., temperature and oxygen concentrations).

  • 22.
    Martens, C.S.
    et al.
    Univ North Carolina-Chapel Hill.
    Shay, T.J.
    Univ North Carolina-Chapel Hill.
    Mendlovitz, H.P.
    Univ North Carolina-Chapel Hill.
    Matross, D.M.
    Harvard University.
    Saleska, S.R.
    Harvard University.
    Wofsy, S.C.
    Harvard University.
    Woodward, W.S.
    Univ North Carolina-Chapel Hill.
    Menton, M.C.
    Univ North Carolina-Chapel Hill.
    Moura, J.M.S.
    Univ North Carolina-Chapel Hill.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Moraes, O.L.L.
    Univ Fed Santa Maria.
    Lima, R.L.
    Univ Fed Para.
    Radon fluxes in tropical forest ecosystems of Brazilian Amazonia: night-time CO2 net ecosystem exchange derived from radon and eddy covariance methods.2004In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 10, no 5, p. 618-629Article in journal (Refereed)
    Abstract [en]

    Radon-222 (Rn-222) is used as a transport tracer of forest canopy–atmosphere CO<sub>2</sub> exchange in an old-growth, tropical rain forest site near km 67 of the Tapajós National Forest, Pará, Brazil. Initial results, from month-long periods at the end of the wet season (June–July) and the end of the dry season (November–December) in 2001, demonstrate the potential of new Rn measurement instruments and methods to quantify mass transport processes between forest canopies and the atmosphere. Gas exchange rates yield mean canopy air residence times ranging from minutes during turbulent daytime hours to greater than 12 h during calm nights. Rn is an effective tracer for net ecosystem exchange of CO<sub>2</sub> (CO<sub>2</sub> NEE) during calm, night-time hours when eddy covariance-based NEE measurements are less certain because of low atmospheric turbulence. Rn-derived night-time CO<sub>2</sub> NEE (9.00±0.99 μmol m<sup>−2</sup> s<sup>−1</sup> in the wet season, 6.39±0.59 in the dry season) was significantly higher than raw uncorrected, eddy covariance-derived CO<sub>2</sub> NEE (5.96±0.51 wet season, 5.57±0.53 dry season), but agrees with corrected eddy covariance results (8.65±1.07 wet season, 6.56±0.73 dry season) derived by filtering out lower NEE values obtained during calm periods using independent meteorological criteria. The Rn CO<sub>2</sub> results suggest that uncorrected eddy covariance values underestimate night-time CO<sub>2</sub> loss at this site. If generalizable to other sites, these observations indicate that previous reports of strong net CO<sub>2</sub> uptake in Amazonian terra firme forest may be overestimated.

  • 23. Mills, Gina
    et al.
    Sharps, Katrina
    Simpson, David
    Pleijel, Håkan
    Broberg, Malin
    Uddling, Johan
    Jaramillo, Fernando
    Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Davies, William J.
    Dentener, Frank
    Van den Berg, Maurits
    Agrawal, Madhoolika
    Agrawal, Shahibhushan B.
    Ainsworth, Elizabeth A.
    Büker, Patrick
    Emberson, Lisa
    Feng, Zhaozhong
    Harmens, Harry
    Hayes, Felicity
    Kobayashi, Kazuhiko
    Paoletti, Elena
    Van Dingenen, Rita
    Ozone pollution will compromise efforts to increase global wheat production2018In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, no 8, p. 3560-3574Article in journal (Refereed)
    Abstract [en]

    Introduction of high-performing crop cultivars and crop/soil water management practices that increase the stomatal uptake of carbon dioxide and photosynthesis will be instrumental in realizing the United Nations Sustainable Development Goal (SDG) of achieving food security. To date, however, global assessments of how to increase crop yield have failed to consider the negative effects of tropospheric ozone, a gaseous pollutant that enters the leaf stomatal pores of plants along with carbon dioxide, and is increasing in concentration globally, particularly in rapidly developing countries. Earlier studies have simply estimated that the largest effects are in the areas with the highest ozone concentrations. Using a modelling method that accounts for the effects of soil moisture deficit and meteorological factors on the stomatal uptake of ozone, we show for the first time that ozone impacts on wheat yield are particularly large in humid rain-fed and irrigated areas of major wheat-producing countries (e.g. United States, France, India, China and Russia). Averaged over 2010-2012, we estimate that ozone reduces wheat yields by a mean 9.9% in the northern hemisphere and 6.2% in the southern hemisphere, corresponding to some 85 Tg (million tonnes) of lost grain. Total production losses in developing countries receiving Official Development Assistance are 50% higher than those in developed countries, potentially reducing the possibility of achieving UN SDG2. Crucially, our analysis shows that ozone could reduce the potential yield benefits of increasing irrigation usage in response to climate change because added irrigation increases the uptake and subsequent negative effects of the pollutant. We show that mitigation of air pollution in a changing climate could play a vital role in achieving the above-mentioned UN SDG, while also contributing to other SDGs related to human health and well-being, ecosystems and climate change.

  • 24. Morán, Xosé Anxelu G.
    et al.
    Gasol, Josep M.
    Pernice, Massimo C.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Institut de Ciències del Mar, CSIC, Spain.
    Mangot, Jean-Francois
    Massana, Ramon
    Lara, Elena
    Vaqué, Dolors
    Duarte, Carlos M.
    Temperature regulation of marine heterotrophic prokaryotes increases latitudinally as a breach between bottom-up and top-down controls2017In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 23, no 9, p. 3956-3964Article in journal (Refereed)
    Abstract [en]

    Planktonic heterotrophic prokaryotes make up the largest living biomass and process most organic matter in the ocean. Determining when and where the biomass and activity of heterotrophic prokaryotes are controlled by resource availability (bottom-up), predation and viral lysis (top-down) or temperature will help in future carbon cycling predictions. We conducted an extensive survey across subtropical and tropical waters of the Atlantic, Indian and Pacific Oceans during the Malaspina 2010 Global Circumnavigation Expedition and assessed indices for these three types of controls at 109 stations (mostly from the surface to 4,000 m depth). Temperature control was approached by the apparent activation energy in eV (ranging from 0.46 to 3.41), bottom-up control by the slope of the log-log relationship between biomass and production rate (ranging from -0.12 to 1.09) and top-down control by an index that considers the relative abundances of heterotrophic nanoflagellates and viruses (ranging from 0.82 to 4.83). We conclude that temperature becomes dominant (i.e. activation energy >1.5 eV) within a narrow window of intermediate values of bottom-up (0.3-0.6) and top-down 0.8-1.2) controls. A pervasive latitudinal pattern of decreasing temperature regulation towards the Equator, regardless of the oceanic basin, suggests that the impact of global warming on marine microbes and their biogeochemical function will be more intense at higher latitudes. Our analysis predicts that 1 degrees C ocean warming will result in increased biomass of heterotrophic prokaryoplankton only in waters with <26 degrees C of mean annual surface temperature.

  • 25.
    Niiranen, Susa
    et al.
    Stockholm University, Faculty of Science, Stockholm Resilience Centre. Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Yletyinen, Johanna
    Stockholm University, Faculty of Science, Stockholm Resilience Centre. University of Olso, Norway.
    Tomczak, Maciej T.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Blenckner, Thorsten
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Hjerne, Olle
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    MacKenzie, Brian R.
    Müller-Karulis, Bärbel
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Neumann, Thomas
    Meier, H. E. Markus
    Stockholm University, Faculty of Science, Department of Meteorology . Swedish Meteorological and Hydrological Institute, Sweden.
    Combined effects of global climate change and regional ecosystem drivers on an exploited marine food web2013In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 19, no 11, p. 3327-3342Article in journal (Refereed)
    Abstract [en]

    Changes in climate, in combination with intensive exploitation of marine resources, have caused large-scale reorganizations in many of the world's marine ecosystems during the past decades. The Baltic Sea in Northern Europe is one of the systems most affected. In addition to being exposed to persistent eutrophication, intensive fishing, and one of the world's fastest rates of warming in the last two decades of the 20th century, accelerated climate change including atmospheric warming and changes in precipitation is projected for this region during the 21st century. Here, we used a new multi-model approach to project how the interaction of climate, nutrient loads and cod fishing may affect the future of the open Central Baltic Sea food web. Regionally downscaled global climate scenarios were, in combination with three nutrient load scenarios, used to drive an ensemble of three regional biogeochemical models (BGMs). An Ecopath with Ecosim food web model was then forced with the BGM results from different nutrient-climate scenarios in combination with two different cod fishing scenarios. The results showed that regional management is likely to play a major role in determining the future of the Baltic Sea ecosystem. By the end of the 21st century, for example, the combination of intensive cod fishing and high nutrient loads projected a strongly eutrophicated and sprat-dominated ecosystem, while low cod fishing in combination with low nutrient loads resulted in a cod-dominated ecosystem with eutrophication levels close to present. Also, non-linearities were observed in the sensitivity of different trophic groups to nutrient loads or fishing depending on the combination of the two. Finally, many climate variables and species biomasses were projected to levels unseen in the past. Hence, the risk for ecological surprises needs to be addressed, particularly when the results are discussed in the ecosystem-based management context.

  • 26. Norkko, Joanna
    et al.
    Reed, Daniel C.
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute. Utrecht University, The Netherlands.
    Timmermann, Karen
    Norkko, Alf
    Gustafsson, Bo G.
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Bonsdorff, Erik
    Slomp, Caroline P.
    Carstensen, Jacob
    Conley, Daniel J.
    A welcome can of worms?: hypoxia mitigation by an invasive species2012In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 18, no 2, p. 422-434Article in journal (Refereed)
    Abstract [en]

    Invasive species and bottom-water hypoxia both constitute major global threats to the diversity and integrity of marine ecosystems. These stressors may interact with unexpected consequences, as invasive species that require an initial environmental disturbance to become established can subsequently become important drivers of ecological change. There is recent evidence that improved bottom-water oxygen conditions in coastal areas of the northern Baltic Sea coincide with increased abundances of the invasive polychaetes Marenzelleria spp. Using a reactive-transport model, we demonstrate that the long-term bioirrigation activities of dense Marenzelleria populations have a major impact on sedimentary phosphorus dynamics. This may facilitate the switch from a seasonally hypoxic system back to a normoxic system by reducing the potential for sediment-induced eutrophication in the upper water column. In contrast to short-term laboratory experiments, our simulations, which cover a 10-year period, show that Marenzelleria has the potential to enhance long-term phosphorus retention in muddy sediments. Over time bioirrigation leads to a substantial increase in the iron-bound phosphorus content of sediments while reducing the concentration of labile organic carbon. As surface sediments are maintained oxic, iron oxyhydroxides are able to persist and age into more refractory forms. The model illustrates mechanisms through which Marenzelleria can act as a driver of ecological change, although hypoxic disturbance or natural population declines in native species may be needed for them to initially become established. Invasive species are generally considered to have a negative impact; however, we show here that one of the main recent invaders in the Baltic Sea may provide important ecosystem services. This may be of particular importance in low-diversity systems, where disturbances may dramatically alter ecosystem services due to low functional redundancy. Thus, an environmental problem in one region may be either exacerbated or alleviated by a single species from another region, with potentially ecosystem-wide consequences.

  • 27.
    Norén, Karin
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. University of California Davis, USA.
    Statham, Mark J.
    Ågren, Erik O.
    Isomursu, Marja
    Flagstad, Öystein
    Eide, Nina E.
    Björneboe, Thomas
    Bech-Sanderhoff, Lene
    Sacks, Benjamin N.
    Genetic footprints reveal geographic patterns of expansion in Fennoscandian red foxes2015In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 21, no 9, p. 3299-3312Article in journal (Refereed)
    Abstract [en]

    Population expansions of boreal species are among the most substantial ecological consequences of climate change, potentially transforming both structure and processes of northern ecosystems. Despite their importance, little is known about expansion dynamics of boreal species. Red foxes (Vulpes vulpes) are forecasted to become a keystone species in northern Europe, a process stemming from population expansions that began in the 19th century. To identify the relative roles of geographic and demographic factors and the sources of northern European red fox population expansion, we genotyped 21 microsatellite loci in modern and historical (1835–1941) Fennoscandian red foxes. Using Bayesian clustering and Bayesian inference of migration rates, we identified high connectivity and asymmetric migration rates across the region, consistent with source-sink dynamics, whereby more recently colonized sampling regions received immigrants from multiple sources. There were no clear clines in allele frequency or genetic diversity as would be expected from a unidirectional range expansion from south to north. Instead, migration inferences, demographic models and comparison to historical red fox genotypes suggested that the population expansion of the red fox is a consequence of dispersal from multiple sources, as well as in situ demographic growth. Together, these findings provide a rare glimpse into the anatomy of a boreal range expansion and enable informed predictions about future changes in boreal communities.

  • 28. Olefeldt, David
    et al.
    Turetsky, Merritt R.
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    McGuire, A. David
    Environmental and physical controls on northern terrestrial methane emissions across permafrost zones2013In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 19, no 2, p. 589-603Article in journal (Refereed)
    Abstract [en]

    Methane (CH4) emissions from the northern high-latitude region represent potentially significant biogeochemical feedbacks to the climate system. We compiled a database of growing-season CH4 emissions from terrestrial ecosystems located across permafrost zones, including 303 sites described in 65 studies. Data on environmental and physical variables, including permafrost conditions, were used to assess controls on CH4 emissions. Water table position, soil temperature, and vegetation composition strongly influenced emissions and had interacting effects. Sites with a dense sedge cover had higher emissions than other sites at comparable water table positions, and this was an effect that was more pronounced at low soil temperatures. Sensitivity analysis suggested that CH4 emissions from ecosystems where the water table on average is at or above the soil surface (wet tundra, fen underlain by permafrost, and littoral ecosystems) are more sensitive to variability in soil temperature than drier ecosystems (palsa dry tundra, bog, and fen), whereas the latter ecosystems conversely are relatively more sensitive to changes of the water table position. Sites with near-surface permafrost had lower CH4 fluxes than sites without permafrost at comparable water table positions, a difference that was explained by lower soil temperatures. Neither the active layer depth nor the organic soil layer depth was related to CH4 emissions. Permafrost thaw in lowland regions is often associated with increased soil moisture, higher soil temperatures, and increased sedge cover. In our database, lowland thermokarst sites generally had higher emissions than adjacent sites with intact permafrost, but emissions from thermokarst sites were not statistically higher than emissions from permafrost-free sites with comparable environmental conditions. Overall, these results suggest that future changes to terrestrial high-latitude CH4 emissions will be more proximately related to changes in moisture, soil temperature, and vegetation composition than to increased availability of organic matter following permafrost thaw.

  • 29. Oulehle, Filip
    et al.
    Evans, Christopher D.
    Hofmeister, Jenyk
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Tahovska, Karolina
    Persson, Tryggve
    Cudlin, Pavel
    Hruska, Jakub
    Major changes in forest carbon and nitrogen cycling caused by declining sulphur deposition2011In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 17, no 10, p. 3115-3129Article in journal (Refereed)
    Abstract [en]

    Sulphur (S) and nitrogen (N) deposition are important drivers of the terrestrial carbon (C) and N cycling. We analyzed changes in C and N pools in soil and tree biomass at a highly acidified spruce site in the Czech Republic during a 15 year period. Total S deposition decreased from 5 to 1.1 g m(-2) yr(-1) between 1995 and 2009, whereas bulk N deposition did not change. Over the same period, C and N pools in the Oa horizon declined by 116 g C and 4.2 g N m(-2) yr(-1), a total decrease of 47% and 42%, respectively. This loss of C and N probably originated from organic matter (OM) that had accumulated during the period of high acid deposition when litter decomposition was suppressed. The loss of OM from the Oa horizon coincided with a substantial leaching (1.3 g N m(-2) yr(-1) at 90 cm) in the 1990s to almost no leaching (<0.02 g N m(-2) yr(-1)) since 2006. Forest floor net N mineralization also decreased. This had consequences for spruce needle N concentration (from 17.1 to 11.4 mg kg(-1) in current needles), an increase in litterfall C/N ratio (from 51 to 63), and a significant increase in the Oi + Oe horizon C/N ratio (from 23.4 to 27.3) between 1994 and 2009/2010. Higher forest growth and lower canopy defoliation was observed in the 2000s compared to the 1990s. Our results demonstrate that reducing S deposition has had a profound impact on forest organic matter cycling, leading to a reversal of historic ecosystem N enrichment, cessation of nitrate leaching, and a major loss of accumulated organic soil C and N stocks. These results have major implications for our understanding of the controls on both N saturation and C sequestration in forests, and other ecosystems, subjected to current or historic S deposition.

  • 30.
    Palkopoulou, Eleftheria
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Swedish Museum of Natural History, Sweden.
    Baca, Mateusz
    Abramson, Natalia I.
    Sablin, Mikhail
    Socha, Pawel
    Nadachowski, Adam
    Prost, Stefan
    Germonpre, Mietje
    Kosintsev, Pavel
    Smirnov, Nickolay G.
    Vartanyan, Sergey
    Ponomarev, Dmitry
    Nyström, Johanna
    Nikolskiy, Pavel
    Jass, Christopher N.
    Litvinov, Yuriy N.
    Kalthoff, Daniela C.
    Grigoriev, Semyon
    Fadeeva, Tatyana
    Douka, Aikaterini
    Higham, Thomas F. G.
    Ersmark, Erik
    Stockholm University, Faculty of Science, Department of Zoology. Swedish Museum of Natural History, Sweden.
    Pitulko, Vladimir
    Pavlova, Elena
    Stewart, John R.
    Weglenski, Piotr
    Stankovic, Anna
    Dalén, Love
    Synchronous genetic turnovers across Western Eurasia in Late Pleistocene collared lemmings2016In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 22, no 5, p. 1710-1721Article in journal (Refereed)
    Abstract [en]

    Recent palaeogenetic studies indicate a highly dynamic history in collared lemmings (Dicrostonyx spp.), with several demographical changes linked to climatic fluctuations that took place during the last glaciation. At the western range margin of D.torquatus, these changes were characterized by a series of local extinctions and recolonizations. However, it is unclear whether this pattern represents a local phenomenon, possibly driven by ecological edge effects, or a global phenomenon that took place across large geographical scales. To address this, we explored the palaeogenetic history of the collared lemming using a next-generation sequencing approach for pooled mitochondrial DNA amplicons. Sequences were obtained from over 300 fossil remains sampled across Eurasia and two sites in North America. We identified five mitochondrial lineages of D.torquatus that succeeded each other through time across Europe and western Russia, indicating a history of repeated population extinctions and recolonizations, most likely from eastern Russia, during the last 50000years. The observation of repeated extinctions across such a vast geographical range indicates large-scale changes in the steppe-tundra environment in western Eurasia during the last glaciation. AllHolocene samples, from across the species' entire range, belonged to only one of the five mitochondrial lineages. Thus, extant D.torquatus populations only harbour a small fraction of the total genetic diversity that existed across different stages of the Late Pleistocene. In North American samples, haplotypes belonging to both D.groenlandicus and D.richardsoni were recovered from a Late Pleistocene site in south-western Canada. This suggests that D.groenlandicus had a more southern and D.richardsoni a more northern glacial distribution than previously thought. This study provides significant insights into the population dynamics of a small mammal at a large geographical scale and reveals a rather complex demographical history, which could have had bottom-up effects in the Late Pleistocene steppe-tundra ecosystem.

  • 31. Peters, W.
    et al.
    Krol, M. C.
    van der Werf, G. R.
    Houweling, S.
    Jones, C. D.
    Hughes, J.
    Schaefer, K.
    Masarie, K. A.
    Jacobson, A. R.
    Miller, J. B.
    Cho, C. H.
    Ramonet, M.
    Schmidt, M.
    Ciattaglia, L.
    Apadula, F.
    Helta, D.
    Meinhardt, F.
    di Sarra, A. G.
    Piacentino, S.
    Sferlazzo, D.
    Aalto, T.
    Hatakka, J.
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Haszpra, L.
    Meijer, H. A. J.
    van der Laan, S.
    Neubert, R. E. M.
    Jordan, A.
    Rodo, X.
    Morgui, J. -A
    Vermeulen, A. T.
    Popa, E.
    Rozanski, K.
    Zimnoch, M.
    Manning, A. C.
    Leuenberger, M.
    Uglietti, C.
    Dolman, A. J.
    Ciais, P.
    Heimann, M.
    Tans, P. P.
    Seven years of recent European net terrestrial carbon dioxide exchange constrained by atmospheric observations2010In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 16, no 4, p. 1317-1337Article in journal (Refereed)
    Abstract [en]

    We present an estimate of net ecosystem exchange (NEE) of CO2 in Europe for the years 2001-2007. It is derived with a data assimilation that uses a large set of atmospheric CO2 mole fraction observations (similar to 70 000) to guide relatively simple descriptions of terrestrial and oceanic net exchange, while fossil fuel and fire emissions are prescribed. Weekly terrestrial sources and sinks are optimized (i.e., a flux inversion) for a set of 18 large ecosystems across Europe in which prescribed climate, weather, and surface characteristics introduce finer scale gradients. We find that the terrestrial biosphere in Europe absorbed a net average of -165 Tg C yr-1 over the period considered. This uptake is predominantly in non-EU countries, and is found in the northern coniferous (-94 Tg C yr-1) and mixed forests (-30 Tg C yr-1) as well as the forest/field complexes of eastern Europe (-85 Tg C yr-1). An optimistic uncertainty estimate derived using three biosphere models suggests the uptake to be in a range of -122 to -258 Tg C yr-1, while a more conservative estimate derived from the a-posteriori covariance estimates is -165 +/- 437 Tg C yr-1. Note, however, that uncertainties are hard to estimate given the nature of the system and are likely to be significantly larger than this. Interannual variability in NEE includes a reduction in uptake due to the 2003 drought followed by 3 years of more than average uptake. The largest anomaly of NEE occurred in 2005 concurrent with increased seasonal cycles of observed CO2. We speculate these changes to result from the strong negative phase of the North Atlantic Oscillation in 2005 that lead to favorable summer growth conditions, and altered horizontal and vertical mixing in the atmosphere. All our results are available through

  • 32. Saurer, Matthias
    et al.
    Spahni, Renato
    Frank, David C.
    Joos, Fortunat
    Leuenberger, Markus
    Loader, Neil J.
    McCarroll, Danny
    Gagen, Mary
    Poulter, Ben
    Siegwolf, Rolf T. W.
    Andreu-Hayles, Laia
    Boettger, Tatjana
    Dorado Linan, Isabel
    Fairchild, Ian J.
    Friedrich, Michael
    Gutierrez, Emilia
    Haupt, Marika
    Hilasvuori, Emmi
    Heinrich, Ingo
    Helle, Gerd
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jalkanen, Risto
    Levanic, Tom
    Linderholm, Hans W.
    Robertson, Iain
    Sonninen, Eloni
    Treydte, Kerstin
    Waterhouse, John S.
    Woodley, Ewan J.
    Wynn, Peter M.
    Young, Giles H. F.
    Spatial variability and temporal trends in water-use efficiency of European forests2014In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 20, no 12, p. 3700-3712Article in journal (Refereed)
    Abstract [en]

    The increasing carbon dioxide (CO2) concentration in the atmosphere in combination with climatic changes throughout the last century are likely to have had a profound effect on the physiology of trees: altering the carbon and water fluxes passing through the stomatal pores. However, the magnitude and spatial patterns of such changes in natural forests remain highly uncertain. Here, stable carbon isotope ratios from a network of 35 tree-ring sites located across Europe are investigated to determine the intrinsic water-use efficiency (iWUE), the ratio of photosynthesis to stomatal conductance from 1901 to 2000. The results were compared with simulations of a dynamic vegetation model (LPX-Bern 1.0) that integrates numerous ecosystem and land-atmosphere exchange processes in a theoretical framework. The spatial pattern of tree-ring derived iWUE of the investigated coniferous and deciduous species and the model results agreed significantly with a clear south-to-north gradient, as well as a general increase in iWUE over the 20th century. The magnitude of the iWUE increase was not spatially uniform, with the strongest increase observed and modelled for temperate forests in Central Europe, a region where summer soil-water availability decreased over the last century. We were able to demonstrate that the combined effects of increasing CO2 and climate change leading to soil drying have resulted in an accelerated increase in iWUE. These findings will help to reduce uncertainties in the land surface schemes of global climate models, where vegetation-climate feedbacks are currently still poorly constrained by observational data.

  • 33. Schipper, Aafke M.
    et al.
    Belmaker, Jonathan
    de Miranda, Murilo Dantas
    Navarro, Laetitia M.
    Boehning-Gaese, Katrin
    Costello, Mark J.
    Dornelas, Maria
    Foppen, Ruud
    Hortal, Joaquin
    Huijbregts, Mark A. J.
    Martin-Lopez, Berta
    Pettorelli, Nathalie
    Queiroz, Cibele
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Rossberg, Axel G.
    Santini, Luca
    Schiffers, Katja
    Steinmann, Zoran J. N.
    Visconti, Piero
    Rondinini, Carlo
    Pereira, Henrique M.
    Contrasting changes in the abundance and diversity of North American bird assemblages from 1971 to 20102016In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 22, no 12, p. 3948-3959Article in journal (Refereed)
    Abstract [en]

    Although it is generally recognized that global biodiversity is declining, few studies have examined long-term changes in multiple biodiversity dimensions simultaneously. In this study, we quantified and compared temporal changes in the abundance, taxonomic diversity, functional diversity, and phylogenetic diversity of bird assemblages, using roadside monitoring data of the North American Breeding Bird Survey from 1971 to 2010. We calculated 12 abundance and diversity metrics based on 5-year average abundances of 519 species for each of 768 monitoring routes. We did this for all bird species together as well as for four subgroups based on breeding habitat affinity (grassland, woodland, wetland, and shrubland breeders). The majority of the biodiversity metrics increased or remained constant over the study period, whereas the overall abundance of birds showed a pronounced decrease, primarily driven by declines of the most abundant species. These results highlight how stable or even increasing metrics of taxonomic, functional, or phylogenetic diversity may occur in parallel with substantial losses of individuals. We further found that patterns of change differed among the species subgroups, with both abundance and diversity increasing for woodland birds and decreasing for grassland breeders. The contrasting changes between abundance and diversity and among the breeding habitat groups underscore the relevance of a multifaceted approach to measuring biodiversity change. Our findings further stress the importance of monitoring the overall abundance of individuals in addition to metrics of taxonomic, functional, or phylogenetic diversity, thus confirming the importance of population abundance as an essential biodiversity variable.

  • 34. Sierra, C. A.
    et al.
    Müller, M.
    Metzler, H.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Trumbore, S. E.
    The muddle of ages, turnover, transit, and residence times in the carbon cycle2017In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 23, no 5, p. 1763-1773Article in journal (Refereed)
    Abstract [en]

    Comparisons among ecosystem models or ecosystem dynamics along environmental gradients commonly rely on metrics that integrate different processes into a useful diagnostic. Terms such as age, turnover, residence, and transit times are often used for this purpose; however, these terms are variably defined in the literature and in many cases, calculations ignore assumptions implicit in their formulas. The aim of this opinion piece was i) to make evident these discrepancies and the incorrect use of formulas, ii) highlight recent results that simplify calculations and may help to avoid confusion, and iii) propose the adoption of simple and less ambiguous terms.

  • 35.
    Silver, W.L.
    et al.
    Univ Cal - Berkeley.
    Thompson, A.W.
    Univ Cal - Berkeley.
    McGroddy, M.E.
    Univ Cal - Berkeley.
    Varner, R.K:
    Univ New Hampshire.
    Diaz, J.D.
    Univ Fed Sao Paulo.
    Silva, H.
    Univ New hampshire.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Keller, M.
    US Forest Service.
    Fine root dynamics and trace gas fluxes in two lowland tropical forest soils.2005In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 11, no 2, p. 290-306Article in journal (Refereed)
    Abstract [en]

    Fine root dynamics have the potential to contribute significantly to ecosystem-scale biogeochemical cycling, including the production and emission of greenhouse gases. This is particularly true in tropical forests which are often characterized as having large fine root biomass and rapid rates of root production and decomposition. We examined patterns in fine root dynamics on two soil types in a lowland moist Amazonian forest, and determined the effect of root decay on rates of C and N trace gas fluxes. Root production averaged 229 (±35) and 153 (±27) g m<sup>−2</sup> yr<sup>−1</sup> for years 1 and 2 of the study, respectively, and did not vary significantly with soil texture. Root decay was sensitive to soil texture with faster rates in the clay soil (k=−0.96 year<sup>−1</sup>) than in the sandy loam soil (k=−0.61 year<sup>−1</sup>), leading to greater standing stocks of dead roots in the sandy loam. Rates of nitrous oxide (N<sub>2</sub>O) emissions were significantly greater in the clay soil (13±1 ng N cm<sup>−2</sup> h<sup>−1</sup>) than in the sandy loam (1.4±0.2 ng N cm<sup>−2</sup> h<sup>−1</sup>). Root mortality and decay following trenching doubled rates of N<sub>2</sub>O emissions in the clay and tripled them in sandy loam over a 1-year period. Trenching also increased nitric oxide fluxes, which were greater in the sandy loam than in the clay. We used trenching (clay only) and a mass balance approach to estimate the root contribution to soil respiration. In clay soil root respiration was 264–380 g C m<sup>−2</sup> yr<sup>−1</sup>, accounting for 24% to 35% of the total soil CO<sub>2</sub> efflux. Estimates were similar using both approaches. In sandy loam, root respiration rates were slightly higher and more variable (521±206 g C m<sup>2</sup> yr<sup>−1</sup>) and contributed 35% of the total soil respiration. Our results show that soil heterotrophs strongly dominate soil respiration in this forest, regardless of soil texture. Our results also suggest that fine root mortality and decomposition associated with disturbance and land-use change can contribute significantly to increased rates of nitrogen trace gas emissions.

  • 36. Sletvold, Nina
    et al.
    Dahlgren, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Oien, Dag-Inge
    Moen, Asbjorn
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Climate warming alters effects of management on population viability of threatened species: results from a 30-year experimental study on a rare orchid2013In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 19, no 9, p. 2729-2738Article in journal (Refereed)
    Abstract [en]

    Climate change is expected to influence the viability of populations both directly and indirectly, via species interactions. The effects of large-scale climate change are also likely to interact with local habitat conditions. Management actions designed to preserve threatened species therefore need to adapt both to the prevailing climate and local conditions. Yet, few studies have separated the direct and indirect effects of climatic variables on the viability of local populations and discussed the implications for optimal management. We used 30years of demographic data to estimate the simultaneous effects of management practice and among-year variation in four climatic variables on individual survival, growth and fecundity in one coastal and one inland population of the perennial orchid Dactylorhiza lapponica in Norway. Current management, mowing, is expected to reduce competitive interactions. Statistical models of how climate and management practice influenced vital rates were incorporated into matrix population models to quantify effects on population growth rate. Effects of climate differed between mown and control plots in both populations. In particular, population growth rate increased more strongly with summer temperature in mown plots than in control plots. Population growth rate declined with spring temperature in the inland population, and with precipitation in the coastal population, and the decline was stronger in control plots in both populations. These results illustrate that both direct and indirect effects of climate change are important for population viability and that net effects depend both on local abiotic conditions and on biotic conditions in terms of management practice and intensity of competition. The results also show that effects of management practices influencing competitive interactions can strongly depend on climatic factors. We conclude that interactions between climate and management should be considered to reliably predict future population viability and optimize conservation actions.

  • 37.
    Smittenberg, Rienk H.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gierga, Merle
    Göransson, Hans
    Christl, Iso
    Farinotti, Daniel
    Bernasconi, Stefano M.
    Climate sensitive ecosystem carbon dynamics along the soil chronosequence of the damma glacier forefield, Switzerland2012In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 18, no 6, p. 1941-1955Article in journal (Refereed)
    Abstract [en]

    We performed a detailed study on the carbon build-up over the 140-year-long chronosequence of the Damma glacier forefield, Switzerland, to gain insights into the organic carbon dynamics during the initial stage of soil formation and ecosystem development. We determined soil carbon and nitrogen contents and their stable isotopic compositions, as well as molecular-level composition of the bulk soils, and recalcitrance parameters of carbon in different fractions. The chronosequence was divided into three age groups, separated by small end moraines that resulted from two glacier re-advances. The net ecosystem carbon balance (NECB) showed an exponential increase over the last decades, with mean annual values that range from 100gCm-2yr-1 in the youngest part to over 300gCm-2yr-1 in a 6080years old part. However, over the entire 140-year chronosequence, the NECB is only 20gCm-2yr-1, similar to results of other glacier forefield studies. The difference between the short- and long-term NECB appears to be caused by reductions in ecosystem carbon (EC) accumulation during periods with a colder climate. We propose that two complementary mechanisms have been responsible: 1) Reductions in net primary productivity down to 50% below the long-term mean, which we estimated using reconstructed effective temperature sums. 2) Disturbance of sites near the terminus of the re-advanced glacier front. Stabilization of soil organic matter appeared to play only a minor role in the coarse-grained forefield. We conclude that the forefield ecosystem, especially primary productivity, reacts rapidly to climate changes. The EC gained at warm periods is easily lost again in a cooling climate. Our conclusions may also be valid for other high mountain ecosystems and possibly arctic ecosystems.

  • 38.
    Thurner, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Beer, Christian
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Ciais, Philippe
    Friend, Andrew D.
    Ito, Akihiko
    Kleidon, Axel
    Lomas, Mark R.
    Shaun, Quegan
    Rademacher, Tim T.
    Schaphoff, Sibyll
    Tum, Markus
    Wiltshire, Andy
    Carvalhais, Nuno
    Evaluation of climate-related carbon turnover processes in global vegetation models for boreal and temperate forests2017In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 23, no 8, p. 3076-3091Article in journal (Refereed)
    Abstract [en]

    Turnover concepts in state-of-the-art global vegetation models (GVMs) account for various processes, but are often highly simplified and may not include an adequate representation of the dominant processes that shape vegetation carbon turnover rates in real forest ecosystems at a large spatial scale. Here, we evaluate vegetation carbon turnover processes in GVMs participating in the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP, including HYBRID4, JeDi, JULES, LPJml, ORCHIDEE, SDGVM, and VISIT) using estimates of vegetation carbon turnover rate (k) derived from a combination of remote sensing based products of biomass and net primary production (NPP). We find that current model limitations lead to considerable biases in the simulated biomass and in k (severe underestimations by all models except JeDi and VISIT compared to observation-based average k), likely contributing to underestimation of positive feedbacks of the northern forest carbon balance to climate change caused by changes in forest mortality. A need for improved turnover concepts related to frost damage, drought, and insect outbreaks to better reproduce observation-based spatial patterns in k is identified. As direct frost damage effects on mortality are usually not accounted for in these GVMs, simulated relationships between k and winter length in boreal forests are not consistent between different regions and strongly biased compared to the observation-based relationships. Some models show a response of k to drought in temperate forests as a result of impacts of water availability on NPP, growth efficiency or carbon balance dependent mortality as well as soil or litter moisture effects on leaf turnover or fire. However, further direct drought effects such as carbon starvation (only in HYBRID4) or hydraulic failure are usually not taken into account by the investigated GVMs. While they are considered dominant large-scale mortality agents, mortality mechanisms related to insects and pathogens are not explicitly treated in these models.

  • 39. Treat, Claire C.
    et al.
    Marushchak, Maija E.
    Voigt, Carolina
    Zhang, Yu
    Tan, Zeli
    Zhuang, Qianlai
    Virtanen, Tarmo A.
    Räsänen, Aleksi
    Biasi, Christina
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kaverin, Dmitry
    Miller, Paul A.
    Stendel, Martin
    Romanovsky, Vladimir
    Rivkin, Felix
    Martikainen, Pertti J.
    Shurpali, Narasinha J.
    Tundra landscape heterogeneity, not interannual variability, controls the decadal regional carbon balance in the Western Russian Arctic2018In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, no 11, p. 5188-5204Article in journal (Refereed)
    Abstract [en]

    Across the Arctic, the net ecosystem carbon (C) balance of tundra ecosystems is highly uncertain due to substantial temporal variability of C fluxes and to landscape heterogeneity. We modeled both carbon dioxide (CO2) and methane (CH4) fluxes for the dominant land cover types in a similar to 100-km(2) sub-Arctic tundra region in northeast European Russia for the period of 2006-2015 using process-based biogeochemical models. Modeled net annual CO2 fluxes ranged from --300 g C m(-2) year(-1) [net uptake] in a willow fen to 3 g Cm-2 year(-1) [net source] in dry lichen tundra. Modeled annual CH4 emissions ranged from -0.2 to 22.3 g Cm-2 year(-1) at a peat plateau site and a willow fen site, respectively. Interannual variability over the decade was relatively small (20%-25%) in comparison with variability among the land cover types (150%). Using high-resolution land cover classification, the region was a net sink of atmospheric CO2 across most land cover types but a net source of CH4 to the atmosphere due to high emissions from permafrost-free fens. Using a lower resolution for land cover classification resulted in a 20%-65% underestimation of regional CH4 flux relative to high-resolution classification and smaller (10%) overestimation of regional CO2 uptake due to the underestimation of wetland area by 60%. The relative fraction of uplands versus wetlands was key to determining the net regional C balance at this and other Arctic tundra sites because wetlands were hot spots for C cycling in Arctic tundra ecosystems.

  • 40. Turetsky, Merritt R.
    et al.
    Kotowska, Agnieszka
    Bubier, Jill
    Dise, Nancy B.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hornibrook, Ed R. C.
    Minkkinen, Kari
    Moore, Tim R.
    Myers-Smith, Isla H.
    Nykanen, Hannu
    Olefeldt, David
    Rinne, Janne
    Saarnio, Sanna
    Shurpali, Narasinha
    Tuittila, Eeva-Stiina
    Waddington, J. Michael
    White, Jeffrey R.
    Wickland, Kimberly P.
    Wilmking, Martin
    A synthesis of methane emissions from 71 northern, temperate, and subtropical wetlands2014In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 20, no 7, p. 2183-2197Article in journal (Refereed)
    Abstract [en]

    Wetlands are the largest natural source of atmospheric methane. Here, we assess controls on methane flux using a database of approximately 19 000 instantaneous measurements from 71 wetland sites located across subtropical, temperate, and northern high latitude regions. Our analyses confirm general controls on wetland methane emissions from soil temperature, water table, and vegetation, but also show that these relationships are modified depending on wetland type (bog, fen, or swamp), region (subarctic to temperate), and disturbance. Fen methane flux was more sensitive to vegetation and less sensitive to temperature than bog or swamp fluxes. The optimal water table for methane flux was consistently below the peat surface in bogs, close to the peat surface in poor fens, and above the peat surface in rich fens. However, the largest flux in bogs occurred when dry 30-day averaged antecedent conditions were followed by wet conditions, while in fens and swamps, the largest flux occurred when both 30-day averaged antecedent and current conditions were wet. Drained wetlands exhibited distinct characteristics, e. g. the absence of large flux following wet and warm conditions, suggesting that the same functional relationships between methane flux and environmental conditions cannot be used across pristine and disturbed wetlands. Together, our results suggest that water table and temperature are dominant controls on methane flux in pristine bogs and swamps, while other processes, such as vascular transport in pristine fens, have the potential to partially override the effect of these controls in other wetland types. Because wetland types vary in methane emissions and have distinct controls, these ecosystems need to be considered separately to yield reliable estimates of global wetland methane release.

  • 41.
    Valdés, Alicia
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Marteinsdóttir, Bryndís
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    A natural heating experiment: Phenotypic and genotypic responses of plant phenology to geothermal soil warming2019In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 25, no 3, p. 954-962Article in journal (Refereed)
    Abstract [en]

    Under global warming, the survival of many populations of sedentary organisms in seasonal environments will largely depend on their ability to cope with warming in situ by means of phenotypic plasticity or adaptive evolution. This is particularly true in high‐latitude environments, where current growing seasons are short, and expected temperature increases large. In such short‐growing season environments, the timing of growth and reproduction is critical to survival. Here, we use the unique setting provided by a natural geothermal soil warming gradient (Hengill geothermal area, Iceland) to study the response of Cerastium fontanum flowering phenology to temperature. We hypothesized that trait expression and phenotypic selection on flowering phenology are related to soil temperature, and tested the hypothesis that temperature‐driven differences in selection on phenology have resulted in genetic differentiation using a common garden experiment. In the field, phenology was related to soil temperature, with plants in warmer microsites flowering earlier than plants at colder microsites. In the common garden, plants responded to spring warming in a counter‐gradient fashion; plants originating from warmer microsites flowered relatively later than those originating from colder microsites. A likely explanation for this pattern is that plants from colder microsites have been selected to compensate for the shorter growing season by starting development at lower temperatures. However, in our study we did not find evidence of variation in phenotypic selection on phenology in relation to temperature, but selection consistently favoured early flowering. Our results show that soil temperature influences trait expression and suggest the existence of genetically based variation in flowering phenology leading to counter‐gradient local adaptation along a gradient of soil temperatures. An important implication of our results is that observed phenotypic responses of phenology to global warming might often be a combination of short‐term plastic responses and long‐term evolutionary responses, acting in different directions.

  • 42. Voigt, Carolina
    et al.
    Marushchak, Maija E.
    Mastepanov, Mikhail
    Lamprecht, Richard E.
    Christensen, Torben R.
    Dorodnikov, Maxim
    Jackowicz-Korczynski, Marcin
    Lindgren, Amelie
    Stockholm University, Faculty of Science, Department of Physical Geography. Lund University, Sweden.
    Lohila, Annalea
    Nykänen, Hannu
    Oinonen, Markku
    Oksanen, Timo
    Palonen, Vesa
    Treat, Claire C.
    Martikainen, Pertti J.
    Biasi, Christina
    Ecosystem carbon response of an Arctic peatland to simulated permafrost thaw2019In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 25, no 5, p. 1746-1764Article in journal (Refereed)
    Abstract [en]

    Permafrost peatlands are biogeochemical hot spots in the Arctic as they store vast amounts of carbon. Permafrost thaw could release part of these long-term immobile carbon stocks as the greenhouse gases (GHGs) carbon dioxide (CO2) and methane (CH4) to the atmosphere, but how much, at which time-span and as which gaseous carbon species is still highly uncertain. Here we assess the effect of permafrost thaw on GHG dynamics under different moisture and vegetation scenarios in a permafrost peatland. A novel experimental approach using intact plant-soil systems (mesocosms) allowed us to simulate permafrost thaw under near-natural conditions. We monitored GHG flux dynamics via high-resolution flow-through gas measurements, combined with detailed monitoring of soil GHG concentration dynamics, yielding insights into GHG production and consumption potential of individual soil layers. Thawing the upper 10-15 cm of permafrost under dry conditions increased CO2 emissions to the atmosphere (without vegetation: 0.74 +/- 0.49 vs. 0.84 +/- 0.60 g CO2-C m(-2) day(-1); with vegetation: 1.20 +/- 0.50 vs. 1.32 +/- 0.60 g CO2-C m(-2) day(-1), mean +/- SD, pre- and post-thaw, respectively). Radiocarbon dating (C-14) of respired CO2, supported by an independent curve-fitting approach, showed a clear contribution (9%-27%) of old carbon to this enhanced post-thaw CO2 flux. Elevated concentrations of CO2, CH4, and dissolved organic carbon at depth indicated not just pulse emissions during the thawing process, but sustained decomposition and GHG production from thawed permafrost. Oxidation of CH4 in the peat column, however, prevented CH4 release to the atmosphere. Importantly, we show here that, under dry conditions, peatlands strengthen the permafrost-carbon feedback by adding to the atmospheric CO2 burden post-thaw. However, as long as the water table remains low, our results reveal a strong CH4 sink capacity in these types of Arctic ecosystems pre- and post-thaw, with the potential to compensate part of the permafrost CO2 losses over longer timescales.

  • 43. Weyhenmeyer, Gesa A.
    et al.
    Livingstone, David M.
    Meili, Markus
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Jensen, Olaf
    Benson, Barbara
    Magnuson, John J.
    Large geographical differences in the sensitivity of ice-covered lakes and rivers in the Northern Hemisphere to temperature changes2011In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 17, no 1, p. 268-275Article in journal (Refereed)
    Abstract [en]

    Based on a unique dataset of more than 50 000 observations of ice phenology from 1213 lakes and 236 rivers in 12 different countries, we show that interannual variations in the timing of ice-on and ice-off on lakes and rivers are not equally pronounced over the entire Northern Hemisphere, but increase strongly towards geographical regions that experience only short periods during which the air temperature falls below 0 degrees C. We explain our observations by interannual fluctuation patterns of air temperature and suggest that lake and river ecosystems in such geographical regions are particularly vulnerable to global warming, as high interannual variability is known to have important ramifications for ecosystem structure and functioning. We estimate that the standard deviation of the duration of ice cover, viewed as a measure of interannual variability, exceeds 25 days for lakes and rivers located on 7% of the land area of the Northern Hemisphere. Such high variability might be an early warning signal for a critical transition from strictly dimictic, ice-covered systems to monomictic, open-water systems. Using the Global Lake and Wetland Database, we suggest that 3.7% of the world's lakes larger than 0.1 km2 are at high risk of becoming open-water systems in the near future, which will have immediate consequences for global biogeochemical cycles.

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