| 1. |
- Lindroth, Anders, et al.
(författare)
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Storms can cause Europe-wide reduction in forest carbon sink
- 2009
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 15:2, s. 346-355
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Tidskriftsartikel (refereegranskat)abstract
- Disturbance of ecosystems is a major factor in regional carbon budgets, and it is believed to be partly responsible for the large inter-annual variability of the terrestrial part of the carbon balance. Forest fires have so far been considered as the most important disturbance but also other forms of disturbance such as insect outbreaks or wind-throw might contribute significantly to the largely unexplained inter-annual variability, at least in specific regions. The effect of wind-throw has not yet been estimated because of lack of data on how carbon fluxes are affected. The Gudrun storm, which hit Sweden in January 2005, resulted in ca. 66 million m(3) of wind-thrown stem wood on an area of ca. 272 000 ha. Using a model (BIOME-BGC) calibrated to CO2 flux measurements at two sites, the annual net ecosystem productivity during the first year after the storm was estimated to be in the range -897 to -1259 g C m(-2) yr(-1). This is a much higher loss compared with harvested (clear-cut) forests in Europe, which ranged between ca. -420 and -100 g m(-2) yr(-1). The reduction in the carbon sink scaled to the whole wind-thrown area was estimated at ca. 3 million tons C during the first year. By historical data on wind-throw in Europe combined with modelling, we estimated that the large Lothar storm in 1999 reduced the European carbon balance by ca. 16 million tons C, this is ca. 30% of the net biome production in Europe. We conclude that the impact of increased forest damage by more frequent storms in future climate change scenarios must be considered and that intermittent large wind-throw events may explain a part of the large inter-annual variability in the terrestrial carbon sink.
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| 2. |
- Nilsson, Mats, et al.
(författare)
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Contemporary carbon accumulation in a boreal oligotrophic minerogenic mire - a significant sink after accounting for all C-fluxes
- 2008
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 14:10, s. 2317-2332
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Tidskriftsartikel (refereegranskat)abstract
- Based on theories of mire development and responses to a changing climate, the current role of mires as a net carbon sink has been questioned. A rigorous evaluation of the current net C-exchange in mires requires measurements of all relevant fluxes. Estimates of annual total carbon budgets in mires are still very limited. Here, we present a full carbon budget over 2 years for a boreal minerogenic oligotrophic mire in northern Sweden (64 degrees 11'N, 19 degrees 33'E). Data on the following fluxes were collected: land-atmosphere CO2 exchange (continuous Eddy covariance measurements) and CH4 exchange (static chambers during the snow free period); TOC (total organic carbon) in precipitation; loss of TOC, dissolved inorganic carbon (DIC) and CH4 through stream water runoff (continuous discharge measurements and regular C-concentration measurements). The mire constituted a net sink of 27 +/- 3.4 (+/- SD) g C m(-2) yr(-1) during 2004 and 20 +/- 3.4 g C m(-2) yr(-1) during 2005. This could be partitioned into an annual surface-atmosphere CO2 net uptake of 55 +/- 1.9 g C m(-2) yr(-1) during 2004 and 48 +/- 1.6 g C m(-2) yr(-1) during 2005. The annual NEE was further separated into a net uptake season, with an uptake of 92 g C m(-2) yr(-1) during 2004 and 86 g C m(-2) yr(-1) during 2005, and a net loss season with a loss of 37 g C m(-2) yr(-1) during 2004 and 38 g C m(-2) yr(-1) during 2005. Of the annual net CO2-C uptake, 37% and 31% was lost through runoff (with runoff TOC > DIC >> CH4) and 16% and 29% through methane emission during 2004 and 2005, respectively. This mire is still a significant C-sink, with carbon accumulation rates comparable to the long-term Holocene C-accumulation, and higher than the C-accumulation during the late Holocene in the region.
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| 3. |
- Norkko, J., et al.
(författare)
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A welcome can of worms? Hypoxia mitigation by an invasive species
- 2012
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 18:2, s. 422-434
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Klemedtsson, Leif, 1953, et al.
(författare)
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Soil CN ratio as a scalar parameter to predict nitrous oxide emissions
- 2005
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 11:7, s. 1142-1147
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Tidskriftsartikel (refereegranskat)abstract
- Forested histosols have been found in some cases to be major, and in other cases minor, sources of the greenhouse gas nitrous oxide (N2O). In order to estimate the total national or global emissions of N2O from histosols, scaling or mapping parameters that can separate low- and high-emitting sites are needed, and should be included in soil databases. Based on interannual measurements of N2O emissions from drained forested histosols in Sweden, we found a strong negative relationship between N2O emissions and soil CN ratios (r(adj)(2)=0.96, mean annual N2O emission=ae((-b CN ratio))). The same equation could be used to estimate the N2O emissions from Finnish and German sites based on CN ratios in published data. We envisage that the correlation between N2O emissions and CN ratios could be used to scale N2O emissions from histosols determined at sampled sites to national levels. However, at low CN ratios (i.e. below 15-20) other parameters such as climate, pH and groundwater tables increase in importance as regulating factors affecting N2O emissions.
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| 5. |
- Lang, S. I., et al.
(författare)
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Arctic warming on two continents has consistent negative effects on lichen diversity and mixed effects on bryophyte diversity
- 2012
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 18:3, s. 1096-1107
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Tidskriftsartikel (refereegranskat)abstract
- Little is known about the impact of changing temperature regimes on composition and diversity of cryptogam communities in the Arctic and Subarctic, despite the well-known importance of lichens and bryophytes to the functioning and climate feedbacks of northern ecosystems. We investigated changes in diversity and abundance of lichens and bryophytes within long-term (916years) warming experiments and along natural climatic gradients, ranging from Swedish subarctic birch forest and subarctic/subalpine tundra to Alaskan arctic tussock tundra. In both Sweden and Alaska, lichen diversity responded negatively to experimental warming (with the exception of a birch forest) and to higher temperatures along climatic gradients. Bryophytes were less sensitive to experimental warming than lichens, but depending on the length of the gradient, bryophyte diversity decreased both with increasing temperatures and at extremely low temperatures. Among bryophytes, Sphagnum mosses were particularly resistant to experimental warming in terms of both abundance and diversity. Temperature, on both continents, was the main driver of species composition within experiments and along gradients, with the exception of the Swedish subarctic birch forest where amount of litter constituted the best explanatory variable. In a warming experiment in moist acidic tussock tundra in Alaska, temperature together with soil ammonium availability were the most important factors influencing species composition. Overall, dwarf shrub abundance (deciduous and evergreen) was positively related to warming but so were the bryophytes Sphagnum girgensohnii, Hylocomium splendens and Pleurozium schreberi; the majority of other cryptogams showed a negative relationship to warming. This unique combination of intercontinental comparison, natural gradient studies and experimental studies shows that cryptogam diversity and abundance, especially within lichens, is likely to decrease under arctic climate warming. Given the many ecosystem processes affected by cryptogams in high latitudes (e.g. carbon sequestration, N2-fixation, trophic interactions), these changes will have important feedback consequences for ecosystem functions and climate.
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| 6. |
- Pleijel, Håkan, 1958, et al.
(författare)
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Yield vs. Quality trade-offs for wheat in response to carbon dioxide and ozone
- 2012
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Ingår i: Global Change Biology. - : Wiley. - 1365-2486 .- 1354-1013. ; 18:2, s. 596-605
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Tidskriftsartikel (refereegranskat)abstract
- Although it is established that there exist potential trade-offs between grain yield and grain quality in wheat exposed to elevated carbon dioxide (CO2) and ozone (O3), their underlying causes remain poorly explored. To investigate the processes affecting grain quality under altered CO2 and O3, we analysed 57 experiments with CO2 or O3 exposure in different exposure systems. The study covered 24 cultivars studied in 112 experimental treatments from 11 countries. A significant growth dilution effect on grain protein was found: a change in grain yield of 10% by O3 was associated with a change in grain protein yield of 8.1% (R2 = 0.96), whereas a change in yield effect of 10% by CO2 was linked to a change in grain protein yield effect of 7.5% (R2 = 0.74). Superimposed on this effect, elevated CO2, but not O3, had a significant negative effect on grain protein yield also in the absence of effects on grain yield, indicating that there exists a process by which CO2 restricts grain protein accumulation, which is absent for O3. Grain mass, another quality trait, was more strongly affected by O3 than grain number, whereas the opposite was true for CO2. Harvest index was strongly and negatively influenced by O3, but was unaffected by CO2. We conclude that yield vs. protein trade-offs for wheat in response to CO2 and O3 are constrained by close relationships between effects on grain biomass and less than proportional effects on grain protein. An important and novel finding was that elevated CO2 has a direct negative effect on grain protein accumulation independent of the yield effect, supporting recent evidence of CO2-induced impairment of nitrate uptake/assimilation. Finally, our results demonstrated that processes underlying responses of grain yield vs. quality trade-offs are very different in wheat exposed to elevated O3 compared with elevated CO2.
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| 7. |
- Sun, Ge, et al.
(författare)
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Interactive influences of ozone and climate on streamflow of forested watersheds
- 2012
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Ingår i: Global Change Biology. - : Wiley. - 1365-2486 .- 1354-1013. ; 18:11, s. 3395-3409
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Tidskriftsartikel (refereegranskat)abstract
- The capacity of forests to mitigate global climate change can be negatively influenced by tropospheric ozone that impairs both photosynthesis and stomatal control of plant transpiration, thus affecting ecosystem productivity and watershed hydrology. We have evaluated individual and interactive effects of ozone and climate on late season streamflow for six forested watersheds (38-970,000 ha) located in the southeastern United States. Models were based on 18-26 year data records for each watershed and involved multivariate analysis of interannual variability of late season streamflow in response to physical and chemical climate during the growing season. In all cases, some combination of ozone variables significantly improved model performance over climate-only models. Effects of ozone and ozone×climate interactions were also consistently negative and were proportional to variations in actual ozone exposures, both spatially across the region and over time. Conservative estimates of the influence of ozone on the variability (R2) of observed flow ranged from 7% in the area of lowest ozone exposure in West Virginia to 23% in the areas of highest exposure in Tennessee. Our results are supported by a controlled field study using free-air concentration enrichment (FACE) methodology which indicated progressive ozone-induced loss of stomatal control over tree transpiration during the summer in mixed aspen-birch stands. Despite the frequent assumption that ozone reduces tree water loss, our findings support increasing evidence that ozone at near ambient concentrations can reduce stomatal control of leaf transpiration, and increase water use. Increases in evapotranspiration and associated streamflow reductions in response to ambient ozone exposures are expected to episodically increase the frequency and severity of drought and affect flow-dependent aquatic biota in forested watersheds. Regional and global models of hydrologic cycles and related ecosystem functions should consider potential interactions of ozone with climate under both current and future warmer and ozone enriched climatic conditions.
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| 8. |
- Zacher, K., et al.
(författare)
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Ultraviolet radiation and consumer effects on a field-grown intertidal macroalgal assemblage in Antarctica
- 2007
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 13:6, s. 1201-1215
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Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet radiation (UVR) research on marine macroalgae has hithero focussed on physiological effects at the organism level, while little is known on the impact of UV radiation on macroalgal assemblages and even less on interactive effects with other community drivers, e.g. consumers. Field experiments on macrobenthos are scarce, particularly in the Antarctic region. Therefore, the effects of UVR and consumers (mainly limpets were excluded) on early successional stages of a hard bottom macroalgal community on King George Island, Antarctica, were studied. In a two-factorial design experimental units [(1) ambient radiation, 280-700 nm; (2) ambient minus UVB, 320-700 nm and (3) ambient minus UVR, 400-700 nm vs. consumer-no consumer] were installed between November 2004 and March 2005 (n = 4 plus controls). Dry mass, species richness, diversity and composition of macroalgal assemblages developing on ceramic tiles were followed. Consumers significantly suppressed green algal recruits and total algal biomass but increased macroalgal richness and diversity. Both UVA and UVB radiation negatively affected macroalgal succession. UVR decreased the density of Monostroma hariotii germlings in the first 10 weeks of the experiment, whereas the density of red algal recruits was significantly depressed by UVR at the end of the study. After 106 days macroalgal diversity was significantly higher in UV depleted than in UV-exposed assemblages. Furthermore, species richness was significantly lower in the UV treatments and species composition differed significantly between the UV-depleted and the UV-exposed treatment. Marine macroalgae are very important primary producers in coastal ecosystems, serving as food for herbivores and as habitat for many organisms. Both, UVR and consumers significantly shape macroalgal succession in the Antarctic intertidal. Consumers, particularly limpets can mediate negative effects of ambient UVR on richness and diversity till a certain level. UVB radiation in general and an increase of this short wavelength due to stratospheric ozone depletion in particular may have the potential to affect the zonation, composition and diversity of Antarctic intertidal seaweeds altering trophic interactions in this system.
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| 9. |
- Öquist, Mats, et al.
(författare)
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Water availability controls microbial temperature responses in frozen soil CO2 production
- 2009
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Ingår i: Global Change Biology. - : Blackwell Publishing Ltd. - 1354-1013 .- 1365-2486. ; 15:11, s. 2715-22
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Tidskriftsartikel (refereegranskat)abstract
- Soil processes in high-latitude regions during winter are important contributors to global carbon circulation, but our understanding of the mechanisms controlling these processes is poor and observed temperature response coefficients of CO2 production in frozen soils deviate markedly from thermodynamically predicted responses (sometimes by several orders of magnitude). We investigated the temperature response of CO2 production in 23 unfrozen and frozen surface soil samples from various types of boreal forests and peatland ecosystems and also measured changes in water content in them after freezing. We demonstrate that deviations in temperature responses at subzero temperatures primarily emanates from water deficiency caused by freezing of the soil water, and that the amount of unfrozen water is mainly determined by the quality of the soil organic matter, which is linked to the vegetation cover. Factoring out the contribution of water limitation to the CO2 temperature responses yields response coefficients that agree well with expectations based on thermodynamic theory concerning biochemical temperature responses. This partitioning between a pure temperature response and the effect of water availability on the response of soil CO2 production at low temperatures is crucial for a thorough understanding of low-temperature soil processes and for accurate predictions of C-balances in northern terrestrial ecosystems.
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| 10. |
- Alison, Jamie, et al.
(författare)
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Deep learning to extract the meteorological by-catch of wildlife cameras
- 2024
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Ingår i: Global Change Biology. - 1354-1013 .- 1365-2486. ; 30:1
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Tidskriftsartikel (refereegranskat)abstract
- Microclimate—proximal climatic variation at scales of metres and minutes—can exacerbate or mitigate the impacts of climate change on biodiversity. However, most microclimate studies are temperature centric, and do not consider meteorological factors such as sunshine, hail and snow. Meanwhile, remote cameras have become a primary tool to monitor wild plants and animals, even at micro-scales, and deep learning tools rapidly convert images into ecological data. However, deep learning applications for wildlife imagery have focused exclusively on living subjects. Here, we identify an overlooked opportunity to extract latent, ecologically relevant meteorological information. We produce an annotated image dataset of micrometeorological conditions across 49 wildlife cameras in South Africa's Maloti-Drakensberg and the Swiss Alps. We train ensemble deep learning models to classify conditions as overcast, sunshine, hail or snow. We achieve 91.7% accuracy on test cameras not seen during training. Furthermore, we show how effective accuracy is raised to 96% by disregarding 14.1% of classifications where ensemble member models did not reach a consensus. For two-class weather classification (overcast vs. sunshine) in a novel location in Svalbard, Norway, we achieve 79.3% accuracy (93.9% consensus accuracy), outperforming a benchmark model from the computer vision literature (75.5% accuracy). Our model rapidly classifies sunshine, snow and hail in almost 2 million unlabelled images. Resulting micrometeorological data illustrated common seasonal patterns of summer hailstorms and autumn snowfalls across mountains in the northern and southern hemispheres. However, daily patterns of sunshine and shade diverged between sites, impacting daily temperature cycles. Crucially, we leverage micrometeorological data to demonstrate that (1) experimental warming using open-top chambers shortens early snow events in autumn, and (2) image-derived sunshine marginally outperforms sensor-derived temperature when predicting bumblebee foraging. These methods generate novel micrometeorological variables in synchrony with biological recordings, enabling new insights from an increasingly global network of wildlife cameras.
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