| 1. |
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| 2. |
- Schweiger, Oliver, et al.
(författare)
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Multiple stressors on biotic interactions: how climate change and alien species interact to affect pollination
- 2010
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Ingår i: Biological Reviews. - 1469-185X .- 1464-7931. ; 85:4, s. 777-795
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Forskningsöversikt (refereegranskat)abstract
- Global change may substantially affect biodiversity and ecosystem functioning but little is known about its effects on essential biotic interactions. Since different environmental drivers rarely act in isolation it is important to consider interactive effects. Here, we focus on how two key drivers of anthropogenic environmental change, climate change and the introduction of alien species, affect plant-pollinator interactions. Based on a literature survey we identify climatically sensitive aspects of species interactions, assess potential effects of climate change on these mechanisms, and derive hypotheses that may form the basis of future research. We find that both climate change and alien species will ultimately lead to the creation of novel communities. In these communities certain interactions may no longer occur while there will also be potential for the emergence of new relationships. Alien species can both partly compensate for the often negative effects of climate change but also amplify them in some cases. Since potential positive effects are often restricted to generalist interactions among species, climate change and alien species in combination can result in significant threats to more specialist interactions involving native species.
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| 3. |
- Allen, Judy R. M., et al.
(författare)
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Last glacial vegetation of northern Eurasia
- 2010
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 29:19-20, s. 2604-2618
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Tidskriftsartikel (refereegranskat)abstract
- In order to investigate the potential role of vegetation changes in megafaunal extinctions during the later part of the last glacial stage and early Holocene (42-10 ka BP), the palaeovegetation of northern Eurasia and Alaska was simulated using the LPJ-GUESS dynamic vegetation model. Palaeoclimatic driving data were derived from simulations made for 22 time slices using the Hadley Centre Unified Model. Modelled annual net primary productivity (aNPP) of a series of plant functional types (PFTs) is mapped for selected time slices and summarised for major geographical regions for all time slices. Strong canonical correlations are demonstrated between model outputs and pollen data compiled for the same period and region. Simulated aNPP values, especially for tree PFTs and for a mesophilous herb PFT, provide evidence of the structure and productivity of last glacial vegetation. The mesophilous herb PFT aNPP is higher in many areas during the glacial than at present or during the early Holocene. Glacial stage vegetation, whilst open and largely treeless in much of Europe, thus had a higher capacity to support large vertebrate herbivore populations than did early Holocene vegetation. A marked and rapid decrease in aNPP of mesophilous herbs began shortly after the Last Glacial Maximum, especially in western Eurasia. This is likely implicated in extinction of several large herbivorous mammals during the latter part of the glacial stage and the transition to the Holocene. (c) 2010 Elsevier Ltd. All rights reserved.
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| 4. |
- Calfapietra, Carlo, et al.
(författare)
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Challenges in elevated CO2 experiments on forests
- 2010
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Ingår i: Trends in Plant Science. - : Elsevier BV. - 1360-1385. ; 15:1, s. 5-10
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Forskningsöversikt (refereegranskat)abstract
- Current forest Free Air CO2 Enrichment (FACE) experiments are reaching completion. Therefore, it is time to define the scientific goals and priorities of future experimental facilities. In this opinion article, we discuss the following three overarching issues (i) What are the most urgent scientific questions and how can they be addressed? (ii) What forest ecosystems should be investigated? (iii) Which other climate change factors should be coupled with elevated CO2 concentrations in future experiments to better predict the effects of climate change? Plantations and natural forests can have conflicting purposes for high productivity and environmental protection. However, in both cases the assessment of carbon balance and how this will be affected by elevated CO2 concentrations and the interacting climate change factors is the most pressing priority for future experiments.
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| 5. |
- De Kauwe, Martin G., et al.
(författare)
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Forest water use and water use efficiency at elevated CO2: a model-data intercomparison at two contrasting temperate forest FACE sites
- 2013
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 19:6, s. 1759-1779
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Tidskriftsartikel (refereegranskat)abstract
- Predicted responses of transpiration to elevated atmospheric CO2 concentration (eCO2) are highly variable amongst process-based models. To better understand and constrain this variability amongst models, we conducted an intercomparison of 11 ecosystem models applied to data from two forest free-air CO2 enrichment (FACE) experiments at Duke University and Oak Ridge National Laboratory. We analysed model structures to identify the key underlying assumptions causing differences in model predictions of transpiration and canopy water use efficiency. We then compared the models against data to identify model assumptions that are incorrect or are large sources of uncertainty. We found that model-to-model and model-to-observations differences resulted from four key sets of assumptions, namely (i) the nature of the stomatal response to elevated CO2 (coupling between photosynthesis and stomata was supported by the data); (ii) the roles of the leaf and atmospheric boundary layer (models which assumed multiple conductance terms in series predicted more decoupled fluxes than observed at the broadleaf site); (iii) the treatment of canopy interception (large intermodel variability, 215%); and (iv) the impact of soil moisture stress (process uncertainty in how models limit carbon and water fluxes during moisture stress). Overall, model predictions of the CO2 effect on WUE were reasonable (intermodel =approximately 28%+/- 10%) compared to the observations (=approximately 30%+/- 13%) at the well-coupled coniferous site (Duke), but poor (intermodel =approximately 24%+/- 6%; observations =approximately 38%+/- 7%) at the broadleaf site (Oak Ridge). The study yields a framework for analysing and interpreting model predictions of transpiration responses to eCO2, and highlights key improvements to these types of models.
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| 6. |
- Drobyshev, Igor, et al.
(författare)
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Masting behaviour and dendrochronology of European beech (Fagus sylvatica L.) in southern Sweden
- 2010
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 1872-7042 .- 0378-1127. ; 259:11, s. 2160-2171
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Tidskriftsartikel (refereegranskat)abstract
- To identify weather controls of beech diameter growth and masting in southern Sweden, we analyze records of monthly weather, regional masting record, and tree-ring chronologies from five beech-dominated stands. The results indicate a strong weather control of temporal pattern of masting events in southern Sweden over the second half of the 20th century. Negative summer temperature anomaly 2 years prior to a mast year, coupled with positive temperature anomaly in the year immediately preceding the same mast year, is a characteristic weather pattern associated with known mast years. Strong dependence of beech masting behavior on temperature explains the high degree of regional synchronization of masting events. Growth of beech in southern Sweden is strongly and negatively correlated with previous year's summer temperature and positively - with previous year's October temperature. The present study does not provide a conclusive answer in identifying a full set of direct and indirect effects of climatic variables controlling tree-ring growth, since the negative effect of previous year's summer temperature may be a result of a temperature-controlled increase in the beech nut production in the current year. Consistent and significant negative departures of ring-width index during mast years support the hypothesis about a trade-off between investment of bioassimilates into production of beech nuts and tree-ring growth. Alternative explanation of growth anomalies in mast years, relating such anomaly to a negative impact of previous year's growing season, was not supported by the data. We found a limited effect of masting on diameter growth in the following years, indicating that decline in the overall wood production, associated with heavy masting, is short term and typically occurs in the year of actual masting. (C) 2010 Elsevier B.V. All rights reserved.
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| 7. |
- Drobyshev, Igor, et al.
(författare)
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Reconstruction of a regional drought index in southern Sweden since AD 1750
- 2011
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 21:4, s. 667-679
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Tidskriftsartikel (refereegranskat)abstract
- We used a network of eight pedunculate oak (Quercus robur L.) sites (n(trees) = 70) and one Scots pine (Pinus sylvestris L.) site (n(trees) = 53) to develop drought-sensitive master chronologies for the two areas in southern Scandinavia: a SW-area centred on 57AN 12.7AE and a NE-area centred on 58.8AN 18.2AE. The ratio of actual to equilibrium evapotranspiration (AET/EET) was used as a measure of drought during the growing season defined as the period with average daily temperatures above 9 degrees C. Instrumental data were used to parameterize the relationship between tree-ring data and the drought index (DI) over 1922-2000 for the SW area and over 1922-1995 for the NE area. The DI reconstructions explained 29.7% (SW area) and 43.7% (NE area) of the variance in the observed DI index in the calibration period, and were extended back to AD 1770 for the SW area and to AD 1750 for the NE area. Reconstructed drought dynamics suggested strong decadal- and century-scale temporal variability and limited regional synchronicity over 1770-2000. Large variations in DI were observed in both regions in the second half of the 1700s. Dry conditions were synchronously reconstructed in both sub-regions during 1781-1784, 1853-1855, and, to a lesser degree, during 1974-1978. Over the 1945-1975 period the SW area exhibited a trend towards drier growing seasons, whereas no such trend could be identified for the NE area. Analysis of correlation maps indicated that regional DI dynamics reflected two different climate regimes, associated with the Kattegat area (SW reconstruction) and southeastern Swedish coast of the Baltic sea (NE reconstruction).
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| 8. |
- Gaillard, Marie-José, 1953-, et al.
(författare)
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Holocene land-cover reconstructions for studies on land cover-climate feedbacks
- 2010
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 6, s. 483-499
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Tidskriftsartikel (refereegranskat)abstract
- The major objectives of this paper are: (1) to review the pros and cons of the scenarios of past anthropogenic land cover change (ALCC) developed during the last ten years, (2) to discuss issues related to pollen-based reconstruction of the past land-cover and introduce a new method, REVEALS (Regional Estimates of VEgetation Abundance from Large Sites), to infer long-term records of past land-cover from pollen data, (3) to present a new project (LANDCLIM: LAND cover – CLIMate interactions in NW Europe during the Holocene) currently underway, and show preliminary results of REVEALS reconstructions of the regional land-cover in the Czech Republic for five selected time windows of the Holocene, and (4) to discuss the implications and future directions in climate and vegetation/land-cover modeling, and in the assessment of the effects of human-induced changes in land-cover on the regional climate through altered feedbacks. The existing ALCC scenarios show large discrepancies between them, and few cover time periods older than AD 800. When these scenarios are used to assess the impact of human land-use on climate, contrasting results are obtained. It emphasizes the need for methods such as the REVEALS model-based land-cover reconstructions. They might help to fine-tune descriptions of past land-cover and lead to a better understanding of how long-term changes in ALCC might have influenced climate. The REVEALS model is demonstrated to provide better estimates of the regional vegetation/landcover changes than the traditional use of pollen percentages. This will achieve a robust assessment of land cover at regional- to continental-spatial scale throughout the Holocene. We present maps of REVEALS estimates for the percentage cover of 10 plant functional types (PFTs) at 200 BP and 6000 BP, and of the two open-land PFTs “grassland” and “agricultural land” at five time-windows from 6000 BP to recent time. The LANDCLIM results are expected to provide crucial data to reassess ALCC estimates for a better understanding of the land suface-atmosphere interactions.
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| 9. |
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| 10. |
- Huntley, Brian, et al.
(författare)
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Millennial Climatic Fluctuations Are Key to the Structure of Last Glacial Ecosystems
- 2013
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:4
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Tidskriftsartikel (refereegranskat)abstract
- Whereas fossil evidence indicates extensive treeless vegetation and diverse grazing megafauna in Europe and northern Asia during the last glacial, experiments combining vegetation models and climate models have to-date simulated widespread persistence of trees. Resolving this conflict is key to understanding both last glacial ecosystems and extinction of most of the mega-herbivores. Using a dynamic vegetation model (DVM) we explored the implications of the differing climatic conditions generated by a general circulation model (GCM) in "normal" and "hosing" experiments. Whilst the former approximate interstadial conditions, the latter, designed to mimic Heinrich Events, approximate stadial conditions. The "hosing" experiments gave simulated European vegetation much closer in composition to that inferred from fossil evidence than did the "normal" experiments. Given the short duration of interstadials, and the rate at which forest cover expanded during the late-glacial and early Holocene, our results demonstrate the importance of millennial variability in determining the character of last glacial ecosystems.
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