| 1. |
- Gachet, S, et al.
(författare)
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A probabilistic approach to the use of pollen indicators for plant attributes and biomes: an application to European vegetation at 0 and 6 ka
- 2003
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Ingår i: Global Ecology and Biogeography Letters. - 0960-7447. ; 12:2, s. 103-118
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Tidskriftsartikel (refereegranskat)abstract
- Aim This paper presents a probabilistic method for the characterization of pollen taxa using attributes, and for the reconstitution of past biomes. The probabilities are calculated on the basis of European floristic and pollen databases sufficiently large and exhaustive to provide robust estimates. Location The analysis is based on data from approximately 1000 sites throughout Europe. Method We use all the pollen data from the European Pollen Database (EPD), which contains about 50 000 pollen assemblages distributed across Europe and covering the period from the Last Glacial Maximum to the present. Using existing floras, each pollen taxon has been characterized by allocating one or more modes of several attributes, chosen according to the biogeography and phenology of the taxon. With this information, conditional probabilities are defined, representing the chance of a given attribute mode occurring in a given pollen spectrum, when the taxa assemblage is known. The concept of co-occurrence is used to provide a greater amount of information to compensate for difficulties in the identification of pollen grains, allowing a better interpretation when there is little diversity in the pollen assemblage. Results The method has been validated using a dataset of modern samples against existing methods of biome classification and remote sensing data. An application is proposed in which the new method is used to produce biomes for pollen data 6000 years ago. This confirms previous results showing an extension of the deciduous forest to the north, east and south, explained by milder winters in western and northern Europe, and cooler and wetter climate in the Mediterranean region. Conclusion The results show the new method to be efficient, reliable and flexible and to be an improvement over the previous method of biomization. They will be used to test simulations of earth system models running on periods with climate significantly different from the present day, enabling a robust test of the validity of applying these models to the future.
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| 2. |
- Gritti, Emmanuel, et al.
(författare)
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An extended probabilistic approach of plant vital attributes: an application to European pollen records at 0 and 6 ka
- 2004
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Ingår i: Global Ecology and Biogeography Letters. - 0960-7447. ; 13:6, s. 519-533
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Tidskriftsartikel (refereegranskat)abstract
- Aim This paper presents a probabilistic method of pollen spectra analysis. The method relies on a pollen taxon characterization using biotic and abiotic plant attribute modes, and their occurrence in a given pollen spectrum at a specific site. This type of analysis can provide an interpretation, which can lead to the reconstruction of the biome and, to an extent, of the abiotic conditions at the site. Methods The analysis has been carried out at the European scale using data provided by the European Pollen Database for about 1000 sites. This dataset contains about 50,000 pollen spectra from the last 21 ka. In these spectra, each pollen taxon has been characterized by a set of 10 chosen attributes. These have been selected with regard to their relevance in biome reconstruction, but also on the basis of available literature. By using the probability of occurrence of each taxon in a given pollen spectrum, it is possible to calculate an affinity index for the spectrum to the attribute considered. To overcome difficulties caused by pollen identification in low diversified pollen spectra, a co-occurrence concept has been used to give more information. Results The method has been validated on a set of 1327 modern surface samples by comparing the results to the major climatic and environmental variables that control the distribution of the vegetation. A reconstruction exercise on various characteristics of the plants was then carried out on a 6-ka dataset. This confirmed previous studies by showing a strong dominance of deciduous forest over most of Europe, related to a milder climate than at present in the north and a wetter and colder climate than at present in the south. By analysing the change in pollen/seed dispersion strategies and the light requirement, we show that the history of vegetation dynamics in relation to human influences can be assessed using this method. Main conclusions Our results show that the probabilistic method is an objective tool for pollen assemblage analysis. It allows reconstruction of various characteristics of the vegetation at the continental and global scale for periods and sites with significantly different climate conditions. This method can also be used to compare maps of vegetation attributes for the validation of the new generalized dynamic ecosystems models.
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| 3. |
- Gritti, Emmanuel
(författare)
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Global Changes and European Terrestrial Ecosystems
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Global environmental changes are topics of important societal concern and current scientific interest. These changes are driven by many different forcing and feedbacks occurring at various time and geographic scales and are largely influencing the various Earth systems. Despite the fact that the natural component of these changes has always occurred, today it's the anthropogenic component and its magnitude which is worrying. At the European scale, such changes are likely to profoundly affect terrestrial ecosystems in term of physiology, phenology, distribution and evolution. In order to improve our understanding of the effect of global changes on ecosystems, this thesis describes a range of diverse analyses into the different forcing factors for different periods of time. In the first study, palaeorecords show that climatic conditions similar to the ones predicted to occur during the coming century already occurred. European terrestrial ecosystems however were different in structure and composition. Future predictions of climatic conditions associated to plant species specific tolerances ranges have been used in the second and third studies to quantify geographically the risk for such species in being able to find suitable climate space by the end of the century. In general, northern species will face a drastic reduction of their suitable climatic space as southern species are likely to face an expansion in climate space. However, to reach a suitable climate species may have to travel great distances and overcome natural and human barriers. Finally, the last two studies explored with the help of the state of the art dynamic vegetation model LPJ-GUESS, the different interactions between climatic changes, disturbances rates and exotic plant invasion and Mediterranean European ecosystems compositions and functions. Disturbance has been shown to be the main driving factor of these ecosystems characteristics, and influenced largely the likely success of invasions in some ecosystems. However, at the local scale, climatic conditions and the degree of invasion, were likely to influence ecosystems composition, distribution and functions but in a less radical ways. Such approaches, allowed us to explore the relevance of the different forcing factors on ecosystems changes. Future development of these analytic methods by adopting more integrating methods should aim to support societal decisions and actions.
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| 4. |
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| 5. |
- Gritti, Emmanuel, et al.
(författare)
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Vulnerability of Mediterranean Basin ecosystems to climate change and invasion by exotic plant species
- 2006
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Ingår i: Journal of Biogeography. - : Wiley. - 1365-2699 .- 0305-0270. ; 33:1, s. 145-157
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Tidskriftsartikel (refereegranskat)abstract
- Aim To assess at a broad scale the vulnerability of Mediterranean vegetation to alien plant invasion under different climatic and disturbance scenarios. Location We simulated the vegetation biogeography and dynamics on five of the main islands of the Mediterranean Basin: Mallorca, Corsica, Sardinia, Crete and Lesvos. Methods We used LPJ-GUESS, a generalized ecosystem model based on dynamic processes describing establishment, competition, mortality and ecosystem biogeochemistry. We simulated the vegetation distribution and dynamics using a set of plant functional types (PFTs) based on bioclimatic and physiological parameters, which included tree and shrub PFTs defined especially for the Mediterranean. Additionally, two invasive PFTs, an invasive tree type and an invasive herb type, were defined and used to estimate the vulnerability to invasion of a range of different ecosystems. The model was used to simulate climate changes and associated changes in atmospheric [CO2] to 2050 according to two Special Report on Emissions Scenarios climate scenarios (A1Fi and B1) combined with mean disturbance intervals of 3 and 40 years. Results The simulations and scenarios showed that the effect of climate change alone is likely to be negligible in many of the simulated ecosystems, although not all. The simulated progression of an invasion was highly dependent on the initial ecosystem composition and local environmental conditions, with a particular contrast between drier and wetter parts of the Mediterranean, and between mountain and coastal areas. The rate of ecosystem disturbance was the main factor controlling susceptibility to invasion, strongly influencing vegetation development on the shorter time scale. Main conclusions Further invasion into Mediterranean island ecosystems is likely to be an increasing problem: our simulations predict that, in the longer term, almost all the ecosystems will be dominated by exotic plants irrespective of disturbance rates.
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| 6. |
- Ohlemueller, Ralf, et al.
(författare)
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Towards European climate risk surfaces: the extent and distribution of analogous and non-analogous climates 1931-2100
- 2006
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Ingår i: Global Ecology and Biogeography. - 1466-8238. ; 15:4, s. 395-405
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Tidskriftsartikel (refereegranskat)abstract
- Aim Climate is an important determinant of species distributions. We assess different aspects of risk arising from future climate change by quantifying changes in the spatial distribution of future climatic conditions compared with the recent past. Location Europe. Methods A 10' x 10' resolution gridded data set of five climate variables was used to calculate expected changes to the area, distance and direction of 1931-60 climatic conditions under the HadCM3 climate model for four future climate scenarios based on different rates of greenhouse gas emissions (SRES scenarios). Three levels of tolerance ranges determined the thresholds for which future conditions are considered analogous to 1931-60 (pre-warming) conditions. Results For many parts of Europe, areas with pre-warming analogous climate conditions will be smaller and further away in the future than they arc now. For any location in Europe, areas with pre-warming analogous mean annual temperature conditions will, on average, be reduced between 23.7% (B1 scenario) and 49.7% (A1FI scenario) by 2100 when assuming a medium tolerance range. The mean distance to these areas will, on average, increase between 272 km (B1) and 645 km (A1FI). These changes are more pronounced for temperature than for water availability variables and also for narrow tolerance ranges compared to wide tolerance ranges. Using a combined measure of both temperature and precipitation variables, areas with pre-warming analogous conditions are predicted to be in a more northeasterly direction in the future, but there are considerable regional differences within Europe. Main conclusions The results suggest that, for some parts of Europe, the loss of area with any suitable climatic conditions represents the greatest risk to biodiversity, but in other regions the distances that species may have to move to reach suitable climatic conditions may be a greater problem. Quantifying the distance and direction in analyses of change of climatically suitable areas can add additional information for climate change risk assessments.
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| 7. |
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| 8. |
- Ohlemuller, Ralf, et al.
(författare)
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Quantifying components of risk for European woody species under climate change
- 2006
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013. ; 12:9, s. 1788-1799
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Tidskriftsartikel (refereegranskat)abstract
- Estimates of species extinction risk under climate change are generally based on differences in present and future climatically suitable areas. However, the locations of potentially suitable future environments (affecting establishment success), and the degree of climatic suitability in already occupied and new locations (affecting population viability) may be equally important determinants of risk. A species considered to be at low risk because its future distribution is predicted to be large, may actually be at high risk if these areas are out of reach, given the species' dispersal and migration rates or if all future suitable locations are only marginally suitable and the species is unlikely to build viable populations in competition with other species. Using bioclimatic models of 17 representative European woody species, we expand on current ways of risk assessment and suggest additional measures based on (a) the distance between presently occupied areas and areas predicted to be climatically suitable in the future and (b) the degree of change in climatic suitability in presently occupied and unoccupied locations. Species of boreal and temperate deciduous forests are predicted to face higher risk from loss of climatically suitable area than species from warmer and drier parts of Europe by 2095 using both the moderate B1 and the severe A1FI emission scenario. However, the average distance from currently occupied locations to areas predicted suitable in the future is generally shorter for boreal species than for southern species. Areas currently occupied will become more suitable for boreal and temperate species than for Mediterranean species whereas new suitable areas outside a species' current range are expected to show greater increases in suitability for Mediterranean species than for boreal and temperate species. Such additional risk measures can be easily derived and should give a more comprehensive picture of the risk species are likely to face under climate change.
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