| 1. |
- Hickler, Thomas, et al.
(författare)
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Precipitation controls Sahel greening trend
- 2005
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Ingår i: Geophysical Research Letters. - 1944-8007. ; 32:21
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Tidskriftsartikel (refereegranskat)abstract
- The Sahel region has been identified as a "hot spot'' of global environmental change, but understanding of the roles of different climatic and anthropogenic forcing factors driving change in the region is incomplete. We show that a process-based ecosystem model driven by climatic and atmospheric CO2 data alone closely reproduces the satellite-observed greening trend of the Sahel vegetation and its interannual variability between 1982 and 1998. Changes in precipitation were identified as the primary driver of the aggregated simulated vegetation changes. According to the model, the increasing carbon uptake through vegetation was associated with an increasing relative carbon sink; but integrated over the whole period, the Sahel was predicted to be a net source of carbon.
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| 2. |
- Eklundh, Lars, et al.
(författare)
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Analysing vegetation changes in the Sahel using sensor data from Landsat and NOAA
- 2005
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Konferensbidrag (refereegranskat)abstract
- The semi-arid Sahel zone of Africa has suffered several periods of severe drought since about 1950. We have analyzed AVHRR Normalized Difference Vegetation Index (NDVI) over the Sahel for the period 1982-2002, and found extensive areas of increasing NDVI. To verify these changes we have analyzed Landsat TM and ETM+ scenes from 1984-1986 and 1999-2001 for areas in the Sudan, Central African Republic, Niger, Mali and Mauritania. Changes in the Landsat data were analysed by visual interpretation and change vector analysis. In areas of positive AVHRR NDVI change the analysis of Landsat data generally showed a transition from barren or sparse vegetation to a denser vegetation cover. Rainfall had increased over the course of time in several of these areas. In some areas visual interpretation indicated an expansion of agricultural land.
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| 3. |
- Gräsbeck, Anne, et al.
(författare)
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Dementia in First-Degree Relatives of Patients with Frontotemporal Dementia. A Family History Study.
- 2005
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Ingår i: Dementia and Geriatric Cognitive Disorders. - : S. Karger AG. - 1420-8008 .- 1421-9824. ; 19:2-3, s. 145-153
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Tidskriftsartikel (refereegranskat)abstract
- Several studies have found a clustering of dementia in relatives of patients with frontotemporal dementia (FTD). This study analysed the familial aggregation of FTD specifically as well as the occurrence of dementia in general in first-degree relatives of patients with FTD. A family history study was carried out on 478 first-degree relatives of 74 index patients suffering from FTD. Cases of organic dementia and of FTD were diagnosed according to internationally accepted diagnostic criteria. Age- and sex-specific incidences of organic dementia and of FTD were calculated as was the proportion of FTD in relation to organic dementia in general; comparisons with clinical and population studies were made. There was a tenfold increase in the incidence of FTD in the first-degree relatives of FTD patients compared with the incidence of FTD in a population study. The proportion of FTD in relation to all types of organic dementia was much higher in relatives of FTD patients compared to the corresponding proportions in clinical and population-based studies. There was a small, non-significant difference between the present family history study and the population studies as regards the incidence of organic dementia. The findings suggest that hereditary and/or shared environmental factors are strongly involved in the aetiology of FTD. There were no indications of familial clustering of organic dementia in general in relatives of FTD patients.
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| 4. |
- Högdahl, Karin, et al.
(författare)
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Continental margin magmatism and migmatisation in the west-central Fennoscandian Shield
- 2008
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Ingår i: Lithos. - : Elsevier BV. - 0024-4937 .- 1872-6143. ; 102:3-4, s. 435-459
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Tidskriftsartikel (refereegranskat)abstract
- The Ljusdal Batholith (LjB) is a major component of the central Svecofennian Domain in Sweden. It is separated from the Bothnian Basin to the north by the 1.82-1.80 Cia crustal-scale Hassela Shear Zone (HSZ). The LjB has emplacement ages of 1.86-1.84 Cia, is mainly alkali-calcic, metaluminous, has epsilon(Nd) values between -0.3 and + 1.2 and was formed in a magmatic arc setting. During the Svecokarelian orogeny the LjB was affected by at least three fold episodes. Large-scale folded screens of migmatised metasedimentary rocks occur in the eastern part of the batholith, and to the north of the HSZ, there is a 50 km wide diatexite belt. The Transition Belt (TrB), consisting of 1.88-1.85 Ga granitoids, is located at the northwestern extension of this belt. A calc-alkaline and peraluminous composition combined with negative epsilon(Nd) values (- 1.7 to -0.8) indicates a large proportion of metasediments in the source for these granitoids. U-Pb SIMS data on zircon rims from migmatites and leucogranites to the north and east of LjB yield ages of 1.87-1.86 Ga, i.e. coeval with the granitoids of the LjB and the TrB. There is thus a close relationship between the LjB, the TrB and the migmatites in both space and time. Syn-migmatitic shearing along the HSZ indicates that a proto-HSZ was initiated already at c. 1.86 Ga, and the location of the proto-HSZ is inferred to be controlled by two older nuclei present in the lower parts of the crust. As crustal-scale shear zone systems are known to act as ascent pathways for sheet-like flow in active orogenies the TrB may represents accumulations of melts that were attracted and extracted by the proto-HSZ and intruded in a block that was not pervasively affected by subsequent shear along the HSZ. An active continental margin setting for the LjB implies subduction at c. 1.86 Ga, and provides a heat source for both the migmatites and the TrB. A later migmatisation at 1.82 Ga has been recorded to the south of the HSZ. Within the LjB the 1.82 Ga stromatic migmatites are folded by F-2 folds, and the fabric is truncated by 1.80 Cia pegmatites.
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| 5. |
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| 6. |
- Sjöström, Martin, et al.
(författare)
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Evaluation of satellite based indices for gross primary production estimates in a sparse savanna in the Sudan
- 2009
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4189. ; 6:1, s. 129-138
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Tidskriftsartikel (refereegranskat)abstract
- One of the more frequently applied methods for integrating controls on primary production through satellite data is the Light Use Efficiency (LUE) approach. Satellite indices such as the Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI) and the Shortwave Infrared Water Stress Index (SIWSI) have previously shown promise as predictors of primary production in several different environments. In this study, we evaluate NDVI, EVI and SIWSI derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite sensor against in-situ measurements from central Sudan in order to asses their applicability in LUE-based primary production modeling within a water limited environment. Results show a strong correlation between vegetation indices and gross primary production (GPP), demonstrating the significance of vegetation indices for deriving information on primary production with relatively high accuracy at similar areas. Evaluation of SIWSI however, reveal that the fraction of vegetation apparently is to low for the index to provide accurate information on canopy water content, indicating that the use of SIWSI as a predictor of water stress in satellite data-driven primary production modeling in similar semi-arid ecosystems is limited.
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| 7. |
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