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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Labour 6 (1992), S. 0 
    ISSN: 1467-9914
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: Abstract. The availability and international comparability of migration statistics pose a severe handicap to analysis and policy debate. This paper explores a few of the underlying policy and conceptual issues at stake and identifies some of the institutional factors contributing to the slow and uncertain in progress in this field.Three main issues are discussed: the statistical definitions of migration; the administrative sources of data; and the international initiatives to improve the comparability of statistics.At the beginning of the 1990s the context appears promising for a renewed effort of national and international organizations and statistical agencies. New opportunities and challenges for the improvement of migration statistics are being developed.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2017-05-02
    Description: Snow cover impacts alpine land surface phenology in various ways but our knowledge about the effect of snow cover on alpine land surface phenology is still limited. We studied this relationship in the European Alps using satellite-derived metrics of Snow Cover Phenology (SCP), namely First Snow Fall, Last Snow Day and Snow Cover Duration (FSF, LSD and SCD, respectively), in combination with Land Surface Phenology (LSP), namely Start Of Season, End Of Season and Length Of Season (SOS, EOS and LOS, respectively) for the period of 2003–2014. We tested the dependency of inter-annual differences (Δ) of SCP and LSP metrics with altitude (up to 3000 meter above sea level (m a.s.l.)) for seven natural vegetation types, four main climatic subregions and four terrain expositions. We found that 25.3% of all pixels showed significant ( p  〈 0.05) correlation between ΔSCD and ΔSOS and 15.3% between ΔSCD and ΔLOS across the entire study area. Correlations between ΔSCD and ΔSOS as well as ΔSCD and ΔLOS are more pronounced in the northern subregions of the Alps, at high altitudes, and on north- and west-facing terrain – or more generally, in regions with longer SCD. We conclude that snow cover has a greater effect on alpine phenology at higher than at lower altitudes, which may be attributed to the coupled influence of snow cover with underground conditions and air temperature. Alpine ecosystems may therefore be particularly sensitive to future change of snow cover at high altitudes under climate warming scenarios.
    Print ISSN: 0148-0227
    Topics: Biology , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
    Publication Date: 2018-02-13
    Description: Land surface phenology (LSP), the study of seasonal dynamics of vegetated land surfaces from remote sensing, is a key indicator of global change, that both responds to and influences weather and climate. The effects of climatic changes on LSP depend on the relative importance of climatic constraints in specific regions—which are not well understood at global scale. Understanding the climatic constraints that underlie LSP is crucial for explaining climate change effects on global vegetation phenology. We used a combination of modelled and remotely-sensed vegetation activity records to quantify the interplay of three climatic constraints on land surface phenology (namely minimum temperature, moisture availability, and photoperiod), as well as the dynamic nature of these constraints. Our study examined trends and the relative importance of the three constrains at the start and the end of the growing season over eight global environmental zones, for the past three decades.
    Print ISSN: 1748-9318
    Electronic ISSN: 1748-9326
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering
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  • 4
    Publication Date: 2018-02-13
    Description: Timing and accumulation of snow are among the most important phenomena influencing land surface phenology in mountainous ecosystems. However, our knowledge on their influence on alpine land surface phenology is still limited, and much remains unclear as to which snow metrics are most relevant for studying this interaction. In this study, we analyzed 5 snow and phenology metrics, namely timing (snow cover duration, SCD); last snow day, LSD), accumulation of snow (mean snow water equivalent, SWE m ), and mountain land surface phenology (start of season, SOS; length of season, LOS) in the Swiss Alps during the period 2003–2014. We examined elevational and regional variations in the relationships between snow and alpine land surface phenology metrics using multiple linear regression and relative weight analyses, and subsequently identified the snow metrics that showed strongest associations with variations in alpine land surface phenology of natural vegetation (NV) types. We found that the relationships between snow and phenology metrics were pronounced in high elevational regions and alpine natural grassland and sparsely vegetated areas. SOS was influenced primarily by SCD, secondarily by SWE m , while LOS was equally affected by SCD and SWE m across different elevational bands. We conclude that SCD plays the most significant role compared to other snow metrics. Future variations of snow cover and accumulation are likely to influence alpine ecosystems, for instance their species composition due to changes in the potential growing season. Also, their spatial distribution may change as a response to the new environmental conditions if these prove persistent.
    Print ISSN: 0148-0227
    Topics: Biology , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Publication Date: 2014-05-03
    Description: Land Surface Phenology (LSP) is the most direct representation of intra-annual dynamics of vegetated land surfaces as observed from satellite imagery. LSP plays a key role in characterizing land-surface fluxes, and is central to accurately parameterizing terrestrial biosphere–atmosphere interactions, as well as climate models. In this paper we present an evaluation of Pan-European LSP and its changes over the past 30 years, using the longest continuous record of Normalized Difference Vegetation Index (NDVI) available to date in combination with a landscape-based aggregation scheme. We used indicators of Start-Of-Season, End-Of-Season and Growing Season Length (SOS, EOS and GSL, respectively) for the period 1982–2011 to test for temporal trends in activity of terrestrial vegetation and their spatial distribution. We aggregated pixels into ecologically representative spatial units using the European Landscape Classification (LANMAP) and assessed the relative contribution of spring and autumn phenology. GSL increased significantly by 18–24 days/decade over 18–30% of the land area of Europe, depending on methodology. This trend varied extensively within and between climatic zones and landscape classes. The areas of greatest growing-season lengthening were the Continental and Boreal zones, with hotspots concentrated in southern Fennoscandia, Western Russia and pockets of continental Europe. For the Atlantic and Steppic zones, we found an average shortening of the growing season with hotspots in Western France, the Po valley, and around the Caspian Sea. In many zones, changes in the NDVI-derived end-of-season contributed more to the GSL trend than changes in spring green-up, resulting in asymmetric trends. This underlines the importance of investigating senescence and its underlying processes more closely as a driver of LSP and global change. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
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  • 6
    Publication Date: 2015-11-25
    Description: Monitoring Land Surface Phenology (LSP) is important for understanding both the responses and feedbacks of ecosystems to the climate system, and for representing these accurately in terrestrial biosphere models. Moreover, by shedding light on phenological trends at a variety of scales, LSP has the potential to fill the gap between traditional phenological (field) observations and the large-scale view of global models. In this study, we review and evaluate the variability and evolution of satellite-derived Growing Season Length (GSL) globally and over the past three decades. We used the longest continuous record of Normalized Difference Vegetation Index (NDVI) data available to date at global scale to derive LSP metrics consistently over all vegetated land areas and for the period 1982-2012. We tested GSL, Start- and End-Of Season metrics (SOS and EOS, respectively) for linear trends as well as for significant trend shifts over the study period. We evaluated trends using global environmental stratification information in place of commonly used land cover maps to avoid circular findings. Our results confirmed an average lengthening of the growing season globally during 1982-2012 – averaging 0.22-0.34 days/year, but with spatially heterogeneous trends. 13-19% of global land areas displayed significant GSL change, and over 30% of trends occurred in the boreal/alpine biome of the Northern Hemisphere, which showed diverging GSL evolution over the past 3 decades. Within this biome, the “Cold and Mesic” environmental zone appeared as an LSP change hotspot. We also examined the relative contribution of SOS and EOS to the overall changes, finding that EOS trends were generally stronger and more prevalent than SOS trends. These findings constitute a step towards the identification of large-scale phenological drivers of vegetated land surfaces, necessary for improving phenological representation in terrestrial biosphere models. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
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  • 7
    Publication Date: 2018-12-17
    Description: Garonna AP, Foscari A, Russo E, Jesu G, Somma S, Cascone P, Guerrieri E THE SPREAD OF THE NON-NATIVE PINE TORTOISE SCALE TOUMEYELLA PARVICORNIS (HEMIPTERA: COCCIDAE) IN EUROPE: A MAJOR THREAT TO PINUS PINEA IN SOUTHERN ITALY Abstract : Invasive pests are considered a major threat to biodiversity, conservation and agriculture. The Italian peninsula is a major site of intensive commercial exchange and transport of plants and goods, being consequently one of the European countries most invaded by alien insects. Hemiptera Coccomorpha are the largest group of non-native species recorded in Europe. For example, in the last 70 years more than 50 scale insect species have been accidentally introduced into Italy, 50% of which are now well established. This study was conducted to investigate the biology and the damage of the non-native pine tortoise scale Toumeyella parvicornis Cockerell (Hemiptera: Coccidae) accidentally introduced a few years ago into southern Italy. T. parvicornis is multivoltine in the invaded territories, being able to complete at least three generations per year, overwintering in the adult female stage. Oviposition periods during 2015-2017 surveys occurred from late April to end of May, from July to first half of August, and from mid-September to November. Fecundity was positively correlated to body size of gravid females and varied among the generations. Investigations on natural control by autochthonous species showed a seasonal activity of Metaphycus flavus (Hymenoptera: Encyrtidae), parasitizing mainly immature male individuals. The morpho-molecular approach confirms the hypothesis of an ongoing shift of parasitoid populations from other indigenous soft scales to the invasive one. Unfortunately, the low level of natural control was ineffective in hampering the spread of T. parvicornis, and preventing the dieback of local pine species, Pinus pinea, as observed in all invaded areas. Keywords : Invasive Pest, Europe, Toumeyella parvicornis, Life History, Pinus pinea, Natural Control iForest 11 (5): 628-634 (2018) - doi: 10.3832/ifor2864-011 http://iforest.sisef.org/contents/?id=ifor2864-011
    Electronic ISSN: 1971-7458
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 8
    Publication Date: 2018-02-01
    Print ISSN: 1748-9318
    Electronic ISSN: 1748-9326
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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