Classification et cartographie du paysage sur base écologique avec application à l'Italie

It is well known that although the geographic landscape and the ecosystem are both terrestrial units involving physical and biological components, including man and his activity, they are in nature extremely different. The geographic landscape is a complex of directly perceptible forms produced by the interaction (synergism) of three main components (synergizing) present in varying degrees and in unstable equilibrium (physical base, the biotic element and the results of human activity); whilst the ecosystem may not be directly perceived and is composed of a stable system of matter and energy, contained in the living and non-living parts of an environment, where exchanges between the two parts take place in a continuous flux (Odum, 1958). The geographic landscape is characterized by formal, structural aspects, whereas the ecosystem is, by nature, functional and biological and is dominated by two cycles, one of matter and the other of energy, within which man can be included in varying degrees. Ever since man began to alter the natural biological processes with his constructive, destructive and polluting activity, structures have emerged within the ecosystem which show local modifications in quality and energy imbalance. These have survived in the form of truncated anthropo-ecosystems (Delpoux, 1972), where the artificially interrupted trophic chain survives with a disturbed energy balance. Imbalances are caused by alterations which are difficult to perceive directly in ecosystems, but are observable in landscapes which have been modified in response to such changes. The ecosystem must, therefore, be considered a determinant of landscape. Hence it is possible to distinguish fairly precisely the existence of different types of landscape on the basis of the material and energy balance of their associated ecosystems where ecosystem and geographic landscape are closely linked by cause and effect. Hence the term landscape ecology (Landschaftsöcologie;Troll, 1939) where the term “ecology” is taken to mean “the functional study of the dynamics of a system of action, determining landscape” (Schmithüsen, 1973). If the energy balance and the natural and human transformations of ecosystems are jointly considered, it is possible to obtain a significant ecologically based landscape classification. The first category is that of ecologically balanced landscapes, within which transfer phenomena are cyclic as energy, or even matter, are completely utilized by their biological constituents. This applies to all natural landscapes, even those with a dominant natural factor, that are unaffected by human action; their limits can therefore be considered similar to those of natural ecosystems. Amongst these can also be included areas with a gathering economy and primitive and subsistence farming. By contrast with these is the category of ecologically unbalanced landscapes where the presence of man in the environment has transformed natural ecosystems into anthropoecosystems with different characteristics. Two types can be distinguished, one hyperenergetic with a positive energy balance and thus an exporter of energy, the other hypoenergetic characterised by a negative energy balance,and thus importing energy (Delpoux, 1972). In hyperenergetic landscapes man intervenes with advanced agriculture and animal husbandry and thus transforms in different ways and in varying degrees the natural setting. They therefore include agrobiosystems, typical of specialized agriculture, intensive polyculture and plantation monoculture, and trophobiosystems typical of rationalized animal husbandry. Both produce vegetable and animal foods for the market. In hypoenergetic landscapes, the production of organic substances with an energy value becomes increasingly deficient, so that the biological community has to become dependent on external contributions; they mainly occur in high density population landscapes with low productivity rural activities due to poor natural conditions, poor organization, or a high degree of urban and industrial development. To these categories, which are mainly dependent on the ratio of population to resources, can be added that of degraded landscapes or ecosystems, caused by natural degradation (exogenous or endogenous) or by pollution and despoliation (biological and mineral) caused by human activity. Then follow landscapes with artificial or substitution ecosystems (urban or industrial) the elements of which are characteristically formal in appearance. The last category is that of ecologically integrated and complex landscapes, the result of the combination of two or more different ecological aspects (rural and urban, and, for example, outside this group, rural and industrial, agricultural and moderately urbanized) which interdigitate and encroach upon each other. On the basis of this classification, it is possible to discern the distinguishing features typical of landscapes and thus our ability to delimit their extent on maps. They have been applied in the production of an ecologically based landscape map of Italy at an original scale of 1:1,500,000, a reduced black-and-white version of which has been reproduced in the main body of this paper. As a first attempt at such a representation it is both adequate and useful and provides a basis for further work and analysis. The exercise confirms that the consideration of landscape, especially humanized landscape, in an ecological perspective, supplies important information for the interpretation of its structure from a functional and physiological stand-point, as well as for the understanding of its dynamics. It also facilitates the consideration of the environment as a whole, presenting more effectively the problems of its evaluation and consequently adds to our appreciation of its economic and social significance.     

Correlation of precipitable water vapour values over the United States with physical and chemical parameters Part I: Seasonal trends with precipitation and its nitrate content. Geographic changes of nitrate

Summary The analysis ofReitan's data on precipitable water vapour in the atmosphere, and data ofJunge on the nitrate content of precipitation, is extended onto a seasonal basis. Computations indicate consistency between precipitable water vapour, precipitation and its nitrate content, within a semiemprical law proposed, and especially for the warmer trimestres of the period July 1956–June 1957. A simple expression correlating the atmospheric content of precipitable water vapour over stations situated between sea level and 580 ft of altitude, with temperature, is suggested and tested. Increasing trends of atmospheric nitrate with latitude are established for all seasons of the period examined.Contribution of the Centro Nucleazione Aerosoli of the National Research Council of Italy, Via Vettore 4 (Monte Sacro),Rome.     

Annual variation of the effects of diffuse radiation on the photodissociation of ozone

Previous work has shown the importance of the diffuse solar field in the photochemistry of atmospheric active species, the solar zenith angle being an effective parameter. In view of the diurnal and seasonal variability of this single quantity, in this paper estimates are presented of the daily-integrated values of the photodissociation coefficient of ozone throughout the year, for a purely molecular atmosphere in the absence of scattering and when the effects of molecular scattering are included, and for an absorbing-scattering turbid atmosphere characterized by two different aerosol loads. Also, different values of the ground albedo have been taken into account.Results are shown for a latitude of 45^oN. The seasonal dependence is strong at altitudes below 20 km and less marked above 20 km. For an albedoA=0.3, the inclusion of molecular scattering increases the daily-integrated photodissociation coefficients approximately by 20% and 40% at 15 km and by 15% and 22% at 30 km, at the winter and summer solstice respectively. The presence of a heavy aerosol load modifies these results by a further factor which is approximately –5% and 10% at 15 km at the winter and summer solstice respectively, and is approximately constant at 8% throughout the year at 30 km.     

On ground-level visibilities in the Po-Valley during winter,and on their intercorrelations

Summary Results of intercorrelations between daily average visibilities, at 18 Observatories situated in the Po-Valley, indicate the existence there of several areas within which conditions of fog are similarly affected. The position of those areas reflects the influence of geographic and topographic factors on fogs which regularly recur, during the cold seasons, in that extensive part of Northern Italy.     

The South American palaeomagnetic data and the main episodes of the fragmentation of Gondwana

The South American palaeomagnetic poles published after the Upper Mantle Conference on Solid Earth Problems held at Buenos Aires in 1970, are summarized.The Late Palaeozoic-Cretaceous section of the South American polar wandering curve is now defined on the basis of twenty palaeomagnetic poles; these poles define five “age groups” at Late Carboniferous, Permo-Carboniferous, Middle Permian, Triassic and Cretaceous times.The comparison of the Late Palaeozoic-Mesozoic sections of the polar wandering curves of South America, Australia and Africa suggests that the former fragmentation of the Gondwana occurred in Late Carboniferous or Permo-Carboniferous times and that the origin of the South Atlantic Ocean took place after the Middle Jurassic (160 m.y.) but before the Early Cretaceous (120 m.y.).     

The use of predictive modeling techniques for optimal exploitation of spatial databases: a case study in landslide hazard mapping with expert system-like methods

. A case study is presented in which different probabilistic prediction models (Bayesian probability, fuzzy logic "and", "or", "sum", "product", "gamma" operations, and certainty factors) are used to produce landslide hazard maps for a hilly and mountainous region in the northern Apennines, Italy. Seven data layers are exploited to detect most vulnerable areas: lithology, distance from the geological lineaments, annual rainfall amount, land cover type, topographic slope and aspect, and the distance from hydrographic network segments. The results of the different predictions are compared using the prediction rate index and critically discussed, to evaluate the possibility of using readily available databases for land planning.     

Landslide Susceptibility Models Utilising Spatial Data Analysis Techniques. A Case Study from the Lower Deba Valley,Guipuzcoa (Spain)

A quantitative methodology for landslide susceptibility zonationis described and its application to a study area in the lower part of the Deba Valley (Guipúzcoa,Spain) presented. Susceptibility models were obtained on the basis of statisticalrelationships between known mass movements and conditioning factors. A landslide rupturehypothesis was set and a digital database consisting of seventeen causal factors layers constructed.The modelling procedure was implemented utilising a GIS. The susceptibility analysis methodis based on the Favourability Functions approach, and two different mathematicalframeworks: probability theory and Zadehïs fuzzy set theory. Several landslidesusceptibility models were produced and validated using different sets of independent landslide data.The predictive capability of models was determined.     

Large-Scale Temperature Changes across the Southern Andes: 20th-Century Variations in the Context of the Past 400 Years

Long-term trends of temperature variations across the southern Andes (37–55° S) are examined using a combination of instrumental and tree-ring records. A critical appraisal of surface air temperature from station records is presented for southern South America during the 20th century. For the interval 1930–1990, three major patterns in temperature trends are identified. Stations along the Pacific coast between 37 and 43° S are characterized by negative trends in mean annual temperature with a marked cooling period from 1950 to the mid-1970s. A clear warming trend is observed in the southern stations (south of 46°S), which intensifies at higher latitudes. No temperature trends are detected for the stations on the Atlantic coast north of 45° S. In contrast to higher latitudes in the Northern Hemisphere where annual changes in temperature are dominated by winter trends, both positive and negative trends in southern South America are due to mostly changes in summer (December to February) temperatures. Changes in the Pacific Decadal Oscillation (PDO) around 1976 are felt in summer temperatures at most stations in the Pacific domain, starting a period with increased temperature across the southern Andes and at higher latitudes.Tree-ring records from upper-treeline were used to reconstruct past temperature fluctuations for the two dominant patterns over the southern Andes. These reconstructions extend back to 1640 and are based on composite tree-ring chronologies that were processed to retain as much low-frequency variance as possible. The resulting reconstructions for the northern and southern sectors of the southern Andes explain 55% and 45% ofthe temperature variance over the interval 1930–1989, respectively. Cross-spectral analysis of actual and reconstructed temperatures over the common interval 1930–1989, indicates that most of the explained varianceis at periods >10 years in length. At periods >15 years, the squaredcoherency between actual and reconstructed temperatures ranges between 0.6 and 0.95 for both reconstructions. Consequently, these reconstructions are especially useful for studying multi-decennial temperature variations in the South American sector of the Southern Hemisphere over the past 360 years. As a result, it is possible to show that the temperatures during the 20thcentury have been anomalously warm across the southern Andes. The mean annual temperatures for the northern and southern sectors during the interval 1900–1990 are 0.53 °C and 0.86 °C above the1640–1899 means, respectively. These findings placed the current warming in a longer historical perspective, and add new support for the existence of unprecedented 20th century warming over much of the globe. The rate of temperature increase from 1850 to 1920 was the highest over the past 360 years, a common feature observed in several proxy records from higher latitudes in the Northern Hemisphere.Local temperature regimes are affected by changes in planetary circulation, with in turn are linked to global sea surface temperature (SST) anomalies. Therefore, we explored how temperature variations in the southern Andes since 1856 are related to large-scale SSTs on the South Pacific and South Atlantic Oceans. Spatial correlation patterns between the reconstructions and SSTs show that temperature variations in the northern sector of the southern Andes are strongly connected with SST anomalies in the tropical and subtropical Pacific. This spatial correlation pattern resembles the spatial signature of the PDO mode of SST variability over the South Pacific and is connected with the Pacific-South American (PSA) atmospheric pattern in the Southern Hemisphere. In contrast, temperature variations in the southern sector of the southern Andes are significantly correlated with SST anomalies over most of the South Atlantic, and in less degree, over the subtropical Pacific. This spatial correlation field regressed against SST resembles the `Global Warming' mode of SST variability, which in turn, is linked to the leading mode of circulation in the Southern Hemisphere. Certainly, part of the temperature signal present in the reconstructions can be expressed as a linear combination of four orthogonal modes of SST variability. Rotated empirical orthogonal function analysis, performed on SST across the South Pacific and South Atlantic Oceans, indicate that four discrete modes of SST variability explain a third, approximately, of total variance in temperature fluctuations across the southern Andes.     

Répartition des minéraux argileux et contrôle tectono-eustatique dans les bassins de la marge tunisienne

We have studied the clay assemblages found in the different palaeogeographic domains located at the several Tunisian margin basins, ranging in age from Palaeozoic to Neogene. This study has allowed us to characterize and highlight the relationship between the clay distribution in time and space and the geodynamic and eustatic events. Marine regressions, with the intensification of erosion, seem to be responsible for illite increases, whereas transgressions, in concordance with a warm and dry climate, coincide with the smectite dominance. The minimum marine level coincides with the abundance of palygorskite. Mineralogic changes in the clay assemblages as well as in the proportion of the different clay minerals will tentatively be related to erosive tectonic events and/or to subsiding and rifting events, marked by the inheritance or the neoformation of the several clays.