In the Veneto Città Diffusa, the decentralized urban landscape of the Veneto Region, Northeast Italy, the economic growth of recent decades brought about increased urbanization and agricultural intensification. The process of change has been accompanied by the extension and/or maximization of centralized services of drinking water, irrigation, waste water and drainage to meet greater demands for the provision and disposal of water. Accordingly, the structure of a formerly poor rural landscape has been adapted to support an affluent industrialized and urban one. However, all this has had detrimental side effects, which, in time might seriously compromise the quality of life in this landscape. On one side, the transformations that occurred have in fact given rise to unexpected problems of drought, flooding and pollution of water; and recent changes in climate patterns have further intensified these risks. On the other side, the long term fine grained carrying structures of the landscape fabric –like roads, field ditches, stream and river corridors, dirt roads, paths etc.-, as the very basis of the landscape’s unique ecological diversity, and once used to convey the area’s flows now risk general extinction. The existing road system is also increasingly under pressure to intensify traffic that creates congestion, pollution and unsafe conditions. From a planning and design perspective, this calls for adequate methods and tools that can help designers to tackle the needs for more sustainable water flows as well as the needs for a recovered ecological integrity (including spatial intelligibility) of this urban landscape. This can be of a great importance also for a better understanding of other territories of urban dispersion which are spreading especially over the European and –although in very different forms- the American continents. The present research aims to contribute to the planning and design answers to these urgent problems. For this purpose, the urban landscape of the Veneto Città Diffusa was approached with principles derived from an Integrated Water Management approach (IWM) that, recently, has been successfully applied in the urban context as an alternative to the technocratic approach of maximizing flows. Storage of water is the key principle, for it can bring about decentralized storage, which means new and different water flow management and spatial arrangements. This can ultimately be obtained through the placement and implementation of small scale and decentralized infrastructures.By focusing on the interrelation between flow patterns and spatial arrangements in a small portion of the Veneto Città Diffusa –i.e. the case study landscape- the study has elaborated and confirmed two specific closely related assumptions.The first assumption is that the recent loss of landscape diversity and the increasing problems of flood, drought and water pollution of the Veneto Città Diffusa are closely related and ascribable also to the processes of centralization of the water flows that accompanied the area’s economic growth. The changes of flow patterns and spatial arrangements of the case study area that happened over the last decades were systematically observed in a threefold area-flow-actor perspective. Insights into the present arrangements of irrigation, drainage, drinking water and waste water at the scale of the Consorzio di Bonifica Valli Grandi e Medio Veronese waterboard also accompanied the investigation. The diagnosis showed that the centralized systems arranged to perform greater inflows and outflows, draw heavily on resources and often risk exceeding the region’s ecological carrying capacity. Moreover, the centralized arrangement often conflicts with the decentralized character of the settlements. No synergetic relations have been developed between the man-made water system and the existing pervasive fine grained elements of the landscape. Instead, this rich capital asset has been left behind and even neglected. And such forms of negligence have ultimately brought about a massive loss of biodiversity, accessibility and spatial intelligibility of the local landscape.This leads to the second assumption that has been researched: in the decentralized urban landscape of the Veneto Città Diffusa, answers that design measures can give in response to increasing water-flow dysfunctions and loss of diversity can be based on decentralized water storage systems that make use of the existing fine grain structures of local landscapes –ditches, streams, land depressions, former pits, hedge-rows, dirt roads, paths etc.- and promote a local-based utilisation of resources (resilience), while fostering a stronger local identity, biodiversity and accessibility for more coherent spatial arrangements. Building on the Ecological Conditions Strategy conceived by Tjallingii (1996), a set of guiding models was developed. In the models, the principles of Integrated Water Management were tuned to those fine grained landscape elements that still structure the low plains of the Veneto –the built lot system, the agricultural field system, the road system, the stream system and the excavation site system. Principles and models of integration and decentralization drove the exploration of design options for different levels of decentralized management of water in the case study area. The creative design process of learning produced a useful toolbox of design models. The design exploration also proved that the dispersed urbanization of the Città Diffusa can be made suitable to accommodate modern integrated and decentralized water systems that, by re-activating the existing carrying structures, also contribute to recovering the landscape. Decentralized urbanization can actually be an ally in the search for sustainable and legible settlements that also reuse and recycle water locally.Designing an integrated water system that fits with the Città Diffusa and contributes to the ecological integrity of this urban landscape remains an important challenge. The tools that can be of practical help to designers and decision-makers who are willing to undertake this challenge were investigated and worked out. Nonetheless, the way to realize the outlined strategies is complex and affected by uncertainty. In this context more research is needed to investigate the effects of decentralization at the level of the region on one side, and on the other side to investigate how these integrated systems can be set to fit present institutional and market frameworks. In conclusion, the study generated concrete proposals for one or more pilot projects that will be extremely important to creating consensus in the decision process during the testing of models and strategies. / info:eu-repo/semantics/nonPublished

L'équilibre arbre-herbe dans la savane tropicale est reconnu comme l'une des principales<p>énigmes de l'écologie des plantes. Les origines du difficile équilibre entre ces formes de vie<p>sur des dizaines de millions de kilomètres carrés à l'échelle mondiale sont en partie attribuées<p>aux perturbations fréquentes induites par les feux de végétation dont les effets varient dans<p>l'espace et dans le temps selon les conditions environnementales. Les résultats de recherche<p>dépendent de l’échelle et les conclusions tirées d’études locales sont rarement transposables à<p>d’autres échelles. La question du transfert d'échelle s’avère donc cruciale dans l'étude des<p>effets du feu, et nécessite une approche transdisciplinaire.<p>En raison de la variété des échelles couvertes, cette étude constitue une première dans la<p>confrontation de données sur l’historique des feux dérivé de l'imagerie satellitaire à des<p>données de terrain incluant des mesures détaillées sur la structure et la composition de<p>végétation, ainsi que des propriétés édaphiques et topographiques. Elle s’est focalisée sur la<p>composante ligneuse de par son caractère pérenne et son influence sur les processus<p>écologiques majeurs. Sur une zone de plus de 2000 km², le Parc National du W du Niger<p>(PNWN), où le feu est utilisé comme outil pour la gestion et la conservation des écosystèmes<p>semi-arides, une carte de l'historique des feux a été élaborée à partir d'images MODIS de 250<p>m de résolution spatiale et de résolution temporelle journalière couvrant une période de sept<p>années (2002-2009). Pour comprendre la variabilité, à la fois dans l'espace et le temps, de la<p>propagation du feu dans la végétation, nous avons étudié les caractéristiques de distribution<p>des feux en termes de régime du feu (i.e. période d'occurrence et fréquence) et de structure<p>spatiale (métriques paysagères). Les relations causales plausibles entre les régimes du feu, les<p>conditions édaphiques et topographiques à l'échelle régionale comme locale, et les<p>caractéristiques de la végétation ligneuse (composition et structure) ont été examinées à<p>travers des analyses multivariées et des modèles d'équations structurales. Nous avons aussi<p>examiné plus en détails les stratégies adaptatives mises en oeuvre par les ligneux, et les<p>interactions biologiques qui sous-tendent l'organisation spatiale des ligneux à travers une<p>approche des processus ponctuels.<p>Les résultats montrent que l'activité du feu dans le PNWN se caractérise par une hétérogénéité<p>spatio-temporelle induite principalement par les conditions édapho-topographiques via la<p>structure de la végétation ligneuse. Les feux précoces de gestion créent des pare-feux<p>efficaces, limitant une large extension des feux de saison tardifs. Cependant, ces feux tardifs<p>pourraient ne pas être aussi destructifs comme qu’on le suppose généralement. En effet,<p>l'adaptation des espèces aux différents régimes defeu correspond à des stratégies de croissance<p>contrastées. Dans le cas des feux tardifs, les surfaces terrières et hauteurs moyennes les plus<p>fortes sont rencontrées, permettant aux arbres de résister au feu. Quant aux zones non<p>affectées par les feux l'analyse "patron-processus" désigne clairement la facilitation entre<p>ligneux comme un processus fondamental de l'organisation spatiale périodique du couvert, une<p>structure émergente qui empêche le passage du feu. Bien qu’ils ne se substituent pas aux<p>études expérimentales, ces résultats basés sur une expérimentation naturelle à large échelle<p>apportent des informations nouvelles précieuses tant au niveau fondamental que pour la mise<p>en place d'une gestion raisonnée du PNWN.<p><p><p>The tree-grass equilibrium in tropical savanna is recognized as one of plant ecology's main<p>conundrums. The origins of the difficult balance between these life forms over tens of millions<p>of square kilometers worldwide are in part attributed to the frequent disturbances caused by<p>vegetation fires effects of which vary in space and time depending on local environmental<p>factors. Research results are scale-dependent and findings from local studies are rarely<p>transposable to higher levels of ecosystem organization. The question of scaling (scale<p>transfer) is therefore crucial in the study of fire effects, and requires a multidisciplinary<p>approach.<p>Because of the variety of scales covered, this study is a premiere in the confrontation of<p>satellite-imagery derived fire history data with detailed field data including measurements of<p>vegetation parameters (structure and composition), as well as soil and topographic properties.<p>The study focuses on the woody component, because of its perennial character and its<p>influence on major ecological processes. On an area of more than 2000 km², the W National<p>Park of Niger (WNPN) where fire is used as a tool for the management and conservation of<p>semi-arid ecosystems, a fire history map was elaborated from MODIS images with a 250 m<p>spatial resolution and a daily temporal resolution over a period of seven years (2002-2009). To<p>understand the variability, both in space and time, of fire propagation in vegetation, we studied<p>the fire distribution characteristics in terms of fire regime (i.e. timing and frequency) and<p>spatial structure (landscape metrics). Plausible causal relationships at regional and local scales<p>between fire regimes, edaphic and topographic conditions, and the woody vegetation<p>(composition and structure) characteristics were examined through multivariate analyses and<p>structural equations models. We also examined in detail the woody species adaptive strategies<p>as well biological interactions, which underlie their spatial organization, using point statistics.<p>Results show that the WNPN fire's activity is characterized by spatial and temporal<p>heterogeneity induced mainly by edaphic and topographic conditions via the structure of the<p>ligneous component. Prescribed early season fires create effective firewalls, limiting wide late<p>season fires. However, these late fires might not be as destructive as is commonly assumed.<p>Indeed, species adaptation to different fire regimes corresponds to contrasting growth<p>strategies. In the case of late fires, increased basal areas and mean tree heights were<p>encountered, enabling trees to resist fire and escape flames. As for the unburned areas, the<p>"pattern-process" analysis clearly indicates that facilitation between shrubs is a fundamental<p>process determining the woody cover periodic spatial organization, an emergent structure that<p>prevents fire spread.<p>Although they do not replace experimental studies, these results based on a large-scale natural<p>experiment provide valuable new information both on a fundamental level and for setting up<p>the rational management of the WNPN. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished