Naturalité (environnement)

Résumé

La naturalité, dans son sens environnemental, renvoie au caractère sauvage d'un paysage ou d'un milieu naturel faiblement ou non maîtrisé par l'Homme. Il s'oppose ainsi aux concepts de ruralité et d'urbanité qui impliquent une forte anthropisation. Il s'agit d'une traduction, reconnue depuis les années 1960, du mot anglais wilderness. La définition de la naturalité peut être tirée du Wilderness Act qui introduit la notion dans les termes suivants : est qualifié de wilderness un milieu naturel tel que « la terre et sa communauté de vie ne sont point entravés par l'homme, où l'homme lui-même n'est qu'un visiteur de passage ». thumb|Bison d'Amérique du Nord (Bison bison) : image d'un milieu sauvage ou gestion multiusage durable des pâturages américains ? Définitions La définition de la naturalité varie selon le domaine considéré. En droit, sous l'Ancien Régime, la naturalité était l'état d'une personne née dans le pays dans lequel elle habitait, le droit de

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https://fr.wikipedia.org/wiki/Naturalit%C3%A9_(environnement)

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The Emancipation of Destruction – Transforming Gällivare (Suède)

Linus Godet

Gällivare is a remote city in the middle of the northern Swedish wilderness. The city was established as iron ore was found in the ground just over a century ago. Until the 60's the mining industry and the city grew together in what seemed to be a perfect symbiosis. But as times changed and the industry had to adapt to a globalized market and bigger production volumes, the symbiosis was broken. The mines started expanding at a much higher speed, and the same industry that once founded the city is now threatening its whole existence. The last decades have been a story of destruction and relocations. The problems of dealing with destruction and relocating people have overshadowed the needs for visions and dreams. Experts from all over the world have gathered to solve the situation. The first step will be to build a knowledge center for cities in movement. Gällivare offers a very rare context. Most of the moving cities of the world are moved within a short period of time, while Gällivare is moving step by step every year. Many moving cities are actually disappearing as the inhabitants are forced to move, which makes documentation and research very difficult. Gällivare offers the opportunity to take part of the whole process, from planning to relocation. The knowledge center is the starting point for the visionary work of transforming Gällivare.

2009

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Disturbance-grazer-vegetation interactions maintain habitat diversity in mountain pasture-woodlands

Alexandre Buttler, François Gillet, Alexander Ludwig Johannes Peringer

Low-intensity livestock grazing is a widespread management tool in order to maintain habitat diversity in mountain pasture-woodlands for nature conservation purposes. Historical photographs indicate that forest disturbance significantly contributed to forest-grassland mosaic pattern formation. Disturbance grazer interactions are however poorly understood and the effects of logging or windthrow are rarely considered in management plans. Moreover, disturbance-grazer interactions are crucial for the maintenance of open habitats in the upcoming "rewilding" approach of nature conservation. We aimed to understand the effects of forest gap creation by the breakdown of senile trees or by single-tree cutting and of large forest openings by windthrow or logging on mosaic pattern formation in pasture-woodlands that were grazed by cattle and dominated by tree species with distinct regeneration ecology (Picea abies vs. Fagus sylvatica). We used the process-based model of pasture-woodland vegetation dynamics WoodPaM and newly implemented a forest disturbance routine. We simulated disturbance and grazing scenarios in an artificial mountain landscape and analyzed mosaic patterns with landscape metrics. We found that grazing in absence of disturbance promoted simply structured mosaics that were preconditioned by topography. Only large-scale forest disturbance disrupted this pattern and maintained the historical heterogeneous distribution of grassland communities across all habitat conditions (especially species-rich mountain grasslands on poor soil). This prerequisite is stronger in pasture-woodlands where the ecology of the dominant tree species promotes forest-grassland segregation (F. sylvatica in our case) and less in naturally thin-canopy mountain forest close to the tree line (P. abies). In wilderness areas, the very low density of grazers may limit the maintenance of open habitats regardless disturbance. (C) 2017 Elsevier B.V. All rights reserved.

Elsevier Science Bv2017

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On the basis of a distributed-source representation of the lightning channel, the mathematical formulations of the so-called engineering lightning return stroke models are generalized to take into account the presence of a vertically extended strike object. The strike object is modeled as a lossless uniform transmission line, and the reflection coefficients are all assumed to be constant. The distribution of current along the lightning channel for each model is expressed in terms of the "undisturbed" current, object height, and current reflection coefficients at the top and the bottom of the object. The undisturbed current is defined as the current that would flow in the channel if the current reflection coefficients at the extremities of the strike object were equal to zero, that is, the characteristic impedances of the lightning channel and the strike object were equal to each other and equal to the grounding impedance of the strike object. The distributed-source representation of the lightning channel adopted in this study allows for a more general and straightforward formulations of the generalized return-stroke models than the traditional representations implying a lumped current source at the bottom of the channel, including a self-consistent treatment of the impedance discontinuity at the tower top

2002

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Disturbance-grazer-vegetation interactions maintain habitat diversity in mountain pasture-woodlands

Alexandre Buttler, François Gillet, Alexander Ludwig Johannes Peringer

Elsevier Science Bv2017