Marie Kenza Bouhaddou

Clotilde Kullmann

Keywords: art, urban planning, urban renewal, street-art, participative art, in between, worksite, cross-cutting skills

For more than fifteen years, art experimentations dealing with urban transformation have been increasing more and more. Artists are now influenced by places and urban planning. Urban planners turn to a new conception that implies more creativity and stances directly inspired by artists. Because of its flexibility, art is a negotiation and an innovation lever. Besides, it is part of urban, in situ, interpersonal relationships and based on process and context reality.

Our hypothesis is that art meeting urban transformation creates new roles and figures prone to change the deal of how urban planning projects are made and how actors got organized. This paper, related to a French context, shows the figures' emergence, identifies their cross-cutting skills, and explains the limits of this hybridization. By comparing two different case studies, we will analyze how these figures make the projects visible, and how they enhance depreciated areas in terms of individual and collective perception so as to include them in the rest of the city.

With the art worlds, these figures appear at the core of artistic projects linked to urban renewal. They can perform roles either in an old or a brand-new way. With the urban worlds, they affect the actors game, modify the relationships and diversify the actors' skills. By doing this they now look for legitimacy.

We will start by presenting our case studies to identify these new figures. Then, we will see how the worksite specific context, as an art playground, enables to change the players game. Finally, we will show the limits and problems of these in-between figures.

For more than fifteen years, art experimentations dealing with urban transformation has been increasing in France. They put art through urban transformation, deal with process (Volvey, 2009), context or situations (Ardenne, 2002), interpersonal relationships (Bourriaud, 2001, Bishop, 2012), new art territories [START_REF] Lextrait | Les Nouveaux Territoires de l'Art[END_REF]. Since 2007 1 , art is a support tool for local policies at a city level. Urban projects have often offered a framework for art projects, artists used to create in the urban space, they now work for and with it (Volvey, 2011) and art is called upon to serve public urban planning and is part of the art work.

Besides, for a long time, artists have been interested in urban transformation and in depreciated spaces such as wastelands (Vivant, 2009, Grésillon, 2008). On the one hand, art worlds are inspired by urban spaces and city making reaches the borders of art worlds. On the other hand, urban planning actors turned to a design implying creativity and sense, as it has been shown by pOlau 2 works because art is a local negotiation lever and a visibility tool at a metropolitan scale. Because of its flexibility from a formal and promotional point of view, art is a negotiation and innovation lever. Plus, it is part of urban, in situ, interpersonal relationships, based on process and context reality (Ardenne, 2009;Bourriaud, 2001 ;Raffin, Lextrait, 2005). It is used as an urban renewal booster to reveal the interstices and to update the urban planning projects exposure. Targeting attractiveness, it is used to promote the suburban territories' image and help to change the perception of what is seen as aesthetic failures of urban renewal [START_REF] Epstein | La Rénovation urbaine, Démolition-reconstruction de l'État[END_REF]Ambrosino, 2012). Territories become a creativity factor and creativity becomes a territorial concern. More and more, art projects take place in the public space and use it as a stage [START_REF] Goffman | Comment se conduire dans les lieux publics. Notes sur l'organisation sociale des rassemblements[END_REF], artists use urban planners' tools and in return urban planners are inspired by artistic ways of working. Beyond seeing art as a means to reveal the city, it is used as a way to give urban developers, as well as residents, a specific conception of the city and of the development projects.

Because the integration of art experimentations during the city making was not part of the urban planners' skills, new figures with cross-cuttings skills appeared to organize and promote the urban planning projects (Vivant, 2016). Therefore, the goal of this paper is to show the roles and effects on the collective perception and the problems to get legitimized, to identify their impact and limits on project management. In order to do this, we have chosen two French case studies dominated by urban transformation issues that engage art in different fields: The Urban Transition Art Festival and The Tree 1 Urban Contract for Social Cohesion and specially the part of the contract dedicated to culture is designed for social priority areas. Its goal is to coordinate urban renewal through a social and cultural action program. 2 The Art and Urban Planning Guide Plan is a report realized in 2015 by The Pole of Urban Arts: an organization dedicated to cultural urban planning.

Nursery. Both cases reflect different approaches, where the actors, institutions and artists are placed at various levels and interact differently than in a traditional urban planning project, regarding the organization and visibility of the project (starting, co-carrying, and logistic help). Their mobilization enables the perspective of several artistic and urban effects that can be generated by implying new figures in the artistic project management. How does art meeting urban transformation enable the emergence of new figures, changes the project content in terms of sense of time, image and perception and actors network? What do all these new collaborations reveal about how the city is made today?

Comparing is distinguishing, putting in order and ranking ideas. It is also a question of differentiation, borders and categories. Moreover, it suggests thinking beyond categories, and by showing coherence and recurrence to reduce complexity (Détienne, 2009). For Robinson (2015) to get a global vision, we need to think our comparison's methods over. Therefore, instead of comparing similar typologies, she focuses on finding parallels between constitutive elements of urban systems and comparing their practices. In the same way, we will analyze under which conditions and how the organizers methods, either from art worlds or from urban planning worlds, affect the whole game.

Dealing with urban planning projects still ongoing and for institutional and political reasons, we have chosen to anonymize our case studies and the actors participating. The Urban Transition Art Festival is the name of a street art festival that took place in 2014 in a fort close to a large French city, a brownfield site and a former military zone. The festival has been ordered by the site owner, an urban planning agency, while waiting for the site reclassification into an eco-district. The artistic project temporarily highlighted the unknown and enclosed site, usually closed to the public. Organized by a third party, it has attracted 30 000 visitors in 4 months. The Tree Nursery is a spontaneous graft on the urban renewal project that was not initially included. It has been both intended by a contemporary artist and a local youth cultural center in 2009, in an urban renewal site of a large city. After meeting the residents of the whole neighborhood, the artist proposed a tree nursery project where a group of residents (called the godfathers/mothers) could adopt, plant and take care of 38 trees during the urban renewal project.

For the purpose of this paper, the actors' networks of both case studies have been analyzed, people involved in the urban and artistic project have been interviewed and artwork productions have been examined3 .

First, we will present our two case studies and explain the urban reasons of their elaboration. Then, in a second part, from our case studies, we will analyze the way the specific worksite and urban transformation context has been used as an art playground, allows changing the players game and the project management. This step will be followed by the presentation of the new figures and their role in the project management and the artistic content. Finally, we will show the effect and the limits of implying new figures in the urban planning worlds4 , in terms of actors' network changes and impact on the urban planning project.

.

New figures using art to enhance the transformation of depreciated areas

The emergence context of the new figures, at the crossroads of art and urban planning is a context of spatial transformations (requalification and urban renewal), and as a consequence, complex social, economic, urban and political issues and a necessary public visibility. As argued by Stéphane Tonnelat (2010), doubt and uncertainty lead to think the urban planning linked to art.

As already mentioned, the institutional commitment of the in-between figures in worksite contexts is linked to different evolutions of the economic, politic and urban context in France since the 1980's.

Firstly, it can be understood through an old artistic attraction for urban transformation and margins, far from public authorities and traditional art institutions. As stated in introduction, art is nowadays thought in, for and with space (Volvey, 2011) and worksite offers a whole word for artistic imagination (Tonnelat, 2010). As a closed time and space, the worksite is structured by discipline, security and rules, that makes it a space of obedience as much as a space of critical controversy. Secondly, it can be explained by the insecurity of working conditions, both in art and construction trades. This insecurity forced the town planners and artists to diversify their skills and action fields. Thirdly, these contexts shall be combined with the evolution of urban transition goals. Beyond spatial construction, urban projects may generate economic growth rather than follow it. Besides, it is supposed to take care of the inhabitants' situation at the local scale. With this in mind, reasons and collaboration methods of the in-between figures with the urban planners vary, as we will illustrate through our two case studies.

a. An art project commissioned by urban developers to enhance a wasteland and respond to cultural and technical purposes: The Urban Transition Art Festival case

The Urban Transition Art Festival was held in 2014 in an enclosed fort close to a metropolis, expecting to be renewed as an eco-district by its owner, a public urban planner. Historically, this fort had been used as a military fortification between 1846 and 1969 to reinforce the protection around the metropolis.

The place was then used as a police station, a municipal pound and a car scrap yard until being finally abandoned in 2014. The same year, the urban planner of the area started a project to create a development construction area 5 for a new eco-district. The development operation was important because, even if the site was isolated from the cities around, it had a great attractiveness potential as the municipal train station was planned to be built there and will make it more accessible at the metropolitan scale.

Before the beginning of the urban renewal, while the site was empty, the planner commissioned and sponsored a festival, entirely dedicated to street art, under the theme of urban transition. This commission was launched for different reasons.

It was a way to respond to the prerogatives of a contract for territorial development 6 that was drawn up at a larger scale, for several agglomerated cities7 . This contract places culture at the heart of the territory production, to be strategically integrated into the metropolitan system, it requires the planning authorities to identify a specific budget -approximately 1% of the total budget of the urban renewal -for a highly demanding and innovative artistic intervention. If the type of artistic interventions were left free of choice, street art projects were the main artistic practices proposed, thanks to its success as a tool for developing tourism. It is based on process, temporary and adaptable to the resources available, can be done in a short time and is cheap compared to other temporary types of art. This agreement was to be monitored by the agency as part of its own urban planning operations. About the fort, the purpose was to enhance the architectural heritage, to make the site visible, attractive for the audience and to improve its image.

While responding to these prescriptions, such a festival organization could also solve technical issues that the urban project directly implied, such as the squatting issue. It could fill and enhance the empty site, for which the agency anyway took charge of security and surveillance expenses.

As stated in introduction, the artistic event was organized by an external figure, which we will name the conductor, hired by the agency. The latter invited fifty artists to work for five weeks and cover the walls of the ancient fort, the grounds and twenty-five cars, especially lent by the former municipal pound for the event. Looking at the purpose of the renewal of this part of unknown space, the purpose was to enhance it at different scales. On the one hand, the goal was to make the old fort visible at a local scale, for the residents of the neighboring districts. On the other hand, the metropolitan context of the festival could be used to catch the tourists' attention in a context of urban competition. In this way, it responded to the dynamics of building the city through culture, and of territorial competition around artistic events [START_REF] Chaudoir | La rue : une fabrique contemporaine de l'imaginaire urbain[END_REF], Vivant, 2009[START_REF] Barbas | Aménager la ville par la culture et le tourisme[END_REF]. In terms of organization, the site was opened several days a week for two months during the summer of 2014 and reopened during the Heritage 6 In 2014, an area was identified as a territory of creation and culture by the municipality localities' metropolis within the context of a development territorial contract signed by both cities and the state.

Days8 in September. Several manifestations attracted almost thirty thousand visitors -according to the event organizers -including local residents and tourists. Indeed, means have been set to attract the inhabitants to do tours organized for different audiences. Moreover, the festival started the same day as a block party and attracted more than hundred people who crossed the national road to enter the fort.

Finally, an urban biennial of performing arts -a festival organized by the neighboring town -also ended in the fort. Hence, in addition to the audience from the neighboring lower-class districts, we observed during our site visits that the event attracted a significant number of middle and upper-class families or street art lovers, which certainly came thanks to the promotion of the event in the media. At the same time, the event was welcomed by art worlds since it was presented during symposiums about street art, as it was confirmed by artists specialized in urban arts.

b. An artistic participative project grafted to the urban renewal project to promote its appropriation: The Tree Nursery case

The Tree Nursery is an artistic experimentation set in a social housing area undergoing urban transformation, where more than 3700 people live. Though it is actually a part of the city, the district keeps the image and the problems of the deprived sink estate areas. It was built between 1957 and 1961 and it is isolated from the rest of the city. It is formed by two areas, separated by a highway bridge.

An urban renewal project has been initiated in order to make the area more accessible starting with the highway bridge demolition in 2009, followed by the roads renovation, the destruction of the housing development and the construction of a new housing area.

Between 2009 and 2015, more than 40 trees' "godfathers/mothers" were involved in taking care and in the maintenance of the tree nursery. They helped to define and organize the actions and created a collective vegetable garden. They also participated in several related projects and even public events the following year.

The project, designed by the artist is an urban tree nursery, planted, looked after and transplanted by a group of inhabitants of the neighborhood. Technically and financially, the project was supported by a local cultural equipment entity. A year after the project started, a group of participants, brought together by the tree nursery work in common, decided to create a self-managed collective garden. It gave birth to several other artistic and research projects as well as a documentary film, a research day devoted to the project under the supervision of an art historian, on March 2013, and the participation to a distinguished exhibition in 2014.

In the case of The Tree Nursery the connection with the audience is quite innovative because it is an integral part of the project. It gives the project its reality and sense. So, even if a great part of the audience is captive because they participate on punctual occasions such as parties or school participation, the projects participants are not only actors but also co-makers.

To resume, we are dealing here with renewal projects spread out over several years and marked by significant stakes of urban transformation, especially in terms of image and local appropriation. The first one concerns an isolated urban wasteland, waiting for a requalification project to become a mixed and attractive neighborhood at the metropolitan scale. The second one is an urban residue of an important urban project involving demolitions and reconstructions spread out over several years. In both cases, artistic projects have been organized by an external figure -a conductor and an artist -to respond to the purpose of the renewal projects. The art was aiming to make the urban transition as visible and sustainable as possible, for the local population as well as the audience. Although these artistic projects present differences in terms of temporality, organization and form, they both question the notion of urban transformation through the integration of art in building sites.

The in-between figures as worksite artistic directors at the core of the stakeholder game

If the integration of artistic projects such as the implantation of perennial sculptures is not recent in the city making policies, organizing artistic events within worksites is a relatively new enterprise for urban planners. As the role of "arts commissioner" performed by the conductor and the artist is common in art worlds, it is quite new in urban planning worlds. From this statement, we will now show how these new figures with cross cuttings skills, in-between art and urban planning, are organizing artistic events and managing projects. Then we will analyze their role and the interactions they had with the other actors.

Finally, we will see how their characteristics have impacted the projects' results by studying situations where they have stick to the projects' structure and others where they have gone beyond the existing framework.

a. A top-down project led by an urban planning figure in a context of success of street art as a tool of urban regeneration

In response to the territorial development contract and because the urban planner did not have the expertise to organize the artistic event alone, he hired the conductor to help define and manage the artistic project.

This conductor has developed skills on consulting and organizing street art events over the past few years, particularly through frescoes realization, on behalf of collectivities or social landlords. For this project, he invited artists to work on the topic of urban transition and organized a visit tour around the fort buildings. Thanks to the characteristics of street art as mentioned above, the route was composed by several kinds of interventions, especially in terms of temporalities, such as urban furniture (pedestals, frescos on the walls, on windows, on the ground or on old broken cars), live artistic performances on fences in front of the visitors, hip hop events, and 3D models (one of the flats placed on the ground in order to illustrate the urban renewal project that the site would be undergoing).

The artistic result was quite traditional since it looked like an open-air exhibition. The artworks were attached to well-defined settings: windows, booths and fences. Given the fact that street art historically comes across as a subversive, spontaneous and alternative practice, it could have been expected that artists would transgress the site boundaries and create new schemes. However, this result can be explained by the introduction of the conductor in the urban project but also by the societal evolution of street art role.

On the one hand, the conductor was at the core of the system and was quite free to lead the experimentation the way he wanted. He invited artists, who acted like contemporary ones, because they complied with a commission, in a collective and traditional art demonstration [START_REF] Becker | Les mondes de l'art[END_REF]. He was the link between every actor, collaborated with different partners of the planning authority, such as the local democracy service of the city in order to get the local audience to participate.

We have here a clear example of adaptation of existing jobs in response to new urban dynamics in which art is becoming a part of the city transformation (Arab, Ôzdirlik, Vivant, 2016). Indeed, before developing his activity at the crossroads of art and urban space, the conductor worked for many years as an urban planner and had some experiences in art worlds, particularly by selling artworks. In addition to these activities, he began to approach research worlds, participated in conferences to present his work and even wrote an academic paper about his practice.

On the other hand, the result of the event is not only linked to this in-between figure. It is also due to the evolution of street art status. Since the 2000s, it has become an instrument of attractiveness in a cultural and event context of metropolization (Gravari Barbas, 2009) and is often presented as a link between innovation, art, socio-economic development and creative city concept [START_REF] Mc Auliffe | Graffiti or Street Art? Negotiating the Moral Geographies of the Creative City[END_REF]. This evolution was made possible after the practice's artification process [START_REF] Heinich | De l'artification. Enquêtes sur le passage à l'art[END_REF] that took it from a non-artistic sphere to a contemporary artistic one. For fifteen years, street art artists have been commissioned to sell their work on the art market. Moreover, first generations became gallery owners, passing from the sphere of off to the one of in (Vivant, 2009). Nowadays, street art is exhibited inside (museums, art galleries etc.) and outside (urban areas, streets, walls etc.) the art institutions.

Furthermore, the term of street art has been imposed as a label, in relation to these various territorial and touristic valorizations. For all these reasons, street artists now respond to artistic contracts and street art can be useful to contribute to institutional requalification driving force.

b. A territory transformative actor that uses worksite as a social and political metaphor

As shown previously, The Tree Nursery was an artistic experimentation grafted to an urban renewal project. In opposition to the festival, this graft was not originally planned, and it is from our point of view the key to the success and durability of this project. Indeed, the artistic project was supported by a local youth cultural center and not by the actors of the urban renewal project. This explains why The Tree Nursery and the urban project have each one evolved in different directions at first. As it was a local project, the youth center and the artist got together with the urban project actors with the territorial mission's9 help. Thanks to the territorial mission, the artist was involved in the urban project technical comities and at last, he could interact with the urban planners and propose an integrated project.

At the beginning, the artistic project only included the creation of a tree nursery for the 38 trees, and the collective vegetable garden was grafted to the tree nursery site. The trees were to be temporary planted before being either included to the new urban project pedestrian promenade or set in the orchard.

Becoming bigger and bigger, it was eventually included to the collective orchard, beside the godfathers/mothers' trees. Furthermore, benches signed by the participants are now marking the pedestrian promenade' route of the urban project.

On the one hand, the vegetable garden being integrated to the urban project and the signature on the benches indicated the artist' ability to negotiate with the technical actors and to be a voice for the inhabitants. On the other hand, the artist was able to let the godfathers/mothers freely express themselves and make their own decisions. Doing this, he did not only allow the "voiceless" to express themselves (Rancière, 2000), but shared his expertise with other actors usually seen as laymen. Here, the artist acculturated himself by becoming a "professional of the building construction" who mastered the technical language. For example, he insisted on the acronyms associated to urban renewal vocabulary 10 . This acculturation can be explained by his atypical background. He was an agricultural worker and a graduate from the Beaux-Arts of Lyon and Concordia University of Montreal. Then he had been trained to environmental pollution at the Science University and to politics at a Political Sciences Institute. His strategy is not only based on imitation (Rancière, 2000) but also on "faire comme" 11 , as well as explained by Stéphane Tonnelat (2010). His goal was to "blur the lines and to allow dissensus" [START_REF] Blanc | Ecoplasties : Art et Environnement[END_REF], beyond the gates within the worlds of art. Indeed, by shifting from one world to another, he enriched his artistic practice. In this way, he is currently participating to a research group studying the relationships between food ecology, art and territory.

Following this, his work exceeded the goals of the original mission. It was expected from him to give the floor to the residents, to allow their emancipation, to change the representation of the district, to reach "captive" publics, to make them build something in common and to share an ethics. Nevertheless, he imposed the prolongation of the experimentation for six years, he succeeded in mobilizing a group of forty godfathers/mothers for such a long time, and he helped them to get organized and to create and self-manage their own shared garden: an area of 750 square meters. The artist transmitted a gardening know-how but also a poetical and political culture. This learning can be illustrated by words such as action, care, empowerment initially used by the artist and now used by the godfathers/mothers. Finally, he negotiated a field that was initially to be allocated to the construction of private houses with the urban planner. This field was finally used to relocate the shared vegetable garden close to the orchard.

On the one hand, we have an actor from the urban world who experienced the artistic field. He was hired by the planner to manage an artistic event within a structured hierarchical system, over a short period of time. All the roles -artists, conductor and sponsor -were clearly distributed and the command was successfully accomplished under the conductor's management. As a consequence, the final result did not go beyond the border of the urban project, and was adapted to serve its goals, as we'll precise it below.

10 CUCS: urban contract for social cohesion, ANRU : National Agency for urban renewal 12 On the other hand, the second case is quite different. It was led by an artist who also has several skills and grafted the artistic project on the urban project. This artistic project was carried out in a transversal way over a long time, with a high degree of uncertainty that allowed experimentation. Every actor, including the artist and the inhabitants, played several roles and had skills that made them move on from art worlds to urban planning worlds. Moreover, we think that the ability, the "faire"12 of the artist (Becker, 1982) has contributed to the actor's autonomy and made him get unexpected results.

Moreover, the figures' profiles and their actions' methods were not the only factors of the course and the issue of the artistic projects. Indeed, art forms also influenced the results, since the temporality of art works -its implementation and terms -whether it is street art or an agri-urban piece is very different.

Though the two figures are very different from one another, from a general point of view, what we have here are in-between figures of workers as shown by Pierre-Michel Menger (2003). They are equally specialized in subjects such as agriculture, landscape, pollution, urban planning, environment and even politics. In both cases, they became mediators between technical actors such as the social housing landlord, the local cultural equipment entity, the city workers in the case of The Tree Nursery. As underlined by Charles Ambrosino ( 2013) who summarizes the analyses of Alison [START_REF] Bain | Constructing contemporary artistic identities in Toronto neighborhoods[END_REF] and Vanessa Matthews (2010), they are sorts of « artist-actors » even if they are considered as pioneers in their field [START_REF] Vivant | La gentrification et ses pionniers : le rôle des artistes off en question[END_REF]. Stephane Tonnelat calls them "transformative actors of the urban operational project". They are able to highlight the sensitive qualities of urban space, to access networks of various actors because they gravitate between different worlds and to mobilize the necessary resources that are for their interests (Ambrosino, 2013). In light of the foregoing, our purpose is now to evaluate in which way our figures have impacted the perception and the actors' game within the renewal project.

Effects and limits of the in-between figures' intervention

Our purpose is now to reveal how these two art projects have impacted urban planning worlds and art worlds. First, we will consider how the collective urban space and project perception have been affected, and analyze the actors' interactions. Since the festival enhanced the transition temporalities, the tree nursery project promoted the relation to the Otherness and space. Secondly, we will evaluate their impact on the development project, in terms of technical and planning issues. Finally, we will analyze the power and the limits of the figures' intervention, especially from their legitimacy point of view.

a. Impacts on the perception of the transition temporalities

First, in the case of The Urban Transition Art Festival, the enhancing of the buildings by street art had an effect on their heritage valuation, which was no longer considered. This change of vision is proven by the reopening of the festival during the Heritage Days on September 2014.

Otherwise, the choice of the urban transition theme by the conductor gave the opportunity to change the collective urban relationship with temporality. The artists reinterpreted the past and the city's memories but also the present embodied by the urban project and the future, through the new neighborhood.

Firstly, the scene did highlight some of the site historic dimensions, for example with an image on the fort walls, illustrating a hip hop festival set in the early eighties within the fort. This reference to an underground practice contributed to justify the choice of street art, also seen as an alternative and marginal art. It testified that the festival was not artificial but deeply linked to the cultural site history.

Furthermore, the painted broken cars underlined the site past, recalling the old site industrial activity. This choice enabled to improve the inhabitant's image of the site. They foremost remember the artistic and underground past of the site, than the rumors of radioactive pollution that have been spread since the beginning of the 20 th century13 . Instead of that, the focus was placed on a positive social dimension deeply rooted in the artistic representation of a local political, social and symbolic figure who welcomed new migrants, have been chosen, and represented in a monumental fresco. Secondly, some of the performances showed several aspects of the urban transformation, such as the "covering" of the worksite's items. The fence and the live performances and creations symbolized the work in progress dimension. Thirdly, the future was forecast by an apartment model on the ground as a reminder of the urban transformation project of a future housing area.

Finally, the principle was to act on the collective perception of the temporality and the image of the area and the urban transition, taking advantage of street art's flexible features, as already stated. This type of art allowed to renew and punctuate the local tourism offer, particularly by proposing successive performances. It crystallized the idea of transformation, and at the same time, marked the space for quite a long time, when it comes to monumental frescoes.

purpose was now to structure the reflections in the long term. In this way, the agency members began to inform themselves about the subject and to attend different research seminaries about this question.

One year after this experience, the agency was thinking of systematically putting wall paintings on the new buildings. It could mean allowing artists to be hired and associated to the architects from the very first stages of a building project. In addition, the agency desired to develop skills internally to be able to reuse artistic projects within urban projects. This dynamic interrogates the diversification of the urban developer role. Nowadays such a wish is integrated to global organization dynamics of this new field, as reflected in the organization of symposiums dedicated to art and urban planning, or to the budget created by the government to enhance awaiting reclassification sites through artistic projects.

This also applies for The Tree Nursery where adjustment needs and do-it-yourself in the project management were observed. The impact of the project on the renewal urban project is above all a matter of human and social interactions: between technical actors and artistic ones, between the artist and the residents. As we have been told by the project cultural mediator, a "language adjustment" happened for the urban planning actors for whom the work is now a question of "adaptation, communication and experimentation" 14 , in other words, by including experimentations as much as doubt and uncertainty. Their roles and prerogatives remain limited. Indeed, nearby the artist, they have been temporarily able to change their practices but there is no indication that the change is going to last so that they can include this new plasticity to the work experience to come. The change was linked to this specific project and there is no indication that they could or should renew these kinds of interactions. This is because the artist was at the trustful connections' crossroad. This skills exchange is due to the fact that the project order was really unclear, allowing for the project to be carried out collectively day after day, without much planning, and without preconceived ideas of the roles and skills each player would have to have (Nicolas Le Strat, 2015). The blur is one of the conditions for The Tree Nursery to be successful. Furthermore, the importance of working in situ for the urban planning worlds have widely been encouraged by the artist who used to organize professional meetings on the tree nursery site to make the actors realize the material and temporality dimensions of the trees and inhabitants.

Overlapping all these temporalities -urban transition, project, inhabitants, trees temporalities -made it possible to question what lasts and what does not, was has to be enhanced and developed and what does not. For example, the buildings in the fort chosen by artists to create frescoes earned a patrimonial value. Thanks to this shift, due to the tree temporality in The Tree Nursery 's case, urban planning 14 Interview excerpt with the mediator project, December 2013 the 20th worlds are now forced to reconsider their methods and consider new ones such as outdoors meetings or directly facing the inhabitants, especially the way the work with the artist that they might one day consider as one of them. However, at this stage, the legitimacy level of these figures is still questioned.

c. Legitimacy and legitimization power of these figures on the artists

Legitimacy has been reduced to the political power for a long time, but now -thanks to the relationships with the authority evolution -, its definition has got diversified. For Hélène Hatzfeld (1998[START_REF] Hatzfeld | Au nom de quoi ? Les revendications de légitimité, expressions de mutations sociales et politiques[END_REF] legitimacy can be democratic, institutional or even be a matter of skills. If institutional legitimacy is based on a frame in which it is based in the context, on the contrary, skills legitimacy is based on effective results, on experience and knowledge.

For the political scientists (2014), legitimacy holders have changed: they are not the powerful authority holders anymore, but specific skills holders -experts -and legitimacy recognition has changed too since legitimacy does not come from outside but from the within -peers, social groups.

In the case of The Tree Nursery, we think at first that legitimacy will come from art worlds since it is an artistic experimentation or from the urban planning worlds since it deals with urban renewal, but finally the cooperation with the urban planning worlds and the solutions the artist has found to avoid the problems -for example by using his own artistic and research networks -but it came from the inhabitants. This recognition is not as easy as it seems, the residents often asked the artist: "what is an artist job?", "What are you doing here?". He answered that he was "a human dimension's artist". Despite this, we can consider that he is still a legitimate artistic production actor. Such legitimacy is due to the value of art and to the art market, because art experts are the only ones to decide and hold the artistic value of artworks [START_REF] Moulin | Plan Guide Art et aménagement du territoire, Ministère de la culture et de la communication Rancière J[END_REF]. This value is an expertise value just as well linked to a group of renowned skills by the institutions as by the art market.

In the case of the festival, the conductor has already proved his legitimacy besides the urban planners.

Maybe he is not an artist but he is nonetheless an expert capable of recognizing the value of art (Moulin, Quemin, 1993). He has his own legitimacy besides the expert of urban planning because he is multi-skilled. By the way, we can suppose that his training and professional experience in the field of town planning allowed him to be taken seriously by the agency. His previous activity showed that he had enough knowledge to manage such an urban planning project. Moreover, since he was not an artist, he would firstly use art as a tool to enhance the area and not in an artistic way. By doing this, the conductor acted on the artists' legitimization towards the institutions and, by repercussion, towards the art market. As a matter of fact, those who are chosen are more visible, recognizable by art world's actors and their popularity rating increases on art market.

With the art worlds, we have here figures who play brand new roles or replay them. New figures reinvent methods and interventions means while using them as mediation tools. Thus, they distort the curator role to include some urban planning skills in it. And at the same time, they could act on the renewal of contemporary art by including new spatial practices and actors form the urban worlds.

Finally, new figures' legitimization involves some position changes apart from the traditional institutions.

They study other legitimization methods that can, for example be translated into a combination between research worlds, symposiums participation, writing articles on their own activity or can concern new collaborations with inhabitants or researchers. At last, we understand that on the one hand, legitimization avoids from institutional places to become a network and a collaboration matter and on the other hand, legitimization actors are not experts of a single field anymore, but multi and crosscutting skills holders.

Illustration 1 Conclusion

Through our two case studies, we have shown how these new figures intervene on the sites' perception by staging urban transformation. They are appreciated because of their in-between art and urban planning position, and their cross-cutting skills, fields and worlds. They enable and make the urban transformation more visible by turning the worksite into an action field for artistic experimentations. The projects clearly gave room to institutional media coverage and brought visibility to the urban planners, even if the communication was not defined by a strategy since the beginning.

Moreover, the two figures acted upon urban planning worlds methods. This impact upon the methods is checked by the urban planners' will to structure and develop this new intervention field and by renewing the interrelations between the actors involved in such projects. It can also be seen from the technical actors point of view, when they work -even temporarily -more directly on the field and they took into account other temporalities than that of the urban planning project.

Finally, these actors bring the legitimacy in urban action question to light. On the one hand, they have to legitimate their own skills, especially when they look more like artists than urban planners. The legitimization methods engage the disciplines' permeability, as it is visible in the merger with research worlds. On the other hand, they allow the other actors' legitimization in the urban planning field (artists, designers but also inhabitants). Such a legitimization confronts the experimental dimension and the lack of studies about projects reception. Furthermore, our two case studies show that these new figures' impacts depend on variable factors such as their training, the type of art, the temporality of the project, but also as the structure level of the actors. As we were defining it as a hypothesis, the more the projects are structured, the less the actors game is changed. It means that uncertainty shall be accepted to consider such projects during urban transformation. In the Tree Nursery case, the final material result was not accepted because the actors' network was not clearly defined, and the project was sustained by the local youth house more than by the urban planner.

At last, our analysis is not a model-based value, because it studies two different figures and projects variable in their spatial context, temporality and actors' game. Our goal is not to generalize the impacts of these projects, but rather the opposite. These two cases are not representative of all art projects developed during urban transformations. They reveal two approaches, more or less structured by institutions in two specific contexts. Institutions want to replicate these kinds of projects within construction sites, or abandoned buildings. But we think that their experimental aspect and the kind of art projects could be an impediment in the case of their imitation. Indeed, is it possible to replicate the same street art concept in different contexts, knowing that street art is successful because of its spontaneity and its unexpected character? Furthermore, projects such as The Tree Nursery, even if they are very innovative in a political and social way are really difficult to consider in a different context, because if the context changes, the actors change so the interactions and the relationships too.

Bibliography

  Ambrosino C (2012), « Ces esthétiques qui fabriquent la ville / Aesthetics experiences that builds cities », in TERRIN J-J (dir.), La ville des créateurs, Saint Etienne, Parenthèses, pp. 180-199 Ambrosino C (2013) ; « Portrait de l'artiste en créateur de ville. L'exemple de South Shoreditch à Londres » in Artistes et territoires créatifs en Europe (volume 1) Arab N, Vivant E, Özdirlik B (2016), Expérimenter l'intervention artistique en urbanisme, Presses Universitaires de Rennes Bishop C (2012), Artificial hells. Participatory art and the politics of spectatorships, Verso

In addition to participant observation, we interviewed some projects stakeholders, and we did a discourse analysis, especially through the external communications, Internet and graphic and written documents.

We borrow the turn of phrase « urban planning worlds » to the interdisciplinary research program « City and Environment » under the supervision of Stéphane Tonnelat in 2010. At first, it points the urban planning professionals that work in two dimensions: care (for the people) and technical urban planning and design.

Building operation guided by the French town planning code (art. L311-1) to organize a site building planning.

It is a public territorial office that gathers several cities close to a metropolis.

Heritage Days take place during the 3rd week in September. During one week-end, historical hotspots open their doors to the public.

A territorial mission sponsored by the city and that works on social, education, job, culture and health problems of deprived areas.

"To do"

Some rumors of radioactive pollution were spread after the experiences led by scientists in the twenties and by the army in the seventies.

On the contrary, The Tree Nursery was not clearly based on the theme of transition. Here, the will to represent the urban transformation did not precisely appear in the commission. This report of the urban transformation is not set up in a testimony but is visible in an action that aims for the inhabitants to be actors in another form of transformation than the one intended in the urban project. Furthermore, the transformation they are involved in deeply impacts their lifestyle, relationships in/to the neighborhood, and to nature. This change is visible in the artistic will of showing the trees taking roots and the integration of the inhabitants in the area, while the whole neighborhood is forced to move and to follow the design of the urban project. The trees are now a means to mention not only the setting of an artistic project, but the lifestyle in social housing areas. They are therefore holders of immigration historymost of the participants are sons of migrants, more or less rooted in the neighborhood -and now concerned by a new form of immigration, because they have been driven out of their apartments into a new place after the urban transformation. The tree figure is used as a symbol representing the French republican values such as Freedom and it became a way to speak about democracy in sensitive urban areas where it is supposed to be away.

In one case, officially choosing the transition theme and street art -whose ephemeral character closely links it to the city's temporality -allowed to stage the site's temporality and thus, to act on its symbolic values. In the other case, the non-structured transition approach enables a change in the relation to the Otherness, to space and nature: a change embodied by trees, which is also related to the collective relationship to time. The traces of the artistic project on the urban project are more political, symbolic and social than material even though the benches of the promenade have been signed by the godfathers/mothers, as a trace of the inhabitants' participation. Changes in the urban project are not that important, but in the light of the number of actors, and of the awkwardness of the decision making, the fact that the nursery trees have been completely integrated into the urban project's design is a sign of The Tree Nursery's impact and success.

Apart from the effects of the projects on the perception of sites, did they adjust with the urban project and get integrated to it without changing anything or did they overflow and modify the urban project