IENE 2016

Allotment gardens are grouped vegetable’ plots gardened for non profit and that gather a group of gardeners. Their history (end of the 19th century for the French context) is strongly linked to the history of railways and roads because they were specially located there (“jardins des cheminots”) or because they found there the opportunity of a non coveted land. These gardens could be part of the road verge, in this case they are illegal and temporary gardens, the gardeners take care of the land out of any frame. They could also be along the road as a buffer between the road and the urban fabric. Then they could be manage by a ONG, the municipality, a social housing organization, private persons… In all the cases, we choose to study urban roads that shelter more than 30.000 vehicles/day (2 ways).

What is the fauna-flora biodiversity of roadside allotment gardens ? Is this biodiversity different from the one of the semi-natural verges? Where does this biodiversity come from and come to? How roadside nature contributes to the ecological network? Could nature and humans cohabite on the roadsides to produce living landscapes? Is it healthy to cultivate the roadside?

To answer those questions, the « roadside-nature » multi-disciplinary research conducted since 2010 - with the financial support of MEDDE and ADEME - articulates an ecological evaluation and a landscape evaluation. The ecology of the gardens in their environment has been studied through biodiversity with a survey of fauna-flora in presence/absence and landscape ecology with maps analysis. The pollutions of the garden (soil, air and vegetables) have been investigated through in situ measures (CEREMA and Agroparistech).

Landscape should be outlined here through its sensory and human dimensions: sightscape, soundscape and taskscape, approached by sound measures and recordings, observations and interviews with gardeners. The specificity of the methodology implemented is to cross-reference quantitative and qualitative datas, ecological and human questionings around the ecological issues.

18 roadside allotment gardens, located in France (A480, A41, N87 /Isère and A86, A6, A13/Ile-de-France), Portugal (E1, subway, railway and the express way /Lisboa) and United-States/California (280 and 101 Freeway /San Francisco) and their nearby « wild » nature have been studied in situ.

3 types of roadside gardens have been highlight in the 3 countries: the island gardens surrounded by roads and railways and disconnected from the urban fabric, the home gardens surrounded by dwellings, the parks gardens included in a public park.

The roadside allotment gardens shelter an ordinary fauna-flora biodiversity, generally more important than the biodiversity of the semi-natural verges colonised with invasive plants. This ordinary biodiversity of the roadside gardens is variable from one site to another (59-169 wild flora species), from one plot to another and from the inside of the gardened plots and the outside. 4 criteria should be take into consideration to understand this variability : era/species ratio (insular geography), maintenance and accessibility of the walkways, gardening practices, ecotonal structure (in-between structures at different scales).

Roadside allotment gardens are ecological dilatations of the roadside and roadbank nature, their habitats are different and complementary. Roadside gardened and « wild » nature contribute to linear ecological network in the surroundings of transport infrastructure: some birds and insects could find temporary habitats and they are for all animals linear corridors.

The dilated structure of the gardens are also very important in terms of soundscape and pollution. Since a 200 meters width, it’s possible to escape the noise of the road and to find a sound level under 53 dBA. Also, the pollutions’ level decrease significantly from 30 meters from the road. Some measures should be implemented in this buffer space (0-30 meters from the road) to avoid to cultivate polluted area.

Roadside allotment gardens are places where human and nature could cohabitate, they are human and nature living landscapes. Indeed the gardeners could have a positive impact on biodiversity and gardens could be corridor for humans (gardeners and visitors) as well as animals.

Otherwise, a strong improvement should be made to cross scales and to articulate ecological network to living landscapes implementation policies. Today, in the French context, the regional eco-network (SRCE) is realized at a too large scale to take the gardens into consideration. Gardens could find a place as a proximity landscape in the development of roadside urban new area where unhopefully the ecological stakes are forgotten or misunderstood. To inform the French context about actor games, the Californian and Portuguese situations reveals different bottom-up and top-down processes to articulate urban and garden development. We will also see that the ecological and pollution issues are taking into account differently (legal and political frames, actors, stakes…) in the two foreign cities.

The road sides could become urban agriculture areas in order to satisfy the social need.

They can be an alternative to expensive maintenance of large areas. These road sides are one of the rare soil areas in the urban artificial context, they contribute to the heat island reduction.

They could be and become a part of urban project that contribute to a better connectivity to retrofit the fragmented fabrics and their atmospheres.