Which trees to choose for the future “urban forest”, Place de Catalunya in Paris?Serge Muller , National Museum of Natural History (MNHN)
On October 12, 2021, the city of Paris adopted its “tree plan 2021-2026” by deliberation. This takes up the 2020 commitments to plant 170,000 trees during the current mandate and, in this context, to contribute to the creation of several “urban forests” in Paris over the coming years.
The most advanced project, which is scheduled to be finalized for the 2024 Olympic and Paralympic Games, is that of Place de Catalunya, near Montparnasse station, in the 14th arrondissement of Paris. This initiative was subject to public consultation from October 21 to November 24, 2021.
By occupying a relatively large area, over one hectare, with the objective of planting around 5,000 tree and shrub seedlings, this project constitutes an interesting opportunity for innovation and experimentation for urban planting operations. .
Which species to choose?
The current doctrine formicroforest plantations of the Miyawaki type (on more restricted areas, of the order of a few hundred m 2 ) is to make very dense plantations (of the order of 3 plants per m 2 ) and to use only indigenous species, that is to say species naturally present in the region, corresponding to the “potential natural vegetation” of the territory.
However, the current native forest of Ile-de-France seems in very bad shape , threatened as it is by the current climate change.
It would thus seem more innovative, and relevant, to seek to create an urban forest "of tomorrow": adapted to the climatic conditions of the second half of the 21st century and taking into account the results of studies and modeling of the potential areas of distribution of forest species by 2100 .
This knowledge and predictions lead to the proposal to create a Mediterranean holm oak forest there, in a sub-Mediterranean variant, with downy oak, Provencal hackberry, Montpellier maple, field maple, white service tree, mountain ash, flowering ash, yew, etc.
And, for the shrub layer, species such as arbutus, boxwood, male dogwood, wood laurel, oval serviceberry, laurel, tin viburnum, butcher's broom, pistachio terebinth, buckthorn , common myrtle, etc.
All these species are part of the composition of the Mediterranean holm oak forest (or “yeuseraie”). They are all present spontaneously on the French Mediterranean territory. Some of them (such as pubescent oak, country maple, white and torminal service trees, male dogwood, oval serviceberry, boxwood, etc.) are naturally present in the Paris region, particularly in habitats the most thermophilic (the downy oak forest).
Holm oak and hackberry from Provence
All the species mentioned above have in fact already been planted in populations separated from each other in Paris (in parks, gardens, squares, squares and/or streets) and show good adaptation to local conditions there.
This is particularly the case of the hackberry of Provence , of which more than 4000 trees are already present in Paris with a very satisfactory development.
The holm oak likewise has more than 800 trees recorded in the open data of the city of Paris; it develops very well there, the most imposing tree, in the Montsouris park not far from the place of Catalonia, having a circumference of the trunk of more than 250 cm for a height of 15 m.
The interest of the project would thus be to constitute, on the basis of the association of these species already present, but dispersed in different places of Paris, a Mediterranean to sub-Mediterranean urban forest and to study its adaptation and its evolution as plant community and ecosystem.
It could also be interesting to create, if possible, a certain heterogeneity in the local ecological conditions, therefore of the soil and the water regime (some areas wetter and others drier).
This could allow the occasional establishment of a cooler or humid station forest with white poplar and oxyphylle ash and, in other drier sectors, xerophilous forests with Mediterranean pines such as the parasol pine, which are very present (60 trees) in the Atlantic garden of the Montparnasse station in the immediate vicinity of the Place de Catalunya, and the Aleppo pine, also planted in Paris.
An opening to other continents
If for the place of Catalonia, there is a certain logic in creating a European Mediterranean forest, for other projects of "urban forests" on more or less large areas in Paris, it could also be interesting to create temperate forests thermophiles made up of species from other continents (North America, Near or Far East, even the southern hemisphere)… obviously adapted to the current and future climatic conditions of the city of Paris and made up of non-invasive species.
Here again, taking into account the performance of trees of these species already planted in Paris or on the outskirts, in particular in parks, botanical gardens and arboretums, could provide very useful information on the adaptation of these species to environmental conditions. current and future in the city of Paris.