Tour eiffel arbre

In Paris, which trees to adapt the city to climate change?

Autumn landscape in the Parc de Bagatelle, a high place of woody diversity in the botanical garden of Paris. Serge Muller , Provided by the author
Serge Muller , National Museum of Natural History (MNHN)

The city of Paris has a very important tree heritage, as evidenced by the city's open data presenting the identity and location of more than 205,000 trees in the capital.

Added to this number are all the trees not managed and monitored by the management of green spaces and the environment of the city of Paris, such as those in the Jardin des Plantes, the Parc de la Cité Internationale, the Jardin du Luxembourg, the Tuileries Garden and many other parks and private gardens.

More than 700 species of trees in Paris

Accurate counting of tree species in Paris comes up against several other difficulties, such as the unclear limit between tree and shrub (in principle height greater than 5 or 7 m for a tree), as well as intraspecific taxonomic variations, some subspecies or varieties being sometimes perceived as true species by certain authors.

The counts made from open data and additional data on other green spaces, not counted in this database, nevertheless allow us to consider that there are currently more than 700 different species of trees in Paris (such as than considered in the open data, sometimes also taking tall shrubby species into account), which is quite remarkable all the same.

It is logically the Paris arboretum, in the heart of the Bois de Vincennes, which, over its 12 ha, concentrates the greatest number of them, with around 485 species (and overall more than 800 taxa, counting the subspecies, varieties and cultivars). The botanical garden is home to more than 270 species of trees over 23.5 ha (many of which are obviously shared with the arboretum), while the park of the international city displays 235 species of trees out of 34. Ha.

The large urban parks created during the Haussmann era also each have more than 100 different species of trees: around 115 for the Buttes-Chaumont park (24.7 ha), 140 for the Montsouris park (15.5 ha), and even 150 for Parc Monceau over 8.4 ha. Squares of smaller dimensions can also host a significant tree diversity, such as that of the Oath of Koufra (2.7 ha) with more than 50 distinct species, including some very rare species in the botanical parks of Paris, for example oaks from Hungary ( Q. frainetto ) and Japan ( Quercus acutissima ), as well as black oak (Q. nigra) , an American species.

Dominant species, others very rare

The dominant species in the city of Paris are plane trees, chestnut trees, lime trees and maples, which together make up more than 50% of the city's trees. These trees have historically often been planted in dense, monospecific stands, which increases their susceptibility to pathogens. As well-represented secondary species , we can cite Japanese sophora, ashes, pines, oaks, etc.

The iron tree or Persian parrotia, a densely bushy species that is very decorative in the fall. Serge Müller

Other species, on the contrary, are much rarer, some being represented by less than 5 individuals in the green spaces of the capital. For example, the remarkable conifer Wollemia nobilis , a new species discovered in 1995 in Australia, is not mentioned in the open data. It is present in the Jardin des Plantes, the Parc des Bagatelles as well as in that of the Quai Branly and perhaps also in some other secret gardens of the capital.

The most diversified genus in the green spaces of Paris is the genus Quercus , corresponding to the oaks, with more than 40 species and a few hybrids planted in the capital. Another very well represented genus is Acer , corresponding to maples, with 36 different species and 4 hybrids.

What place for indigenous species?

The city of Paris has committed to planting 170,000 trees during the 2020-2026 term of office . Should we opt mainly for indigenous species in Île-de-France? Indeed, the biodiversity plan of the city of Paris proposes, in its action 21, "to promote regional plant species" . The native species in Île-de-France, few in number ( about twenty species of trees ), must obviously have their place there, provided that they are adapted to current environmental conditions and to come in the coming decades.

The tall ash is a native species in Île-de-France that is very threatened by the spread of chalarose, a fungal disease. Serge Müller

In the “real forests” of Ile-de-France outside built-up areas, this choice of favoring native species (and excluding exotic species as much as possible) in plantations is fully justified . This orientation must also be applied in the suburban forests of Paris (Bois de Boulogne and Bois de Vincennes) with the aim of increasing the naturalness of these forests.

On the other hand, this option appears much more debatable in the city center, because non-native species are often better adapted there to current and future environmental conditions and can provide greater ecosystem services there than native species .

On the other hand, potentially invasive alien species can be easily identified and controlled there. The diversification of the plant palette by allochthonous species should thus allow an increase in ecosystem services and an embellishment of the urban landscape.

70% of the species in our cities at risk

According to the latest estimate published in early 2022 , the world's ligneous flora would be rich in more than 73,000 species of trees, of which 9,000 remain to be described, most of these species being restricted to tropical regions and therefore not adapted to the climatic conditions of the city. from Paris.

Thousands of tree species exist, however , in temperate American and Eurasian regions , which still leaves great possibilities for the enrichment and diversification of the woody flora of Paris.

Experiments introducing such exotic species to Paris could thus make it possible to assess their potential for acclimatization in our cities and the ecological services that they would be likely to provide, particularly in the context of current climate change .

This diversification of species in cities appears all the more crucial as more than 70% of current species in our cities, including all native species in Île-de-France, will be at risk from climate change by now. to 2050 in Paris and other major French cities .

For example, there aresome 435 species of oak trees in the world, found mainly in the temperate zones of the northern hemisphere.

[ Nearly 80,000 readers trust The Conversation newsletter to better understand the world's major issues . Subscribe today ]

A large number of them have been introduced into arboretums in France and neighboring countries. Thus more than 300 species of oaks are in the arboretum of Pouyouleix (Dordogne), more than 250 species in that of JL Hélardot (Corrèze), many also in the arboretum of Wespelaar near Brussels , etc. Enough to further enrich the collections of oaks in the parks and gardens, as well as the boulevards and avenues of the city of Paris!

The Chinese cork oak ( Quercus variabilis ), a very decorative, fast-growing species, still not very present in Paris. Serge Müller

An enrichment to continue

It is obviously in the first place the arboretum of Paris and the botanical gardens (including the botanical garden, in connection with the arboretum of Versailles-Chèvreloup ) which are intended to diversify the woody flora of Paris, but the parks, squares, cemeteries and other green spaces in the capital can also contribute.

This enrichment can also lead to the creation of coherent woody units on the biogeographical level. Thus, as part of the project of the city of Paris to create an urban forest in place of Catalonia (XIV th arrondissement), we proposed to create a forest of the sub-Mediterranean type .

On the same principle , temperate forests of the American or Asian type, or even southern hemisphere, allowing the public to benefit without moving from a first glimpse of the tree communities of these regions. The Conversation

Serge Muller , Emeritus Professor, researcher at the Institute of Systematics, Evolution, Biodiversity (UMR 7205), National Museum of Natural History (MNHN)

This article is republished from The Conversation under a Creative Commons license. Read the original article .

Back to blog