From tree planting to planting “green frames” Our cities have become greener in recent years through the conservation or creation of wetlands, shared gardens or green roofs.
However, this restructuring does not come without compensation. production of plants pollen or allergen volatile molecules can, for example, has a negative effect on health. In addition, these green spaces also encourage the establishment of vertebrates (birds, rodents, etc.), insects (mosquitoes, etc.) and other ticks (ticks, etc.), which act as reservoirs or carriers of infectious agents responsible for diseases. can be. not only for humans but also for plants and animals. Unwanted guests whose circulation can be facilitated by the connection of vegetated areas between themselves and outside the city…
All these factors should be taken into account when deciding on the establishment, management and use of urban green spaces by residents.
Why green cities?
Sustained improvement of the health and well-being of urban residents is a priority and major challenge for states and local governments. The task is even more complex in the global context of climate change and globalization, which make environmental and biodiversity conservation imperative.
Urban greening is one of the approaches implemented to achieve this goal and making tomorrow’s cities livable, healthy, resilient and sustainable. It consists of incorporating natural elements into the urban environment, both green spaces and water bodies effectively combats heat islands, reduce air pollution and so on promoting biodiversity in the city.
The presence of green areas in the city also affects the improvement of the well-being of city residents, as shown by numerous studies conducted around the world. It provides a significant contribution to the greening of cities improving the physical and mental health of residentsespecially by suggesting opportunity to exercise outdoorsor by strengthening social cohesion.
However, it should be emphasized that the least advantaged neighborhoods are often left on the fringes of urban development projects and thus widening inequalities in the complex and fragmented environments that are modern cities.
In addition, the conservation or restoration of plant biodiversity in cities may allow the creation of particularly favorable environments for the establishment and reproduction of undesirable invertebrate or vertebrate species, carriers or transmitters of infectious agents with high epidemic potential.
Relationships between vector risks and green spaces
There is little research on the topic to date, but several reports highlight the relationship between the presence of green spaces and the risk of vector transmission in urban centers.
Hence the dengue epidemic that raged in Tokyo in 2014 It was limited to Yoyogi Park. Located in the heart of the city, this place is known as the haven of tiger mosquitoes (Aedes albopictus), the vector of the virus responsible for this disease.
Similarly, between 2009 and 2012, an increase in leishmaniasis cases was observed in Madrid. was related to forest development This contributed to the spread of the midge vector and rabbit reservoir of the parasitic protozoan responsible for the disease in the immediate vicinity of the capital.
ECDC also notes in its latest report the role that urban parks can play In the entry of West Nile virus into our cities. Transmitted by mosquitoes of the genus Culex (“common” mosquitoes, abundant in all French cities), this virus infects not only birds, but also horses (horses, donkeys, ponies, etc.) and humans, in whom it may cause encephalitis. But parks in cities attract many species of birds. Cases of West Nile fever were first detected in Bordeaux in the summer of 2023, underscoring the importance of this warning.
Southern cities also faced problems. In the coming years, most urban growth will occur there, especially on the African continent. It is in these places that the consequences of climate change will be the most acute.
If the greening of cities in southern countries is not yet on the agenda of political decision-makers, some cities such as Dakar are nevertheless relatively green. This is particularly due to the importance of urban agriculture, which is widely promoted as a means of feeding the population and generating income.
But these spaces are very favorable for the development of mosquitoes Anopheles gambiaethe vector of the parasite responsible for malaria increases the risk of disease transmission in the heart of the densely populated city and surrounding areas.
Ecological corridors favoring the penetration of vectors
Connecting large urban parks with peripheral forests through ecological corridors can also facilitate the introduction and release of small rodents and even larger animals (wild boar, etc.). They can carry other infectious agents: ticks, parasitic ticks that carry many pathogenic microorganisms can sometimes cause serious diseases encephalitis, certain hemorrhagic fevers, and Lyme borreliosis.
Park connectivity and tree density in Staten Island (New York, United States) in 2017 affected the density of tick populations Ixodes scapularis and their rate of infection by the responsible agent Borrelia burgdorferi Lyme disease. This trend is confirmed With Lyme disease and cases increasing in Europe as welltick-borne encephalitis It has been observed since 2010 in urban and surrounding areas with vegetation.
The risks are not limited to humans
Plants themselves are not immune to vector risks that may arise in cities, and the agronomic consequences of such outbreaks can be significant for suburban plantations.
Thus, in California, contamination of citrus plantations surrounding cities with yellow dragon disease (HuangLongBing, HLB). seems to originate from the private gardens of the cities mentioned. The disease is caused by bacteria spread by a small sap-sucking stinging insect, the Asian citrus psyllid.Diaphorina citri). However, it appears that citrus trees planted by individuals provide a reservoir for psylla populations.
This example illustrates the role of ornamental plants in introducing disease into the city, which can then be exported to the periphery on cultivated or uncultivated crops. A situation of particular concern to organizations that monitor the health of plants and products, especially vines and fruit trees.
Greening cities is essential for a sustainable future. But just as we have to think about what species to plant because of climate change, water scarcity, or even the risks of developing pollen allergies, it is important to anticipate the effects these regulations will have on vectors and vectors. don’t pass
Collaborative research involving all citizens and urban, public health, veterinary and environmental stakeholders should help inform public policies on planning and deploying green and blue networks in tomorrow’s urban areas to achieve ambitious outcomes.