Disturbances linked to human activity - overexploitation, deforestation, climate change etc. - are all threats to the genetic diversity of plants. However, city dwellers with cultivated gardens can play a key role in protecting species. A multidisciplinary study combining genetics and ethnoecology recently showed the diversity of species of safou trees planted in Yaoundé, the capital city of Cameroon.
The safou (Dacryodes edulis) is a fruit tree native to the Congo Basin and is generally grown in coffee and cocoa agroforestsA forest in which the composition of fauna and flora is managed by human populations, but also in cultivated gardens in villages and large towns in the region. “We compared the level of genetic diversity of safous in a production zone far from the city, equivalent to 200,000 hectares, to that of safous planted in a 250-hectare district of Yaoundé,” explains Jérôme Duminil, Geneticist at the DIADE research unit. “Despite the difference in size, the genetic diversity of safous in rural and urban areas is almost identical.”
From field to city
How can such a wealth of biodiversity in a megalopolis with a population of over 3.9 million be explained ? The answer lies in the fact that Cameroon is a rich cultural melting pot: 300 to 400 different ethnic groups live together within the country. When these villagers migrate to the city, they take seeds from their favourite safous with them to plant once they are settled there. These exchanges with the countryside continue during visits and family events (weddings, births etc.) If a city dweller likes a particular safou fruit Fruit of the safou treebrought by visitors, they will plant it in their backyard. They will do the same thing if they bought it at a market.
93% of the Dacryodes edulis seeds planted in Yaoundé thus come from outside the city. Half of the seeds used for planting were bought at markets either in the capital or further away in towns and villages such as Makénéné, which is 200km away and is known for the quality of its fruit. The other half of the seeds (41% of the sample) come from rural areas. In contrast to these results, over 75% of the seeds used to grow safou trees in regions far from the cities mainly come from the area where the villager who planted them lives.
Protecting a favourite safou
“The safou plays an essential role in the lives of Cameroonians,” says Marie-Louise Avana, Ethnoecologist at the University of Dschang in Cameroon. “Among all ethnic groups, it is appreciated because it is easy to cook. A natural source of salt and fats, like avocados, it is used to accompany various starchy foods such as manioc, potatoes, corn and plantain, and is also given to children as a treat. Safou seeds germinate easily. The tree is evergreen with dense foliage that provides shade: it offers a space to relax in for the families in their backyard. Even if they don’t have much space, Cameroonians will make sure they plant a safou on their land.”
By planting the safou, the inhabitants of Yaoundé maintain a cultural and symbolic link with their home region. They are also unknowingly preserving the tree's genetic heritage. This intraspecific diversityGenetic diversity within the species is essential to enable the species to adapt to threats. “For example, if a farmer only grows a single variety that is not resistant to a certain disease, pest or to climate change, they will lose their entire crop,” explains Stéphanie Carrière, ethnoecologist at the SENS research unit. “The presence of several morphological types within the farm and the village helps farmers to adapt to climatic and economic fluctuations. This helps develop the resilience of farming systems.”
Unfortunately, green spaces and gardens in cities are gradually being impinged upon by increasing urban densification and may become scarce. “The public authorities must be made aware of this: green spaces are essential for the population’s quality of life as well as for the protection of biodiversity” concludes the researcher.