Afforestation plans in Africa could go wrong

The state of mature ecosystems must be taken into account before launching massive reforestation plans in sub-Saharan Africa, according to geoecologist Julie Aleman, a visiting researcher at the Université de Montréal’s department of geography.

“The biomes in the region we studied, which includes all the countries south of the Sahara, are divided into two fairly distinct types: savannah at around 70 percent and tropical forest for the rest,” said Aleman, co-author of a new. important study on African biomes.

The study, involving around 30 researchers, many from Africa itself, was published this week in Proceedings of the National Academy of Science.

“When we look at the assemblage of tree species in each biome, we find that each is extremely different,” said Aleman. “Furthermore, if we look closely at the history of these biomes, we realize that they have been stable enough for 2,000 years. Reforestation with tropical forest species in the areas most associated with savannahs would therefore be a mistake.”

Without wishing to point the finger at countries that could make this mistake, Aleman stressed that the reforestation plans involve the planting of billions of trees. The intention is also good, countries must try to avoid artificially creating tropical forests where savannas have dominated for several millennia, he said.

Furthermore, the choice of the selected species is decisive. Acacias are more associated with open environments, for example, while Celtis trees are forest specific. In some cases, eucalyptus plantations have turned out to be “ecological disasters,” according to Aleman.

On the trail of the past

He carries out his work at UdeM’s paleoecology laboratory, whose mission under director Olivier Barquez is to retrace the past of biomes. Aleman’s principal collaborator, Adeline Fayolle, a professor at the University of Liege, Belgium, collected the floristic data (tree species lists) for the new study.

“To do this, we conducted a kind of old-fashioned data mining, in the sense that we analyzed a large amount of existing data, published and sometimes archived in forgotten documents, buried in the dust, as well as recently acquired data in the field, to try to understand the history of the region, “said Aleman.

The study takes into account the floristic, environmental and paleoecological data to better understand the ecological functioning of the forests and savannas, aided by the analysis of 753 sites in both environments. The environmental factors that have the greatest impact on these environments are rainfall and its seasonality, as well as temperature, the researchers found.

One of the most notable phenomena in the savannah is the frequency of the disturbances that affect them. Weeds can flare up up to three times a year in some places, for example. To protect public health, local governments sometimes want to limit these fires. These decisions are legitimate, but they can have significant ecological consequences, the co-authors say.

This is because, for the most part, large trees are unaffected by the flames and the ashes regenerate the soil.

Almost devoid of wildlife

The impact of human activity can be seen wherever researchers have done their research, but mainly in Tanzania, Congo and the Central African Republic. In some cases, some areas are almost devoid of wildlife.

Already in 2017, when Aleman published an article in the African edition of the online platform The Conversation, he constantly tried to alert the public to threats to African ecosystems. The conversation.

He believes that the situation is not desperate but that governments must be careful how they intervene so as not to make things worse. Aleman hopes the new study will lead to a better understanding of the biological reality of the African continent.

“This is a rather theoretical contribution,” he said, “but I think we can use it to inform reforestation policies.”