Planting is, like grass covering, carried out in the rainy season. It may take place on an area that has been previously covered with or without grass, depending on the need to establish a grass cover upstream of the reforestation phase.
The trees are planted in a mesh size of about 3x3 to 5x5 metres, alternating species between nitrogen fixators (Ingas, Clitorias, Moutouchis, etc.) and other forest species (Macaque Comb, Vismia..) or fruits (Mombins, Ficus, Jamelon) so as to promote cooperation and competition between each individual planted. In the end we get a density of about 1,000 trees/ha with a great diversity.
However, most of the species used remain so-called pioneer species, capable of growing in full sun and adapted to poor soils such as those of mining sites. In addition they generally have a very important vegetative growth up to 4-5 m/year, this allows the rapid installation of a tree cover conducive to the coming of the surrounding fauna, very important vector of seeds from the forest and fertility (feces)
The shade created by these pioneer species will allow secondary species to gradually find conditions adapted to their installation and thus allow the contribution of a new natural and spontaneous diversity, evidence of reawakening of the natural cycle of recolonization by the forest.
Our planting way
Thanks to the students of the VALORESS license (2019-2020) for their involvement in the revegetation work during their visit of the Saint-Elie mine.
Use of Seed Bombs
In order to revegetate hard-to-reach or steep areas, the use of seed bombs proved to be the solution. Seed bombs are balls made of organic matter and clay containing a variety of seeds. The organic matter contained in the seed bomb allows the seeds to grow quickly by providing them with all the necessary nutrients, and the clay serves as a binder to ensure the cohesion of the whole. Moreover their application is very simple, just throw them on the areas to be revegetated. This technique is therefore very useful in slopes or crevices.
For the manufacture of seed bombs tests have been carried out since 2017 at the Saint-Elie site. Despite a relatively high number of failures, these tests helped to optimize the manufacturing process and the composition of seed bombs, until finding the right recipe!
Subsequently, seed bomb plantations at the Saint-Élie mine proved promising. The plants from the bombs grow well, form thick trunks, deep roots and green foliage. After more than two years of testing and tracking seed bombs, the results are as follows:
- Longer germination and higher than nursery mortality
- Good tree development after germination
- Bomb trees appear more robust than nursery trees
- Seed bombs are currently the most suitable technique for slope revegetation
The reforestation of mining sites allows the Amazon rainforest to recolonize environments that it could never recolonize or in hundreds of years. The results presented above were obtained during the GUYAFIX project in association with SOLICAZ.
Since the GUYAFIX project, SMSE has continued this effort to revegetate its site by planting nearly 100,000 trees (2012-2019) and dispersing nearly 30,000 seedbombs. This dynamic of revegetation should allow during 2020 to rehabilitate the last sectors of the Saint-Elie mine.
The results of this method are visible in a few years, but it will still take decades for the Amazon rainforest to regain the greatness and biodiversity that make it famous around the world.