## 2 Materials and Methods  
### Site Description and Soil Sampling  
The work was undertaken in French Guiana, South America. The sampled soils (Figure 1) for this study were rehabilitated after gold mining extraction. After closing the alluvial mine pit, rehabilitation consisted of reconstituting the soil excavated during mine exploitation.  
The first three sites were in the Belizon forest (N 04\({}^{\circ}\)22.200\({}^{\prime}\)/W 052\({}^{\circ}\)19.328\({}^{\prime}\)). The mining operation lasted five years and ended in January 2013. All sites in the Belizon have had the same mining history. In February 2013, an ecological restoration programme was initiated with macrocuts of _Clitoria racemosa_, a species of local fabacea. The recovery of _C. racemosa_ macrocuts has not been effective on all sites in the Belizon forest. On the Bel1 site, vegetation covered between 5% and 10% of the soil surface with a majority of cypareaceae species (_Cyperus_ sp. and _Carex_ sp.). On the Bel2 site, vegetation covered more than 70% of the site and almost the entire site is dominated by _Lycopodiella_ sp. with the presence of some cypareaceae species. On the Bel3 site, macrocuts of _C. racemosa_ were recovered and the trees are nearly 5 m high.  
The following three sites were taken from the former Yaoni mine site (N 04\({}^{\circ}\)30.930\({}^{\prime}\)/W 052\({}^{\circ}\)21.275\({}^{\prime}\)). Mining activity at the Yaoni sites lasted several years and ended in 1997. These three sites also have the advantage of having the same mining history. The first two Yaoni sites (Yao1 and Yao2) have not been restored by specific protocols and the low vegetation cover, mainly _Lycopodiella_ sp., _Cyperus_ sp. and _Carex_ sp., is the result of  
Figure 1: Illustration of some examples of different stages of ecological restoration on formers Guyanese gold mining sites and geographical location of the Yaoni and Belizon mines in French Guiana. Non-restored site (**top left**), ecological restoration with herbaceous species after 3 years ((**top right**), Bel1), ecological restoration with fabaceous species after 3 years ((**bottom left**), Bel3), ecological restoration with fabaceous species after 18 years ((**bottom right**), Yao3). The pictures were taken during a second sampling campaign in April 2016 on sites undergoing ecological restoration.  
spontaneous vegetation development. The Yao3 site has been completely restored by associations of fabaceous species, notably _Acacia mangium_ and _Clitoria racemosa_.  
At each site, soil samples were collected from depths between 0-10 cm with an auger in April 2016. The sampling for the five sites consisted of sampling five plots (\(n=5\)) per site, with three sub-samples per plot that were pooled at the laboratory. The sampling of five replicas per site was mainly conditioned by the topography of the terrain, the accessibility of the plots and the feasibility of sampling. Soil samples were immediately sealed in sterile hermetic polyethylene bags for transportation to the Cayenne IRD laboratory. Samples were then dried at ambient temperature (25 \({}^{\circ}\)C) until they were air dried (i.e., approximately three weeks). These 90 collected samples (6 sites \(\times\) 5 plots \(\times\) 3 samples per plot) were then sieved at 2 mm, homogenized, and hermetically sealed at 4 \({}^{\circ}\)C until used.