Composition, richness, and abundance of biocrusts in artisanal onyx mining sites in a tropical semidesert of central Mexico

This study evaluated biocrusts in artisanal onyx mining sites in a Mexican tropical semidesert. Biocrusts in abandoned waste dumps from mining and in reference sites with natural vegetation were collected to measure their composition, richness, and abundance. The biocrust species and taxonomic groups were related to soil properties, and vegetation structure of waste dumps and reference sites. Biocrust composition and richness were similar between waste dumps (27 spp.) and reference sites (25 spp.). However, bryophyte abundance was lower in waste dumps (7%) than in reference sites (13%). Soil had lower litter cover (19 ± 5 %), organic matter (1.1 ± 0.03 %), moisture (7.6 ± 0.05 %), and total nitrogen (0.04 ± 0.0 %) in waste dumps than in reference sites (57 ± 9 %, 5.8 ± 0.1 %, 18.7 ± 0.04 %, 0.13 ± 0.0 %, respectively). These results suggested that cyanobacteria, lichens, and to a lesser extent, bryophytes developed in waste dumps, despite their poor soil conditions, potentially initiating their natural restoration. However, our study did not establish causal relationships among mining, soil properties, and biocrusts. Therefore, observed differences in biocrust abundance might be influenced by uncontrolled factors, including pre-existing spatial heterogeneity, varying soil origins, or site-specific histories. • Waste dumps (7.6%) had lower soil moisture than reference sites (18.7%). • Waste dumps also had low soil organic matter (1.1%) and nitrogen content (0.04%). • Biocrust richness (25-27 spp.) and abundance (84-85%) were similar in both sites. • Bryophytes abundance was lower in waste dumps (7%) than in reference sites (13%). • Biocrusts were able to develop and potentially restore waste dumps of onyx mining.