FLORA COMPOSING UNDERSTORY VEGETATION OF FORMER BAUXITE MINING LAND IN TANJUNGPINANG, RIAU ISLANDS, INDONESIA

<p><strong>Background. </strong>The aim of this research is to identify plant species that constitute the vegetation and species abundance in ex-bauxite mining land in Tanjungpinang City, Riau Islands Province, Indonesia. <strong>Objective</strong>. To identify vegetation composition and species abundance on ex-bauxite mining land. <strong>Methodology </strong>A nested plot sampling method was used to randomly identify the species at two ex-bauxite mining sites (Dompak and Senggarang) and a non mining site in Senggarang. Each site, measuring 1x1 meter, with 12, 14, and 12 plots were also examined using the understory plant samples. Furthermore, observations were made on the morphological characteristics of plants to determine the herbarium preparation process, identify the species, and validate the scientific names of plants. <strong>Results. </strong>The research found that understory plants in the three sites consisted of 17 families with 24 species with the Cyperaceae family contributing five more species than any other families. The three species with the highest importance value indices at each site were: at Dompak namely, Poaceae (51%), <em>Waltheria indica </em>(26.50%), and <em>Dicranopteris linearis </em>(21.80%); at Senggarang, <em>Palhinhaea cernua </em>(37.10%), <em>D. linearis </em>(37.02%), and Poaceae (36.37%); and the not a former bauxite mine site in Senggarang is <em>D. linearis </em>(70,00%), Poaceae (64.00%), and <em>Melastoma malabathricum </em>(23.07%). The Sorensen similarity index values for the three locations were 46.7% for the Dompak and Senggarang sites, 41.7% for the Dompak site and the non-former bauxite mining site, and 50% for the Senggarang site and the non-former bauxite mining site, respectively. <strong>Implications. </strong>Morphological species identification and herbarium preparation were used to identify and validate the vegetation composition on the former bauxite mining land in Tanjungpinang. The data obtained is valuable for understanding the natural recovery patterns of the land and provides insight into species suitable for further rehabilitation in the Riau Islands. The result showed that invasive species such as Poaceae and <em>Dicranopteris linearis </em>should be prioritized in revegetation programs. The research also addresses a gap in scientific knowledge regarding critical species for the successful rehabilitation of degraded lands. <strong>Conclusion. </strong>The research found that understory plants in the three sites consisted of 17 families with 24 species. The importance value index at each site was 51% for Poaceae (at Dompak), 37.10% for <em>P. cernua </em>(at Senggarang), and 70% for <em>D. linearis </em>(at non-former bauxite mine site in Senggarang). The Sorensen similarity index values for the three sites were 46.7%, 41.7%, and 50% for the Dompak and Senggarang sites, Dompak, and the non-former bauxite mining sites. </p>