Identification of indicator species at abandoned red mud dumps in comparison to residential and forest sites, accredited to soil properties

Plant community structure studies on derelict sites are providing significant insights into vegetation dynamics to ensure the success of future revegetation projects in such areas. Therefore, the present study was conducted to evaluate the changes in soil physico-chemical and biological properties at abandoned red mud dumps (RMD) compared to residential (RS) and forest (FS) sites, coupled with their consequent impacts on the plant community structure. An attempt was also made to identify the indicator species that thrive only under unfavourable red mud conditions. Soil at RMD showed relatively high bulk density, alkalinity, salinity and exchangeable sodium percentage along with poor nutrient status and low microbial activity. Though toxic metals (Cd, Cr and Pb) were higher at RMD, their phytoavailabilities were lower compared to FS site. Number of herb-, shrub- and woody species at RMD were although low, but a significant number of species were acclimatized to the unfavourable soil conditions. Shrub species were maximally affected at RMD, followed by woody- and herbaceous species. Important value index of sensitive species was low while that of tolerant species was higher, and was accredited to altered soil properties. Presence of invasive species such as Acacia nilotica, Caesalpinia bonduc, Stylosanthes scabra and Urena lobata at only RMD may be used as an indication for high toxic metal contamination along with high alkalinity, salinity and poor nutrient contents. Principal component and canonical correspondence analyses revealed that woody and herbaceous species were mainly affected by soil alkalinity, salinity, exchangeable cations, bulk density, porosity, moisture content and phytoavailable metals. Shrub species were primarily influenced by soil organic carbon, nitrogen, available phosphorus, bulk density, porosity, moisture content, soil biological parameters, total (Fe, Mg, Cd, Cr and Pb) and phytoavailable metals. Domination of herbaceous species in the plant community indicated their tendency towards a definite selection strategy in response to altered soil properties. The identified tolerant herbaceous species may be suitable candidates for future red mud reclamation strategies.