Impacts of Gleditsia triacanthos L. (Fabaceae) on soil characteristics: insights from the free state highveld grasslands of South Africa

Abstract Invasive alien plants are one of the significant threats to ecosystems globally. These species are known to have detrimental effects, including adverse effects on biodiversity, water quality and, in some cases, soil health. Many invasive species have no adverse impact on soil health, but certain species, such as those within the Fabaceae, have distinct impacts. An invasive Gleditsia triacanthos (Fabaceae) is rapidly spreading and becoming an aggressive transformer of the temperate grasslands in South Africa. This species has several environmental impacts, its influence on soil properties in grassland biomes remains to be determined. We investigated the effects of G. triacanthos on selected soil properties across five locations within the grassland biome. At each location, soil samples were collected near the roots of G. triacanthos and at the same depth at an adjacent, uninvaded grassland. The soils collected under G. triacanthos in all the locations had significantly higher concentrations of organic C, N, P, K, Ca and Mg. Clay percentage and exchange acidity were also significantly increased under G. triacanthos , while soil bulk density and pH were decreased. Gleditsia triacanthos did not impact Zn, Mn and Cu. The results reveal the soil enrichment under G. triacanthos , which is detrimental to the biodiversity and, thus, the functioning and productivity of this vulnerable ecosystem. To prevent further impacts, management of the tree is recommended.