Invasive Milk Thistle (Silybum marianum (L.) Gaertn.) Causes Habitat Homogenization and Affects the Spatial Distribution of Vegetation in the Semi-Arid Regions of Northern Pakistan

Abstract

Global biodiversity management is of concern due to invasive plant species that dramatically disturb the native communities causing biological homogenization. Therefore, the present research investigated the impacts of Silybum marianum, an aggressive invasive alien species, on communities’ diversity and environmental variables in Khyber Pakhtunkhwa, Pakistan. Phytosociological characteristics and diversity indices of the communities were sampled in seventy-five sites using the quadrate method. These sites were categorized based on invasion intensities, i.e., fully invaded sites with a 100% importance value index of the selected species, severely invaded sites with >60% of IVI, and partially invaded sites with >30% of the chosen species. The community composition significantly changes with changes in invasion intensity. Similarly, S. marianum invasion has a pronounced impact on the community’s diversity showing significant differences among the three categorized groups (p < 0.05). The canonical correspondence analysis revealed 29.9% variance where soil texture, nutrients, and elevations were influential variables in maintaining the community’s structure and composition. The study concludes that S. marianum dominated well-established communities in the existing soil and environmental variables; therefore, it was found to be influential in disturbing the native communities and may severely harm the crop plant and agricultural system in the future.