Alien plant invasions in Mediterranean-type ecosystems lead to a decrease in native plant species richness. Studies show that invasions by plants from similar climates have a stronger impact, with Australian Acacia species causing the most significant declines in native species. Annual herbs, trees, and creepers have the greatest impact on native species richness, while graminoids have minimal effects. Shrublands, old fields, and dune vegetation experience significant declines in native species richness, while forests show insignificant changes. Studies conducted on smaller scales or over longer periods demonstrate stronger impacts of alien invasions compared to larger scales or shorter periods.