Restorative seeding controls annual invasive species, but perennials can thrive in the long term despite treatments in sand grassland restoration

Abstract

Biodiversity loss caused by invasive alien species is a major problem in planetary perspective. Ecological restoration is an important tool to counteract invasions, but invasive species may negatively affect restoration if present in the landscape. We investigated long-term changes in annual and perennial invasive alien species abundance in three sandy grassland restoration experiments. We evaluated the dependence of annual and perennial invasive species abundance on initial restoration intervention, invasive species propagule pressure from the surrounding landscape, and time since interventions. Restoration interventions (seeding, mowing and carbon amendment) were conducted at a total of eight sites in the Kiskunság region of Hungary. The interventions took place between 1995 and 2003 and were monitored for 17–25 years. To assess invasive propagule pressure around the experimental sites, total shoot numbers in adjacent 1 m by 1 m plots along 100-meter-long transects were counted in 2020–2021 from the center of the eight experimental sites. Invasive propagule pressure within a 100-meter buffer did not explain changes in the abundance of annual and perennial invasive species. The cover of annual invasive species has mostly decreased over time, and treatment (mainly seeding) could accelerate this process. The cover of perennial invasive species increased over time irrespective of applied treatments and landscape invasive propagule pressure. Our research showed that seeding with native species is an effective tool for restoring sandy grasslands and preventing the spread of annual invasive species, but our toolbox for preventing perennial invasion in grassland restoration is limited.