Long-term study reveals Native seeding controls annual, but not perennial, invasive plants in sand grassland restoration

The HUN-REN, CER-IEB Restoration Ecology Research Group monitored vegetation changes over 17-25 years across eight restoration sites, subject to different restoration interventions: seeding with native species, mowing, and carbon amendment. The goal was to understand how these treatments influence the abundance of annual and perennial invasive alien plants over time, and how abundance of invasive species in a 100 m buffer affects invasion dynamics at restoration sites.

The results were promising for annual invaders. In most cases, their cover declined over time, especially when native seeding was applied. Seeding proved to be the most effective treatment in suppressing these fast-spreading, short-lived species. However, the picture was different for perennial invaders. These species continued to increase in cover over the decades, regardless of which restoration techniques were applied or the abundance of invasive species within a 100-meter radius of the sites.

Surprisingly, the study found that immediate local invasion pressure had little explanatory power—suggesting that broader landscape-scale processes and long-distance dispersal may play a more important role in shaping invasion outcomes. Mowing, although often used in restoration to control shrub, weeds or invasive species, was found to potentially facilitate the establishment of invasives by opening "colonisation windows" for opportunistic species already present in the landscape.

The authors emphasize that current restoration approaches are not enough to address the long-term threat posed by perennial invaders. Once established, these species are notoriously difficult to eradicate, and their increasing dominance can undermine biodiversity and the success of ecological restoration. This highlights an urgent need for more proactive, species-specific strategies that address the life history traits and dispersal mechanisms of problematic perennials.

Ultimately, the study calls for a shift in restoration planning—from a site-based perspective to a more integrated, landscape-level approach. Effective grassland restoration must consider not only what happens within the target area, but also the broader ecological context: the availability of native and invasive propagules, the disturbance regime, and the long-term resilience of native communities.