Dynamics in vegetation and seed bank composition highlight the importance of post‐restoration management in sown grasslands

Abstract

Sowing grasses supports the rapid development of a closed perennial vegetation, which makes the method universally suitable for fast and effective landscape-scale restoration of grasslands. However, to increase their diversity and to create a natural-like species-rich grassland is a challenging task. Understanding the role of seed bank compositional changes and vegetation dynamics can help to design management regimes that support the establishment of target species and suppress unwanted weeds. Our aim was to reveal the effect of post-restoration management on the vegetation and seed bank dynamics in grasslands restored in one of the largest European landscape-scale restoration projects. Eight years after restoration, we sampled the vegetation and the seed bank in 96 quadrats located in 12 restored grasslands in the Great Hungarian Plain. In each grassland stand, we studied and compared a mown (mown from Year 1 to Year 8) and an abandoned plot (mown from Year 1 to Year 3 then abandoned from Year 4 to Year 8). Mown and abandoned plots showed divergent vegetation and seed bank development. Abandonment led to the decline of sown grasses and higher cover of weeds, especially in the alkaline grasslands. Our study underlined that the developing seed bank had a limited contribution to the maintenance of biodiversity in both grassland types. We found that 5 years of abandonment had a larger effect on the seed bank than on the vegetation. We stress that long-term management is crucial for controlling the emergence of the weeds from their dense seed bank in restored grasslands.

The present and future of grassland restoration

“…Key issues explored in the Special Issue include grazing (Blackburn et al 2021 b ), fire, mowing, land‐use legacies (nitrogen deposition, weed invasion), soil seed banks (Valkó et al 2021), and abandonment of disturbance (Hernandez et al 2021; Price et al 2021; Reis et al 2021; Valkó et al 2021; Blackburn et al 2021 b ). Although restored grasslands have a disturbance requirement, optimal management may differ in restored grasslands from reference sites due to differences in species composition, land‐use legacies, weed invasions, or other factors.…”

“…Here, the optimal management to reduce exotics and increase native richness was hoeing, and though other techniques reduced exotic cover, they did not meet the restoration goal of also increasing native species richness and cover. In restored grasslands, Valkó et al (2021) demonstrated that ongoing disturbance management was needed to maintain cover of sown target species and reduce weeds. Here, remnant grasslands were less dependent on management, confirming differences in restored compared to remnant sites.…”

“…Price et al (2021) concluded that grazing‐sensitive species are likely lost both above‐ and belowground with a long legacy of stock grazing, and fragmentation reduces dispersal opportunities. Valkó et al (2021) found that the seed bank had limited potential to maintain richness of restored grasslands and tended to be dominated by weeds. Hence, a common message is that disturbance management alone is unlikely to lead to positive outcomes if native seed banks are exhausted.…”

“…Many of the papers in this Special Issue highlight the importance of long‐term management and monitoring to determine optimal management strategies. In most cases, abandonment of management negatively affected restored grasslands compared to grazing, fire, and/or mowing (Hernandez et al 2021; Price et al 2021; Reis et al 2021; Valkó et al 2021). Hence, restoration projects should ensure that resources are available for ongoing management at the planning stages.…”

Efforts at the beginning pay off: sowing grasses and forbs simultaneously supports restoration of species-rich grasslands and improves weed control in ex-arable land

“…high nutrient availability) and biotic (i.e. low competitive pressure) ltering in abandoned croplands allows the establishment of weedy vegetation from the weed-contaminated soil seed bank [21,22,23] . Weed encroachment provides ecosystem disservices that can also affect the neighbouring natural habitats and agricultural elds.…”