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Using local hay seed for suppressing invasive alien plants in grasslands

When putting into practice restoration ecology principles to combat Invasive Alien Plant Species (IAPS) the first question to ask ourselves is: spontaneous succession or technical reclamation? It is widely recognised that IAPS are a serious threat to native species diversity and can alter ecosystem services such as decreasing habitat quality. In particular, alien herbaceous species often colonise degraded or disturbed grassland areas such as fallow agricultural areas, abandoned fields and natural/semi-natural grasslands subject to fire, mowing and pasture. Here, the establishment of IAPS can alter both biotic and abiotic factors such as nutrient cycling and competition. In addition, IAPS may make it problematic to restore native grasslands since they may rapidly establish themselves at the expense of native plants (Tjelmeland, Fulbright, and Lloyd-Reilley 2008) thereby impeding the growth of native plants by competition mechanisms or by modifying succession trajectories (Simberloff, 2010). Once a grassland is subject to biological invasion, the aim is to try to restore the area to its pre-invasion biodiversity levels and ecosystem functions (Reid et al. 2009). Generally, there are two main, but different, strategies that are employed: a) spontaneous succession (passive restoration) or b) technical reclamation (active restoration) followed-up by site management (mowing) for the control or suppression of IAPS (Prach and Hobbs 2008; Gentili et al. 2017). After the mechanical removal of IAPS, most land managers leave invaded lands alone to allow natural succession to restore native plant communities (Prach and Pysĕk 2001). However, during the first phases of grassland restoration, field observations have frequently highlighted the inability of native species to furnish adequate amounts of propagules relative to the high propagule propensity of IAPS. This suggests that, in the short-term, passive approaches to restoration may be unsuitable to promote the reestablishment of native-dominated communities and avoid IAPS re-invasion (Schuster, Wragg PD, and Reich 2018). Although good examples of passive recovery of grasslands have been reported (e.g. Řehounková and Prach 2008), in cases where highly invasive IAPS are present, we support the idea that technical reclamation should be the preferred option. Indeed, actively filling empty or degraded spaces, that might otherwise be colonised by IAPS, can accelerate the natural dynamics of native species and aid the recovery of ecosystem functions (Gilardelli et al. 2016; Gentili et al. 2017).