Biological invasions limit the effectiveness of land abandonment as a conservation strategy

Context: Agricultural intensification has led to widespread biodiversity loss. The concepts of rewilding and land sparing suggest that agricultural land abandonment may reverse biodiversity decline in intensively managed agricultural areas. For example, the Green Deal policy in the European Union mandates the abandonment of 4% of agricultural land for nature conservation. Objectives: We examined if scientific literature describes connections between land abandonment and concepts related to land abandonment such as rewilding, land sparing with biological invasions. Then, we studied if invasion of alien plant species may undermine potential benefits for local native biodiversity from land abandonment. Methods and results: Our literature review suggests that land abandonment is often linked to alien plant invasions (314 articles) however current conservation strategies implementing land abandonment such as land sparing and rewilding often do not consider the risk posed by the invasion and colonization of the abandoned land by alien plant species. Using a case study of alien goldenrods Solidago spp. we showed via meta-analysis that abandoned agricultural land is often dominated by these invasive plants in Central Europe. Our results show that goldenrod invasion on abandoned land leads to higher biodiversity declines than extensive agricultural management on uninvaded land. Moreover, our simulation study showed that biodiversity did not increase with the share of abandoned fields in a landscape if they are invaded by alien goldenrods. Conclusions: The negative effects of alien species invasion on biodiversity, ecosystem services, and in consequences agricultural yield may limit the effectiveness of land abandonment as a conservation strategy. Hence, we argue that strategies such as agricultural rewilding that include extensive land management rather than abandonment alone, may be a better to safeguard biodiversity in agricultural landscapes in the presence of invasive alien plant species.