Mowing and management to reduce nutrient levels have often been successfully used to restore species-rich grasslands in various parts of Europe. However, such treatments have failed to restore the species-rich Central European mountain grasslands dominated by Polygonum bistorta. P. bistorta builds an extensive underground rhizome system that monopolizes available nutrients in these nutrient-poor grasslands, enabling this species to persist at high densities even in the presence of mowing. Therefore, we tested a restoration approach using a factorial combination of fertilization and mowing, as well as a litter removal treatment. The experiment was run over 5 years and species composition response to these treatments was recorded at two spatial scales.
Mowing suppressed flowering and cover of P. bistorta and promoted target grassland species and richness. Fertilization prevented nutrient impoverishment and increased height and dominance of the broad-leaved grasses with which many species-rich grassland herbs could coexist. The additive effect of the mowing/fertilization treatments was strong enough to act as a driver of P. bistorta suppression and associated community change. The litter removal treatment, however, had little effect on plant composition.
The experiment demonstrates that in nutrient-limited grasslands, increasing nutrient levels in addition to mowing to manage competition for light can be used to control dominants. This contrasts with restoration of systems where after abandonment increased nutrient levels lead to the establishment of tall dominants that suppress other species by competition for light.