The Promotion of Grassland Forb Abundance: A Chemical or Biological Solution?

Techniques that increase the biodiversity value of species-poor grassland are required if conservation targets aimed at reversing the decline in species-rich grassland are to be met. This study investigated the diversification of swards dominated by Lolium perenne by testing the efficacies of two treatments applied to reduce competitive exclusion of species introduced as seed. The ‘biological’ treatment was the addition of the hemiparasitic plant species Rhinanthus minor, whilst the ‘chemical’ approach was the application of a selective graminicide, fluazifop-P-butyl (Fusilade 250EW). Changes in plant community composition were monitored for a period of 2 years. Values of plant species richness increased significantly between years regardless of treatment, but to a greater extent in plots sown with R. minor. The number of established sown species and their cover values were also significantly greater in association with R. minor. Fluazifop-P-butyl had no significant effect on species richness and tended to promote unsown species rather than those introduced as seed. Overall, the R. minor treatment was associated with the greatest impact on sward composition, facilitating establishment and development of the introduced species and promoting forb abundance.