Methods of enhancing botanical diversity within field margins of intensively managed grassland: a 7-year field experiment.
Abstract
Increased intensification in agricultural grasslands has led to well-documented declines in the associated flora. Manipulation of field margins for biodiversity enhancement in arable systems has been extensively investigated. However, there is a paucity of corresponding long-term research within intensively managed grasslands. We investigated a combination of establishment and management methods to enhance botanical diversity of newly established field margins in intensively managed grasslands. Three methods of field margin establishment were investigated including fencing, natural regeneration by rotavation, or seeding with a wildflower mixture. Subsequent sward management by either grazing or mowing was tested at three margin widths. Success of establishment was addressed in terms of persistence of species richness, plant community composition and incidence of noxious weeds. Seeding with a wildflower mixture was the most successful establishment method to enhance plant species richness and this effect persisted throughout the 7 years of the experiment (x¯16.4±0.43 SE plant species richness per 1×3 m2 quadrat). Mown (x¯=6.01±0.30 SE) and rotavated (x¯=9.7±0.34 SE) treatments contained significantly fewer plant species; grazed controls contained 9.83±0.24 species. Grazing led to a significant, but modest increase in species richness in fenced and rotavated plots compared to the mowing treatment, but had no effect in seeded plots. Grazing also led to an increased frequency and cover of competitive grasses in the seeded treatment. Although margin width was not found to significantly influence species richness, there was increased herb cover and reduced abundance of noxious weeds in the wider seeded margins. Synthesis and applications. The choice of establishment method and subsequent management of grassland field margins significantly affected their conservation value. The botanical diversity of margins within intensively managed pasture can be enhanced by sowing wildflower seed mixtures. This diversity can be maintained over time through appropriate management, i.e. either the reduction of high grazing pressure by seasonal fencing, or annual mowing. Management approaches that involve minimal change are currently adopted in many agri-environment schemes (such as fencing and/or the cessation of nutrient inputs) but did not produce swards of conservation value in this study.