Temporal and spatial variation of the vegetation seed bank and seed-rain in set-aside and adjacent habitats
In this study set-aside development was monitored (1989-1992) at Aldroughty Farm, Morayshire as part of an integrated project looking at plant and animal dynamics in set-aside, crop and semi-natural habitats. The vegetation, seed bank and seed rain were monitored in adjacent set-aside, semi natural and cropped areas. Initially set-aside vegetation consisted of annual arable species, but wind dispersed species and longer-lived perennials invaded rapidly. This process was more rapid on smaller plots and ingress of perennials occurred more quickly closer to the field margin. There was little invasion from adjacent semi-natural habitats and the field margin was the most important source of colonising species. Cropped areas were not significantly affected by adjacent set-aside. Seed banks were analysed using germination and extraction techniques which gave different estimates. Highest densities were found on set-aside land indicating the problems associated with returning set-aside to agricultural production. Changes in the seed bank were less apparent than in the vegetation, but within-year variation was great and carryover of seeds from October to March was low. The seed rain was monitored using gravel traps. Densities were highest on set-aside and lowest in the crop and wood. Individual species exhibited different phenologies in seed shedding, but peak deposition coincided with cutting. Dispersal from the set-aside into the crop was very low and dispersal distances were small. Vegetation and seed rain were similar in species composition in the set-aside areas. Although the seed rain was similar to seed bank samples taken immediately after seed shed, a large proportion of seeds did not enter the seed bank. Set-aside land did not develop into semi-natural habitat, however species diversity increased and the land provided a food source and an undisturbed habitat for animals. The real concern is the return of set-aside land to agricultural production, because of increased seed bank densities.