Studies of the feasibility of re-creating chalk grassland vegetation on ex-arable land. II. Germination and early survivorship of seedlings under different management regimes.
Germination and establishment of the chalk grassland perennials Pimpinella saxifraga, Scabiosa columbaria, Plantago media and Achillea millefolium were compared in undisturbed chalk grassland, and in ex-arable land where the vegetation was either uncut, cut and maintained at a height of 3 cm, or completely cleared. Virtually no germination was recorded for all four species in uncut quadrats on ex-arable land. Germination of Achillea and Plantago was highest in cleared ex-arable and that of Pimpinella highest in cut ex-arable. The ratio of germination in cleared and cut ex-arable increased as size of seed decreased between the species. Germination of the largest-seeded species, Pimpinella, was not significantly different in cut ex-arable and in laboratory conditions. Differences in seedling survival were sought between the vegetation types, using concurrently recruited cohorts of seedlings of each species. The significant results were consistent for all species; overall seedling survival was highest in cut ex-arable, intermediate in cleared ex-arable and lowest in chalk grassland. Analysis of residuals revealed that the greatest differences in proportional survivorship between treatments occurred during the first 2 weeks of cohort life, regardless of the date of cohort recruitment, suggesting that vegetation type is a more potent determinant of mortality risk than climatic conditions during this early period of growth. Comparisons of residuals also demonstrated that survivorship decreased from cut ex-arable to cleared ex-arable to chalk grassland. Sites where vegetation is short may be more favourable for seedling establishment than uncut sites because of lower competition, and better than cleared sites because the short vegetation cover moderates temperature fluctuations and retains more soil moisture. It is concluded from this and related studies, that sowing suitable species, and implementing a management regime which reduces, but does not remove all vegetation cover, will maximize the chances of establishing chalk grassland species on ex-arable sites. Management prescriptions which include mowing and grazing on ex-arable land will make the best use of the environmental opportunities, presented by agricultural extensification, to restore ecologically valuable communities.