STUDIES ON THE FEASIBILITY OF RECREATING CHALK GRASSLAND VEGETATION ON EX-ARABLE LAND .1. THE POTENTIAL ROLES OF THE SEED BANK AND THE SEEDRAIN

1. This study is an investigation of the potential of the seed bank an d the seed rain to promote the re-establishment of chalk grassland veg etation on an ex-arable site which had not been cultivated for 10 year s. Comparisons are drawn with the composition of the seed bank as reco rded in a study undertaken close to the current site 6 years after cul tivation ceased. 2. The seed bank had the following composition: 46.6% grass seeds, 38.6% perennial forbs, 8.4% biennial forbs and 6.3% annu al forbs. In comparison, annual forbs had accounted for 49.5% of the s eed bank 6 years after cultivation ceased. The seed bank was concentra ted near the top of the soil profile and grass seeds showed a more mar ked decline in abundance with depth than forb species. However, common annual forb species mostly germinated from the lower soil strata. The common grasses and perennial forbs were species with wide ecological amplitudes, characteristic of fertilized, neutral grassland. 3. Only 2 0 of the 68 forb species recorded in the seed bank were characteristic components of adjacent ancient chalk grassland. These species account ed for less than 20% of the total forb seed bank. Only two out of 11 r ecorded grass species were characteristic of the ancient chalk grassla nd, and these accounted for only 0.3% of all grass seedlings. The gras s component of the seed bank was dominated by Agrostis stolonifera. 4. The species richness of the seed bank has increased in recent years d ue mainly to acquisition of seeds of non-annuals. However, species cha racteristic of the ancient chalk grassland have made little contributi on either to the seed bank or to the vegetation growing on the site. T hose chalk grassland species which were most abundant in the seed bank tended to be short-lived species and they occurred mainly at the marg ins of the ex-arable site, close to the adjacent chalk grassland. Even here they rarely accounted for more than 20% of the germinable seed b ank. They were strongly concentrated at the soil surface, indicating t heir deposition since cultivation ceased. 5. Agrostis spp., Phleum pra tense and Holcus lanatus accounted for over 50% of the recorded seed r ain. Of the commonly trapped species, analyses of mean dispersal bread ths indicated that forb species characteristic of the adjacent chalk g rassland would be comparatively slow invaders of ex-arable habitats. 6 . The vegetation on transects across the ex-arable site contained few of the species which occurred in the adjacent old chalk grassland. Cha lk grassland species were more abundant in vegetation at the margins o f the ex-arable site, but even here similarity indices between the ex- arable vegetation and the chalk grassland vegetation were normally bel ow 25%. 7. The slow invasion of species from the adjacent chalk grassl and into this ex-arable site, which is ideally placed for their coloni zation, suggests that seeds of such species will often need to be arti ficially introduced to prevent ex-arable sites becoming dominated by f ast-growing more weedy species. Further management would also be neces sary to prevent more weedy species subsequently invading and eliminati ng the chalk grassland species.