A field investigation of germination from the seed bank of a chalk grassland ley on former arable land.
Abstract
The role of the seed bank and seed rain as an inoculum for the establishment of vegetation was investigated on permanently exposed soil and on soil with a vegetation cover developing after disturbance at a former arable chalk grassland site in Sussex. Germination was compared with that observed from soil samples under greenhouse conditions. On plots with permanently exposed soil surfaces, forb species showed spring germination peaks and their small seed banks were rapidly exhausted. Only a few grass species, including Holcus lanatus and Festuca ovina germinated; their numbers peaked in autumn. Germination overall was dominated by seeds of weed species of arable cultivation. On plots with recovering vegetation, forbs showed a large spring germination peak and a smaller autumn peak. On both plot types there was a marked flush of germination immediately after soil disturbance. Many arable weed species showed peak germination in spring. For several species the peak germination period was delayed beneath a developing vegetation cover. Germination in the greenhouse exceeded that on exposed plots and on plots with recovering vegetation by 15 and 44 times, resp. Rank orders of abundance of germinating species were not statistically different under the 2 sets of field conditions, but both differed significantly from that observed under greenhouse conditions. It was therefore concluded that assessing the likely course of vegetation development in the field by extrapolating from seed banks germinated under greenhouse conditions is likely to produce erroneous conclusions. In the field, germination of species characteristic of chalk grassland vegetation was limited to minor components of this vegetation type with small seed banks and germination patterns showing no response to disturbance. In the absence of appropriate seed additions, there is little potential for re-establishment of chalk grassland vegetation from the seed bank and seed rain; former-arable sites on chalk soils are likely to become rapidly dominated by weed species of arable cultivation.