Soil seed bank dynamics in relation to topographic position of a mixed-deciduous forest in southern New England, USA

We examined the floristic significance of soil seed banks in relation to valley, midslope and ridge sites in a 70-90-year old forest in northeastern Connecticut. A-horizon mineral soils were collected to 5 cm depth in the early spring from forest understory sites across the topography. Samples from each of the sites were exposed to full sun within a greenhouse. Records of germination were made at regular intervals over a 60-day period. These showed significant differences among sites in number of species and total number of germinants. Greatest numbers of species and germinants were recorded from valley sites and these progressively declined from midslope to ridgetop. Twenty-five different species were identified. Species were grouped into growth habits - graminoids, herbs, shrubs, trees, and vines. Over 61% of all germinants across all sites were graminoids. Seventy-four percent of all germinants in the valley sites were graminoids, with over 93% of them represented by two Sedge species, Carer glaucodea and C. lupulina. On the ridgetop sites graminoids were more evenly distributed among six different species. The percentage in each growth habit changed rank across topographic position with germinants of graminoids and trees most abundant on valley sites; herbs, on midslopes, and shrubs, on ridgetops. All germinants, except for those of the trees, Carer spp., and two herb species were weedy species that were not characteristic of the existing vegetation. Germinants of the trees, Carer spp., and herbs that were characteristic of the existing vegetation were mostly confined to soils from the valley sites. Two weedy herbs, Plantago major and Verbascum thapsus, are exotic introductions that originally came from Europe. Only one vine, Vitis aestivalis, from a midslope site germinated. Species diversity is higher on midslope sites than valleys and ridgetops. The significance of these findings in relation to site productivity and disturbance history is discussed. (C) 1998 Elsevier Science B.V.