Seed bank composition of a northeastern US tussock swamp

A seedling and sporeling emergence assay was conducted on 50 soil cores tak en from within Carer stricta tussocks (intra-tussock) and from paired, adja cent inter-tussock areas in the Hawkins Conservation Area, South Hadley, Ma ssachusetts, USA, to test the hypothesis that local heterogeneity in water levels alters seed bank composition and subsequent seedling emergence patte rns. Soil cores were sliced into 2.5-cm-thick sections and split into flood ed and drawn-down treatments. Germination of buried seeds and spores was as sessed in these treatments under greenhouse conditions for 6 months. Eighte en species emerged from both treatments combined: 17 from inter-tussock sam ples and 12 from intra-tussock samples. Pooled across sample depths and wat ering treatments, more species of grasses, forbs (exclusive of Impatiens ca pensis), and woody plants germinated from intra-tussock samples, while more pteridophytes germinated from the inter-tussock samples. Emergence of pter idophytes, grasses, and forbs was associated significantly with sample dept h. More pteridophytes germinated from samples close to the swamp surface, w hile grasses and forbs were most abundant in samples 10-20 cm below the sur face. In the drawn-down treatment, pteridophyte and forb seedlings were mor e plentiful from inter-tussock samples. In contrast, more forb seedlings em erged from intra-tussock samples in the flooded treatment. This variation i n forb emergence seems to reflect differences in species composition within and between tussocks. Twenty-two species occurred in the standing vegetati on of the study area, but only nine of these also occurred in the seed bank . The composition of standing vegetation atop and between tussocks did not differ significantly. Grasses, which dominated the seed bank, were absent f rom standing vegetation. Grasses clearly represent a persistent population of seeds in the seed bank, while forbs are more transient within the seed b ank. The depth-stratified species composition of the seed bank also suggest s patterns of temporal succession in the aboveground vegetation of this New England tussock swamp.