SEEDBANK CHARACTERISTICS OF A NEBRASKA SANDHILLS PRAIRIE

Evaluating seedbank ecology is critical for understanding plant commun ity development and successional patterns and for identifying factors regulating population dynamics. The relationships among seedbank compo sition, seedbank depth, seed dormancy, and vegetative expression were evaluated for a range site on a Valentine fine sand soil (mixed, mesic Typic Ustipsamments) in the Sandhills Prairie. Twenty soil samples we re collected at each of 2 depths (0 to 5, 15 to 20 cm) in early June 1 990 and 1991 from 12 macroplots (32 X 32 m) representing 3 range condi tion classes. A seed extraction and germination trial was conducted to determine the diversity, size, and germinability of the persistent se edbank. Seedling emergence was counted in a greenhouse, with and witho ut a 14-day prechilling(3 to 5 degrees C) stratification treatment, to characterize seedbank dormancy. Fourteen grass species, 17 forb speci es, and Schweinitz flatsedge (Cyperus schweinitzii Torr.) were identif ied in the seed bank. Two additional genera (Carer and Euphorbia) also occurred in the seedbank. Only 10 species occurred in 8 or more macro plots in both years. Aboveground botanical composition was not correla ted with (P > 0.10) seedbank species composition. More germinable seed s occurred in the 0 to 5 cm depth (P < 0.01) than the 15 to 20 cm dept h. Also, the species diversity and seed number were greater in the sha llower depth. Germination percentage was low for all types of vegetati on. Lambsquarters (Chenopodium album L.) and annual eriogonum (Eriogon um annuum Nutt) had the largest seedbanks, but germination was less th an 6%. Sand dropseed [Sporobolus cryptandrus (Torr.) Gray] and sand lo vegrass [Eragrostis trichodes (Nutt.) Wood] were the most abundant per ennial grasses and accounted for about 60% of the germinated seeds. Pr echilling increased seedling emergence of grasses CP < 0.01), forbs (P < 0.01), and grass-like species (P < 0.01). Perennial grasses emerged first, forbs later, and grasslike species exhibited a bimodal emergen ce pattern. Based on germination percentage and emergence data, sand d ropseed has the potential to colonize openings in the Sandhills prairi e, possibly to the exclusion of many annuals occurring in the seedbank .