Subterranean Seed Production and Population Responses to Fire in Amphicarpum Purshii (Gramineae)

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Abstract
(1) Early in the summer growing season, annual peanutgrass (Amphicarpum purshii) rapidly forms a seed bank by producing large, subterranean seeds. This study tests the hypothesis that, since this species grow mostly in the fire-prone Pine Barrens of New Jersey [USA], this adaptive trait might enhance population survival after a fire. (2) At two sites in southern New Jersey, plots containing either Andropogon litter (site A) or perennial herbs (site B) were burned on 28 October 1983, and subsequent performance of Amphicarpum plants monitored during the 1984 growing season. (3) At both sites, only seedlings from subterranean seeds were found. At site B where the burn removed perennial herbs, plants had significantly greater biomass and reproductive output than those in paired unburned plots. (4) In an Amphicarpum population at Atsion, New Jersey, where a pitch forest had burned in the previous season, plants in the burned area over 1 m tall and produced 50 times as many aerial spikelets as those in an adjacent unburned forest. (5) Dry heat treatments of subterranean seeds significantly reduced germinability at temperatures as low as 60 .degree. C. (6) The temperature in experimental burns was 85 .degree.C at the soil surface, but high temperatures did not penetrate deeper than the top 1 cm of the soil. The subterranen seed placement of Amphicarpum occurs at an average depth of 3 .cntdot. 5 protected from the potentially detrimental effects of high temperature at and above the soil surface.