As the mean annual temperature of northeast North America rises as a component of global climatic change, it is important to understand how the predominant vegetation of the region will be affected. Existing experimental and correlative evidence from field sites suggests that temperature rise will significantly modify soil processes, nutrient availability, and plant growth. We investigated the responses of temperate deciduous forest vegetation to artificial soil warming at 20 sampling dates during the 1992 and 1993 growing season. We explored whether soil warming measurably altered growth and the temporal dynamics of leaf and fruit production in 26 species of three contrasting plant growth forms (herbaceous perennials, shrubs, and canopy trees). We hypothesized that soil warming would exert differential effects on emergence, phenology, leaf expansion rates, growth, photosynthesis, and vegetative and sexual reproduction among species, with implications for changing community structure in these forests. Timing of leaf emergence and flower production was not affected by treatment in saplings; however, mature trees and shrubs leafed out slightly earlier and in larger numbers in heated plots. Soil warming significantly enhanced relative growth in stem diameters of woody plants, especially shrubs, in 1992. This effect was less pronounced in 1993. Species richness was lower in heated plots than in intact control plots in both years; disturbed but unheated control plots showed the lowest species richness of all plots. Changes in relative abundance of herbaceous species from 1992 to 1993 were not significantly affected by treatment. Rank abundances of species were more stable between years in the heated and disturbance-control plots than in the intact plots. Total density of herbaceous species was highest in heated plots during April and May of both years, reflecting greatly accelerated emergence of two dominant species, Maianthemum canadense and Uvularia sessilifolia, due to heating. Stem densities declined later in the season, however, and were lower in the heated plots than in the intact control plots. Photosynthetic rates of the two dominant herbaceous species were not affected by soil warming. Of all life forms, herbaceous species (spring ephemerals) were most sensitive to soil warming. Their early appearance could influence carbon and nitrogen acquisition by later-emerging woody species in these deciduous forests. Early leaf-out in woody shrubs and trees can also influence season-long dynamics of water use and carbon sequestration in forests. Soil warming may select for certain tolerant species and reduce species richness in temperate deciduous forests.