Effects of emergence time on survival and growth in an early old-field plant community.

The time at which plants emerge from the soil is shown to be correlated with both survival and growth in each of four years in a plant community emerging after yearly plowing. For all seven species investigated, earlier emerging individuals generally had both a higher biomass and probability of survival. There were differences among species in the effect of emergence time on biomass, with the growth of upright, annual species being more suppressed by later emergence than the growth of other species. No significant differences were found among species in the effects of emergence time on survival. It was expected that differences among species in the effect of emergence time on fitness might lead to a correlation between the patterns of emergence time and species characteristics such as growth form or lifespan. Mean emergence times did vary significantly among both the seven species and the four years of the study. However, there was no correlation between emergence time and species lifespan, growth form, abundance, or competitive ability. The lack of a correlation between the selection pressure on species and their emergence time could be due low heritability, insufficient time for selection and evolution, and/or selection on correlated characters.