Growth and fate of individual plants in a natural self-thinning stand of Impatiens pallida located along a disturbed forest edge in SE Pennsylvania were followed from canopy closure to onset of flowering. Mortality in the primary study population was 25%. Lodging was an important cause of death. Smaller plants were more likely to lodge and to suffer herbivore damage. Lodging, independent of plant size, accounted for 16% of mortality; effects of herbivory on mortality (independent of plant size) were not significant, however. Death caused by lodging in a natural self-thinning population supports the hypothesis that biomechanical constraints may have substantial effects on self-thinning relationships and patterns of size structure change in herbaceous plant populations. A decrease in above-ground biomass occurred in 21% of surviving plants in the main study population, but 88% of the surviving plants displaying negative growth flowered by the end of the study. Growth curves were approximately linear over the course of the study period. Survival of plants with negative growth affects the function relating biomass (B) to density (D) and the function relating size inequality to mean plant mass over the course of self-thinning. Had these plants died during the study period, the observed log B-log D slope (-1.73) would have been very close to the mean thinning slope observed across many species (-0.85). Because many non-growing and shrinking plants survived, size inequality did not decrease during self-thinning. -from Authors