Effects of microsite disturbances and herbivory on seedling performance in the perennial herb Helleborus foetidus (Ranunculaceae)

Abstract

The impact of small scale disturbances on the early seedling performance components of Helleborus foetidus (Ranunculaceae) was studied through a transplant experiment. The aims of this study were: (i) to determine if the herbivory pattern depends on microsite disturbance, by the analysis of two of its components, seedling encounter (the probability of at least one seedling being harmed) and seedling exploitation (the proportion of seedling tissue removed once encountered); (ii) to test if seedlings of H. foetidus in disturbed microsites will survive in a greater proportion than seedlings in undisturbed microsites; (iii) to investigate if seedling survival is correlated with the degree of herbivory. Microsite disturbances had a large effect on the herbivory pattern. Seedlings growing in undisturbed vegetation had a 2-fold higher likelihood of being grazed and suffered 1.38-fold higher damage than those growing in disturbed plots. At the end of this experiment, after fourteen months, only 10.4% of the seedlings transplanted were still alive due to seedling desiccation, but no differences on seedling survival were found between disturbed and undisturbed plots. The effect of herbivory and the interactive effect of herbivory and disturbance on seedling survival only reached statistical significance dependent upon site. We concluded that although small scale disturbances had a large impact on herbivory patterns; they had only a minor role in the early seedling survival of H. foetidus. Only locally, small scale disturbances showed an effect on seedling survival through herbivory. Abiotic factors like summer drought and spatial variations determined the early survival of H. foetidus seedlings to a major extent.