The effect of timing and amount of leaf removal on survival,growth and reproduction in the perennial herb Sanicula europaea L.

In Sweden the deciduous forest perennial Sanicula europaea L. (Apiaceae) is frequently subjected to leaf loss due to cattle grazing and trampling. In a two-season field experiment, the effects of the extent, timing and repetition of leaf removal on survival, growth and reproduction in S. europaea were examined. Removal of vegetative tissue in S. europaea reduced future survival, growth and flowering probabilities. The magnitude of these effects depended both on the extent and the timing of the season of the leaf losses, as greater leaf losses had more negative effects than moderate and early removals had more negative consequences than late. Moreover, the probability of an individual to regrow the same season after severe losses was higher when losses occurred early in the season than when they occurred late. And, those defoliated early that did regrow, did so to a larger extent than those defoliated later. Experimental responses were more pronounced after a second year of leaf removals, indicating that repeated herbivory exhausts resources. Thus, herbivory causing losses in vegetative tissue will affect the performance of S. europaea. However, the impact depends on the extent and timing of the leaf losses. This should be considered in managing policies and cattle should, if possible, not be introduced early in the growing season.