Herbivory, litter and soil disturbance as determinants of vegetation dynamics during early old-field succession under set-aside

Early-successional old fields are a major component of the European landsca pe. While a range of factors governing vegetation development in old fields has been identified, empirical and theoretical studies have tended to conc entrate on plant competition as the dominant driving force behind successio n. We studied the influence of three little researched, yet inter-related, factors on the early stages of an old-field succession: litter cover, soil disturbance and herbivory. Physical and chemical techniques were used to ex clude large vertebrates and insects from experimental plots. These treatmen ts had little effect on plant recruitment. A litter-removal experiment, nes ted within the exclusion treatments, revealed a significant inhibition of f orb seedling germination by litter cover. However, the majority of seedling s died during the first month following emergence, whether or not litter wa s removed. A second experiment, involving the factorial combination of moll usc exclusion and soil disturbance, revealed that the response to disturban ce was dependent on life-history characteristics of the plants. However, th e dominant factor regulating community composition was seedling herbivory b y molluscs. Molluscs caused high rates of forb seedling mortality and promo ted the transition from a forb-dominated, to a grass-dominated community. H erbivory is often assumed to influence plant community dynamics through eff ects on competitive interactions. However, direct effects of herbivory, on the survival of seedlings, may be a significant factor structuring plant co mmunities in ruderal, or other annual dominated systems.