Effects of grazing on seedling establishment: the role of seed and safe‐site availability

Abstract. The first objective of this paper was to assess the effects of grazing on seedling establishment of two species whose relative abundance at the adult stage is affected by grazing in a contrasting fashion. Second, we evaluated the relative importance of seed versus safe‐site availability in explaining the effect of grazing on seedling establishment. We monitored seedling establishment on a grazed area, on two areas which had not been grazed for two and seven years, and on plots which had been experimentally defoliated. The species compared were Dan‐thonia montevidensis, a native perennial grass which dominates both grazed and ungrazed communities, and Leontodón taraxacoides, an invading exotic rosette species from the Compositae family. Continuous grazing enhanced seedling establishment of both species through its effect on the availability of safe sites. Seed availability accounted for only one, but very important, grazing effect: the lack of response by L. taraxacoides to the defoliation in the seven‐year old exclosure. Its seed supply was depleted by exclusion of grazing and, consequently, its short‐term regeneration capacity after disturbance was lost. 1990 IAVS ‐ the International Association of Vegetation Science