Factors controlling seed predation by rodents and non-native Sus scrofa in Araucaria araucana forests: potential effects on seedling establishment

Abstract

Post-dispersal seed predation can severely limit plant recruitment, but its ultimate impact could be modulated by environmental factors and by the composition of the granivore guild. Here, we analyze the relative impact of the non-native wild boar and native rodents on seed survival and seedling establishment of the mast conifer Araucaria araucana. Predation, seed survival and seedling establishment were measured at different microsites and distances from 11 isolated trees in Lanín National Park (Argentina) over a period of marked fluctuation in seed production. Wild boar consumed between 10 and 30% of available seeds on a 13-day period, threefold less than rodents. Wild boar predation was mainly affected by forest canopy composition, while microsite conditions influenced both kind of predators, with high chronic rodent predation underneath dense vegetation and moderate (but interannually variable) wild boar predation at poorly vegetated microsites. Predation by rodents was spatially clustered at the microsite scale, particularly during non-mast years; while predation by wild boar was spatially structured at a coarser scale and less modified by masting. The exclusion of wild boar increased significantly the amount of surviving seeds, resulting in higher seedling establishment in intermediate production years, but not affecting it during the mast year. At tree level, seedling establishment was negatively correlated with predation; while at stand level, cone production accounted for most of the seedling establishment variability. The current wild boar population may not be affecting the seedling establishment at population scale, probably due to minimization of its impact by the Araucaria masting strategy. However, if wild boar population numbers continue to increase, their impact may shift from individual tree scale to stand scale, threatening Araucaria forest regeneration.