Seedling emergence and early survival of Carduus spp. in three habitats with press and pulse disturbances

Species may reach novel habitats through dispersal but nevertheless be restricted in their establishment at different life history stages by local conditions. However, disturbances may alter local conditions within a habitat and hence change establishment outcomes. We investigated the establishment of two non-native weeds of pastures and roadsides, Carduus nutans and Carduus acanthoides, in three contiguous habitats (abandoned pasture, forest edge, and forest) under three disturbance treatments: no disturbance, initial disturbance only (pulse disturbance; i.e., temporary), and initial disturbance with weeding (press disturbance; i.e., sustained). For both species, establishment was not limited by seedling emergence in any habitat, although emergence in the pasture and forest edge relied heavily on disturbance. Combined emergence and survival in the pasture and forest edge were also significantly increased by disturbance, but disturbance had no effect in the forest, where seedlings were unable to survive. Our results show how the spread of a species into different habitats may be limited at different life history stages under different disturbance regimes.