Landscape-level persistence and distribution of alien feral crops linked to seed transport

Without anthropogenic seed input to found new populations, Brassica spp. are unlikely to persist in this landscape beyond ten years. To avoid overestimating the extent of naturalised populations over time it is important to account for local population extinctions. The abundance of feral crops that occur as casuals in the landscape, along with other aliens that are maintained by external seed inputs, could be controlled by managing propagule sources. In themselves, casual populations are unlikely to facilitate gene flow or act as sources of further population spread.