Invasive species removals and scale – contrasting island and mainland experience

Résumé

Recent years have seen large increases in the number and size of successful invasive species eradications from islands. There is also a long history of large scale removals on larger land-masses. These programmes for mammals and terrestrial plants follow the same cost-area relationship although spanning 10 orders of magnitude in scale. Eradication can be readily defined in island situations but can be more complex on larger land-masses where uncertainties defining the extent of a population, multiple population centres on the same land-mass and ongoing risks of immigration are commonplace. The term ‘complete removal’ is proposed to describe removal from an area with ongoing eff ort to maintain the area as clear, as features in many larger scale mainland programmes. Examples of complete removal to a boundary, in patches and in habitat islands are discussed. While island eradications continue to grow in scale, new legislation such as the lists of Species of European Union Concern will also drive increasing management on larger land-masses. However, these lists include large numbers of species that are already widespread. Methods are needed to prioritise species to reflect both the risks posed and the feasibility of management, including the effects of scale on cost and effectiveness.