Palms fanning out: a review of the ecological provisioning services provided by Washingtonia filifera and W. robusta in their native and exotic settings.
Background: Dispersed by the horticultural industry, Washingtonia filifera and W. robusta have become one of the most ubiquitous ornamental palm species throughout all temperate zones. Aims: This paper systematically reviews the state of knowledge of the ecological provisioning services provided by these palms. Methods: Review of the extant literature based on a combination of systematic database searches with snowballing. Results: Globally, Washingtonia are a major urban food source for native and invasive animal species. The majority of vectors contribute little to medium-or long-range dispersal. Avian and terrestrial species with a high connective potential facilitate long-distance dispersal. The dead leaves surrounding the stem serve as habitat for numerous native and invasive species. Conclusions: The horticultural plantings of Washingtonia in areas adjacent to but contiguous with their endemic range have allowed a number of user species to expand their range, with one example (Icterus cucullatus) in excess of 1000 km. In non-contiguous areas of introduction (e.g. Europe, Middle East, South Africa or Australia) several species native to those ecosystems have adapted to feeding on Washingtonia drupes, but only few species have adapted to using Washingtonia as habitat.