Effects of floristics, physiognomy and non-native vegetation on riparian bird communities in a Mojave Desert watershed

1. In the deserts of the south-western United States of America, as in many ecoregions around the world, invasion of non-native plants is modifying the structure and composition of riparian vegetation. 2. Restoration of native plant species frequently proves to be ecologically and economically difficult. In the Muddy River drainage in the Mojave Desert (Nevada, USA), eradication of one the most aggressive invasive plants, Tamarix ramosissima (salt-cedar), often reduces the structural and compositional diversity of the remaining vegetation. This can have negative effects on native animals, including birds. 3. The objectives of our work were (i) to examine relationships between avian diversity and measures of vegetational diversity (species richness, dominance of non-native plants and vegetation structure [total vegetation volume]), (ii) to explore the extent to which avian community composition was associated with vegetation composition (floristics) or vegetation structure (physiognomy), and (iii) to consider the potential effects of alternative land management and ecological restoration strategies on the biodiversity of birds and other native fauna in watersheds in the arid south-western USA. 4. Species richness of all birds and of breeding birds was best modelled by total vegetation volume alone. Neither species richness of plants nor dominance of non-native plants had a statistically significant effect on species richness, abundance or evenness of birds. 5. Species composition of birds between sites was more similar when floristics was more similar, and vice versa. Species composition of birds was not correlated with physiognomy. 6. Species richness of native birds in the Muddy River drainage appears not to suffer from invasion of non-native plants, provided that the vegetational community retains sufficient structural diversity. 7. The composition of the bird community is closely related to floristics, and other taxonomic groups may exhibit different responses to vegetation structure and composition. Therefore, explicit strategies for landscape-scale management, restoration and maximization of native faunal diversity should consider how removal of invasive plants may affect physiognomy and floristics of the vegetational community as a whole.