Assessing the influence of riparian vegetation structure on bird communities in agricultural Mediterranean landscapes

Natural vegetation has been lost and fragmented in agricultural landscapes worldwide, due to the intensive land use activities. This is also true for riparian ecosystems, where agricultural practices have simplified their structure with significant cascading impacts on wildlife diversity. In this study, three representative Mediterranean riparian habitat types within an agricultural matrix landscape were studied to assess their importance for bird communities. The riparian habitat types had deciduous trees and were with: (a) natural vegetation along a torrent (NaT), (b) natural vegetation along a stream (NaS) and (c) plantation along a stream (PlaS). Three point count surveys were conducted to identify and count the birds within 15 sites in each habitat type during the bird breeding season of 2011. In addition, 11 vegetation structure variables around each point were measured. The canopy cover of the overstory and understory trees, the mean height of the overstory and midstory trees and shrubs, and the percentage of herbaceous vegetation, explained the spatial distribution patterns of the 35 bird species recorded in the study, and the structure of their communities in each riparian habitat type. The NaT was the most diverse habitat type in terms of bird species. However, the value of NaS and PlaS should not be neglected since they supported different bird communities and indicator species compared to the NaT. In Mediterranean riparian areas, by maintaining a complex vertical structure of the riparian vegetation, bird species number and diversity can be enhanced, while targeted riparian management can result in desirable communities or species, depending on their requirements.