Mixing-in native thorny shrubs greatly improves the habitat quality of short rotation coppice strips within a modern agroforestry system for breeding birds

Abstract

Silvoarable agroforestry systems (AFS) with short rotation coppice strips (CS) are novel land-use systems that combine fast-growing trees with croplands to simultaneously produce woody biomass and arable crops. Since their effects on biodiversity remain underexplored, we studied nesting site selection and breeding success of tree- and shrub-breeding birds in three different CS variants, located on an AFS experimental site in northern Germany: CS-C (poplar clones only), CS-A (aspen trees and poplar clones) and CS-E (native woody species and poplar clones). Thereby, the study focused on the question of whether CS can be enhanced for breeding birds by integrating native woody plants that typically grow in hedgerows (variant CS-E). CS-E significantly outperformed CS-C and CS-A, hosting two-thirds of all nests, 70 % of breeding attempts, and two-thirds of successful broods, despite comprising only one-third of the CS area. Native woody plants, covering only about 10 % of the total CS area, accounted for nearly 70 % of all nests and two-thirds of breeding attempts and successful broods. By contrast, poplars (aspen and poplar clones as the actual crop), occupying nearly 90 % of the CS area, accounted for only 30 % of all nests and breeding attempts, respectively, and 22 % of successful broods. Number of nests per 1000 trees was 13 times higher in native woody plants (26.0) than in poplars (2.0) and thorny shrubs of the Rosaceae family such as Rosa or Crataegus species and Pyrus pyraster were particularly preferred for nesting. To improve the habitat quality for breeding birds, we therefore recommend the integration of native woody plants, especially thorny Rosaceae species, into CS in modern AFS.