Abstract
In a mountain context, the forest-shrub ecotone is an area of high biodiversity. Relatively little is known about the habitat requirements of birds in this habitat, yet it is facing potential threats from changes in grazing practices and climate change. Moreover, it is not clear at which scale habitat associations should be assessed in Alpine birds. Further information on key habitat components affecting bird communities of the ecotone is needed in order to inform management strategies to counteract potential habitat loss, and to better inform predictions of how bird communities may be affected by future environmental change. Data on bird occurrence and broadscale (land cover) and finescale (vegetation structure and shrub species composition) habitat variables were collected in an Alpine forest-shrub ecotone in Val Troncea (northwestern Italian Alps) in order to address two objectives: to identify the key habitat variables associated with the occurrence of individual species and with the diversity of the bird community; and, to assess which scale of habitat measurement (broadscale, finescale or both combined) is needed to model bird occurrence. Broadscale variables, or combinations of broadscale and finescale variables, tended to have the best performing models. When combined models performed best, shrub species identity was included in many cases. Shrubs also played an important role in explaining variations in species diversity and richness. Vegetation structure was of relatively little importance, either for individual bird species or for species richness and diversity. These findings suggest that management should strive to maintain a mosaic of habitats whilst minimizing forest encroachment, which could be achieved through targeted grazing. Broadscale habitat data and data on shrub species composition should provide a sufficient basis for identifying relevant species-specific habitat parameters in a mountain environment in order to model future scenarios of effects of habitat change on the bird community of the alpine forest-shrub ecotone.
Zusammenfassung
Die Rolle von groß- und kleinräumigen Habitateigenschaften für Verbreitung und Diversität von Vögeln des Waldgrenz-Ökotons der Alpen
Das Waldgrenz-Ökoton der Alpen ist ein Gebiet, welches durch eine hohe Biodiversität gekennzeichnet ist. Obwohl aktuelle Bedrohungen durch Klimawandel und Veränderungen in der Beweidungspraxis omnipräsent in diesem Areal sind, sind die Habitatansprüche, welche für die Vögel in diesem Bereich gelten, bislang kaum erforscht. In welchem Maßstab diese Habitatanforderungen für Alpenvögel erfasst werden sollten, ist ebenfalls nicht bekannt. Es ist daher erforderlich, jene Habitatelemente zu identifizieren, die eine Schlüsselrolle für die Vogelgemeinschaften im Waldgrenz-Ökoton der Alpen spielen. Mit Hilfe dieser Informationen wird es in Zukunft möglich sein, potentiellem Habitatverlust entgegenzuwirken und Vorhersagen zu treffen, wie Vogelgemeinschaften des Ökotons auf zukünftige Umweltveränderungen reagieren könnten. Durch die Aufnahme von Daten über das Vogelvorkommen sowie groß- (Landbedeckungsdaten) und kleinräumigen (Daten zur Vegetationsstruktur und zur Straucharten-Zusammensetzung) Habitatdaten im Waldgrenz-Ökoton des Naturparks Val Troncea (NW Italien) wurden zwei Zielstellungen verfolgt: Die Identifikation von Habitatelementen, welche für das Vorkommen einzelner Arten sowie für die Vogeldiversität und den Vogelartenreichtum von wesentlicher Bedeutung sind und die Beurteilung des Maßstabs zur Habitatdatenaufnahme (großräumig, kleinräumig oder eine Kombination aus beidem), welcher erforderlich ist, um das Vorkommen einer Art modellieren zu können. Großräumige Habitatvariablen oder eine Kombination von groß-und kleinräumigen Habitatvariablen führte zu den besten Modellen. Wenn die besten Modelle durch eine Kombination von Habitatvariablen erzielt wurden, war die Identität der Strauchart eine oftmals beinhaltete Variable. Generell spielten Sträucher eine wichtige Rolle, um Variationen in der Vogeldiversität und dem Vogelartenreichtum zu erklären. Von geringer Relevanz für individuelle Vogelarten sowie Vogelartendiversität und -reichtum waren kleinräumige Habitatvariablen zur Vegetationsstruktur. Diese Ergebnisse zeigen, dass zukünftige Naturschutzmaßnahmen darauf abzielen sollten, das Habitatmosaik im Waldgrenz-Ökoton zu erhalten und einer Ausbreitung des Waldes entgegenzuwirken. Dies könnte durch gezielte Beweidung erreicht werden. Großräumige Habitatdaten sowie Daten zur Strauchartenzusammensetzung stellten zudem eine solide Basis dar, um relevante artspezifische Habitatansprüche für alpine Vogelarten zu identifizieren und potentielle Auswirkungen zukünftiger Habitatveränderungen auf die Vogelgemeinschaft des alpinen Waldgrenz-Ökotons modellieren zu können.
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Acknowledgements
We thank Luca Maurino and the other rangers and staff of Val Troncea Natural Park for their great help. We are also grateful to Massimiliano Probo and Michele Lonati for providing survey locations, and to Lorenza Lerda, Giulia Masoero and Sara Minolfi for help with fieldwork. D. C. was funded by a Ricerca Locale grant from the University of Turin.
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Communicated by T. Gottschalk.
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Jähnig, S., Alba, R., Vallino, C. et al. The contribution of broadscale and finescale habitat structure to the distribution and diversity of birds in an Alpine forest-shrub ecotone. J Ornithol 159, 747–759 (2018). https://doi.org/10.1007/s10336-018-1549-9
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DOI: https://doi.org/10.1007/s10336-018-1549-9