Winners and losers: How the elevational range of breeding birds on Alps has varied over the past four decades due to climate and habitat changes.

Luciano Bani,Emanuel Rocchia,Olivia Dondina,Valerio Orioli,Massimiliano Luppi

doi:10.1002/ece3.4838

Abstract

Climate warming and habitat transformation are widely recognized as worrying threatening factors. Understanding the individual contribution of these two factors to the change of species distribution could be very important in order to effectively counteract the species range contraction, especially in mountains, where alpine species are strongly limited in finding new areas to be colonized at higher elevations. We proposed a method to disentangle the effects of the two drivers of range change for breeding birds in Italian Alps, in the case of co‐occurring climate warming and shrub and forest encroachment. For each species, from 1982 to 2017, we related the estimated yearly elevational distribution of birds to the correspondent overall average of the daily minimum temperatures during the breeding season and the estimated amount of shrubs and forest cover. Using a hierarchical partitioning approach, we assessed the net contribution (i.e., without the shared effect) of each driver. Both temperature and shrub and forest cover showed a positive trend along the time series and resulted the most likely causes of the significant elevational displacement for 21 of the 29 investigated birds. While shrub and forest cover was found to be an important driver of the expansion of forest bird range toward higher elevations, the effect of temperature on favouring the colonization of previously climatically unsuitable forests at higher elevations was not negligible. Shrub and forest expansion resulted the main driver of the range contraction for edge and open habitat species, which suffered a distribution shrinkage at their lower elevational boundary. In light of climate warming, these results highlighted how the net range loss for edge and open habitat species, caused by shrub and forest encroachment consequent to land abandonment, should be counteracted by implementing proper conservation management strategies and promoting sustainable economic activities in rangeland areas.

Highlights

Habitat transformation is still recognized as one of the major human drivers of species distribution changes at a global scale (Foley et al, 2005), a rising attention has been addressed in the last de‐ cades to the effects produced by climate change on biota (Parmesan & Yohe, 2003; Thuiller, 2007; Walther et al, 2002)
Until a few de‐ cades ago, grazing by herds restrained the forest cover in mountain areas, but after the abandonment of pastures, shrubs and forests widely expanded, and even the tree line tended to raise in elevation, probably as a consequence of the synergic action of climate warming and land abandonment (Gehrig‐Fasel, Guisan, & Zimmermann, 2007; Leonelli, Pelfini, di Cella, & Garavaglia, 2011; Parolo & Rossi, 2008; Pernollet, Korner‐Nievergelt, & Jenni, 2015)
In the long‐term period, the abandonment of pastures and climate warming may promote the shrub and forest expansion at the expense of open habitat in mountain areas, leading to a general com‐ plex pattern that can vary between geographical areas (e.g., Rocchia, Luppi, Dondina, Orioli, & Bani, 2018)

Summary

| INTRODUCTION

Habitat transformation is still recognized as one of the major human drivers of species distribution changes at a global scale (Foley et al, 2005), a rising attention has been addressed in the last de‐ cades to the effects produced by climate change on biota (Parmesan & Yohe, 2003; Thuiller, 2007; Walther et al, 2002). Climate warming may affect species ecology with contrasting, additive or even synergic effects with the other co‐occurring processes (e.g., land‐use changes, pollu‐ tion, harvesting, and species interactions; Mantyka‐Pringle, Martin, & Rhodes, 2013; Oliver & Morecroft, 2014). This is noticeable in those areas where different relevant environmental changes act simultaneously. The main purpose of this study was to investigate the drivers of the elevational range changes of breeding birds in Central Italian Alps, separating the effects produced by climatic (temperature in‐ crease) and habitat (shrub and forest recolonization) drivers. Since species‐specific ecological traits are known to affect species responses to environmental changes (Copeland, Bradford, Duniway, & Butterfield, 2018; Dondina, Orioli, D'Occhio, Luppi, & Bani, 2017; Dondina, Orioli, Massimino, Pinoli, & Bani, 2015; Luppi, Dondina, Orioli, & Bani, 2018; Williams et al, 2010), we considered the species’ breeding habitat and migration habit as ecological traits potentially affecting the elevational responses of birds

| METHODS

Findings

| DISCUSSION