作者： L Zapponi , E Minari , L Longo , I Toni , F Mason
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摘要: Old and dead trees are the main source of natural cavities and hollows used as shelter by many species of vertebrates (Gibbons & Lindenmayer 2002) and invertebrates (Müller et al. 2013). For the majority of these species, tree hollows represent an irreplaceable microhabitat (Gibbons & Lindenmayer 2002). Obligate hollow nesters have been estimated to be as much as 5% of the European and North American birds, most belonging to the orders Passeriformes, Piciformes and Strigiformes (Newton 1994). Most of these species are secondary cavity nesters, ie, relying on the presence of cavities created by other birds, insects or wood decay processes. The availability of cavities limits the population size of such species, as proved by the experimental addition and removal of nestboxes (Dhondt 2012). The nest site limitation has been generally observed in humanlandscapes, but forest type and age, as well as community complexity, can contribute to the shortage of these microhabitats (Cornelius et al. 2008). Also, the presence of microhabitat-bearing trees represents a crucial factor for the diversity and abundance of saproxylic beetles (Bouget et al. 2014a). The availability of microhabitats on living trees is often reduced by current silvicultural practices, since thinning usually removes trees more prone to exhibit or develop hollows (Larrieu et al. 2012). The rarity of these key resources offered by old and hollow trees is increasing in Europe, threatening the conservation of associated organisms (Sebek et al. 2013). Considering the long timespan taken for such cavities to naturally develop, conservation planners should act to halt hollow scarcity …