Benefits of Rewilding for Biodiversity
Rewilding will cause biodiversity changes with some species declining in abundance, that is, loser species, and other species increasing in abundance, that is, winner species (Russo 2006; Sirami et al. 2008). We reviewed 23 studies identifying a positive response of species to decreasing human pressure or to restoration of their habitat following land abandonment (Supplementary Information, see also Chap. 4 to 8). In total, we identified 60 species of birds, 24 species of mammals, and 26 species of invertebrates that could benefit from farmland abandonment (Supplementary Table 1). We also identified 101 species negatively affected by land abandonment (Supplementary Table 2), but 13 of those species can be classified as both “winner” and “looser” depending on the study and the region. Much of the agrobiodiversity associated with High Nature Value Farmland will be in the “loosing” category. In contrast, many of the winner species have declined or became functionally extinct in traditional agricultural landscapes, such as large carnivores (see Chap. 4). These species will benefit from forest regeneration and the connection of fragmented natural habitats (Keenleyside and Tucker 2010; Russo 2006).
Revegetation promotes the increase of the organic matter content and the water holding capacity of soils (Arbelo et al. 2006). This can lead to higher biomasses and densities of earthworms (Russo 2006) and other invertebrate families (Supplementary Table 1.A).
Some forest birds benefit from forest regrowth after farmland abandonment (Pointereau et al. 2008), such as woodpeckers, treecreepers, and tits (Supplementary Table 1.B). Some birds of prey have benefited from increases in rodent populations (Pointereau et al. 2008). Perhaps more surprisingly, populations of several bird species of the Eastern European steppe have increased after agricultural activity decline (Hölzel et al. 2002). Some, such as the Little Bustard ( Tetrax tetrax), have benefited from the tall and dense grassland of the regrown steppes. This contrasts with the concerns that the decrease of open areas in Western Europe is contributing to the decline of steppe species. Therefore the biodiversity consequences of rewilding depend on the geographical context.
Likewise, rural abandonment makes the land suitable for a comeback of large mammals (Supplementary Table 1.C). Large grazers are benefiting from the lower hunting pressures that usually accompany abandonment (Breitenmoser 1998; Gortázar et al. 2000). European carnivore species have been increasing since the 1960s in abundance and distribution, as stable populations of Eastern Europe are naturally recolonizing abandoned landscapes of Scandinavia, the Mediterranean, and the Alps (Enserink and Vogel 2006; Boitani 2000; Stoate et al. 2009).
It is also important to consider the trophic interactions between species and the cascading effects driven by rewilding. For example, amphibians and otter ( Lutra lutra) populations are known to benefit from the restoration of ditches by beavers ( Castor fiber) in abandoned areas of Eastern Europe (Kull et al. 2004). The presence of lynx in some parts of Switzerland reduced the roe deer and chamois browsing impact by regulating both populations (Breitenmoser 1998).
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