Forest Restoration by Land Separation
Rewilding by setting aside farmland to restore or create non-farmed habitat rarely happens –except in the case of farmland abandonmentas farmers tend to use and expand into all available land since this is usually the most profitable choice in terms of direct use value (TEEB 2010). This approach to rewilding competes with land for agricultural production at the field scale. Nevertheless, rewilding and agricultural production can coexist at the regional scale by a combination of habitat restoration and creation and maintenance of productive land for rewilding. Thus, rewilding sensu Navarro and Pereira (Chap. 1) might be considered more as land separation at the local scale, but it could also be seen a land sharing option at larger scales. Two major contrasting approaches for large-scale woodland or forest restoration in agricultural landscapes are: (1) passive restoration through secondary succession or forest regrowth following abandonment of agricultural land, e.g. cropland and pastures where extensive livestock farming has been removed; and (2) active restoration through addition of desired plant species. Forest regrowth and tree plantations on cropland enhance species that are characteristic of shrubland and forest environments, but are detrimental to species that are characteristic of open farmland environments and to agricultural production (Rey Benayas and Bullock 2012).
Passive restoration is cheap (although it may include opportunity costs) and leads to a local vegetation type. It is generally fast in productive environments, but slow in low productivity environments, as woody vegetation establishment is limited (Rey Benayas et al. 2008). The restoration capacity of woody ecosystems depends on the magnitude and duration of ecosystem modification, i.e., the “agricultural legacy” (Dwyer et al. 2010). A key bottleneck that hinders revegetation in large, continuous agricultural landscapes is the lack of propagules due to absence of parent trees and shrubs (García et al. 2010), which might be overcome by strategic revegetation as explained above. Passive restoration can be seen as a rewilding process (see Chap. 1), and it is of particular importance for large carnivores and herbivores such as the Brown bear Ursus arctos and the European bison Bison bonasus. The reintroduction of these species, whose habitat is expanding due to land abandonment, is often the subject of heated debates. The International Union for Conservation of Nature (2012) has recently published a document related to reintroductions and other translocations that is much more flexible than its previous 1998 Guide for such actions.
Active forest restoration basically comprises the planting of trees and shrubs (Stanturf et al. 2014). It is needed, for example, when abandoned land suffers continuing degradation, local vegetation cover cannot be recovered and secondary succession has to be accelerated. Indeed, one criticism of the passive rewilding approach is that the establishment of forest and other natural habitats in degraded landscapes may be impossible without more active interventions (Hodder and Bullock 2010). There are differences in the wildlife and ecosystem services provided by passive vs. active restoration, and there is much debate about the ecological benefits of tree plantations. For instance, Bremer and Farley (2010) found that plantations are most likely to contribute to biodiversity when established on degraded lands rather than replacing natural ecosystems, and when indigenous tree species are used rather than exotic species. Similarly, a meta-analysis of faunal and floral species richness and abundance in timber plantations and pasture lands on 36 sites across the world concluded that plantations support higher species richness or abundance than pasture land only for particular taxonomic groups (i.e. herpetofauna), or specific landscape features (i.e. absence of remnant vegetation within pasture) (Felton et al. 2010). Cropland afforestations in southern Europe, which are mostly based on coniferous species, may cause severe damage to populations of open habitat species, especially birds, by replacing high quality habitat and increasing risk of predation (Reino et al. 2010). Further, these planted forests have been shown to be suitable habitat for generalist forest birds but not for specialist forest birds (Sánchez-Oliver et al. 2014), whereas secondary succession shrubland and woodland favour bird species that are of conservation concern in Europe (Rey Benayas et al. 2010).