Conservation Objectives: Semi-Natural Biotopes Versus Rewilding
Conservation objectives are the subject of much debate for regions with a long history of human alteration, like in most of Europe (Merckx et al. 2013). Climax forests have been replaced, often millennia ago, by so-called semi-natural biotopes, which are essentially different versions of earlyto mid-successional natural seral stages, arrested from developing towards mature woodland. Nowadays, only scattered fragments of ancient woodland remain, and these have suffered continuous but varying disturbance regimes by humans. For example, up to a century ago most European woodland was maintained as coppice or coppice-with-standards. Today much woodland plantation has a uniformly closed canopy, which is shadier than is found in ancient forests with little history of human disturbance. A consequence of these various ways by which the development towards climax forest has been arrested, is that the rarest types of arboreal habitats in west-European countries today are those associated with rotting wood on ancient trees. These saproxylic habitats are associated with high extinction rates (Hambler et al. 2011), and support numerous invertebrate specialists, especially beetles and flies, and some moths (Thomas et al. 1994). Although many species undoubtedly suffered great losses (and extinctions) over the centuries during the transition from natural forest to semi-natural habitats, others (e.g. species associated with early-successional stages) did benefit or managed to adapt successfully to these semi-natural biotopes (e.g. heaths, meadows, coppiced woodland) (Young 1997; Monbiot 2013).
Since the 1950s, agricultural intensification, forestry intensification, urbanization, and farmland abandonment have all severely decreased such semi-natural biotopes in quantity, quality, and connectivity, and with them their specialist fauna and Lepidoptera. As a result, most European 'conservationists' traditionally seek to sustain or restore semi-natural biotopes, and do so by maintaining very specific disturbance regimes, often simply by copying traditional agricultural practices, since most large wild herbivores were excluded centuries ago (New 2009). Nevertheless, popular management operations to influence vegetation structure, such as burning and grazing/mowing, need careful planning (mainly to ensure refugia) as they may destroy much of the existing invertebrate fauna if applied too intensively, too infrequently, on too large a scale or at unsuitable times of year (New 2009). Hence, although wrongly applied conservation management may have unintended negative consequences, management is seen as a good thing overall, whereas rewilding is often perceived as a threat (Merckx et al. 2013).
Abandonment of human disturbance does indeed pose a threat to many specialist species that have become adapted to certain semi-natural biotopes, especially when they have nowhere else to go because natural succession dynamics are currently too disturbed and suitable natural patches are too small and/or isolated. On the other hand, the recovery of native forest ecosystems due to farmland abandonment is likely to benefit a majority of Lepidoptera, since most moths (which make up 95 % of Lepidoptera) are reliant on woody foodplants or wooded biotopes. Forest recovery will obviously favour endangered specialist faunal groups too (e.g. closedwoodland Lepidoptera, Gastropoda, and saproxylic groups).