Local and landscape drivers of butterfly richness and abundance in a human-dominated area

In Europe, butterflies have declined over the last decades mainly because of the increasing urbanization and the agricultural intensification occurred in lowlands areas. Drivers of butterfly decline were identified in changes of both local scale habitat characteristics and landscape-scale land-use coverage. Thus, to counteract the negative trend of butterfly populations, management actions that simultaneously have an effect on local and landscape scale environments are needed. The present research was performed in northern Italy, in a human-dominated area of about 170 km2. From April to September 2014 and 2015, we surveyed butterflies in 494 50-m sections, grouped into 44 line transects. First, using a multi-scale GAMM, we analysed the simultaneous effect of local (nectar index, crop type, presence of woodlands and hedgerows and degree of shelter) and landscape (fractional cover in 500-m buffer of arable lands, meadows, woodlands and artificial surfaces) variables on butterfly richness and abundance. We evaluated the contribution of local and landscape variables by a variation partitioning approach. Second, we performed a GAMM to investigate the effect of specific management practices adopted in meadows, hedgerows and field margins on butterfly communities. Our results showed that the evaluation of the effect of local scale characteristics on butterfly communities definitely cannot disregard the landscape context. We thus suggest maintaining urban and agricultural areas alternated by a mosaic of nectar-rich land-covers, such as meadows and alfalfa, forest patches and hedgerows. Our study also allowed to formulate management guidelines of specific habitats. Accordingly, meadows should be managed by reducing the number of cuts, while wide herbaceous margins, characterised by a high grass layer rich in dicots, should be maintained in arable lands. To avoid a barrier effect and to guarantee the presence of a well-developed shrub layer, which provides high nectar resources, it is also necessary to avoid an excessive growth in hedgerows height. Results evidence that the adoption of these management guidelines and of a proper landscape planning strategy, can lead to play an important role in butterfly conservation even within human dominated areas.