Does intensive cutting regime maintain lowland dry heathlands habitat? The case study of Milano Malpensa airport (Northern Italy)

Airports are anthropogenic settlements which can harbour large portions of open habitats, including grasslands, which may host high species richness. Milano Malpensa Airport is the second main Italian airfield. One of its main open habitats is lowland dry heathland, frequently mown to fulfil aircraft safety requirements. The same habitat was formerly common in the surroundings of the airport, but it is nowadays endangered by management cessation and consequent tree (mainly Prunus serotina) encroachment. We compared heathland structure and vegetation composition in Calluna vulgaris populations within Malpensa Airport and outside it, where three degradation stages (identified by increasing P. serotina encroachments) were studied. We performed 52 surveys (10 within the airport, 18 in the less encroached heathland, 12 in the intermediate, and 12 in the most encroached) where we visually estimated the percentage cover of all plant species and we assessed heather density and height. Heathlands inside the airport (subjected to up to two cuts per year at 5 cm above ground) were richer in plant species and with a higher rejuvenation rate, but with a relevant cover of alien species and of plants typical of more intensive and disturbed grasslands. Among the heathlands outside the airfield, the two with the highest encroachment harboured few, tall, degenerate heather individuals, and were invaded by P. serotina and Molinia arundinacea. Among all, the heathland showing the best habitat conservation status was that outside the airport with the lowest P. serotina encroachment. There, heather population structure assumed a typical shape of young communities, likely due to the high light availability related to the low tree species cover. Additionally, the limited presence of bare soil compared to heathland inside Malpensa likely hampered the colonization by both alien species and pioneer plants of other environments. These outcomes showed that an intensive cutting regime in lowland dry heathlands can counteract habitat loss due to tree encroachment, which has been confirmed as one of the main threats to its conservation. However, cut frequency and height should be carefully determined to hinder the expansion of plants belonging to other habitats while encouraging the typical floristic composition.