Population trends of Rosalia alpina (L.) in Switzerland: a lasting turnaround?

Many species that depend on old trees and dead wood are suffering from habitat losses and intensive forest management. For the conspicuous cerambycid beetle Rosalia alpina, a relative sampling analysis combined with a distribution model showed a population decrease in Switzerland between 1900 and World War II. This negative trend can be ascribed to the abandonment of traditional management such as wooded pasture and to the expansion of high forest promoted by modern forestry. Since that period, the population of R. alpina, has been increasing and each single relict population of this species was maintained. These positive population trend can be explained by less intensive forest management and a shift from fuel-wood production to timber wood. Today, many more old beech trees and much more dead wood remain in Swiss forests than 50 years ago. Consequently, the habitat conditions necessary for the development of the Rosalia longicorn have improved, especially on steep terrain in colline and submontane regions. However, it is still uncertain whether current population sizes can guarantee the survival of this species in the long term, especially as fuel-wood production is expected to become more intensive in Switzerland in future decades. The conservation of this species requires, therefore, the establishment of natural forest reserves and dead wood islands or the restoration of wooded pastures with scattered habitat trees. The Rosalia longicorn could then act as an umbrella species for other species that depend on old trees and dead wood.