Late-Holocene vegetation and land-use dynamics in the Southern Alps (Switzerland) as a basis for nature protection and forest management

Regional and national parks have been created to preserve biodiversity and quasi-natural ecosystems, but uncertainties about local environmental history hinder the assessment of important nature-conservation baselines (e.g. natural vegetation composition, role of human activities). We use pollen, plant macrofossils, microcharcoal and radiocarbon dating to reconstruct the environmental dynamics at two mires in the mountain belt of southern Switzerland (Segna and Piano). Two major vegetation changes occurred during the past 3000 years: (1) Picea abies, Abies alba and Fagus sylvatica forests developed into monospecific beech forests and (2) F. sylvatica was reduced and open land expanded. The first change occurred at AD 450 at Segna and AD 1500 at Piano, the second at AD 1600-1700 at both sites. At Segna the A. alba decline occurred during a relatively warm and dry period when local fires and human impact increased. Similarly, at Piano the shift to Fagus-dominated forests was probably induced by human impact. The final decline of F. sylvatica and expansion of open land is clearly related to an intensification of human activities at both sites. Our results suggest a pronounced sensitivity of A. alba to human disturbance in the mountain belt and show that biodiversity is positively related to land use, while human activities decisively reduced woodland diversity. In conclusion, promoting natural succession and A. alba would significantly increase woodland diversity and may significantly contribute to stabilize forests under climatic conditions significantly warmer than today. Biodiversity conservation efforts should concentrate in areas where agriculture has a long history.