Climate and human forcing of montane vegetation dynamics during the past 15,600 years in the Simmental, Northern Swiss Alps

Abstract

To assess future responses of mountain ecosystems to anthropogenic climate warming, a thorough understanding of long-term vegetation responses to past climatic and land-use changes is required. Currently, little is known about former vegetation and land-use dynamics at intermediate elevations in the Swiss Alps, which act as an important ecotone between lowland and subalpine ecosystems. Here, we present a palaeoecological reinvestigation from Chutti (941 m a.s.l.), a small mire located in the montane belt of the Simmental (Simmen valley) in the north-western Swiss Alps. Using pollen, spores, stomata, microscopic charcoal, and X-ray fluorescence (XRF), we reconstructed vegetation, fire, land-use, and environmental dynamics over the past c. 15,600 years. Our pollen record shows four major vegetation transitions: the first transition at c. 14,600 cal yr BP marked the expansion of boreal forests with Juniperus, Betula, and Pinus, the second at c. 11,500 cal yr BP the expansion of temperate continental forests composed of, e.g., Ulmus, Tilia, and Acer, the third at c. 7000 cal yr BP the prevalence of temperate oceanic forests dominated by Abies alba, and the fourth at c. 4800 cal yr BP the massive spread of boreal Picea abies. While the first three vegetational changes were likely controlled by climate, the latter was induced by land use. The strong landscape opening during the Bronze Age (4150-2750 cal yr BP; 2200-800 cal yr BCE) was linked to the existence of a hill-top settlement close to the site. The degree of vegetation openness during the Bronze Age, but also during subsequent epochs, is unique for a site in the Northern Swiss Alps and comparable to more central places on the Swiss Plateau. Based on our results, we argue that if sustainable farming practises are not reinforced, future climate change will result in massive vegetation reorganisations in the Northern Swiss Alps, including the re-expansion of temperate forests.