Human and climate-environment interactions in Pyrenean landscapes: a Lateglacial-Holocene multiproxy reconstruction

Mountain ecosystems present a complex challenge in disentangling the drivers of their long-term transformation. The subalpine belt of the Pyrenees, once forested, is now characterised by a mosaic of forest patches and open landscapes, and has represented a key region in herding practices until the last century, when land-use changes have led to a reforestation of this area. However, the relative contributions of climate and human activity in driving its change remain intensely contested. We present a high-resolution, multi-proxy reconstruction of landscape dynamics over the last 25 000 years from the southern Pyrenees. We have integrated mammal herbivores, fire regime and vegetation dynamics through sedimentary ancient DNA, pollen and charcoal analyses. With this approach, we aim to compare these proxies and identify the timing and drivers of vegetation change and to distinguish anthropogenic from climatic forces. Our results reveal a multi-phase evolution, with Lateglacial and postglacial forest expansion followed by Mid-Holocene openness, initially triggered by the cooling at the initial phase of the Neoglacial period, but subsequently maintained by pastoral activities. We find that humans opportunistically exploited this openness from the Mid-Holocene onwards, later transitioning to active landscape management through fires and grazing. This study demonstrates that current Pyrenean landscapes are not a product of exclusively humans or climate, but of their synergy over millennia. Effective conservation strategies must integrate an understanding of this deep ecological history with the emulation of traditional practices to preserve these unique, human-shaped biodiversity hotspots.