Colluvial legacies of millennial landscape change on individual hillsides, place-based investigation in the western Pyrenees Mountains

Abstract

We detect transition to agropastoral land use in a mountain landscape by radiocarbon dating physical signatures (sedimentation rates, charcoal concentrations, magnetic susceptibility) of conversion from native forest to pasture contained within colluvial stratigraphic sections. Focus is on two study sites located on toeslopes directly beneath zero-order hollows draining several hectares in the commune of Larrau (Pyrénées Atlantiques, France) along the international drainage divide of the western Pyrenees. Sample sites maximize likelihood of spatially and temporally uniform slopewash sedimentation. This constitutes a place-based approach to decipher the chronology of agropastoral activities within individual fields, which is applicable to other mountain ranges of the world. Stratigraphic columns were augured in contiguous 10 cm sample levels, which produced temporal resolution of decades to several centuries. We interpret relatively high concentrations of charcoal, rapid sedimentation, and magnetic susceptibility patterns as evidence of the intentional use of fire to transform forests into pastures. Results indicate that intentional burning and clearing probably were initiated by the Late Neolithic (ca. 5000-6000 cal. BP). However, intense burning, extensive forest clearance, and erosional degradation occurred later during the Bronze Age at one site, and during the Iron Age at the other site. This non-synchronous pattern of charcoal abundance and sedimentation rates is consistent with human agency of land clearance driving the chronology rather than paleoclimatic drivers. Stratigraphic zones of rapid sedimentation at both sites constitute-legacy‖ sediment of great antiquity. Our results are consistent with similar shifts in fire regimes and vegetation assemblages derived from direct association with anthropogenic proxies (e.g. pastoral pollen taxa, fungal spores of sheep dung, and archaeological sites) elsewhere in the Pyrenees and other

Archaeopedological analysis of colluvial deposits in favourable and unfavourable areas: reconstruction of land use dynamics in SW Germany

“…In most cases the dating of charcoals gives a maximum age of the formation of the related colluvial layer, which in some cases can be more than 3000 years older than the corresponding OSL age of the colluvial layer (e.g. [ 6 , 76 , 77 ]). In some cases, the results of both dating methods yield similar or even the same results, which gives a robust chronostratigraphy of colluvial deposits (cf.…”

Living on a flammable planet: interdisciplinary, cross-scalar and varied cultural lessons, prospects and challenges

“…With the introduction and intensification of agricultural and pastoral land-use, high elevation areas (greater than 900 m.a.s.l. ), south facing slopes and valley bottoms were deforested, thus initiating annual to decadal fire return intervals on more xeric slopes [36,62,64]. This activity increased the overall flammability of the landscape by extending the ranges of fire-adapted vegetation.…”

Climate–human interactions contributed to historical forest recruitment dynamics in Mediterranean subalpine ecosystems

“…This is confirmed by high‐elevation paleoecological records (above 2,000 m a.s.l.) that, through drops in arboreal pollen levels and evidence of severe paleofires, reveal intense deforestations at local to regional scales (Ejarque et al, 2009; Leigh, Gragson, & Coughlan, 2016; Leunda et al., 2017; Miras, Ejarque, Riera Mora, Orengo, & Palet Martinez, 2015). In the Apennines (central Italy), extensive grazing promoted a landscape transformation from primary forests and secondary woodland to grassland as many settlements ascended into high‐elevation environments (Mensing et al., 2013; Piovesan, Mercuri, & Mensing, 2018; Schoolman et al., 2018), which is also supported by palynological studies from southern Italy (Florenzano, 2019).…”