Chronology and pedogenic effects of mid- to late-Holocene conversion of forests to pastures in the French western Pyrenees

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

“…The zones of maximum sedimentation rates during the Bronze Age at Mulhedoy (up to 7 mm y -1 ) and during the Iron Age at Ihitsaga (also up to 7 mm y -1 ) are well outside of the forested background range, as indicated by the slow rates of 0.04 to 0.4 mm y -1 during the early Holocene. In addition, Leigh et al (2015) surmised rates of >1 mm y -1 to be outside of the range for humid-temperateforested mountains. Thus, it is highly likely that both Ihitsaga and Mulhedoy were both -degraded‖ with highly eroded soils during their phase of maximum forest clearance, yet both of these sites have since recovered to exhibit relatively slow sedimentation rates < 1 mm y -1 from completely pastured watersheds.…”

“…This is significant because it demonstrates that hillslopes degraded by erosion can recover with time, given appropriate soil conservation and sustainability practices. Indeed, Leigh et al (2015) found that many present-day pastured soils in Larrau had thicker A horizons, more organic matter, and lower bulk density than their forested counterparts, so that the stereotypical model of landscape degradation from grazed lands is not always the outcome.…”

“…Five pairs of samples were collected from each respective pasture and forest site. This set of paired pasture/forest samples was previously documented for bulk density measurements (Leigh et al 2015). Magnetic susceptibility results from these 20 pairs clearly demonstrate that the samples from regularly burned pastures register very significantly higher magnetic susceptibility values than the unburnt forests ( Fig.…”

“…Bedrock consists of well stratified Mesozoic mudstone, shale, dolostone, and limestone that is steeply tilted and folded (Moores and Fairbridge, 1997) and capped by a thin mantle of noncalcareous silty to clayey yellowish-brown residuum. The residuum ranges from 0 to about 2 m thick, consisting of Alfisol type soils that tend to be more organically enriched in present-day pastures (Leigh et al, 2015).…”

“…The Mulhedoy site accumulates slopewash on a bedrock bench that allows somewhat more divergent flow than at Ihitsaga. The Mulhedoy site was the object of a previous investigation (Leigh et al, 2015), but many new radiocarbon dates have been obtained and analytical techniques have been modified and improved since that study was conducted, comprising a new data set.…”