Linking land cover changes in the subalpine and montane belts to changes in a torrential river.

Abstract

Channel cbanges are the consequence of cbanges in sediment yield from the slopes and in the connectivity between slopes and channels
bccause of distinct land use and climate inJpacts. In Ibis study, we investigated the characteristics and evolution of a short reach in the
headwater of the !juez River, central-soutbem Pyrenees. Assessment of a series of sedimentar)' and geomorphic structures confirtned major
cbanges to the valley boUom, mainly related to changes in the intensity of human activity. 'The oldest sedimentar)' structure is a terrace leve!
located 3 10 4 m above the current alluvial plain. General deforestation, overgrazing and recwring tires in the montane belt ( 1100-1600 m a.sJ.)
have led 10 increased soil erosioo and connectivity, and to tbe triggering of debris llows thal have been deposited on the fluvial tmace. Woody
fragments from within the debris llows were dated using acceleraror mass spectrOmetry '"e radiocaroon tcchniques (AMS), yielding ages
between 1 00 and 115 cal years BP, whicb coincides with tbe period of maximum deforestalion and human density in the Pyrenees.
Depopulation and fannland abaodonment since tbe beginning of tbe 2001 oenrury has resulled in generalliJcod natural and artificial reforestation,
a shrinkage of the eroded arcas aod a decline in connectivi¡y bdween slopes and the channel. 1be rnost impor1an1 consequence has been cbannel
incision and oarrowing, and the development of a sedimed annour !ayer. Active sedimenl b8llSpOI1 is continui.Qg, although there has been a
decrease in sed.iment yield from the slopes. Copyright O 2014 John Wiley & Soos, Ltd.