8 research outputs found
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Uncoupling human and climate drivers of late Holocene vegetation change in southern Brazil
In the highlands of southern Brazil an anthropogenitcally driven expansion of forest occurred at the
expense of grasslands between 1410 and 900cal BP, coincident with a period of demographic and
cultural change in the region. Previous studies have debated the relative contributions of increasing
wetter and warmer climate conditions and human landscape modifcations to forest expansion, but
generally lacked high resoltiuon proxies to measure these efects, or have relied on single proxies to
reconstruct both climate and vegetation. Here, we develop and test a model of natural ecosystem
distribution against vegetation histories, paleoclimate proxies, and the archaeological record to
distinguish human from temperature and precipitation impacts on the distribution and expansion of
Araucaria forests during the late Holocene. Carbon isotopes from soil profles confrm that in spite of
climatic fuctuations, vegetation was stable and forests were spatially limited to south-facing slopes
in the absence of human inputs. In contrast, forest management strategies for the past 1400 years
expanded this economically important forest beyond its natural geographic boundaries in areas of
dense pre-Columbian occupation, suggesting that landscape modifcations were linked to demographic
changes, the efects of which are still visible today
The Rio Peruaçu Basin: An Impressive Multiphased Karst System
International audienceThe Rio Peruaçu basin is located on the left bank of the Rio São Francisco, in the north of the state of Minas Gerais. While its upper portion collects the waters flowing from the sandstone formations of the Urucuia, its lower part cuts into the Bambuí limestones, carving out a narrow canyon about 200 m deep for which the site is known. Over more than 17 km, the stream opens a bed that disappears underground six times. These underground sections are the remainders of an extensive and complex primitive karst network. Although some segments consist merely of simple but majestic arches, others, such as the Brejal and especially the Janelão, offer kilometers of underground galleries that can attain exceptional dimensions. For example, the Janelão cave reaches a ceiling height of 106 m and a width of 60 m. This canyon is punctuated by large and flat areas that function as reservoirs, namely the poljes of Silu and Terra Brava, and at the confluence with the Rio dos Sonhos. The system results from a complex Cenozoic evolution, including several spectacular episodes. As currently reconstituted, this evolution comprises at least three main episodes. The impressive landscapes of this region are not its only interesting feature: humans have occupied the basin since prehistoric times, as attested by about a hundred rock shelters and open-air dwelling sites that have not yet revealed all their secrets