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Dense vegetation promotes denudation in Patagonian rainforests
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  • Christian H Mohr,
  • Violeta Tolorza,
  • Viktoria Georgieva,
  • Henry Munack,
  • Klaus M Wilcken,
  • Réka-Hajnalka Fülöp,
  • Alexandru T Codilean,
  • Eric Parra,
  • Sebastien Carretier
Christian H Mohr
University of Potsdam

Corresponding Author:[email protected]

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Violeta Tolorza
Universidad de la Frontera
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Viktoria Georgieva
Universidad Austral de Chile
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Henry Munack
University of Wollongong
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Klaus M Wilcken
Australian Nuclear Science and Technology Organisation
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Réka-Hajnalka Fülöp
Australian Nuclear Science and Technology Organisation
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Alexandru T Codilean
University of Wollongong
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Eric Parra
University of Potsdam
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Sebastien Carretier
Université de Toulouse
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Abstract

A geomorphological key paradigm predicts that intact forests are erosional idle, however comprise an efficient weathering machine sustaining high soil production rates. Only during times of disturbance, e.g., by earthquakes, those forests are observed to jump up to high-erosion-state, then being capable of releasing some of Earth’s highest sediment yields involving massive pulses of organic carbon. Coastal temperate rainforests, in particular, do not only store unparalleled carbon stocks building up a globally important carbon sink, but are also home to high (endemic) biodiversity. Here we document extraordinarily high catchment-averaged denudation rates, across multiple disturbance cycles, under the dense vegetation of the Patagonian rainforests. There, 10 Be-derived denudation rates of >0.8 m kyr^-1 exceed any known value from the entire Chilean Andes orogen, a highly variable >3.000 km long natural laboratory involving steep climatic and topographic gradients. We argue that such high denudation rates are consistent with a first-order control of the rainforest itself. High biomass loads exert a soil surcharge that promotes landsliding already along a relatively low critical slope angle. In contrast, denudation rates from more arid, and less forested sectors of the Chilean Andes though going along with steeper critical slope angles remain below half of our new rates derived from the Patagonian rainforests. Taken together, our study provides indication that denudation, to a higher degree than hitherto agreed on, operates as a continuous process involving soil production, vegetation, physical erosion and ecohydrological processes. Such a holistic denudational continuum, finally, is different from prevailing views that vegetation generally stabilizes hillslopes, thus promoting steep slope gradients, however, limiting landsliding activity.