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.