Restoring dense vegetation can slow mountain erosion

Tropical mountain areas may undergo rapid land degradation as demographic growth and intensifi ed agriculture cause more people to migrate to fragile ecosystems. To assess the extent
of the resulting damage, an erosion rate benchmark against which changes in erosion can be evaluated is required. Benchmarks refl ecting natural erosion rates are usually not provided
by conventional sediment fl uxes, which are often biased due to modern land use change, and also miss large, episodic events within the measuring period. To overcome this, we combined
three independent assessment tools in the southern Ecuadorian Andes, an area that is severely affected by soil erosion. First, denudation rates from cosmogenic nuclides in river sediment
average over time periods of 1–100 k.y. and establish a natural benchmark of only 150 ± 100 t km–2 yr–1. Second, we fi nd that land use practices have increased modern sediment yields
as derived from reservoir sedimentation rates, which average over periods of 10–100 yr to as much as 15 × 103 t km–2 yr. Third, our land cover analysis has shown us that vegetation cover
exerts fi rst-order control over present-day erosion rates at the catchment scale. Areas with high vegetation density erode at rates that are characteristically similar to those of the natural
benchmark, regardless of whether the type of vegetation is native or anthropogenic. Therefore,our data suggest that even in steep mountain environments sediment fluxes can slow to
near their natural benchmark levels with suitable revegetation programs. A set of techniques is now in place to evaluate the effectiveness of erosion mitigation strategies.