Restoring dense vegetation can slow mountain erosion to near natural benchmark levels

Background

Tropical mountain areas may undergo rapid land degradation as demographic growth and intensified 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 reflecting natural erosion rates are usually not provided by conventional sediment fluxes, which are often biased due to modern land use change, and also miss large, episodic events within the measuring period.

Research goals & methods

This study compares three assessment methods for erosion rates in the southern Ecuadorian Andes, an area that is severely affected by soil erosion, using present-day sediment yields from 37 reservoir catchment measurements and vegetation cover generated by remote sensing and field surveys. 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, 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–1. Third, land cover analysis indicates that vegetation cover exerts first-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.

Conclusions & takeaways

The study suggests 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.