Erosion proxies in an exotic tree plantation question the appropriate land use in Central Chile

In South-Central Chile, slopes degraded by former erosion have been afforested with exotic tree species since the 1950s for erosion protection. From 1975 on, primary and secondary forests have increasingly been replaced by tree plantations. This practice is often justified by claiming plantations would similarly protect the soil from erosion, even on areas which used to be natural forest. We assessed if plantations offer a comparable level of erosion protection as the natural forests. A six-year-old Eucalyptus globulus (Labill.) plantation was compared to an adjacent secondary forest using soil profiles and erosion proxies, i.e. topsoil parameters linked to erosion and 137Cs inventories. These pointed to higher erosion in the plantation: the mean bulk density of the plantation was 22% higher compared to the forest site, the gravel content in the plantation was 61% higher, the organic matter content was 20% lower, the mean thickness of the litter layer was 2.2 cm lower and the total sand content was 20% higher. The soil loss of the plantation was estimated to be between 4.8 cm (mean profile truncation) and 6 cm (137Cs approach). These results clearly hint to the conclusion, that the tree plantations in South-Central Chile might promote soil erosion instead of preventing it. Thus, current land use management practices seem to impose erosion risks on Chilean soils raising concern about the sustainable development within the study site.