Developing Soil Conservation Strategies Protecting Chilean Forest Highlands From Erosion

With the support of the Joint FAO/IAEA Division, the research foundation Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT), the Government of Chile and the Universidad Austral de Chile initiated a project aimed at investigating the impact of forest harvesting on fine sediment yield. This called for measuring the contribution of the main sediment sources – catchment surface, forest roads and stream channels – in forested catchments in south-central Chile during and after tree harvesting operations.

The catchments chosen and paired for study – Nacimiento and Los Ulmos – are located about 400 kilometres apart. They have similar soil types, but greatly differing mean annual rainfalls of 1 200 and 2 500 mm per year, respectively.

The project found that, prior to harvest operations, sediment sources are predominantly roads and streams. After the harvest, however, there is a marked movement of surface material from forest slopes caused by soil disturbances during the harvesting process. Using sediment source fingerprinting, the relative contributions of the different sources in the study catchments to the sediment yields are currently being quantified to establish appropriate countermeasures.

Radionuclides such as caesium-137, lead-210, beryllium-7, potassium-40 and radium-226, as well as the organic carbon and total nitrogen content of soils and sediments, are used as fingerprints to identify key sources of fine sediment that reach the water bodies and to quantify the relative contribution of each source to the total sediment yield. The ability to trace the sources of these sediments, and hence to identify hotspots of land degradation, are essential in efforts to develop and optimize appropriate and cost-effective soil conservation strategies at the landscape level.

The ability of the fingerprinting technique using fallout radionuclides to trace sources of these sediments and to identify hotspots of land degradation, is essential to efforts to develop and optimize appropriate and costeffective soil conservation strategies at the landscape level.

Looking to the future, applying the information about degradation of hotspots and sources of fine sediments identified by the project promises a reduction in the negative impact of commercial forestry operations on water quality. The information also supports improved and data-based decision-making processes for implementing enhanced and cost-effective sediment management practices. This will improve the factual basis of Chile’s policy on Sustainable Forest Management Certification. In addition, an increased understanding of sediment sources and their relative contributions to fine sediment yields from forested catchments in southcentral Chile, particularly during critical periods of disturbance by harvesting operations, will be applicable to other regions and landscapes with sediment-related environmental problems.