Monitoring forest soil properties with electrical resistivity

Maintenance and monitoring of soil fertility is a key issue for sustainable forest management. Vital ecosystem processes may be affected by management practices which change the physical, chemical and biological properties of the soil. This study is the first in Europe to use electrical resistivity (ER) as a non-invasive method to rapidly determine forest soil properties in the field in a monitoring purpose. We explored the correlations between ER and forest soil properties on two permanent plots of the French long-term forest ecosystem-monitoring network (International Cooperative Program Forests, Level II). We used ER measurements to determine soil-sampling locations and define sampling design. Soil cores were taken in the A horizon and analysed for pH, bulk density, residual humidity, texture, organic matter content and nutrients. Our results showed high variability within the studied plots, both in ER and analysed soil properties. We found significant correlations between ER and soil properties, notably cation exchange capacity, soil humidity and texture, even though the magnitude of the correlations was modest. Despite these levels of correlations, we were able to assess variations in soil properties without having to chemically analyse numerous samples. The sampling design based on an ER survey allowed us to map basic soil properties with a small number of samples.