Absorptive root areas of large pedunculate oak trees differing in health status along a road in South Bohemia, Czech Republic

The health status of 200- to 400-year-old trees growing in an area alongside a road was described in detail on the basis of evaluation of hazard trees in urban areas and analyzed using the acoustic scanning and modified earth impedance (MEI) methods. Acoustic analysis was used to characterize tree trunks and coarse roots; MEI was used to characterize the active absorptive root surfaces (the electric impedance of soils and sapwood were also included). Several groups of trees were distinguished according to the extent of damage (slight, serious or extreme), which was easily detectable from the MEI results. It was confirmed that both methods gave similar results, which also corresponds to the detailed observations. Instrumental measurements provided additional information about trunk and root injuries, which cannot be directly observed. A combination of both methods is recommended to achieve the most reliable results. This unique approach is applicable for testing eventual threats by old ill trees for safety reasons over the landscape.