engleski

Comparison of two visual methods for tree risk assessment in Zagreb urban forests

Forests near urban neighborhoods provide benefits for urban dwellers and contribute significantly to the good quality of living. Tree growth in urban forests is unfavorable in comparison with nearby areas outside a city. In some conditions urban trees can be hazardous for the surrounding objects and people in proximity. In order to minimize the possibility of a hazard, regular tree risk assessments are advised as part of urban forest maintenance regimes. Most tree risk assessment activities are done visually using different methods and approaches and taking into consideration the age, location and condition of the inspected trees. The aims of this work were to compare two commonly used methods for tree risk assessment in order to highlight the differences in procedures and to give recommendations to experts in tree risk assessment in urban forests. Two visual methods of tree risk assessment were used in four urban forests of the City of Zagreb, part of the management unit "Park Forest of the City of Zagreb". The methods included Visual Tree Assessment (VTA) and Evaluation of Hazard Trees (EHT). In total 14.2 ha of old urban forests was encompassed and nearly 1600 trees were visually assessed. Tree risk assessment resulted in a small number of trees which were classified with the highest risk rating in all the locations where research was carried out. The results of the two visual methods showed that the differences in tree risk between the investigated species were significant and that sessile oak trees had a significantly higher risk assessment rating than other species. The results obtained from two visual assessment methods differed: sessile oak trees, which were most abundant, showed on average a higher risk assessment rating by the EHT method than by the VTA method in accordance with the classification criteria on the majority of inspected urban forests, although more trees were in the highest risk rating category by using the VTA method. When assessing a large number of trees for risk, an optimal method should be chosen so as to minimize the time needed to examine large portions of urban forests and maximize public safety. The findings about the differences in commonly used methods can help forestry professionals to adjust their assessment activities and identify trees whose failure might present the highest risks.

sessile oak, urban forest, arboriculture, hazard rating

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