Growing and dormant season tree risk assessments

Trees are a ubiquitous part of the urban landscape that provide substantial utility to people. Ensuring that trees pose a minimal risk to personal safety entails systematically identifying their risk and providing recommendations to monitor or mitigate the risk. Tree risk assessment methods vary depending on the capabilities of the assessor, the goals of the tree manager, and the types of data collected. Level 2 tree risk assessments were conducted on 27 trees during the early spring (“leaf-off assessment”) and on 24 trees during the summer (“leaf-on assessment”) in Sheboygan, Wisconsin, US. The trees were identified as having potentially elevated risk levels via a Level 1 windshield assessment during both seasons. The total number of Level 2 trees in both assessments was similar, and, in total, they represented 2% of the population of the Level 1 assessment. All leaf-off trees were reassessed during the summer to evaluate changes in risk factors and overall risk. Overall, 41 trees were found to be low risk (80%), 8 (16%) were moderate, and 2 (4%) were high. The most common defect observed in the leaf-off assessment was missing/decayed wood (n = 10), while deadwood (n = 12) was the most commonly observed defect in the leaf-on assessment. The data suggest that small proportions of trees in a Level 1 risk assessment warrant the closer inspection of a Level 2 assessment and that further research should be conducted to elucidate the significance of the frequency that common defects may be observed during specific times of year.