Comparing various techniques to measure tree vitality of live oaks
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Accurately measuring tree vitality is important for arborists because urban trees are frequently impacted by various stressors. A research study was conducted to evaluate different techniques to determine vitality of live oaks (Quercus virginiana P. Miller). Glucose and starch content of trees was measured in a laboratory and compared with field techniques for assessing tree vitality, including a portable blood glucose meter, Lugol's solution, chlorophyll fluorescence Fv/Fm, and cambial electrical resistances (Shigometer). An initial trial was conducted on a group of trees exhibiting varying stress levels. Results showed a strong association between glucose content determined in the laboratory and field results using a portable blood glucose meter. Irrespective of the visible level of stress observed in the initial trial, there was no significant change in Shigometer and Fv/Fm values between trees indicating that these techniques were less sensitive at detecting stress. A second trial focused on correlating the results from the techniques with the visual health of trees. Glucose content determined in the lab and Lugol's solution did not have significant differences among different vitality groups, while starch content analyzed in a lab, Fv/Fm and Shigometer measurements taken in the field revealed significant differences between trees exhibiting poor and good vitality. Results indicated that electrical resistance readings can detect vitality differences in trees that were affected by severe stress conditions. This study revealed that a portable blood glucose meter appears to offer an easy and reliable technique for assessing glucose content in trees. However, lab analysis of glucose and starch content did not correlate well with visual differences in tree health or other tools used to evaluate vitality in the field. Results indicate that vitality is a complex variable to be assessed and that visual symptoms are still required in the tree vitality determination. 2010 Elsevier GmbH.
