"CAMBIAL ELECTRICAL RESISTANCE DOES NOT ASSESS VITALITY OF INDIVIDUAL SWEET GUM TREES"
This article, from the Web of Science database, features both topics of American Sweetgum (Liquidambar styraciflua) and urban settings. It was featured in the Journal of Arboriculture 18(1): January 1992, written by J. Clarki, R. Kjelgran, J. Hushagen and J. Fiore.
They focus on cambial electrical resistance (CER) as a measure of tree vigor, specifically in urban areas, such as the mentioned six sites in Seattle, Washington. The CER measure the electrical flow resistance in tree's stems, as a function of the content (cells and solute) in the tree's cambium. Most healthy trees would have the thickest cambium, and have a low CER reading.
The experiment discusses the many factors involved, including the soil details, growth and development of the sweetgums at each site, seasonal ranges of CER, and other variation and informative characteristics of the grown trees that were tested.
Interestingly, they found that the most rapidly growing trees did not subsequently rate with the lowest CER values, as being most vigorous.
This led them to synthesize that CER, in fact, did not show a true relationship of the urban trees' vigor here, but was a flawed measure because there was too much variation in CER readings. The multiple significant factors that contributed to this are listed and discussed.
However, CER measuring of vigor has been reportedly successful in other experiments, but never in situations like this, with the evaluation "of single trees in diverse urban environments."
Clark, J., Kjelgran, R., Hushagen, J., & Fiore, J. (1992). Cambial electrical resistance does not assess
vitality of individual sweet gum trees. Journal of Arboriculture, 18(1), 1 – 5.
http://apps.webofknowledge.com.ezproxy.cul.columbia.edu/full_record.do?product=UA&search_mode=GeneralSearch&qid=13&SID=7Cp5UU4GBkFQHOcFoaK&page=1&doc=3
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