From the Scientific American article a major assumption on the part of the scientists is that:
"nature does not make trees that are both thin and tall. Instead short trees are thin and tall ones thick."
Tree height and width are correlated, but I disagree with this assumption as stated in the article, especially for urban trees. Here in Denver you can see a 50 foot tall aspen volunteer at 10 inch DBH next to an ancient 20 foot tall apple tree at 30 inch DBH. Even in the natural forests around Colorado, you can see dense stands of towering lodgepole, where the trees vary in DBH from 6 to 20+ inches at the same height (with some thinner short saplings mixed in)! When you get into a clearing where the trees stop competing for sunlight, you can see lone lodgepole pines that are shorter with a huge trunk and canopy.
