Part of a colony?

When I got out of my truck at this loading zone, I thought I was hallucinating, or maybe having a serious memory lapse.  All last summer, I thought, there was a small Black Cottonwood growing out of a crack in the pavement right against the building, maybe 3 feet to the right of the one you see here.  It even survived last winter because i remember seeing it at least for the first half of this past summer. Then I noticed this area was recently repaved and a number of cracks were filled with an asphalt product.  Click on the photo for an enlargement to see the details.  That operation probably killed the little Cottonwood struggling to survive against the building.  Then, VOILA! a new one pops up 3 feet away from the building.  Maybe there's just one cottonwood in this whole area and it includes the above-ground trees in the background beyond the driveway, and this new one and the deceased one are just growths from the vast underground root system.  Don't laugh.  The Black Cottonwood is in the same family as the Quaking Aspen found around here at higher elevations.  In northern states of the Midwest and at high elevations in Colorado, among other places, many square miles of aspens are known to be interconnected below ground and function as one giant organism,  In some ways like the interconnected coelenterates in a coral reef.  Fascinating.