Sour cherry trees can pollinate sweet cherry trees. I'm not sure if they make the best pollinator, but they are certainly capable of doing so. If you take a cherry that resulted from a blossom that was cross-pollinated here and take out the seed, that seed can grow into a hybrid tree, which can eventually produce fruit of its own (I know that in the case of the hybrid cultivar 'Mesabi' it's even self-fertile). However, the seeds inside this fruit are sterile and cannot grow. Like breeding a horse and donkey together to create a mule, there is no third generation. The reason is a chromosomal difference, sweet cherries are diploid (2n=16) while sour cherries are tetraploid (2n=32). A hybrid between the two results in a triploid cherry, which is why it cannot further sexually reproduce. However, flowering cherry species just happen to have the same chromosome count as Prunus Avium (i.e. sweet cherries), so that means they are capable of freely interbreeding. But it should be noted the two are still not in the same species. The question then is what does this really mean? Even when it comes to the different wild varieties of Japanese flowering cherry, oftentimes crossbreeding them together results in a hybrid that grows less vigorously than its parents, or is not very well adapted to its environment. Sometimes this may become more evident several generations down the line (you might read up more on how Outbreeding Depression works). Cultivated varieties of flowering cherry, almost all of which resulted from hybridization over hundreds of years) are much less hardy than their original wild pure-species relatives. We can even see some level of graft incompatibility combining different varieties of cherries within the same species, the tree does not grow quite as vigorously or as big as if it were grafted onto its own rootstock.

It looks like normal bark to me. Some varieties produce thicker bark than others. Some produce it earlier, faster than others. Some cuttings are taken from older, "barkier" wood than others. That would often depend upon what is available at the particular nursery and how high the demand is for the variety. You can't compare one variety to another and expect all of them to produce new basals at the same time nor same rate. Some will, but many will not throw new growth in unison. If the variety is not as strong growing as the next as an own root plant, it isn't going to push new basals as rapidly. Some simply refuse to push new basals (grow "Hell'n Trouble" for first hand grief with that!) while others shoot them out like crazy. It all depends upon the genetics of the particular rose variety; its condition at the moment and how suited it is to your conditions du jour. Kim

If there has been a transition to different leaves with a different habit, with no flowers being seen you may have had sweet cherry rootstock sprouts grow up to overwhelm and replace a cultivar that was grafted on top. I often see this happening with Japanese flowering cherry trees here, even though the appearance of the scion and rootstock may be markedly different from one another at flowering time. If that is the case with your tree the portion that died may have been the last bits of the scion finally being killed off by the competition from the rootstock sprouts.

Brandon7 and anyone else, I thought I would post some higher-res photos and an update. Again the tree is about 2 or so years old at about 8.5 feet high and 2.5-3 feet wide. I've started a slow-drip deep watering and we've had sporadic rain at about an 1" at a time at best. Additionally, very hot temperatures upper 90s. Soil is fertile and I keep the mulch away from the trunk. Some branches are becoming bare, although on others, new growth shows. In the one photo, the new growth has a hole, much like all of the other growth. Also, all the growth has the brown spots, etc, with leaves yellowing and dying off. Please see photos. Also, unsure if this is typical to the bark-type, but there are these spots on the trunk area that are orangish-yellow. Seems to scrape off easily.