Ask Mr. Smarty Plants

This sounds like an essay question for a student. Mr. Smarty Plants does not write essays. Furthermore, the Lady Bird Johnson Wildflower Center is dedicated to the growth, propagation and protection of plants native not only to North America but to the areas in which they grow natively. We are wondering if you meant the most common, most numerous, what?

Since we are in Austin TX, we are not even clear on where or what exactly the Piedmont is, so we found this article in Wikipedia with maps and descriptions.

We are sure there are many non-native trees in the Piedmont area of North Carolina. What we can do is refer you to our Native Plant Database; where, using the Combination Search, you can indicate the state of North Carolina and tree for the Habit. From that search, we got a list of 203 trees native to North Carolina. You will need to determine which counties are considered to be in the Piedmont. Then as you follow each plant link to our webpage on that tree, scroll down to Additional Resources at the bottom of the page. Click on USDA Plant Profiles, which will take you to an informational page on that plant from the USDA. The State of North Carolina should be green, indicating the tree grows at least in one county in North Carolina. Click on North Carolina on the map, and you can ascertain which counties have that tree growing in them.

From there, you are on your own, unless you can find a source on the Internet that has already counted them, and we did not. You might try searching on "Trees in the Piedmont of North Carolina." We tried that and got a number of references.