The generally accepted
answer is that once a root has been transplanted the taproot is lost. One would think that if you carefully dug up a 1 year old seedling that the tap root could be saved.
But using this
study as a guide that's not possible. From the
apple study:
"The development of root systems was extremely rapid, the roots reaching a Maximum depth of 8.8 and a lateral spread of 12 feet the first year, and 14.8 feet and 21.2 feet the second. During the third year the maximum lateral spread reached 29.4 feet and the maximum depth reached was 17 feet. This greatly exceeded the lateral spread of three-year-old tops, which was about 6 feet, and the height of the trees, which was 7 to 8 feet."
Doesn't sound to me like you could save most of the root system.