Tanoaks develop deep taproots (22) and also  develop intricate systems of lateral roots which may approach the  soil surface and grow downhill, eventually emerging from the soil  where they form burls that produce sprouts.

   

The sapwood of tanoak is extremely thick, reaching a high of 66  percent even on large trees. This condition helps trees to live  after the bark has been stripped for tannin production or after  trees have been girdled for eradication. Some girdled trees have  lived as long as 30 years.