Trees do not protect you or your structure from being hit by lightning. Ground cable should be buried to a sufficient depth to avoid displacement or damage.
Tree Damage Photos
In sandy, rocky, or very dry soils, an extensive ground system may be necessary.
Underground sprinkler systems, water pipes and other metal objects are very good grounds
Large trees with trunks measuring three (3) feet or more in diameter should have two (2) ground cables extending beyond spread of branches and connecting to proper ground system
Ground cable should be buried to a sufficient depth to avoid displacement or damage.
FACT: Tall trees DO NOT PROTECT. As a matter of fact, they could actually make things worse. Lightning usually jumps from the tree to the house because of all the grounded metal items inside and outside the house. Metal is a MUCH better conductor of electricity than a tree.