Survival of a lightning strike is a function of two main elements; when in the storm the tree is hit, and the path the electricity takes. In the early lightning displays before the rainfall, the tree is dry and the path usually is deeper into the wet tissue of the tree. Rain wet trees may get a reprieve as current may pass along the wet bark. Strikes that are vertical kill a vascular column in the tree. A strike that helixes, or spirals, cuts or damages all the columns in the tree. Imagine the structure of a tree as a bundle of soda straws held together and stacked one bundle on top of another. The water is passed vertically, bundle to bundle with little diffusion to the sides.(Some species are better than others at latteral diffusion) The bulk of the transportation of fluids occurs just under the bark, in the current growth ring. Spiral injuries of lightning cut all the pathways. Electricity can be deflected away from the wood by metal structures, wires, clotheslines and such. Lightning protection systems handle the charge that way. Electrical resistence is lower in decayed wood, and a strike can internalize and ground through the interior of a tree with a substantial internal column of decay. The mechanism that kills trees is not electrocution. It is a steam explosion of the vaporized sap. Wood can be splintered internally, rendering the tree unstable and dangerous to climb without many obvious visual clues. For God's sake, you guys be careful on lightning struck trees, and always consider the potential targets if the tree fails. Trees fail two ways, a standing dead biological failure, and a mechanical failure of a tree that still has green leaves. So, a tree may survive a strike, only to decay and fall years later.
