Like any plant, oak trees die for a wide variety of reasons, including bacterial or fungal infection, shock from habitat, temperature or water changes, insect damage or a lightning strike. When an oak tree is ill, it displays certain characteristics that give it the appearance of death. As a result, you may find it difficult at first glance to determine if an oak tree is actually dead. Determine if your oak tree is dead by completing a thorough investigation of the tree and the area around it.
Confirm that your oak tree has signs of new growth in spring, such as new twigs, branches, leaves and buds. If the oak tree has dead leaves and no new growth of any sort, then it's most likely dead.
Inspect the top branches of your oak tree, especially if dead branches have broken off recently or if only the lower branches have new growth. If you see that the top has died but the lower branches are still alive, your oak tree isn't completely dead yet -- but will likely die. If all the branches on the tree are dead, it is likely that it's already dead.
Scrape the bark at different locations on your oak tree. Yellow or brown coloration instead of green in all or most of the areas indicates a dead or dying tree.
Look for signs of decay, such as interior desiccation, crumbling or fungus growth. In addition, check the tree for signs of interior insect or animal habitation, such as bore holes, insect colonies or bird nests. Many types of insects and animals, such as wood borer beetles, ants and woodpeckers, overtake an oak tree when it's dead or nearly dead.