Answer: Without looking at the tree and its immediate environment, I can't really diagnose the problem. Too much shade can make for a sparse canopy, as can droughty conditions. As a rule, oaks are not pruned, except to remove dead or diseased or damaged branches. However, pruning the branches back will encourage sprouting of the latent buds further down on the branch, which over time will help the canopy become thicker and more dense. If you decide to prune, do so during a dry season so you don't introduce or encourage diseases.
Good luck with your oak tree.
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