If you are able, you might just go speak with the neighbor. You could tell him of your concerns and request that he clear the downed trees. Further, you could let him know that he took down trees of yours as well. As to that, you might propose a settlement to resolve this issue.
If you prefer to avoid direct contact, you might consider writing a demand letter. Such a letter would "demand" a particular response. Here, that would likely be the removal of the trees and compensation for the trees of yours that he removed.
As a final resort, you might consider a civil lawsuit. While there is currently no basis for a lawsuit regarding the downed trees, you could certainly sue for the destruction of your trees.
As to the demand letter and the lawsuit, you could potentially handle these on your own. However, it would certainly be prudent to consider retaining an attorney. A competent civil litigator in your area would be familiar with the local rules and could help ensure the best possible result.
Please let me know if anything requires clarification.
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