Tell him to Google "liability of tree damage".
http://www.post-gazette.com/business/businessnews/2012/11/23/Responsibility-for-damage-caused-by-falling-trees-is-a-subject-fraught-with-confusion/stories/201211230153
http://threevillage.patch.com/groups/mark-t-freeley-esqs-blog/p/bp--damage-from-a-neighbors-tree-due-to-the-stormwho-4d654a98e1