Residents in New Dorp Beach said they worry people climbing dunes will weaken them.
Officials found more than 50 feet of charred fencing and empty cases of beer.
Off-roaders destroyed plantings designed to stop floods, the Parks Department said.
The visit was part of a three borough tour of resiliency sites in Sandy damaged neighborhoods.
The city wants to reconstruct berms in Oakwood Beach that were damaged in a 2009 fire.
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