About 15 Ka ago the ice front was receding north there, so I'm guessing your trees grow on glacial moraine or outwash in thin soil. (dotearth.blogs.nytimes.com)
The carnage took place along the flood - prone outwash plain on the south and east shores of the island, located at the crest of the New York Bight, where geography funneled the ocean's angry waters. (discovermagazine.com)
These moraines were directly linked to the main outwash plain where Monte Verde was emplaced, that is, the fluvial system in the study area was part of a much wider surface directly draining glacier discharge. (journals.plos.org)