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)
They are not sheer cliffs, but steep piles of glacial moraine, rock and dirt. (sbnation.com)
(6) The most prominent oscillation — already noticed in glacial moraines in Scandinavia around the turn of the century — had begun with a rise in temperature, named the Allerød warm period. (history.aip.org)