Hawthorn tree (Crataegus monogyna) in limestone pavement. On the windswept, treeless uplands of Yorkshire Dales National Park, UK, one of the ways a tree can survive in its early years is to grow in the micro climate of a grike fissure. The limestone pavement in which it grows is a deeply fissured formation called clints (the tabular blocks) and grikes (the deep fissures) so typical of glaciated karst landscapes. Hawthorns are a small tough tree that can survive the adverse conditions.