Photo 1. The bark of the hop hornbeam tree is smooth on the windward side but cracked on the opposite, leeward side (Photo by M. Randić)
WHY IS A TREE’S BARK SMOOTH ON THE WINDWARD SIDE?
Nature field guides often teach us that, in a pinch and without a compass, we can use moss, the width of rings on tree stumps, or other indicators in nature, to determine the cardinal directions. They also tell us that tree bark facing north is, as a rule, rougher than bark facing south.
However, on the northern slope of Žbeljac Hill at the foot of Mali Platak, we came across hop hornbeam trees (Ostrya carpinifolia) where the bark was smooth on the north and north-east sides but cracked and rougher on the south side (Photos 1 and 2). This phenomenon was especially obvious on trees which grow along the edge of the stand and are more exposed to the bora wind (Photo 3). At present, we assume that the bora wind is the main “agent” of this phenomenon; perhaps ice crystals or particles of rock or sand, carried by the wind, hit the bark on the windward side and act like tiny projectiles, “polishing” and smoothing the bark.