In an earlier blog, I wrote about the American beech tree’s ability to retain its leaves long past the winter months; a survival strategy known as marcescence. The American beech tree is unique in another way: it is the only one of ten species of the genera Fagus in the temperate region of the northern hemisphere to occur in North America. It’s just another reason for my love of this tree.
Considered the patriarch of the eastern hardwood forest, the presence of American beech trees (Fagus grandifolia) usually indicates a rich forest flora. I say “usually” because intense browsing by white-tailed deer can completely wipe out the forest understory. Nonetheless, it is always fun to explore a forest that has its share of this beautiful tree.
During one of my winter hikes through a beech-maple forest at the Banshee Reeks Nature Preserve near Leesburg, Virginia, I noticed a conglomeration of black powdery substance piled high on select branches of some beech trees along the trail. This was the first time I had seen this, so I photographed it and return to my office to begin yet another investigation into the nature of the American beech tree. What is that stuff?!!!
I discovered the black powdery substance is a sooty mold that grows on the sugary honey secretion – called honeydew – of insects such as aphids, scales, and whiteflies.
In the case of the American beech tree, the culprit is most likely the beech blight aphid, which colonize branches of the tree and exudes its honeydew on the branches below the colony. The black mold is caused when the fungus Scorias spongiosa grows on the honeydew deposits. While cosmetically unappealing, the accumulation of sooty mold is harmless to the tree.
So the next time you are hiking in the forest and you see a pile of what looks like burnt charcoal on the branches of an American beech tree, rest assured it’s not from the outdoor cooking of a Keebler elf. It’s just a sooty mold!