Blonding of Ash Trees

Another gentleman and I performed a wetland delineation of a forested wetland (PFO1A) on February 10, 2017.  The site was in Bowie, Maryland, on an unnamed tributary of Collington Branch, which ultimately flows to the Patuxent River.  The woodlot study area was bounded by Dunwood Crossing Drive to the north, Secretariat Drive to the east, Alysheba Court to the south and Dunwood Valley Drive to the west (Prince George’s County ADC Book Map 15-C-7).  Nearby parks included Allen Pond Park and Belt Woods Natural Environment Area.


While working through the forested wetland and floodplain, I noticed that the dominant, mature overstory trees were primarily green ash (FACW), all of which had an unusual appearance of being partially or more often wholly de-barked.


Unbeknownst to me at the time, is that one of the best diagnostic features to confirm emerald ash borer is splitting bark on green ash trees.  Woodpeckers relish the larvae and pupae under the bark of infested trees.  When feeding, woodpeckers chip away at the outer bark exposing lighter-colored areas of the inner bark.  This phenomenon, called woodpecker “blonding,” is a reliable indicator that the tree is infested with emerald ash borer.  Apparently, if I were to have looked closer for physical signs of the beetle, I would have seen the ‘D’ shaped exit holes in the bark of the ash trees.


Emerald ash borer will attack healthy green ash trees, although adults may prefer to feed on or lay eggs on stressed trees.  When emerald ash borer populations are high, which was the case at my location, small trees can die within 1-2 years of initial infestation, while larger trees may take 3-4 years before succumbing to this pest.


The ash in my study woodlot stood out like sore thumbs because of the blonding damage, and it made me realize that once these trees die, how much more the forest will become an open, disturbed marsh, not dissimilar to beaver flooding damage.  This was my first opportunity to see a level of borer infestation that will eventually wipe out this particular woodlot, and how much of an impact the borer will have in our region into the near future, where green ash is a major player of bottomland forests.


The photos do not do justice to how pronounced the phenomenon appeared in the field.  Now that I understand what I saw, it reminds me of how bad Dutch elm disease (American Elm) and chestnut blight (American Chestnut) were to those species.