EAB larvae are phloem feeders, and these grubs bore elaborate galleries just under the bark, as seen in the photo above. The end result is that the tree eventually can no longer uptake water and nutrients and it dies. In the Midwest, Green Ash and White Ash, Fraxinus americana, are the most common ashes and thus the most frequently killed, but EAB does not discriminate. Our other three species (in Ohio) are also destroyed.
As ash trees can comprise up to 40% of forest communities, especially in low-lying damp areas such as in this photo, the impact of EAB is extreme. There most certainly will be losers, in addition to the ash themselves. A host of moth species are ash-dependent; their caterpillars must feed on the foliage of these trees. Their prognosis is dicey at best, and we may lose a number of these animals. There are undoubtedly many other ash-dependent organisms as well. Any genus of tree as prolific as are the ashes will serve as important keystones for many animals.
The downfall of ash will also spawn some winners, at least in the short term. An obvious group of beneficiaries are woodpeckers. The fat juicy EAB grubs are easily available to these chisel-billed hammerheads, and woodpeckers quickly learn to exploit this new food source. In fact, I believe it was abnormally high woodpecker activity that first alerted people to the initial infestation in Michigan.
Here in Ohio, there is little question that woodpecker populations are increasing across the board. This increase has been apparent for a while. I edited the winter season for the Ohio Cardinal for 2009-10, and made this comment under the Downy Woodpecker account, after noting that its Christmas Bird Count total was easily the largest ever reported: One must wonder what temporarily beneficial impact the runaway proliferation of the invasive Emerald Ash Borer is having on woodpecker populations.
A few recent papers SUCH AS THIS showing increases in certain woodpecker populations tied to EAB, and a recent media request seeking my opinion on the matter, prompted me to revisit the Ohio Christmas Bird Count (CBC) data. While problems may exist with CBC data, I think it works well in documenting woodpecker trends. Woodpeckers, for the most part, are easily identified, and rather conspicuous and likely to be found.
The following graphs represent the collective data of all Ohio CBC's from the years 2003 (onset of the EAB invasion) to 2012 (last year that CBC data is available). I threw in White-breasted Nuthatch, too, as these bark feeders are well known for taking wood boring grubs, including species in the Bupestridae. The results are telling. It'll be interesting to see what this winter's crop of CBC reports brings, but it'll be a while before all of that data is accessible. Likewise, the summaries of woodpeckers for the Ohio Breeding Bird Atlas will be interesting, and the Atlas book should be out sometime in 2014.
There are certainly a host of variables aside from the Emerald Ash Borer that can effect the population status of our woodpeckers. But evidence is increasingly suggesting that the new and abundant food source is stimulating population growth, at least in some species. One thing seems certain. Whatever the causes, it's high times for our woodpeckers.