How Emerald Ash Borer will Affect our Preserves

March 16, 2012

With this week’s report that the emerald ash borer (Agrilis planipennis, or EAB for short) has been found for the first time in southeastern Pennsylvania we are reviewing our strategies for dealing with this imported beetle that kills all native ash trees (members of the genus Fraxinus only, not mountain-ash/Sorbus). A tiny yet mobile insect pest, EAB represents a huge threat to ash trees in North America. It is a different kind of problem than the Asian longhorned beetle which has invaded several ports and urban areas in the U.S., feeds on and kills a variety of native hardwoods, but does not travel far on its own. In contrast, EAB has resisted quarantine efforts but is host-specific to ash. Its larvae burrow under the bark of the trees and destroys the living tissue that conducts water and nutrients between the roots and leaves.

We are not surprised that EAB has made it here. We have always said “when,” not “if.” Not all of EAB’s dispersal has been on its own, however. It has probably been spread on firewood being moved, nursery stock, or other wood products.

White ash (Fraxinus americana) and green ash (F. pensylvanica) together make up something in the order of magnitude of 5% of the forest at places like Crow’s Nest Preserve. There is no way to save all of the ash trees in our forests. Nor is it prudent to cut all the ash trees down while they are still alive (as was done a century ago when the chestnut blight was sweeping across the country)—there is a chance that some native trees, like the non-native ones that evolved in the presence of the emerald ash borer, may have some natural resistance to the pest. These are the ones that could re-colonize our forests someday and return ash trees to the landscape.

Removing ash trees and chipping them may be a strategy to reduce the number of EAB insects in a neighborhood so that remaining trees being treated with insecticide stand a chance of survival—but this is not practical on a forest scale. Removal and chipping has worked to eradicate isolated populations of Asian longhorned beetle from a quarantined area, for example. But those were far more isolated invasions of a much larger, and as noted above, less-mobile insect. And it has to be very thorough to be effective.

Over the last two years stewardship staff of our preserves has been directed to choose a handful of ash trees, mainly specimen trees in the historic landscapes and viewsheds, and spray them with an insecticide, Dinotefuran, applied to the bark and then translocates throughout the tree. Our hope is that a few trees will survive so that we can help protect the genes of ash trees for the future. We also follow the research literature carefully and will adapt our strategies as we can.

What can you do? Still be careful and don’t transport firewood: buy it where you burn it. Keep an eye out for ash trees on the decline and report changes to your local extension agent. Plant a diversity of native trees on your property—preferably from a local nursery that sources its plants locally.

This is a problem that is going to cost billions of dollars nationwide in lost timber, habitat, and property value. Ash wood is used in a lot of products, not the least of which is baseball bats. Pennsylvania forests are a major source of ash wood for major league baseball.

The moral of the EAB story—other than illustrating the risks associated with transporting (intentionally or otherwise) living things to new places—is about diversity. Natural Lands Trust has generally managed our lands to increase diversity because this can confer more resilience to forests that endure threats such as the one posed by emerald ash borer.

As Tim Burris said in a recent post, Pennsylvania “wants” to be woods; naturally, historically unmanaged lands have (except in the presence of heavy pressure from invasive plants) returned to forest cover. But what we get in the future will likely be a different forest than what we’ve had in the past.

Posted by Daniel Barringer on March 16, 2012