Looking Back, Looking Forward: Fraxinus spp. and the Emerald Ash Borer

May 27, 2020 · 4 minute read
Looking Back, Looking Forward: Fraxinus spp. and the Emerald Ash Borer

I knew it was coming. But that didn’t make the inevitable any less heartbreaking.  Seven years ago I peeled off a loose hunk of bark from a fallen green ash tree in the northern Blue Ridge where I grew up and saw what I’d previously witnessed only on educational alerts – the serpentine “galleries” of the invasive Emerald Ash Borer (EAB) larvae.

By 2016 everywhere I looked I saw the defoliated crowns and “blonding” trunks of ash trees that were dying by the dozens (“blonding”—the shedding of bark—is the work of opportunistic woodpeckers mining the EAB larvae that are feeding on the tree’s vascular system, choking off water and nutrients). And just like back home in the mountains, a few years later I would discover I hadn’t realized how many ash trees lived in the James River Park System until they, too, started dying.

Deadly Invertebrate Invader

The aptly named Emerald Ash Borer, native to most of Asia from the Russian Far East to Japan, made its first documented appearance in North America in southeast Michigan in the summer of 2002 after most likely stowing away in cargo packing material made from wood. A year later it was detected in Fairfax County, Va. but was eradicated before its reconfirmation there in 2008. Regulatory quarantines on firewood ensued, distinctive purple monitoring traps deployed. But Emerald Ash Borer implacably spread throughout Virginia (with a 2019 Richmond region date-stamp) as well as to 35 U.S. states and the District of Columbia and five Canadian provinces, leaving tens of millions of dead ash trees in its wake. (For more on the biology and spread of EAB, visit the Virginia Department of Forestry’s EAB Story Map.)

Elegy for Fraxinus spp.

There are about 40 species of the genus Fraxinus worldwide, 16 in the United States, and of the four found in Virginia, White Ash (Fraxinus americana) and Green Ash (Fraxinus pennsylvanica) are the most common. Found throughout Virginia, White and Green Ash historically made up 2-3 percent of the forest composition and pulled duty as dependable residential and municipal shade trees.  

“The compoundly pinnate leaf structure of Fraxinus”

In a dense forest environment, ash trees didn’t grab my attention. I underappreciated them. But Fraxinus is a giver—ecologically and culturally. Its wood is ideal for tool handles, furniture, veneers, and most iconically, baseball bats. Its loose clusters of pale green to nearly purple flowers fruit to flat, winged seeds that feed songbirds and mammals. According to entomologist Doug Tallamy, in Bringing Nature Home: How You Can Sustain Wildlife with Native Plants, Ash species in Eastern deciduous forests host 150 species of Lepidoptera (butterflies and moths). The National Park Service in the National Capital Region cites 27 insect species including moths, butterflies, and bees that are restricted to ash as their host plant.

Those specialized host relationships include our own native ash borers, but against the invasive Emerald Ash Borer the trees have no defenses; native trees and invasive insects did not co-evolve to develop adaptive checks and balances.  The flashy invader reproduces prolifically, matures quickly, and spreads rapidly both under its own wing-power and by human actions. Where EAB has been present the longest, the mortality rate of Ash trees is nearly 100 percent. With them goes all that they gave—cooling shade, streambank stabilization, food and shelter for wildlife, and a mutually interdependent web of life whose loss is incalculable. In forests, the sunlit clearings they open in the canopy are ripe for colonization by invasive plant species (replanting hard-hit areas with a range of well-suited locally native tree species is a strategy for staving off invasives and fostering biodiversity).

The compoundly pinnate leaf structure of Fraxinus

The survivors

The U.S. Forest Service has dubbed surviving ash trees “lingering ash” and these apparently resistant individuals (a different kind of one percent!) are the subject of long-term genetic research, a  possible key to a future for Fraxinus

For now, frontline response to this late stage of Emerald Ash Borer’s assault continues to focus on treatment of trees that haven’t yet succumbed. The Virginia Department of Forestry operates a cost-share reimbursement program available to individual property owners and organizations. In 2019 the James River Park System applied for and received cost-share grant funding and treated thirteen trees in the Huguenot Flatwater Woods and Pony Pasture park units. Since then, the park system partnered with the Invasive Plant Task Force (and its fiscal agent, Friends of the James River Park) to successfully apply for a private foundation grant that is now funding treatment of an additional 40 trees. Volunteers are identifying good candidates that haven’t suffered more than 30 percent canopy loss. If you notice a tree with a blue ring painted on its trunk: that’s a survivor receiving treatment on a two-year cycle.

Characteristic “blonding” on a green ash tree.

Never say die

Reckoning that the Emerald Ash Borer was inexorably advancing toward the northern Blue Ridge, the same year I first suspected their presence I planted a half dozen green ash bareroot seedlings from the Virginia Department of Forestry in the woods where I had grown up and where ill-fated mature ash trees still gave the appearance of flourishing. If they survived, I reasoned, by the time they matured the Emerald Ash Borer might just be a bad memory. I wish I had planted more. Now I keep an eye on the canopy in Richmond’s parks, hoping to spot a survivor.