The ashes of Maple Grove

The solstice this year was cold enough for ice crystals in the soil and crevices of fallen trees, warm enough for crane flies on the wing. In the hollows where the cold air pools, the ground was frozen and brittle. On the warmer slopes, it was clayey, plastic. Fungal mycelia were bedded down with the earthworm castings. A chainsaw buzzed in the neighborhoods to the west of Maple Grove. The Burlington Northern Santa Fe rumbled along the tracks at the north edge of the Forest Preserve.

I have been walking in these woods almost weekly for the past three years, more irregularly for the seven years before that. Around 2007, two years before my family and I moved to Downers Grove, emerald ash borers arrived in DuPage County from their point of entry in 1990s southern Michigan (the data is an inference, not an observation, as they weren’t discovered there until 2002¹). I work at The Morton Arboretum, where great attention was paid to the arrival of this xylophilous east Asian beetle. It was clear by the time that it arrived that the loss of the ashes would be inexorable, and over the course of a year or two, The Arboretum took down almost all of the great ash trees in the East Woods. I remember advising a friend to do likewise with the few ashes he was considering treating for EAB on his own property. They are goners, I reasoned. Why protect what you can’t hope to save? My neighbor, who is also a friend, was gracious. He is an actuary, and I get the sense that he thinks about things similarly. Whether he agreed with me I don’t know, but we are still friends.

This day, the solstice, after bumping into the crane fly, I encountered an ash approximately 80 feet tall, still clothed in bark, but loosely. I could peel it back easily with my hands, like the margins of a robe or cracked sheathing off of electrical cable. The inner surface of the bark was frosted, the bole inside was slowly being emptied out by carpenter ants, sawdust filling the gap at the base, the surface pebbled with excavations and etched, intricately, with emerald ash-borer trails. The bark rattled upward for 20 feet from where I had loosened it. At the foot of the tree, the crown had rained branches, perhaps in a storm. One had impaled the forest floor like a loosed javelin. No one had been hurt. Lichens from the canopy had fallen 50 or 70 feet and were now understory lichens, just for awhile, until they would be overtaken by someone else colonizing the fallen branches. The history of lichen succession that was for decades proceeding in open air at the top of this tree stood at the beginning of a new chapter, when it would be overwritten by succession in the rich forest leaf litter.

This was a magnificent tree. I noted its location and started to walk again. Within 20 feet there was another dead standing ash, then another. I looked around. More than ever before, I was struck by the hulking ash boles shattered on the forest floor or standing with broken crowns, splintered branches dangling. In the northern half of Maple Grove Forest Preserve especially, it seems the lion’s share of the fallen trees are ashes. There are fallen sugar maples and red oaks and bur oaks as well, of course, for these are the dominants of the forest now. But roughly two out of every three trees I encountered on the ground this day was an ash, and almost all of them a foot and a half or more in diameter.

An entire partition of this forest has gone down in the course of a decade. When I first walked in Maple Grove Forest Preserve, there must have been some emerald ash borers in the forest, but I was ignorant of them. Since their quiet arrival in our quiet town, the beetles have been inscribing passageways under the bark, devouring the phloem that carries food down from the leaves, and scratching up the outer layers of xylem that carries water upward from the roots. It’s been a slow but invisible death² under our noses, as the insects worked on the trees from the crown downward³. They arrived as adults, chewing on the leaves, and would have been apparent to the attentive as the upper branches died⁴. But as those rich upper leaves wilted and the trees were weakened, the beetles moved their way downward and choked the trees off at their trunks. The final death has been abrupt as it seemed: even if the insects were there for a decade, the trees gave up over the course of a couple years.

Ashes have been drawing in carbon and giving back for 1000s of years in these woods, and they are the sole food or breeding home for an estimated 43 invertebrate species and a nonexclusive source for an additional 240⁵. Green ash alone was, ten years ago, the fourth most important urban tree species in the Chicago region based on basal area, the eighth most important in terms of carbon sequestration, and the single most abundant street tree⁶. Loss of the ashes will profoundly affect the forests we walk through.

I have been watching these trees come down increasingly over the past three years. But it was really this fall that I became aware of the magnitude of the problem. In the past six months alone, numerous trees have fallen right over or beside the paths I walk most often.

But this day was the solstice, when “promise wakens in the sleeping land,”⁷ and I was more than usually aware that even dead, the ashes are not quite done giving. There are the ash seedlings that we find all over the woods: what their future is we don’t yet know, but it’s hard to imagine that it’s promising. But it’s not just the seedlings I look to today. The adults themselves have become knitted through with fungal hyphae, feeding woodpeckers in abundance as they desiccate in place and become riddled with new insect tunnels and their attendant bacteria, then shatter and fall to the ground. The carbon they’ve stored up will return to the forest in a slug, enriching the soil, forming bedding and fertilizer for wildflowers and new trees.

We are living through the third eradication by disease in roughly a century of an eastern North American tree: American chestnut, American elm, now the entire genus of ashes. It’s going fast, but it’s not over yet, and we won’t feel the last shocks for awhile. In the meantime, there is a lot of natural history wrapped up in death, decomposition, and the anticipation of what lies on the other side of the gap. We are being handed tragedy on a grand scale and obliged, at this point, to wring what insights we can out of it and make better decisions next time, so far as we are able. I am reminded of T.S. Eliot’s “Ash Wednesday:”

Because these wings are no longer wings to fly
But merely vans to beat the air
The air which is now thoroughly small and dry
Smaller and dryer than the will
Teach us to care and not to care
Teach us to sit still.⁸

We are now two weeks into the new year. It rained all through the night on Friday, turning to snow some time Saturday morning. St Joseph Creek was running high by the afternoon. The pond in the middle of the preserve was so high I didn’t recognize it at first, depositing ice five to 20 feet from its edge that would slump when the water beneath receded a few days later, and the upper surfaces of the leaves and branches were frosted with wet snow that, by the time I found it, was bristly with needles of ice. Everything looked cleanly hairy, like a scurfy enchanted lawn.

Walking around the edge of a wetland perched at the top of the hill near the south edge of the preserve, I passed an enormous red oak that was rotted out inside, cracked open at fifteen feet above the ground. It’s not just ashes that are going down, but for now, it’s mostly ashes. It will be for decades.

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1. Jonnes, Jill. 2015. Urban Forests: A Natural History of Trees and People in the American Cityscape, ch. 18. Viking, New York.↩
2. Here I am indebted to Tricia Bethke, Forest Pest Outreach Coordinator at The Morton Arboretum, who graciously talked through some of the history and biology of emerald ash borer with me. Any errors are however mine.↩
3. USDA Northern Research Station. 2016. Biology of the Emerald Ash Borer (web resource). url: https://www.nrs.fs.fed.us/disturbance/invasive_species/eab/biology_ecology/planipennis/ [accessed 2020-01-20; last updated 2016-03-14]↩
4. Jonnes, Jill. 2015. Urban Forests: A Natural History of Trees and People in the American Cityscape, ch. 18. Viking, New York.↩
5. Gandhi KJK, Herms DA. 2010. North American arthropods at risk due to widespread Fraxinus mortality caused by the Alien Emerald ash borer. Biological Invasions 12: 1839–1846.↩
6. Nowak, David J.; Hoehn, Robert E. III; Bodine, Allison R.; Crane, Daniel E.; Dwyer, John F.; Bonnewell, Veta; Watson, Gary. 2013. Urban trees and forests of the Chicago region. Resour. Bull. NRS-84. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 106 p. https://doi.org/10.2737/NRS-RB-84.↩
7. From “The Shortest Day” by Susan Cooper.↩
8. T.S. Eliot, “Ash Wednesday.”↩