The pattern is new in every moment

The last Saturday morning in January, the snow in Maple Grove was wet and eroding, pocked by thick rain. The ironwoods in the midstory were marcescent with finely toothed, nut-brown leaves that filled the branches of the tiny trees and could be seen throughout the woods. The musclewoods standing at the northeast entrance to the preserve were hanging onto their senesced leaves, which were translucent, sparse and unevenly distributed along the branches. In some trees, they were curled along the lowest limbs; in others, they were arrayed mostly along one edge. The fine distinctions that separate these two species originated an estimated 9 to 30 million years ago1, yet the two look like cousins, one patrolling the interior of Maple Grove, the other leaning by the entry. They look more like one another, to my eye, than modern humans look like chimpanzees.

The snow was soggy and took stains more easily than usual. It pooled in slushy depressions and where water ran across the trail, and there it was dark with clay and secondary compounds from fallen leaves. An asymmetrical corona of discolored snow encircled the bases of many of the oaks and maples. I had seen this before and chalked it up to the effects of water running down the trunk, thought nothing more of it. On this walk, however, I had the benefit of having Brooklyn, our dog, with me, and she was a reluctant walker. So I stood longer than I usually do, waiting with her, considering the pattern.

As I looked at tree after tree, I gradually realized three things. First, the asymmetric stain around the bases of the trunks did not seem to be associated most strongly with where the snowmelt was trickling down the trunk, but rather to fall more as shadows would, cast by the inclining trunks. The more canted the tree, the more asymmetrical the discoloration. Second, the stains did not just fall under the trunks: they also ran laterally away from the trees where there were low-hanging branches overhead, as though coloring had been dripped from the branches. Third, the stains were much stronger under the sugar maples than under any other trees, and the lateral streaks in particular seemed to be limited to the maples.

We had been suffering the normal freezing and thawing of a northern Illinois winter, when I would expect the sap to run, and these observations in combination made me wonder whether what I was observing was in fact exudate from fissures in the bark, forced outward by a combination of root pressure and the changing internal pressures of the tree as temperatures fluctuate and the sap alternately shifts back and forth between liquid and solid. When daytime and night temperatures cross the boundary between freezing and thawing, sugar maple sap tends to run more freely2, and this effect may be enhanced by rain3. I tasted the snow beneath several maples, hoping for dilute sugars, but I could not detect a difference in taste. It is possible that all I was seeing was the discrepancy in color of snowmelt off the bark of one tree versus another, though if that were the case, I would expect the snow beneath the oaks to be more strongly stained, as their bark has a relatively high tannin content4. I obviously have more watching and reading to do.

The narrow sugar maples scattered in the woods are prominent now against the snow. Many have cankers like swollen knees, trunks as big around as large zucchinis or watermelons tipped on end, bark curling around the edges of the scars as though to fill them in. You see a few great trees in the woods that have grown around their cankers, and some wear the old wounds well. Many trees, however, appear to have been killed by the fungus, Eutypella parasitica5, before they can grow much more than a foot or so in diameter. Then they stand dead and their bark is stripped off down to their shins, and they are polished by the elements and become like walking sticks jammed into the forest floor, but never returned for. I am just learning about this now–how, I ask myself, am I just learning about this now?–so I am not yet certain that every cankery tree I’m seeing in Maple Grove is a sugar maple. But many I am certain of.

There are chickadees and juncos singing in the woods and neighborhoods, and a fox passed the neighbor’s yard the other morning while I walked the dog. The neighbor’s chickens didn’t say a word, and the fox paid them no mind. Perhaps our neighbor has gotten rid of the chickens. The ice on the road comes and goes. The snow thaws to slush during the day, then freezes each footstep into raggedness by night. Frost settles on fallen logs and drips down the north face, where it freezes into a clear glaze; on the south side of the logs, the skim of water bleeding down is burned off by the sun, and that side is dry. The sun bakes the south-facing roof of our house dry. The north side still has a smear of greasy snow. The forest is by turns melting away and freezing in place.

Tuesday night, the dog and I took a walk in Maple Grove as the great horned owls were calling. Now that I have seen them once, I notice what I believe to be maple cankers everywhere. Some are the size of grapefruits. Some are ten feet long and start twelve feet above the ground. One tree is as big around as a city-street trash can and hollowed out with rot, inrolled bark framing the yawning mouth of the trunk, the interior streaked black with fungus.

The snow has had a few more days to melt and thaw and become icy, and it draped like chain mail over the logs. The sun was going down as we walked through, and the stains beneath the trees were predominantly under the white oaks, not under the maples. Was I misremembering? I looked for the same musclewood I had seen on Saturday, just from the opposite direction, and through the woods I could not see it. The snow had been flipped upside down in a band running 10 feet out from the trails, as the squirrels turned over every leaf in search of acorns. In a few days, almost nothing had changed, but the few things I’d been fixated on had shifted under foot.

… There is, it seems to us,
At best, only a limited value
In the knowledge derived from experience.
The knowledge imposes a pattern, and falsifies,
For the pattern is new in every moment

T.S. Eliot, “East Coker
Wild yam fruits, East Woods, 2020-01-29

This afternoon there were ironwood fruits scattered over the snow in the Arboretum’s East Woods, papery wild yam capsules hanging from the vine, stick-tight achenes of white avens on stiff stems leaning over the snow. The snow beneath a black oak was stained dark brown from the decomposing husks. Squirrel excavations were everywhere. The trails were icy, and the dusting of snow over the top captured squirrel tracks perfectly.

Gray squirrel tracks, East Woods, 2020-01-29

I’ve had this experience often before, of thinking I’ve found a pattern, then disbelieving it, then realizing over time that some pattern was real under what I’d noticed the first time, but not what I’d thought initially, more nuanced. We all have. The habit of science is the conditioning of one’s mind not to settle on spurious patterns, to recognize when the pattern has congealed. We may we do this quantitatively, or we may cultivate habits of mind that make us wary of our false beliefs. Either way, it seems to be a week of both watching for patterns and watching out.

Plants referenced:

  • Acer saccharum – sugar maple
  • Carpinus caroliniana – musclewood
  • Dioscorea villosa – wild yam
  • Geum canadense – white avens
  • Ostrya virginiana – ironwood

  1. The most recent common ancestor of ironwood and musclewood is estimated based on fossil calibration of whole chloroplasts at 17.1 Ma, but with considerable uncertainty; this is the case with almost all such estimates. Yang X-Y, Wang Z-F, Luo W-C, Guo X-Y, Zhang C-H, Liu J-Q, Ren G-P. 2019. Plastomes of Betulaceae and phylogenetic implications. Journal of Systematics and Evolution 57: 508–518.
  2. Kim YT, Leech RH. 1985. Effects of Climatic Conditions on Sap Flow in Sugar Maple. The Forestry Chronicle 61: 303–307.
  3. Johnson LPV. 1945. Physiological Studies on Sap Flow in the Sugar Maple, Acer saccharum Marsh. Canadian Journal of Research 23c: 192–197.
  4. White, bur, and red oak–the Quercus species present in Maple Grove–are not among the oaks with the highest bark tannin content, but they still appear to be higher in tannins than the sugar maple, which comes in at an estimated 0.4-2.7% vs the averages of 4.5-6.5 of the local oaks. Rowe JW, Conner AH. 1978. Extractives in Eastern Hardwoods: A Review. Madison: Forest Products Laboratory, USDA Forest Service. 67 pp.
  5. For an interesting and readable account of the natural history and biology of maple canker: Kessler KJ, Hadfield JS. 1972. Eutypella canker of maple. Forest Pest Leaflet 136. Washington, D.C.: USDA Forest Service.

St. Louis Canyon before dawn

Friday morning a week ago, right in the middle of January, I woke early at Starved Rock State Park. I was housed with a group of my colleagues in the lodge, which is perched at the edge of the long trail paralleling the Illinois River. The trails there mostly overlook the river, with occasional loops down to connect the bluff-top trails with the shoreline trails. They are intersected by sandstone canyons that open into the river, with waterfalls spilling over one ledge after the next. I have been here many times with my family when the boys were younger, and we have hiked these trails in both directions from the lodge numerous times. I had not been here in years.

I headed toward St. Louis Canyon. The first half hour of my walk preceded the dawn, but the trails were as broad and hard as sidewalks, impressed into the soil and easily felt beneath one’s boots. It would be difficult to accidentally veer from the path, which is handy, especially in the dark: four feet off the trail in some places would make for a potentially lethal tumble onto the road or trails below. The ice crusted over the creeks babbling along the sandstone was the color of moonlight. The moon itself was murky behind the clouds, fading into and out of view. I stood on each bridge I crossed and watched the water gurgling beneath the ice, which piled up around the edges of the watercourses and framed the edges of the sandstone ledges where they gave way to the canyon below, where the ravines open up into a rich forest until it tumbled into the broad, slow river.

There was no snow. In the veiled moonlight the leaf litter of white and red and black oaks was quilted together with fallen branches and hop hornbeam leaves to frame the trail. The night before, my colleague Jake had pointed out a black oak that was cracked open below. He guided our attention upward. There, the narrow crown was rotated to lean against the adjacent trunk. The tree trunk had failed, perhaps in a storm, presumably in part because it was hollowed out with rot. At knee level, the bark was twisted and buckled on the outer face, straight on the inside where it was tacked at the base by the bole leaning away from the trail toward the north. I passed this tree now as I walked. All along the ridgetop this dry-mesic oak forest stretched, rimmed by junipers near the edge and white pines on the shoulder of the bluff. No birds were singing, and only the occasional car passed on the road below.

I reached the switchback just before the road at the west end of the trail. It was still dark, but the sky to the east was becoming a lighter shade of gray. The sound of cars rolling by on Highway 178 faded in and then subsided as I followed the creek weaving out of St. Louis Canyon alongside and under the trail. The walls of the canyon rose around me. The small river crashing nearly 80 feet1 from the creekbed at the top of the fall to the rocks below muffled the nearby road. I stood and watched it, and even in the dark I could see the water flashing as it fell. I laid down in the gravel and listened for perhaps 20 minutes. There was nothing to hear but water.

It was still dark, but the sky sifted through the white pines rimming the canyon top was lightening up in the east. I studied a carpet of liverworts (Marchantia) on the cliff wall, pressing my face to it to see what I could make of the fleshy lobes in the predawn. The forest above had been obvious even in the dark: this subtler forest I only noticed as day started to break. As the sky grew lighter, chickadees started to move around, febeeing to one another. The days are growing longer.

I walked up and out. By the time I reached the ridgetop, it was light. The 15 minutes before sunrise go remarkably quickly, relaxing into dawn over the course of just a few minutes. I came across several trees that appeared to have been gnawed to pieces. One had rained wood chips, forming a halo on the forest floor at its base that glowed like a sun rising through the oak leaves. Another had been chewed nearly to the ground. I don’t believe this is porcupine activity, though perhaps, nor beaver (we were too high up, and I saw no true beaver trees). It is a mystery whose answer will likely be obvious one day when I least expect it to. We ate as a group, then hiked around Wildcat Falls, where there were Pennsylvania sedge and black oak with mossy rugs between, a krummholz-like copse of stunted oaks, white cedars on the edges of the ravines. We stood and watched Wildcat Falls filling the canyon with snowy ice shards. We passed white oaks spackled with Aleurodiscus and Auricularia, rhizomorphs of Armillaria. We admired the magnificent root system of a white pine that was exposed by erosion as it careened downhill toward the trail and trees whose wood had twisted as they grew, vessels intruding upon one another in systematic asymmetry: anatomy becoming morphology, morphology becoming forest structure, structure becoming the ways in which trees and forests shape the human environment.

Which is what we were at Starved Rock to talk about. So we hiked out, past a grove of rock polypody, the undersides of whose fronds were pocked with spores, and fallen black oak shoot tips, evergreen leaves of white avens, decomposing trees hosting gardens of bonnets or split open to reveal an unexpected grove of turkeytail fungi. Snow was on its way, and we returned to our meeting with the sense of efficiency that you get when weather is coming and everyone in the group wants to get home. We drove back to the Arboretum after lunch.

I biked home from the Arboretum just after sundown, as the snow was beginning, when you have that delightful feeling of the snow just a little icy, pricking your cheekbones as home pulls you in, and you know it’s warm there and your family is home and it will be supper time when you get there, and there’s tea and maybe a movie that night.

The next day was snowy, then temperatures dropped to the low teens, where they should be in January. It was now a month past the solstice. Someone I was reading last year–probably Burroughs–pointed out that the climatic height of the season lands about one month after the astronomical turning point: the hottest summer and the deepest winter are each about one month after their respective solstices. I had never thought of this, but our temperatures bear it out: the hottest day of the year in Chicago is July 18, not June 21; the coldest is January 29 instead of December 212. Monday afternoon, I watched a great blue heron fly off over the road just as I was riding out of the Arboretum. Wednesday afternoon, stepping out of the house with the dog at 4pm, I felt as though I were looking through a bank of ice. At Maple Grove Forest Preserve, the snow was pierced by Carex jamesii. There were gray squirrel excavations and an orange mycena mushroom desiccating on a log in the snow. American pokeweed was crumpled cross-legged in the thicket where it had grown in abundance late into fall. Armillaria rhizomorphs were everywhere: on red oaks, on sugar maples, everywhere that bark was stripping from a tree.

I read back over what I’ve written and say aloud to myself some of the words I’ve chosen (Armillaria, babbling, copses and creekbeds, dawn). I suspect that only humans worry about the words we choose. Only a human could drift so far from itself as to say, as N. Scott Momaday wrote, “… and always I listen to my writing. I must hear it or else I cannot appropriate it to my spirit.”3 Only a group of humans would get together in a place as beautiful as Starved Rock to talk about trees. Yet we do. In the bargain, we get to enjoy the hell out of the waterfalls. We get to recognize that the world is beautiful. Can the other animals do that? I doubt it. I think the exchange is worth it.

It rained today, and the chickadees were singing. It’s dark out now, the snow is eroding away. I understand we are supposed to have more snow tomorrow, but the temperatures are projected to waver around freezing, so I don’t know whether it will stick around. I hope so. I so enjoy these few months of winter.

  1. Great Lakes Waterfalls. url: (accessed 2020-01-19).
  2. Average temperatures in Chicago; scroll down to see the plot across the year:
  3. N. Scott Momaday. 2018. Preface to House Made of Dawn, originally published 1966, 50th Anniversary Edition issued by Harper Perennial Modern Classics, New York.

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.

  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: [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.
  7. From “The Shortest Day” by Susan Cooper.
  8. T.S. Eliot, “Ash Wednesday.”