It was not the smoothest pitch.
”Oaks are awesome.” the email began. “That is why Illinois renamed October OAKtober in 2015. But Chicago oaks are under attack from the following: Oak wilt; Bur Oak Blight; Oak Anthracnose; Root Rot; Sudden Oak Death...”
My reply was not a sarcastic “Oh no, not oak wilt!” But an enthusiastic “Yes!” to discussing the oak situation with an arborist. The reason? My hidden agenda, a cloud of guilt over the pin oak I planted in my front yard almost 20 years ago and murdered.
“People like to live around oak trees,” said Shawn Kingzette, a certified arborist at Davey Tree, based in East Dundee. “But our oak ecosystems are at risk.”
We talked about oak ailments. Sudden Oak Death, for instance, is caused by a fungus carried in the soil of rhododendrons. “It’s a relatively new disease, especially in the Midwest,” Kingzette said. “It’s a phytophthora fungus.”
Then I brought up the lost pin oak. Tall, with pointy leaves. I did my best to see it into the world, but ... sniff! ... it died. My fault?
“With pin oaks we have a saying: ‘The right tree in the right place,’” he began, soothingly. “It could be the soil you have. Pin oaks like an acidic, good-draining soil. It might not have been the right setting for a pin oak to thrive. You might not have done anything specifically wrong.”
Whew. While I had him on the line, I had to ask: those deeply lobed leaves; what’s the purpose? I assumed they cut down on wind resistance.
“I don’t know whether you believe in God,” Kingzette began, betraying himself as a non-reader of the column. “But just the beauty, the shape. The rounded lobe of the white oak, the pointed lobes of a pin. I’m sure there’s some benefit, but it’s just pretty.”
A decent answer, but that can’t be it. Time to break out the big guns. I called Andrew Hipp, the Morton Arboretum’s resident oak expert, University of Chicago lecturer, author of 50 papers, winner of a Fulbright Scholarship for his work on oak phylogenesis — how the types of oak spread over the eons and around the globe. What’s with the lobes?
“You’re jumping into an active area of research,” Hipp said. “People don’t all agree on why northern temperate trees tend to have lobed leaves. Most oaks in the world do not have lobed leaves.”
They don’t? I didn’t realize that. How American of me, to assume what we’ve got here must be the rule everywhere.
“In Mexico, there are 160 oak species, and lobing is vanishingly rare,” Hipp said. “The leaves are scalloped, or with spiking margins. If you went to East Asia, there are 110 species, and lobing is almost absent.”
And some say I never break hard news in the column. Hipp shared my wonder, initially.
“When I start working on oaks, I was flabbergasted,” he said. “I didn’t even know I was looking at an oak.”
As to what function the lobes might have, I was on the right track with wind resistance.
“There are some theories why northern temperate trees are more lobed,” he said. “It turns out in oaks in the United States, species with more lobed leaves tend to be in drier sites. There is reason to believe one of the benefits of being lobed could be it reduces the temperature of the leaf. Another reason: there’s a mechanical advantage, if you have thin leaves, the tree has less weight to bear.”
The oldest oak fossils are about 56 million year old, found in Austria.
“Oaks arose at a time when temperatures were much warmer than they are now — the Early Eocene Climate Optimum, right around 52 million years ago across what is North America and Eurasia,” Hipp said.
If they arose during a warmer period, does this mean climate change is good for oaks?
“No, to the contrary,” he said. “They arose then, but did not flourish until temperatures dropped; 50 percent of diversity in oaks arose in the last 10 million years, a time of precipitous temperature decline. In Mexico red oaks and white oaks went crazy, in East Asia there was a spike in diversification in ring cupped oaks. They were constrained to the far North, but as temperatures decreased, broad leafed evergreen forests were pushed out, and in comes the temperate forests previously way up in the North. That’s when the oaks went wild.”
Oaks are ambassadors for globalization and the mixing of populations.
“One reason oaks are so damned important is, if you snuff out oaks your whole world changes,” Hipp said. “They beg the question: what on earth is a species? They hybridize readily, with lots of gene float between the species. Oaks share genes that are advantageous. Gene flow between species help oaks adapt to novel climates, help them migrate. They share genes while species maintain their distinctiveness. I want to understand why we have the biodiversity we have. Oaks are intellectually very satisfying and economically very important.”
Speaking of vibrant gene melting pots, I wondered about the oak situation in Chicago. About 13,000 of the city’s 545,000 trees — just along streets, not counting parks or private property — are oaks, according to senior city forester John Lough.
“We’re planting as many oaks as we can get our hands on,” Lough said. “It’s a great tree and given the right circumstances, it can thrive.”
Lough said oaks have a reputation for being slow-growing, but “with proper care they will grow at the same rate as any tree.”
Then he said something I did not know — if you have a parkway, you can ask the city to plant a tree there, and it will. It’s free, but might take a few months.
“It’s a service we provide,” he said. “By all means, don’t forget to request an oak tree.”