Since it is better to be cold and dry than cold and wet, I prefer November in Winnipeg over Vancouver. I had flown almost half way across Canada on a red eye after a few days in and out of the cold rain at the University of British Columbia Botanical Gardens, and my boots were finally dry. Even so, the windy Manitoba morning kept geese flying low and my Winnipegger companions hunkered down as we descended a wooded ravine to dig roots for class. The cold soil was hard enough to break a shovel, but we still found growing root tips and lots of lively critters under the frozen duff. And I ran into some old friends. The stumpy, twisty bur oaks that hugged the stream bank greeted me, and, along with the promise of perogies in a warm Ukranian diner, made the early winter morning not so bad at all.
Southern Manitoba is almost as far north and west as bur oaks grow. Winnipeg is the only large prairie-province city with a substantial canopy of native bur oaks. My life as a far-flung tree geek takes me to distant places like Vermont’s Battenkill watershed and the flats of western Kansas where I can still keep the company of my old friend bur oak. Even while lost along the Lebanese border I was welcomed by her close cousins, the white oaks of the Levant and western Syria. Maybe I was just desperate for a familiar face.
Members of the genus Quercus are the most widely distributed hardwood trees of the northern hemisphere, and the white oak group is the most widely distributed of these. Bur oak has the largest range in North America and the broadest environmental tolerances of any of our native oaks. But because of its native range, adaptive capacity and promiscuity (they hybridize easily), they are also quite variable in form and individual hardiness. In places like Winnipeg (where life can be hard even for locals) the greatest promise for oak planters are the offspring of local native stands. The winter bur oaks of that cold ravine are not the same bur oaks one might find in warmer climes, and trees of southern origin (“provenance”) would likely live short, unproductive lives if they were to survive the first winter at all.
Native Names for Native Oaks
Because of their wide range and diversity of form and habit, botanists sometimes refer to the southern populations as Quercus macrocarpa var. macrocarpa, and those of more northern regions as Q. macrocarpa var. oliviformis. A further distinction is made by some for the extreme northwest populations, Q. macrocarpa var. mandanensis. Those experts who make these distinctions do not always agree on the characteristics of each variation or “cline,” but the northwestern clines do tend to be smaller in stature and acorn size. Bur oaks of southern provenance tend to open buds and grow leaves earlier in the spring and hold green leaves later in the fall than their northern kin, which makes them more susceptible to cold injury when planted up north.
My friends who are germinating bur oaks pay close attention to seed source and add a qualifier to the species label that indicates provenance. The result is a “Black Hills South Dakota Bur Oak,” a “Douglas County Nebraska Bur Oak,” and so on. Another way to do this would be to use abbreviated forms of the original local names given to native bur oaks. The Black Hills bur oak would be the “utahu bur oak,” and the Douglas County oak would be the “tashka bur oak,” each according to the native peoples that lived among bur oaks and were sustained by them, thus preserving the distinctive provenance in name. This indigenous approach would require good research and verification of the native tribal names for bur oak and diligent recording of acorn origin in terms of location, habitat and even individual trees.
If you want to do the right thing by planting a bur oak where bur oaks are native, then provenance matters. A Tennessee-source bur oak planted in an arboretum in a Nebraska town is not a native tree—regardless of what the interpretive plaque says or the Latin nomenclature devised by an 18th-century Swedish botanist. But the modified Linnaean system of binomial nomenclature used by modern botanists does allow for a third epithet. When a naturally occurring subdivision of a species requires delineation, then “variety” can be added. Therefore, combining the local Native American name with the Latin botanical name yields Quercus macrocarpa var. patki (after the Pawnee name) for bur oaks originating from wild stands in certain parts of northwest Kansas and southwest Nebraska, for example.
I’m certainly in no position to tell botanists what to do, but I will bring it up at our next native tree growers meeting. I’m also not a purist; I’ve planted many oaks of unknown or distant provenance. But if we want to take the long view and plant trees with the best chance of thriving with the most ecological benefit, then provenance matters.
Part two of this article, to be published in the August issue, discusses the seasonal “clock” by which trees function within the plant community.