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Plant Focus

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Dwarf cultivars can be ideal for a small garden. Here are three "mini oaks". 

Oaks in Two Parks of the Northern Great Plains

Fans of oaks are impelled to seek out the local Quercus representatives wherever their travels may lead, serendipitous though the destinations may be. This report highlights two sites near the limits of the footprint of Quercus macrocarpa in north central North America: the Prairie Arboretum in Freeman, in southeast South Dakota, and the Assiniboine Forest, in Winnipeg, Manitoba. In both places, Q. macrocarpa is the only native oak (Garner et al. 2019).

Q muehlenbergii
Quercus muehlenbergii in the Prairie Arboretum, July 2017

Yours truly has had the pleasure of visiting Freeman—my wife’s hometown and home of her parents—for many years. A small town of some 1,300 people set in a rather flat, agricultural landscape, since 1999 Freeman has been the site of the Prairie Arboretum—a community effort to provide an educational and recreation resource for the region focused on trees. The arboretum was developed by volunteers from 40 acres of former pasture and dedicated in 2002 (Waltner 2019).

This year, for the first time, I also visited Manitoba in July for a conference on reconciliation between indigenous peoples and descendants of European settlers. I was fortunate to find a time to visit the Assiniboine Forest on the west side of Winnipeg, about 450 miles due north of Freeman. Also a flat place—even more so!

Assiniboine
Assiniboine Forest marsh; the woodland at the edge begins with Salix spp., Populus woods on the left, Quercus macrocarpa comes close only as the smaller dark green tree in the center, the taller struggling tree, and the dark green tree at the right.

The Prairie Arboretum

The oak collection at the Prairie Arboretum focuses, one might say, on cultivars of Q. macrocarpa. The labeling includes ‘Ashworth’, ‘Corki’, ‘Kreide’, and ‘Simoni'. The collection also features species from the nearer parts of the American Midwest—Q. alba, Q. coccinea, Q. ellipsoidalis, Q. muehlenbergii, and Q. rubra—plus the East Asian species Q. acutissima and a delightful hybrid otherwise unknown to your reporter, the “bur live oak”, Q. ×burnetensis (Q. macrocarpa × virginiana).

Burnet's oak
Quercus ×burnetensis (Q. macrocarpa × virginiana), July 2017

I was able to speak recently, though briefly, with Lyle Preheim, who led the design of the Arboretum and established the parameters of the collection (and did much of the planting!). He is a farmer in the Freeman area and a tree enthusiast, having long experimented with grafting oaks and other species. The cultivar selection is an experiment in process. For example, three grafted individuals of the “bur live oak” were planted originally, and two failed. The third appears well adapted to the location and is producing seed. Lyle has successfully grafted additional young plants from the survivor and will soon plant out two of them, restoring the original design of a triangle of specimens. He and colleagues plan more additions and replacements for specimens lost in the Arboretum’s first years.

Simoni
Quercus macrocarpa ‘Simoni’, July 2017

What strikes the visitor from a milder climate is the impact of the wind on these young trees! The prevailing wind in summer, when the trees are in leaf, is from the south. Most of the trees in the open area of the Quercus collection, all planted within the last 20 years, have grown up bending with this wind. They have the sculpted look of conifers in the high mountains or at the coast. The specimens of Acer, Fraxinus, and Tilia in the arboretum do not have such a marked northerly lean.

Quercus rubra
Quercus rubra in the open at the Prairie Arboretum, July 2017

The bur oak does not grow randomly or naturally along the borders of farmland in the Freeman region, at least in these days, and, for reasons unknown, oaks do not often appear in the shelterbelts planted at farmsteads. The arboretum did install an experimental shelterbelt of Q. rubra set to the north and west of a line of Acer ginnala, some of which in turn lies behind a row of Picea. The northern red oaks are healthy and produce good crops of acorns. Where their tops reach above the neighboring maples, they splay out in a broad crown.

Quercus rubra shelterbelt
Quercus rubra shelterbelt with Acer ginnala, July 2019

In the greater shelter of the town, residents have planted a few isolated Q. macrocarpa and Q. rubra, and these individuals grow with the typical symmetry of park and urban plantings. Also, in a somewhat more sheltered location in the arboretum, three specimens of Q. ×bimundorum 'Crimschmidt' (trade name CRIMSON SPIRETM) grow in a nicely erect and healthy form.

Crimson Spire
Q. ×bimundorum 'Crimschmidt' (Q. robur × alba, trade name CRIMSON SPIRETM), July 2017

To find Q. macrocarpa growing naturally in the vicinity of Freeman, you can go about six miles west to the banks of the James River and tributaries like Wolf Creek, where some inhabitants refer to the trees as “scrub oaks.” Or you can go about 10 miles south to an upland called Turkey Ridge, where the prairie gives way on the north-facing slopes to steep ravines known locally as “the Gulches.” From the moist soil of these ravines, the Q. macrocarpa grow big and very broad, creating a mutually reinforcing shelter zone. May the young trees of the Prairie Arboretum one day have this majesty too!

Turkey Ridge
Quercus macrocarpa growing out of the shelter of “The Gulches,” Turkey Ridge, South Dakota, April 2019

Freeman is in hardiness zone 4b, at about 1500 feet, with 26 inches (660 mm) of annual precipitation on average.

Q macrocarpa ‘Kreider’
Quercus macrocarpa ‘Kreider’, July 2017

The Assiniboine Forest

The Assiniboine Forest lies almost due north of Freeman, at W 97.25 ⁰ per Google, versus the Prairie Arboretum’s location at W 97.44 ⁰. The Assiniboine Forest is 700 acres of semi-undisturbed native habitat within the City of Winnipeg, saved from urban development by the Crash of 1929. It is now bordered by residential areas on the west and institutional grounds (such as Canadian Mennonite University) on the east. It is primarily an aspen-oak woodland, with a large wetland in the center.

Populus woodland
Mixed Quercus macrocarpa and Populus woodland at a meadow’s edge, Assiniboine Forest, July 2019

Outside the marsh area, it appears moisture in the soil allows almost complete forest cover, though the trees are not large. Q. macrocarpa grows here primarily with Populus tremuloides and P. balsamifera, along with six species of native Salix. Other native trees include Acer negundo, Fraxinus pennsylvanica, and Ulmus americana. While your reporter was not visiting to explore the understory, the Cornus stolonifera, Corylus americana, and Prunus spp. could not escape notice. The park’s plant list identifies four plums in the mix: P. americana, P. nigra, P. pensylvanica, and P. virginiana.

Assiniboine Forest
A pure stand of Quercus macrocarpa

It was a marvel to walk in a mixed woodland and suddenly cross through an almost pure stand of Quercus and then a little further on a similarly pure stand of Populus. Although I have no experience with what a healthy recruitment regime would look like, it did appear to me that young plants were plentiful, even if the oaks are heavily browsed by deer.

Quercus macrocarpa
Quercus macrocarpa, common size (12-18 feet—blue water bottle hanging in the leftmost tree gives scale)

Winnipeg is in hardiness zone 3b, elevation 800 feet, with about 20 inches (505 mm) of annual precipitation on average.

References

Garner, M., K. Pham, A.T. Whittemore, J. Cavender-Bares, P.F. Gugger, P.S. Manos, I.S. Pearse, and A.L. Hipp. 2019. Population genetics of Quercus macrocarpa. International Oaks 30: 131-138.

Waltner, J. 2019. The Freeman Prairie Arboretum: A 20-year history. Freeman Courier. https://www.freemansd.com/article/freeman-prairie-arboretum-20-year-history (accessed Aug. 1, 2019).



Photos © Dirk Giseburt