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| Bur oak leaves usually turn brown in autumn, but they can be bright yellow under the right conditions. |
Each autumn, the Helen Allison Savanna Scientific and Natural Area brightens the landscape in harvest hues, as the bur oak’s brown and the pin oak’s dark scarlet leaves rise above the golden grass. While no maintained trails run through the savanna, old logging trails and degraded footpaths can be used for a 0.8-mile round trip hike (named the Bur Oak Trail here for convenience sake).
To reach the trailhead, from Minn. Hwy. 65 east of Bethel, take 237th Avenue east. Turn right/south on Gopher Drive, which becomes 229th Avenue. Go right/south on Durant Street; the junction of 229th and Durant marks the natural area’s northeast corner. In a little more than 1000 feet, park off the side of the road and head west into the natural area.
When Euro-Americans arrived some two centuries ago, oak savanna once covered around 8700 square miles of Minnesota, stretching in a band from north of what is now the Twin Cities to the Iowa border. Today, just 1 percent of that savanna remains.
A transition area between prairie and woods, the savanna attracts a lot of wildlife, including white-tailed deer and turkey, which feed on the plentiful number of acorns that drop from the trees, while the red-headed woodpecker enjoys bugs in the oaks’ trunks.
Bur oak
The dominant tree in the savanna is the bur oak. It can grow quite tall – up to 98 feet – but most Minnesota savannas have far younger and hence shorter trees. Their trunks also are massive, reaching up to 10 feet in diameter.
Not surprisingly, a big tree like the bur oak produces big acorns – in fact the bur oak bears the largest of all North American acorns. Some of them reach up to 2 inches in length and 1.5 inches wide.
If conditions are right, the bur oak’s leaves will turn yellow in autumn. Older bur oaks often boast gnarly branches, making it a perfect Halloween tree.
The bur oak is Minnesota’s ninth most common tree. Though king of the oak savanna, it can be found in every county of the Gopher State.
Pin oak
Northern pin oak also is common in the savanna. Though considered a medium-sized tree and usually shorter than the bur oak, in has been known to achieve some impressive height and girth. The record pin oak in Minnesota rose 95 feet tall with a diameter of 4.5 feet before toppling in a wind storm.
While usually paling in size to the bur oak, the pin oak more than makes up for it with its autumn leaves. They typically turn either a deep maroon or a rusty red. As winter arrives, the color diminishes to brown.
Pin oak also is less prevalent in Minnesota than the bur oak. You won’t find it in most western prairie counties or the northern aspen-oak forests.
While many of Minnesota’s oak savannas have been plowed under into farm fields or paved over into urban areas, the suppression of fire also has contributed to the ecosystem’s demise. Without natural fires, shrubs – especially the invasive buckthorn – take over the grasslands. Bur oaks persist, though, as those older than 12 years are fire-resistant thanks to their thick bark.
As trails are not maintained in the natural area, you’ll want to wear pants, long-sleeve shirt, and hiking boots while traversing it.
The oak savanna continues north of the natural area at the University of Minnesota’s Cedar Creek Ecosystem Science Reserve. While the trails there are in much better shape than those at the Helen Allison, stick to the latter. Scientific research is underway at Cedar Creek, so casual visitors aren’t allowed.
