Behold, the mighty oak

Given their place in folklore and literature, it’s no wonder that I’m a fan of oak trees. Oaks have graced the works of Shakespeare and the tales of Robinhood, were sacred to the Druids of the British Isles as well as ancient gods including Zeus and Thor.

Yet, born and raised on the farm in Basswood, we didn’t have much opportunity to interact with them. Oaks were “southern trees,” something you read about in a Mark Twain story, or in Merry Olde England.

Which demonstrates my ignorance, of course. As the vast majority of readers will know, oaks are a common tree in southwestern Manitoba, found south and east of a rough line drawn from Miniota to Neepawa, and then north to Dauphin. And this doesn’t include the oaks that grow further north of this line in the Assiniboine and Little Saskatchewan River valleys.

Bur oaks, the native oak in Manitoba, are a tough tree of the prairies and plains of the American mid-west. They are well adapted to the grasslands as their thick corky bark protects them from heat and drought. The bark also shields them from damage from all but the hottest fires.

If you have ever walked through an oak forest, you would likely have noted the deep pile of dead leaves at the base of the trees. These leaves provide fuel for the frequent, low intensity grass fires which you would normally have found in the plains of the northern United States and southern portion of Manitoba before the onset of large-scale agriculture. These fires actually favour oaks, as the flames eliminate other woody competition such as aspen while doing little damage to the oaks themselves.

However, circling back to the relatively distinct demarcation line of “oaks and, then no oaks” across southwest Manitoba, you might note an interesting phenomenon. Despite their adaptations, oaks have a northern limit. While they can handle some cold, they are generally relegated to areas that fall into the 3b (and warmer) zone of the Manitoba plant zone hardiness map. In case you don’t have that particular map handy, it might be easier to say that oaks don’t thrive in areas where the coldest winter temperatures go below -37 C.

Which leads me to the discussion about my perceptions that oaks are spreading north. As I have outlined in previous articles, acorns are a prime food for bears and turkeys. Beginning at the end of August, you will find me wandering around staring up into the tops of oaks, both to assess the quality and quantity of acorns and also hopefully to see a bear or two.

And every year I notice that there are more oaks growing and thriving in areas where they should have no business being. Specifically, I am referring to areas in Riding Mountain National Park where oaks have not been common, including an area south of Frith Beach on Clear Lake, and at the bison enclosure at Lake Audy. Both areas are (or were) firmly in hardiness zone 3a, with winter low temperatures of -40 C.

I write “were” because the expansion of oaks provides further proof that our local area is feeling the direct results of a warming climate. Admittedly, these particular trees on the northern fringe of the expanding range are quite small and gnarly looking, especially when compared to the surrounding aspen and spruce forest. But judging from the amount of bear poop and torn tree limbs, bears are making increasing use of this expanding, albeit raggedy-looking, food source.

On this theme, 2025 has been a bit hit and miss in terms of oak reproduction. While the acorn crop along the escarpment of Riding Mountain National Park was pretty dismal, the oaks in other areas seemed to outdo themselves. Rae and I spent some time among the oaks in the Pembina valley in late August, and the acorns littering the ground made for treacherous strolling, akin to walking on marbles.

This is a pretty clear case of predator swamping, which I have written about in the past. Briefly, this is where trees produce huge crops of nuts one year with the objective of overwhelming the squirrels, bears, and wild turkeys with an abundance of food. With any luck, at least some of the nuts escape being eaten and are able to grow into a new generation of trees. In subsequent years, the trees skip producing seed, leading to some lean seasons for the animals that depend on these foods to make it through the winter.

This is a great strategy for a long-lived species such as oaks. Given that they can live for over a hundred years, producing a bonanza of acorns every two or three years can still produce a lot of offspring over a lifetime.

Finally, on the topic of predator swamping, in my last article I was remarking about the quality and quantity of Saskatoon berries in southwestern Manitoba. I can now add that it seemed to be a good year for Saskatoons across the country. Daughter Katrien, living in St. John’s, Newfoundland and Labrador, reported that the berries were big and plentiful on the east coast, while our own investigations in British Columbia in early August bore ample fruit too (pun intended).

Why did this year produce so many berries across the country? Is this a case of predator swamping in Saskatoons? And stranger still, how did all the bushes communicate to each other that this was the year to produce? This is yet another example of the mystery of life on earth, and a reminder that we know, and perceive, so little of the natural world. It keeps me humble!

» Ken Kingdon lives in the heart of the Riding Mountain Biosphere Reserve. Send him a text at 204-848-5020 if you have stories to share.