I get how the same genus of animal can end up in different parts of the world, birds or insects for instance, but how did a plant as rooted as an oak get so widespread?
Researchers think it’s due to what they call “parallel evolution.” There are different parts of the world where conditions like temperature, sunlight and rainfall are similar. In those areas, plants can evolve similarly as well. Scientists have found fossilized Quercus pollen on multiple continents.
But how do oaks spread regionally on a smaller scale?
With a lot of help. Plants like dandelions or milkweeds have light, wispy seeds that carry easily in the wind or on the feathers of a bird. Small animals may eat these seeds and then poop them far away from the original plants.
Acorns are too heavy to spread like that, so they rely on streams, animals and people. Water carries them downstream to new habitats. When squirrels or other animals forget where they’ve buried acorns they’ve gathered, those acorns can grow into oaks. The process takes hundreds of years, but it works. People who liked oaks for their shade and lumber planted acorns as well. But that’s not to say I’m not worry about our future.
Oaks are worldwide and live a long time, so what’s the worry?
Yes, we live a while. Some of my acorns grew into trees before humans had electricity. In DuPage we can live to be 250 years old. But we don’t live forever, and if there aren’t enough larger younger oaks to replace us, our numbers could start thinning.
But an oak can produce around 10,000 acorns in a year. How can there not be enough replacements?
Only one in 10,000 grows into a mature oak and only if conditions are just right. If other brushy, woody plants take over an area before a sapling gets big enough, it won’t get enough sunlight to grow into a mature tree. And although humans have helped spread oaks worldwide, they’ve also turned oak habitats into farms and buildings, meaning less space for those saplings to grow. Add natural threats like oak wilt and gypsy moths, and our numbers can drop even more. And that can be the start of a chain reaction because we’re a keystone species.
What’s a “keystone” species?
A keystone species is a member of an ecosystem others can’t live without. If a keystone species disappears, the entire ecosystem can change — or not exist at all.
More than 100 different animals eat our acorns. Fungi, bacteria and worms that live at our feet decompose dried leaves and other plant parts so the nutrients locked within them can return to the soil.
Hummingbirds pull lichens that grow on our trunks to build their nests, and squirrels winter in the crooks of our branches. Insects on our bark are vital “fast food” stops for warblers and other migrants in spring and fall.
Certain wasps lay their eggs inside our twigs, which form mostly harmless woody “galls” as the larvae grow under the surface. Woodpeckers and other birds look for galls for the tasty meals inside.
Humans use our wood to build homes, and our roots soak up enough water each day that we help prevent flooding in developed areas. The list goes on, but you get the idea.
Oaks are truly amazing. But sadly we’re out of time. Any parting words for our readers?
Absolutely. This fall the Forest Preserve District and other agencies are holding special OAKtober programs highlighting all of the roles we Quercus play in DuPage. Readers can find ones in DuPage preserves in the calendar of events.
They can also celebrate by visiting forest preserves like Herrick Lake, St. James Farm, Waterfall Glen, and Meacham Grove, where we’ll be showing off our spectacular colors. If they’re interested in planting oaks in their own yards, “Extra Care of Oaks” goes more into that.
Excellent. Thank you for joining us.
And thanks to your readers for caring about oaks!