Poplars, or aspens, are one of our most common trees, and it’s not unusual to see a group of them all growing together. But look closely and you may just find that you’re not looking at a group of trees at all. You may, in fact, be looking at part of a clone network, the biggest living creature in Muskoka.
Quaking aspen (Populus tremuloides) is the most widely-distributed tree in North America. It’s found in every province and territory, throughout New England and the Great Lakes states, and in mountains as far south as Mexico. It goes by a number of names, including Aspen Poplar, Trembling Aspen, and Poplar.
The tree that trembles
The quaking, or trembling, is a reference to the lightness of its leaves. Even the slightest of breezes, too light to cause other trees to move, will set aspen’s leaves gently fluttering, creating the appearance that the tree itself is trembling. Sit quietly beneath an aspen tree on a calm day, and you may be rewarded with a gentle shuffling sound from above, as though thousands of butterflies are flapping their wings above you.
Aspens are easy to identify – the bark looks a little like a grey-green version of a silver birch, pale and smooth with dark horizontal lines.
They grow quickly and are among the first trees to colonize an area after a fire or land clearing. The individual trees don’t live long by tree standards – 150 years is about the maximum – and an aspen that’s more than 80 feet tall or 20 inches in diameter is a giant.
What makes aspens really interesting is the way they grow. They produce cottony seeds which emerge before the leaves in spring to be blown on the wind and will germinate within days of landing on moist soil. But they can also grow new stems from their lateral roots.
Aspen roots aren’t deep, but they are wide, and they spread rapidly. Where conditions are right, the roots will send a sucker above the soil surface, which becomes another tree stem.
The tree will repeat this process again and again, sometimes thousands of times. The first stems might die off after a century or so, but by then there can be thousands of other stems growing from the same roots. Collectively, the group of trees is called a clone, since they are all genetically identical.
Not all aspens that grow in a single stand are part of the same clone – there can be several clones intermingling, just as there may be other trees or plants whose roots share the same soil and whose stems battle for the sunlight. Scientists can tell the clones apart by DNA analysis, but the rest of us can get a pretty good idea by looking at small differences, like the size and shape of the leaves, the time they turn colour, and the specific shade of yellow they exhibit.
Aspens are male or female, so sex can also distinguish clones from each other. You’ll need to look closely at the flowers, or catkins. Males grow long and straight, dangle below the branch, and fall sooner; females are firmer and grow out from the branch, staying on the tree much later in the spring.
So how big and old can an aspen clone get? Huge and ancient! The biggest known creature on earth is a single male aspen clone in southwest Utah. It covers 106 acres of land, is estimated to weigh 6,600 tons, and estimates of its age range from 80,000 to a million years.
This giant is known as Pando. He has survived glaciers and countless wildfires – even when fires have destroyed every one of his trunks (currently numbering around 40,000), Pando’s roots live underground and just send up new trunks when the threat is over.
Aspens only produce seeds when conditions are right, and conditions haven’t been right in Pando’s area since the last glaciers receded; it’s likely been about 10,000 years since he last produced seeds.
Unfortunately, it seems that Pando is slowly dying. Ranchers are allowed to let their cattle graze in the area for two weeks every year, and humans have eliminated the wolves and bears that used to keep deer populations in check. These browsers are eating all the new stems that emerge, and nearly all of Pando’s current stems are nearing the end of their lives.
Fortunately, there are efforts underway to fence off areas so that Pando can continue to regenerate.
Nobody knows the size or age of the biggest stand of aspen is in Muskoka. But when you’re out in the woods this fall, enjoying the brilliant yellow of the aspen leaves, consider that you could be looking at something that has been growing here for hundreds, or even thousands of years.