Home / Blog / The Science of Autumn Leaves

Blog


The Science of Autumn Leaves

Liz Clift

Pando, which is Latin for ‘I spread,’ is a clonal colony of Quaking Aspen (Populus tremuloides) and is believed to be one of the world’s oldest and most massive living organisms. Here are its A/S/L stats (that’s right, all of you who were teenagers when AOL chat became a thing, we’re absolutely going down that road):

Age: 80,000 years
Sex: Male
Location: Fishlake National Forest, Utah

Pando may seem a bit old, so let me put that in perspective on the human scale. Somewhere around 80,000-60,000 years ago, Homo sapiens was first making its way into Asia. We had not yet created permanent drawings (60,000-40,000 years ago) or reached Australia or Europe.

With so many years (and roots!) under its belt, Pando has developed quite the mass. With its large root system, and approximately 40,000 trees, it is estimated to weigh roughly 13 million pounds and cover 106 acres. If you search online for Pando, you’re likely to find autumn pictures of it—which is to say, autumn pictures of aspen filled with golden leaves. I haven’t seen Pando in person yet, but it’s on my bucket list!

fallpando02

Depending on where you live, aspen might be a regular part of your autumn leaf experience. Folks in our Denver office have noticed that aspen in some areas of the mountains are already starting to change color, and a local news station recently put out its annual peak colors guide, which lasts through mid-October. Earlier this week, we were talking about what makes for the best fall color (cool nights and warm days with lots of sunshine), and because we’re biologists and ecologists, we think that the science of leaf color is pretty cool. Check it out!

Fall color is caused by four main groups of biochemicals:

  • Chlorophyll
  • Carotenoids
  • Anthocyanins
  • Tannins

You probably know that chlorophyll is what makes leaves green. But, did you know that it is constantly being “renewed” during the summer, and that is part of what helps leaves keep their vibrancy? As the days shorten and nights become cooler, chlorophyll breaks down faster than it is produced, and the carotenoids are revealed.

aspens-1

Carotenoids are responsible for most of the yellows and oranges we see in nature (like the ubiquitous orange carrot!). Although carotene is present throughout the growing season, it is masked by the chlorophyll. As carotenoids are revealed, the leaves start to turn yellow (or orange).

Anthocyanins create autumn reds and purples, and are commonly associated with trees like red oaks (Quercus borealis), red maples (Acer rubrum), and sumac (Rhus spp.). Anthocyanins are produced when the sugar concentration in the leaves increases and reacts with anthocyanidins—and many factors can influence the exact color and vibrancy of the color produced. Leaves with more acidic cell sap will usually produce red colors, while more alkaline leaves will turn purple-to-blue.

Tannins occur naturally in the roots, bark, leaves, and fruits of many plants—but are especially associated with oak trees, due to the use of oak tannins in converting animal hides into leather—in fact, the etymology of the word tannin is from an old German word, tanna, which means oak! Tannins are highly astringent and help protect plants from disease, pestilence, and herbivory. This compound become visible when both chlorophyll and carotene have broken down, and result in leaves simply turning brown and falling off the tree.

If you’re able to see autumn leaves in your area—or if you travel to see autumn leaves somewhere else—we’d love to see the photos. Please share them to our Facebook

Comment Below

RSS feed for comments on this post.

 

Sorry, the comment form is closed at this time.