Leaf Science

Oct. 12, 2008

Each year, after the summer season is over, the beaches empty, and the fudge shops slow down their nutty output, Northern Michigan experiences an extra influx of tourism. “Leaf Peepers” take advantage of the less-crowded tourist towns Up North to get an eyeful of Northern Michigan’s colorful fall foliage, that returning profusion of reds, oranges, yellows and browns that signals the start of autumn. But how do these terrific colors happen?
Leaves are green in the first place because of chlorophyll, a pigment that captures solar rays and utilizes the sun’s energy to create a sort of “food” for plants – simple sugars of water and carbon dioxide. In the warm summer growing season, chlorophyll dominates the makeup of the leaf’s chemistry, masking out any of the other pigment colors that may be present, that summer-green brightness.
Once colder temperatures and fewer daylight hours begin to arrive, chlorophyll – which is sensitive to the cold – slows its production and dwindles, leaving room for the other pigments like orange, yellow and brown called carotenoids. Add in secondary pigments (reds and purples) called anthocyanins – to shine through the diminished green tones of the average leaf.
It may not be a very romantic explanation when compared to the views that have inspired many a poet and artist, but this complex interaction of pigments and environmental influences is still a fascinating reoccurence each autumn.

TIME TO FALL
Now, here’s a little mystery to temper with all that technical info above. Scientists are still not completely certain about the function of the color change and the subsequent dropping of the leaves -- they’ve figured out the how, but not necessarily the why. The most widely-accepted theory is that deciduous plants are thought to shed their foliage in fall because it would be too difficult to maintain the regular green leaves (chlorophyll) and leaf density during the cold temperatures and low-light period of winter.
One reason for the color change may be that the anthocyanins, in particular, protect the leaves from the lower temperatures, a kind of “tree sunscreen,” if you will, that helps the plants reabsorb nutrients, such as nitrogen, with more efficiency.
Another hypothesis is that the leaves on some trees change color to help attract birds to their berries in the colder months, in a symbiotic relationship. the birds get a meal and the tree or shrub gets, well, fertilized at a time when the soil is less helpful to the tree than it might typically be in the warmer parts of the year.
And, yet, another idea is that the colors themselves are smartly devised as warning signals towards insects that might use the trees as winter hosts (and thereby damage them). Aphids, for instance, are known to have “red receptors,” meaning they tend to avoid trees with red leaves. So a maple tree turns its leaves red, and voila – it’s taking action to try and keep itself pest-free for the winter months, keeping it healthy until spring.

FINDING THE COLORS
Although autumn colors arrive wherever deciduous trees are found, there are a few regions of the world that are actually well-known for their spectacular fall foliage, namely, the eastern U.S. and Canada; Scandinavia and northern Europe; and finally Russia, and eastern Asia – where leaf-peeping is called koyo or kanpukai, which translates to “red leaves hunting.”
Northern Michigan ranks with New England in the popularity of its color tours, due to the thick forests and distinct color changes that take place from mid-September onward. It’s difficult to predict just how long each year’s autumn colors will last, but you’re generally able to take decent photos through the end of October; and if you know your trees, you’ll even be able to pick your favorite color pallettes for your pictures.
Remember the cholorophyll, carotenoids and anthocyanins mentioned earlier? Well, chlorophyll, of course, is responsible for leaves’ basic green colors, but it’s carotenoids that contribute the yellow, orange and brown tones (they also bring those colors to such things as bananas, carrots and corn), anthocyanins bring in the purples and reds (which they also do for red apples, concord grapes and cherries.)
Those colors are distributed among particular species of trees. so, if you like your leaves in tones of brown, ranging from tan to dusty cocoa, look for oaks, elms or beech trees. If you prefer golden yellows and bronzes, then aspens, poplars, hickory trees, birches, and especially black maples will oblige. Like orange leaves? You’ll find them on sugar maples. Reds can be seen on other varieties of both maples and oaks, plus sourwoods and black tupelos. Dark purple leaves can be found on dogwood trees.
If you’re running late with your photo-taking, seek out some oak trees, which tend to hold on to their colored leaves longer than their associates. If you’re really behind schedule, there are always spruces, cedars, firs and pines – which keep their green needles throughout all but the harshest (as in Arctic) winters due to the anti-freeze-like substances inside their foliage cells and the heavy wax coating on their needles.

ENDANGERED LEAVES
Our glorious fall displays are being affected by global warming. According to the Michigan Tech journal Global Change Biology, forests in North America and Europe have been staying greener longer as CO2 levels are rising. so you might find that seeking out those perfect autumn photos might take a little longer into the fall season each year.
That’s not necessarily bad news, at least not right at first. the trees will initially be more productive with the extra photosynthesis they’ll acquire throughout a longer and warmer growing season (tree growth already appears to be starting earlier in the spring). but, it’s too early to know how older forests or new growth will be impacted over time. Other environmental problems, such as pollution, poor soil conditions, funguses and clear-cutting can show up in trees too that bright, red tree you spy before the autumn season even officially starts, say in late August, might be a result of that tree being under stress and calling up the anthocyanins to help protect it. Yet, another reason to get out in the great Northern Michigan fall weather and get those photos while you can.

Leafy Destinations
Here’s a quick overview of some of the best places to go for fall leaf-peeping in Northern Michigan:
- The Leelanau Peninsula may be one of Michigan’s premier autumn drive destinations. not only is there an abundance of trees, but you’ll also find estate vineyards, lighthouses and beaches for plenty of
variety on your day trip.
- The new Boardman River Nature Center, just south of Traverse City on Cass Road, features 600 acres of some of the best leaf-peeping in the region, with a trail running along the shore of Sabin Dam Pond.
- The Pere Marquette State Forest in Cadillac has plenty of hiking trails, horse campsites and, of course, trees awaiting your photographs, while the Huron-Manistee National Forests (Manistee) make up almost a million acres of public lands. that’s a lot of photo ops.
- Looking for something a little
different? Take a canoe down the winding Au Sable River (Grayling) or treat yourself to a vintage train ride on the Timberliner, which travels from Kawkawlin, just south of Bay City, to Grayling for your scenic viewing.
- Utilizing US 131 and US 31, you can travel from Boyne Falls through Petoskey, up M119 (the “Tunnel of Trees”), through Cross Village, and all the way up to Mackinaw City, with quaint cafés, shops and trees lining the roads along the way.