Fall leaf color along the North Shore

Retta James-Gasser:

Minnesota State Park Naturalist Retta here. In today's podcast I'll talk about the two seasons of fall color on the North Shore of Minnesota's Lake Superior and give an honorable mention to the annual fall salmon run that occurs in North Shore streams.

But first I have to tell you that this is my first experimental park naturalist podcast. If you have comments or suggestions for this podcast or for possible future park naturalist podcasts, please let me know by emailing me at [email protected]. I'll provide the e-address again at the end of this podcast because I'd like to hear from you.

Now on to the North Shore fall color. Fall leaf color on the North Shore of Lake Superior in Minnesota can be beautiful. The landscape is filled with yellows, oranges, and reds and it's punctuated with evergreen trees and various shades of green. This is all set against the sapphire blue expanse of Lake Superior, the world's largest freshwater lake by surface. It's especially beautiful on a sunny day.

There are two seasons of fall color on the North Shore of Lake Superior due to the temperature variations found from along the low Lake Superior shoreline to the inland high country and Sawtooth Mountains, which are a series of eroded volcanic lava flows. The first season begins inland on the highlands around mid-September with color peaking between September 20th through the first week in October. Look for the orange and some red colors that are found on the high ridges where a lot of maple tree grows. The second season occurs directly along the shoreline of Lake Superior. Here the aspen and birch trees produce a yellow burst of color along Highway 61. The yellow color usually peaks during the last week of September and may hang on through mid-October.

I'm often asked what kind of weather causes the best fall leaf colors. That would be sunny, warm days combined with cool, but not freezing nights and not too many rainy days. The exact kind of weather that most people like. In a way, fall leaves are a lot like people when it comes to weather preferences. However, not all leaf color changes are brought on by weather. Damage by insects or other animals, disease, tree roots standing in water, drought, soil temperature change, or other stress to trees can also cause leaves to change color earlier or later than usual.

I'm also asked why leaves change color in fall and how. Usually it's the decreasing daylight hours in fall that acts like a trigger causing the trees to stop making the green chlorophyll in the leaves. When this happens the other colors become apparent. The yellow-orange colors we see in fall were in the green leaves all along, we just couldn't see these colors during summer because the green pigment called chlorophyll acted like a mask to the yellows and oranges. But this is not the case of the red colors. I'll tell you more about red colors later. Just like the Halloween mask disguises a person's identity until the mask is removed, chlorophyll masks the fall yellow and orange colors. The red leaf color develops in late summer. It's a chemical reaction with tree sugars and the cool nights and warm days.

Fall color is a sign that the tree is shutting down for winter. Tree growth slows as cold weather approaches and in deciduous trees photosynthesis, which requires water, eventually stops as the chlorophyll is no longer produced. Since liquid water is not available during winter in northern areas deciduous trees don't need their leaves. So these trees simply get rid of the leaves and the buds that formed during the summer growing season eventually become dormant for winter.

Many evergreen trees such as pine, spruce, fir, and cedar survive winter with their leaves still hanging on because they have special adaptations to compensate for scarce water supplies. Many evergreen leaves are covered with a thick, waxy coating that helps hold water in. Also, some evergreen leaves contain a kind of natural antifreeze that helps prevent injury to water-filled cells.

Just what happens to the fallen leaves? There are several functions for fallen or down leaves. On the forest floor the fallen leaves improve soil condition as the leaves are broken down by bacteria and fungi. But not all leaves are equal. Maples are nutrient pumpers because maples pump nutrients into the leaves before falling off. Oaks are nutrient poor because oaks pump nutrients into the roots and not the leaves for winter. They take a longer time to decompose. Fallen leaves also improve the soil structure by creating air space in the soil for oxygen and water to reach the roots. The fallen leaves shield soil from high temperatures, runoff and erosion, and slows evaporation. And during winter fallen leaves can serve as a blanket to critters and as a source of food.

Fallen leaves in a stream are broken down through bacteria and fungi decomposers and by three categories of insects: shredders, collectors, and scrapers. These insects in turn become prey food for stream predators such as fish, like salmon, which migrate up some of the North Shore rivers to spawn. The annual fall salmon run lasts for about a week-long period and usually occurs between mid-September through mid-October. To find out when the salmon are running inquire at your favorite North Shore state park.

My husband said the salmon deserve more than just an honorable mention, because, after all, the fish are actually doing the work by swimming upstream whereas the leaves just change color and fall off.

All this talk about falling leaves makes me marvel at the aerodynamics of leaves as they fall. My fellow park naturalist friend Linda told me about a "Catch a Falling Leaf" activity.

Linda:

Have you ever tried to catch a falling leaf? It's harder than you think, try it. This is a great activity to do with friends or family or at least watch them as they dance around the woods trying to do so. Some leaves are easier to catch than others because of leaf size and shape and aerodynamics. Maples are the hardest for me, because when I reach for one I create a mini air current that sweeps the leaf away.

Retta:

If you enjoy trying to catch a falling leaf or merely watching for leaf color change you are in luck in Minnesota, because you have over a month to do this. You can visit the northern part of the state when colors can start changing by mid-September and work your way south as the leaves change their colors throughout the state all the way down to the southern border when peak color lingers on through October.

If you access the web you can track leaf color change through Minnesota by looking at the Minnesota Department of Natural Resources homepage at www.dnr.state.mn.us. That's all for now on fall leaf color.

At the beginning of this experimental park naturalist podcast you may recall that I said that I'd like to hear your comments or suggestions. Please send them to me at [email protected]. Thank you kindly in advance for sending your comments. If there's enough interest, perhaps an "Ask a Minnesota State Park Naturalist" podcast could be done in the future.

Thanks for listening and enjoy the Minnesota State Parks naturally.