Year after year, the fleeting season of fall draws visitors to forested areas around the country. There is magic in the oranges of maples, yellows of birches, and reds of dogwood. Fall’s reputation is assisted yet again by the dwindling bug population and cooler, more comfortable hiking conditions.
Join us on the Gunflint Trail as we watch our trees follow the stages of fall in their full glory.
Forest of the Gunflint Trail
Here
on the Gunflint Trail, we are solidly in the border lakes subsection of the Laurentian mixed forest. This landscape was heavily influenced by the passing glaciers of the Wisconsin ice age, which tore all the topsoil and softer rocks away and left high quantities of exposed bedrock. Many of the lakes in this area were also shaped by this event. Some, like Gunflint Lake, were carved out in long, east-west patterns. Others were dammed off by glacial till.
Over the past 10,000 years, life has settled back into this area. Lichens set the stage by breaking up rocks enough for moss to take hold. Once moss was established, they created enough soil for the first plant life. After many years trees were able to take root as well. At this point in time, a thin layer of soil covers much of the landscape, though there are still many places
with exposed bedrock.
Trees of this area include many conifers; balsam fir, white spruce, and jack, red, and white pines are common sites. Among the deciduous trees, paper birch, quaking aspen, mountain maples, and mountain ash can be found. The understory, or plants occupying the forest floor, include lowbush honeysuckle, wild sarsaparilla, many types of ferns, and taller things such as beaked hazel, red elderberry, and flowering dogwood. The Gunflint trail is also home to many wetlands, which have a slightly different forest composition. Alders, tamaracks, willows, white cedar, black ash, and black spruce can be found in these areas. The understory of wetlands includes sweet gale, Labrador tea, bog laurel, and many other plants.
Ideal Conditions for Fall Colors
Though always spectacular, fall colors vary year to year. Environmental conditions throughout the seasons play a part, beginning with the spring. A warm, wet spring conditions gets the ball rolling for good fall colors. It’s also helpful to note that a delayed spring tends to push the color change back a few weeks.
Moving into summer, once again warmth and moisture are key ingredients. Heavy sun helps to produce anthocyanins, which leads to excellent reds in many trees. Carotenoids are always present in trees, however, so yellows and oranges are more stable season to season. Too little or too much rain also tends to dampen colors. Drought conditions in particular tend to weaken fall colors for various reasons, including an early turning and loss of leaves.
For fall itself, warm sunny days with cool nights are ideal. Nights around but above freezing help to brighten the reds and oranges, but an early freeze will knock all the leaves off prematurely. Too much wind or rain is not good in the fall for the same reason; leaves are forced off the trees, which shortens the peak of fall.
This year, we are sitting in a good place for a colorful fall. Our late spring delayed them by a few weeks, but we had plenty of rain and sun this spring and summer. So far, the fall has a comfortable mix of mild rains and sunny days, with only a few windy days. Think back to the weather in your area; what will your fall look like?
The Colorful Journey
All summer long, trees have been busily taking advantage of their short growing season. The sun, the rain, the soil, and a helpful chemical component called chlorophyll have been guiding our trees through the sugar-creating process known as photosynthesis. With our wet spring and summer, we have had amazing growth this year.
However, as the night gains on the day and the warm days begin to dwindle, growth slows in the forest. Chlorophyll, which is responsible for the green spring and summer color of leaves, starts to break down and allow the other pigments to show through.
At the very start, low bush honeysuckle and sarsaparilla litter the forest floor with shades of yellow and red. On the roadsides, thickets of golden ferns join the array.
Next are the maples; the absence of chlorophyll allows the carotenoids and anthocyanins to paint the leaves orange and red, made all the more striking against the still-green leaves of other trees nearby.
A few short weeks after, usually around the equinox, dogwood, mountain ash, and cherry trees begin their own transformation. The anthocyanins in their leaves add more layers of bright red to the lower canopy.
Not too far behind, xanthophyll begins to dye our birches and aspens yellow. Occasionally, one the quaking aspens will surprise us with a gold or bright red pigment as well. Soon after, willow trees add a rusty red tone to the scene.
In the wetlands, black ash trees also begin to blaze yellow. Alders turn yellow to brown in color, and some leaves remain green.
The final tree to turn up here in the north woods would be the tamaracks, the only deciduous conifer native to Minnesota. These trees shine brilliantly amongst the dark backdrop of black spruce.
The Fall
Along our journey through fall, nights have overtaken the days. Day time temperatures now only reach the mid-fifties. The wind has grown bitter and cold. At this point, our trees are completing the last steps to prepare for winter. The woody parts of trees are well suited to cold weather, but the tender leaves are not. This means that trees must either lose their leaves or toughen them up to survive the frigid temperatures.
In response to the changed environment, a hormone reaction sends a message to each leaf to create an abscission layer. This layer slowly separates the leaf petiole (or stem) from the branch by blocking off the leaf veins. This causes leaves to stop photosynthesizing and either display their xanthophylls and carotenoids or start producing anthocyanins. When the abscission layer is complete, a leaf can fall without creating an open wound.
When the weight of a leaf becomes too great, it will fall and drift to the forest floor. Occasionally, a gust of wind will cause a flurry of leaves in all the colors of the season to swirl around you. With this final push, a tree can enter its dormant stage until the following spring.
Some plants, particularly in the wetland understory, will keep their green leaves attached all winter. This is because when a wetland freezes in winter, it essentially becomes a desert. Their leaves become a valuable source of water in those scarce times. Keeping leaves also helps save resources by negating the need to create leaves again in the spring. One plant around here that does this is Labrador tea, a small leafy shrub that litters wetland floors.
The Final Act
A leaf’s purpose does not end after it falls off the tree. Year after year, falling leaves add layers to the forest floor. This provides habitat to many forest critters and helps to recycle nutrients taken up by those leaves. Nutrient cycling occurs when leaves and other fallen plant material decompose, assisted by the huge fall population of various types of fungus. Eventually, all the leaves we see on trees this year will become layers of soil for new trees to contribute to.
This process of soil creation is particularly noticeable here in the Northwoods. As you hike through this area, you can see it happen under your feet. It has taken thousands of years to get the scrapings of soil present in this ecosystem and will take thousands more to turn the new layers of leaves added each year into more soil. Consider this as you tread on the soft ground and watch leaves fall around you.
Unlike the leaves we are so captured by, our journey through the season closes with piles of leaves to jump in, warm sweaters, rosy cheeks, and warm apple cider waiting for after the fun. The Gunflint trail and all its fall scenery awaits!
Tips for Fall Fun
- Dress in layers! The sun can still be comfortably warm, but shady areas and windy days will be chilly.
- Don’t forget your rain jacket. Getting a little rain in summer is one thing, but the colder temperatures make being wet very dangerous.
- For a tasty, woodsy tea, try chopping needles from white, red or jack pine trees. Steep in hot water for 5 to 10 minutes. This tea is great for camping, or any other time spent outside.
- Wear bright colors; it is hunting season up in the north woods, so it’s better to be visible.
- Check out the DNR fall color index to keep an eye on the woods near you.
References:
https://www.dnr.state.mn.us/ecs/212La/index.html
https://www.weatherwx.com/hazardoutlook/mn/boundary+waters+canoe+area+wilderness.html
https://academic.oup.com/treephys/article/40/8/1001/5825605
https://www.britannica.com/story/why-do-leaves-fall-in-autumn
https://www.dnr.state.mn.us/fall_colors/index.html
https://harvardforest.fas.harvard.edu/leaves/factors
Written by Gunflint Lodge Naturalist: Caitlynn LaSota