Fall Colors on the North Shore
Fall Colors on the North Shore – a Sight to Behold
By Kris McNeal
Every autumn we revel in the beauty of the fall colors. The heat of the summer gives way to cooler temperatures and the days grow shorter… and it’s time to celebrate my favorite time of year. Honestly, fall is the best time of year to explore the North Shore. There are typically fewer people around but the weather is amazing and the colors are breath-taking. Our trails are in great shape and the hiking and cycling… even our kayaking… takes on a completely different vibe. It’s fall in Duluth!
Whenever you’ve been out exploring the fall landscape, did you ever wonder why the leaves change color? Why does a maple leaf turns bright red? Where do the yellows and oranges come from? Let’s dig into this a bit. Seeing the fall colors is amazing… but understanding the biology and chemistry behind the changing colors is really cool too!
Why Do Leaves Change Color?
Late September through the middle of October are the best times to visit Duluth and the North Shore for the fall colors. The mixtures of red, purple, orange and yellow that you see across the landscape is the result of – you guessed it – chemical processes that take place in the trees as the seasons transition from summer to winter. Changes in leaf color are actually triggered by the shifting rhythm of the day and night cycle. The long, warm days of summer eventually turn shorter and cooler days in autumn, which causes the tree to begin its preparations for winter dormancy.
During the spring and summer growing season the leaves have served as factories where most of the foods necessary for the tree’s growth are manufactured. This food-making process takes place in the leaf in numerous cells containing a chemical called chlorophyll. Chlorophyll is an extraordinary chemical that absorbs sunlight and uses the sun’s energy to transform carbon dioxide and water to carbohydrates – tree foods like sugars and starches. And as you probably already know… chlorophyll has a green pigmentation and give the leaves their green color.
So chlorophyll is green. But there are additional colors in a leaf that are masked by chlorophyll’s dominant green pigmentation during the growing season. When fall approaches the daylight and temperature diminishes. These triggers cause the tree to stop producing food and chlorophyll. The green chlorophyll disappears from the leaves and the green color disappears. Those other colors I mentioned… the yellows and oranges… are created by another group of pigments which become visible and give the leaves their vibrant coloration.
Which Trees Change Colors?
Botanists make a broad distinction between two general categories of tree – deciduous trees and evergreens (a.k.a. conifers). Deciduous trees are defined as trees that lose their leaves every year – your aspen, oaks, maples, etc. These are the trees that drop leaves on the ground for you to rake into piles and jump into. Trees with needles – like the spruce and pine – are called conifers. Conifers typically retain their needles throughout the year. There is one exception to this distinction. The tamarack appears to be a species of evergreen during the growing season – it has needles. However, the tamarack is actually deciduous and it experiences a late-season color change to lemon yellow before dropping its needles as the snow begins to fly in November.
What Factors Affect the Color Intensity?
Well that’s a great question! Some years experience more intense colors than others and there can be quite a bit of variation across the landscape. As you can probably imagine, there are a couple of factors that affect the intensity of the fall colors.
The big factors are temperature, light, and water supply. Each of these factors has an influence on the intensity and the duration of the fall colors. For example, low temperatures that remain above freezing will produce bright reds in maples but an early frost will weaken their brilliant red color. Early freezes are not typically great for color production. But rainy, overcast days will tend to increase the intensity of fall colors. Interestingly enough, sunny days with low temperatures will cause a rapid chlorophyll break down and a quick transition to the yellows and reds.
The best weather conditions for creating super brilliant fall foliage is a growing season with ample moisture followed by a dry, cool and sunny autumn with warm days and cool but frostless nights.
It’s biology folks!