Autumn in Alberta is a spectacular time of year. From golden poplars in the prairies to fiery red maples in city parks, the landscape transforms into a canvas of warm hues. But what’s really happening inside those leaves to create such a show? Let’s dig into the science of fall colors.

Chlorophyll: The Summer Workhorse

During spring and summer, leaves appear green because of chlorophyll, the pigment that captures sunlight to produce food for the tree through photosynthesis. Chlorophyll is constantly being produced and broken down, so as long as days are long and warm, leaves stay green.

The Role of Shorter Days

As autumn arrives, shorter daylight hours and cooler temperatures signal trees to prepare for winter. The production of chlorophyll slows down, and eventually stops. When the green pigment fades, other pigments that were hidden in the leaf all along begin to shine.

Carotenoids: Golden Yellows and Oranges

Carotenoids are pigments responsible for the yellow and orange hues we see in species like poplars, birches, and ash trees. These pigments are always present in the leaf, but are only visible once the chlorophyll breaks down.

Anthocyanins: Brilliant Reds and Purples

Unlike carotenoids, anthocyanins are produced in the fall. Cool nights and sunny days encourage sugars to get trapped in the leaves, leading to the formation of these pigments. They give us the striking reds and purples seen in maples and certain shrubs, like chokecherries.

Fun Facts About Fall Color in Alberta

• Golden Domination: Alberta’s fall palette is dominated by yellows from aspen and poplar trees, which blanket the prairies and foothills.
• Temperature Matters: Warm, sunny days followed by crisp, cool nights produce the most vivid reds.
• Early Warning System: A dull fall display can signal stress on trees, such as drought or disease.
• Evergreens Stay Green: Spruce, pine, and fir keep their needles year-round thanks to tough, waxy coatings that help them survive Alberta’s cold winters.

Nature’s Seasonal Reminder

The burst of color is more than just a feast for the eyes—it’s part of a tree’s survival strategy. By pulling nutrients back into their roots and letting go of their leaves, trees are preparing for the long, harsh Alberta winter ahead.

So, the next time you’re walking a golden trail in September or admiring a red maple in October, you’ll know you’re witnessing the science—and beauty—of trees getting ready for a season of rest.