By Gabby Sherwood
Between mid-September and early October, Rocky’s mountains, valleys, and lake views erupt into a breathtaking scene of yellow, orange, and red. The fall months are some of Rocky’s busiest of the year, as hundreds of thousands visit the park to see one of its most revered natural wonders: the autumn colors of quaking aspen.
But what’s behind aspen’s fall transformation in Rocky – leaf it to science!
Three main factors influence the stunning color changes in aspen: Leaf pigment, daylight, and weather.
Deciduous trees like aspen continually produce and break down chlorophyll, the green pigment in leaves, during spring and summer. Chlorophyll’s job is to convert sunshine into food and energy through photosynthesis. As the days get shorter and temperatures drop in autumn, aspen stop producing chlorophyll. This allows carotenoids and xanthophylls, yellow and orange pigments –that are present in the leaves year-round, to have the spotlight. Aspen leaves usually change to shades of yellow in autumn. While they can turn orange and red, it’s less common.
The timing, quantity, and brilliance of fall colors also depend on the weather. Sunny, warm days and cool nights favor the likelihood of vibrant fall foliage. Conversely, the early arrival of cooler temperatures and cloudy skies can lead to less dramatic foliage. Soil moisture is another influential factor in the timing of color change and leaf loss in aspen. Drought conditions can cause stress to the tree and lead to premature color change.
But no matter the environmental conditions, aspen drop their leaves to mark their readiness for winter dormancy. Quaking aspen is a highly resilient species. They are able to withstand harsh winter conditions and still emerge each spring with new, vibrant growth.
