Green to Gold: The Trusty Tree Guide to What Causes Leaves to Change Colour in the Fall
One of the beautiful things about living in a park-rich area like Edmonton is the ability to watch the trees change with the seasons. While fall can sometimes feel shorter than it really is, it is hard to deny the stunning colours it brings to those brisk morning walks and evening strolls through the river valley.
After winter leaves the world feeling dreary, spring brings stunning green foliage, signaling that summer is just around the corner. And once summer hits, the combination of bright green grass, trees, and stunning flowers makes the world feel alive. But what causes leaves to change colour? Edmonton arborists from Trusty Tree Services are here with the answer.
You may have gone over this in elementary or even high school, but a quick brush-up just shows how much is going on inside our big green (sometimes orange, yellow, or red) friends. So keep reading if you are ready to learn about what causes leaves to change colour in the fall.
The Chemical Process Behind Leaves Changing Colour
Leaves change colour as the seasons do before eventually succumbing to winter and starting the process all over again. But what is causing those leaves to change colour? Well, the answer might surprise you. It all comes down to a process called photosynthesis, where sunlight, water, and carbon dioxide combine to produce food for the tree. Leaves contain ‘chloroplasts’ and a pigment called chlorophyll; it is the colour green and is responsible for absorbing the sunlight required for photosynthesis. It converts light energy into chemical energy to fuel the tree’s growth. Water is absorbed by the tree roots and transported by the xylem to the leaves. While the carbon dioxide in the air enters the leaves through little pores called stomata.
This occurs in two main stages: one in which the light-dependent reactions take place in the thylakoid membrane of chloroplasts. Chlorophyll absorbs the sunlight, exciting the electrons that start a transport chain. The water molecules in the tree are then split, releasing oxygen as a byproduct. The energy from the electrons helps generate adenosine triphosphate (ATP) and NADPH, which are energy carriers needed for the next stage.
The other stage is light-independent and uses the ATP and NADPH produced in the first stage to convert carbon dioxide into glucose. The sugars provide the necessary energy for respiration, growth, and repair. It is sometimes stored as starch in branches, roots, and the trunk.
But what causes leaves to change colour from bright green to red, orange and yellow? Well, as autumn takes hold, the air is crisp, and sunlight hours shrink, photosynthesis begins to slow. The reduction in photosynthesis production causes the sugar reserves and sugars to dwindle inside the chloroplasts, causing trees to lose their green colour. The production of sugars in the leaf does not stop immediately; instead, the process of gathering sunlight, carbon dioxide and water starts a rapid degradation around 1 to 2 weeks before the first leaf falls.
Once the chlorophyll loses its edge, the carotenoids, which lie dormant as the yellow and orange pigments so synonymous with autumn foliage, are able to show through. They are present through the growing season and are important tree pigments, but they are masked by the chlorophyll, which gives leaves their green colour. The vivid reds come from pigments called anthocyanins. These red and purple pigments are also classic fall colours and are synthesized in autumn due to bright light and cool temperatures. The synthesis of anthocyanins, giving leaves their red hue, is just one of the many answers to what causes leaves to change colour in the fall.
Local Context for Edmonton
Edmonton’s mixed parkland region hosts many native species, including trembling aspen, Manitoba maple, birch, and poplar. Aspen and birch, in particular, are rich in carotenoids, which contribute to their bright golden-yellow colours typical of Edmonton’s fall foliage. Manitoba maples and other species produce anthocyanins, adding red and purple tones, but generally less vivid than in more southern regions due to the cooler climate.
The reduction in photosynthesis lowers the ability to produce red and purple pigments. While peak colour change in Edmonton generally occurs around mid to late September, early frost and high cloud cover, which are directly linked to low light levels and low photosynthesis, cause trees to be a little less green and for leaves to fall and die rapidly.
Environmental Impact and Climate Change
The Department of Biology at Appalachian State University states that trees are extremely sensitive to environmental shifts. Weather conditions, such as precipitation in all forms, temperature fluctuations, sunlight levels, and soil moisture, influence the intensity and timing of colour changes. These can lengthen or reduce the amount of time an individual leaves can go through the chemical changes necessary for sunlight, carbon dioxide, and water to be converted into food, and the length leaves stay on the tree.
It is important to take action against climate change because it can disrupt these natural cues, potentially muting or delaying fall tones in the future by confusing tree physiology. If you want to continue to enjoy the beautiful, huge maple trees and rows of oaks and birches that line the streets with their stunning colours, join us in fighting climate change.
Do You Have a Tired Old Tree? Call Trusty Tree Services Today, the Arborist Edmonton Trusts
If you have ever wondered why leaves change into the fall colour you love, you have come to the right place. Trusty Tree Services thanks you for reading and learning more about our beautiful green, orange, red, and yellow friends. The science behind their incredible transformation may vary depending on weather conditions, but the impression they leave on us all does not. While we all wish that the fall leaves would stay on the tree longer, since the leaves fall so early, we really have to enjoy our time with them here in Alberta.
If you are looking for reliable tree services, count on the arborists from Trusty Tree Services. Whether a tree on your property needs our tree removal services or you are trying to keep your tree looking its best with tree trimming, we are happy to help.
Contact us today for quality tree services you can trust.