Ooh, it's fall. That means pumpkin spice, cooler weather, and in some areas of the world, changing leaves. But what causes these gorgeous, incredible changes? Well, I'm Mimi Fotz, and that's what we're talking about today on Hello from the Van. Science, chemicals, photosynthesis. These are the voyages of the incredible tree. To understand what happens in the fall, we need to go back, back to the beginnings of spring and when those leaves first got their start. I feel like we should personify the trees a little bit. It's hard for me to think about things if I don't think about them as living, breathing, and alive. And an easy way to do that is to just give it a name. So here goes nothing. One of the most common species of tree in the world is a red maple. So let's say that we're going to talk about a red maple named Jack. In the winter, Jack is sleeping. He's sleeping because it's cold, days are shorter and dark, and sleep helps with the hunger. Jack's metabolism, like all trees, slows down. In the spring, when things start to warm up, the days get longer and the sun shines brighter. And our red maple friend starts to wake up too. And Jack, after all that sleep, is hungry. Much like I am in the morning. But deciduous trees, that's the fancy name for trees with leaves, deciduous. You can try saying it with me. Deciduous. Yeah, it's a great word, isn't it? Deciduous trees aren't like birds or humans. They can't just go catch breakfast and then suddenly feel full and energized. Leaves are required to breathe, to grow, and to make food. As the days warm up and get longer, Jack's first priority is then making these leaves. And make the leaves does he ever. As the leaves grow, they go from a bud to then having a blade, that's the leafy part, with a vein system and a stem. That's how the leaf connects to the tree. The blade is made up of hundreds, if not thousands, of tiny cells. And in these cells is a critical substance called chlorophyll. Chlorophyll is what gives the leaves their green color and is also required for a process called photosynthesis. So it's a lot of big words. Chlorophyll, that's the green stuff. Photosynthesis, that's what the green stuff does. Photosynthesis is where the tree takes carbon dioxide and water and combines them with sunlight and chlorophyll. Hang with me, it's a little sciencey. The chemical reaction of the carbon dioxide and water with the chlorophyll results in the production of sugars, which provide energy to the tree. Now the leaves do use a little bit of this energy, but the majority of it is transported in the form of a sugar solution to other parts of the tree that require it. Think the trunk and the roots. But that's not all. There are other substances also running around in those green leaves. They're called flavonoids and carotenoids. Flavonoids are yellow and carotenoids are orange, like carrots. Carotenoid, orange carrot. It's a correlation thing. These chemicals and their corresponding colors are present in the leaves all year long. We just can't see them because they're overpowered by the abundance of chlorophyll. But again, where do trees like our friend Jack get this chlorophyll, flavonoids, and carotenoids? It starts in the roots, but it ends in the leaves. You see, the roots and the trunk of the tree hold the sap. It is brought through the roots and trunk to the stem of the leaf and into the veins. But it can only do this with the help of sunshine. The sun acts as the fuel for this photosynthesis. Much like a traditional car can't go without gas, a tree can't grow without the sun. Without the sun, trees like Jack couldn't make chlorophyll. Remember, we need chlorophyll, sunshine, air, water for trees to grow? Let's go back. It's spring. The world is warming up, and the days of sun are getting longer. Jack is starting to grow leaves, and in those leaves, Jack begins to harvest carbon dioxide and sunshine. And through this chemical reaction of the leaf, he produces a sugary starch-like syrup. This starchy, sugary food is sent to every part of the tree where it is used in building bark and tissue. We humans also sometimes partake of this deliciousness. Have you ever had maple syrup? Yep. That comes from the process of photosynthesis in the leaves that then goes into the trunk as part of that sugary, starchy syrup. We then harvest it, boil it down, and it becomes Canadian deliciousness. But let's get back to Jack and off the maple syrup train here for a little bit. As the tree grows and summer is plentiful, life is good. Sunshine abounds, the days are long, and chlorophyll is all the rage. The leaves are green. But remember how chlorophyll is green? In the summer, there's a lot of chlorophyll, so everything is green. It's a sign of summer. We see it all the time. Food, sunshine, water are also available. This is how trees like Jack are able to grow and thrive in the summer. Everything that they require to grow, it's all plentiful. But before you know it, another season has changed. The days start to get shorter, it gets colder, and food is less plentiful. This change causes trees like our friend Jack to produce a stress hormone called abscissic acid. Try saying that three times fast. Oh my goodness, trying to do this today. Whew! Absissic acid. Absissific acid. Absisic acid. As the tree's stress goes up from a lack of food and an increase in colder weather, this abscic acid begins to close the connection between the leaves and the stems. This is why a fallen tree stem usually looks thinner and almost dried out compared to a healthy, strong stem in the spring or summer, because of the abscisic acid. As the stem dries out from this acid, it also stops receiving water and nutrients from the tree. This is critical because one of those things is chlorophyll. As this highway from root to leaf closes up, so does the access to chlorophyll and the green color lessens. We are then left with flavonoids and carotenoids that have always been there. We've just not been able to see them because they have been overpowered by the chlorophyll. And after a few weeks of cold and stress and absystic acid, Jack and his deciduous tree friends enter a state called dormancy. This is similar to hibernation. It helps the trees to conserve energy. As most of the world understands it, in the mid-bleak winter, trees are not actively growing. It's hard to grow when sunshine is your fuel for photosynthesis and there's not much of that sunshine to go around. So trees hibernate and they stay in that state until the world starts to warm and the days get longer again. And the cycle goes round and round and round. So what we see in the fall when the air gets crisp and cool and the leaves start to change color is actually those trees getting ready to go into hibernation, to go into a state of dormancy. You know, it is incredible to me that chlorophyll masks the incredibleness that is fall. The reds and the yellows and the oranges and the golds have been there all along. We just couldn't see them for the abundance. In the words of LM Montgomery, I'm so glad I live in a world where there are Octobers. I'm Mimi Fotz, and this has been Hello from the Van.