The Science behind Fall Foliage
Recently I have been thoroughly enjoying and appreciating all the Massachusetts fall foliage, but it made me think. Why do the leaves on some trees change color? It comes down to three different variables. These include the pigment in leaves, length of night, and weather.
There are three main color pigments in leaves. The green color comes from chlorophyll (which is necessary for photosynthesis), the yellow/orange/brown color comes from carotenoids, and the red color comes from anthocyanin. Throughout the growing season and the summer, chlorophyll is the main pigment in the leaves, but some carotenoids are present as well. When autumn rolls around, the production of chlorophyll slows down because of the decreased light and level of photosynthesis. At this point anthocyanin and carotenoids in the leaf begin to come out and therefore change color. Each species of deciduous tree has various levels of pigment which causes some trees to turn different colors than others. For example, the leaves on black maple trees turn yellow whereas the leaves on red maple trees turn red. The length of the night is also a significant factor in the color change of leaves.
When the level and intensity of sunlight begins to decrease a layer of cells is formed at the base of the leaf which closes off fluids from being able to reach the leaf. This process traps the sugars in the leaf and anthocyanin can more productively be produced. Leaves fall when the fluids are completely cut off. After the leaves fall, the tree is left bare to survive the winter. It is a good thing that tree trunks and branches are built to withstand the harsh cold.
Weather is another factor in the color change of leaves. The temperature and moisture of the environment are the biggest factors that affect them. When it is warm and sunny, a lot of sugar is produced as it is a product of photosynthesis. During cool nights, more sugar is stored in the leaf because the veins that go into the leaf close. This means that when the days are sunny and warm and nights are cool, the most vibrant colors will come out in the fall. Moisture in the soil also promotes fall colors. Things like drought, a late spring, or a warm fall can affect the timing of the color change by weeks. The most ideal scenario for fall colors is a warm wet spring.
Learning about what affects the color of leaves is eye opening because there are so many natural processes that go on in the environment that are more complicated than we might expect. We have made the changing of the leaves part of our human tradition. Fall is a time that many New Englanders look forward to every year that is defined by the beauty of our vibrant forests. We use this natural phenomenon as a form of annual celebration, and I am excited to continue to celebrate the leaves for many years to come.
Anna Niezrecki (6)
https://www.fs.usda.gov/visit/fall-colors/science-of-fall-colors
Hi Anna! It was really interesting to learn how the process of fall foliage works and the environmental factors that play a role in it. I always wondered why some trees turn yellow or orange while others turn red, which I’ve learned is caused by carotenoids and anthocyanin remaining in the leaves and there being less production of chlorophyll to keep the leaves green. Why do trees that are exposed to the same amount of sunlight and moisture in the same place not all change color at the same time? Why do some trees stay green longer? Do you think it has something to do with the species of tree?
ReplyDelete- Sarah Belcher
Hi Sarah! I think it has something to do with the genetic makeup of the different species. It seems that trees genetically inherit the trait of when they are going to change color. Trees at the same general latitude will all change at the same time no matter what altitude they are at (which changes the temperature). When trees turn color definitely has something to do with the species of tree because of their specific responses to the abiotic changes.
DeleteHi Anna, thank you for sharing! Just last weekend I was talking to my mom about the foliage of the leaves and how they change colors. I was able to give her a broad explanation but am happy to see you have the details for me here! Fall is the best season but unfortunately the colors only stick around for a short amount of time. Based on your article, the most vibrant colors would be if the weather remained warm and sunny. Would warm and sunny weather also produce the longest foliage season or are there other factors that impact length?
ReplyDeleteHi Victoria! It seems that the warmer overall global temperatures, due to climate change, have been delaying the foliage season but making them stick around a little longer as well. The main issue is the warmer nights because cool nights help to keep the sugar in the leaves which give them a brighter color. Extreme weather events can also make the vibrance of the leaves duller.
DeleteHi Anna!
ReplyDeleteI noticed as I was driving back to campus from the south shore last weekend just how beautiful western mass really is! It's crazy how fast the seasons change, I feel like it was just a few weeks ago I was swimming in the ocean at the beach. Is the "peak" time that the leaves are the most vibrant at a certain time every year?
Hi Brenna! The peak time has overall been gradually been pushed later and later every year due to the affects of climate change. The general peak time to see fall foliage depends on where you are but, in western mass its around the same week as Indigenous peoples day.
DeleteHi Anna! The beauty of fall is something that almost everyone can appreciate so it was interesting to read the science behind the beautiful colors of the leaves. I had no idea that the weather also played a role in this color change. Do you think that the sunlight or the weather has a more drastic impact on this change in color?
ReplyDeleteHi Caitlin! I think that weather has a more drastic impact on the color because the temperature at night recently has been increasing due to climate change and the affects are showing. The leaves have a harder time keeping the sugars in the leaves at night which is needed for the bright colors to come out.
DeleteHi Anna! I also have really been enjoying the fall foliage, with my favorites being the bright red leaves that show. But I've always wondered why only such a selective amount of tree leaves turn red versus yellow? Is it solely based on the pigment composition, or would location/terrain of the trees also effect this?
ReplyDeleteHi Lydia! The color that a trees leaves will change to depends on the species and how they have evolved because this is a genetic trait that gets passed on. This all depends on the pigment present in the leaf.
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