Fall Colors – September 2, 2020


It’s September and, in 3 weeks (on the 22nd), it officially will be fall here in the Northern Hemisphere. As the days shorten and temperatures get cooler, trees will begin preparing for the winter ahead, preserving their nutrients for the next growing season in the spring. Part of this process involves their leaves turning color as chlorophyll production stops. This is the pigment that makes leaves green. Left behind instead are carotenoids (yellow pigments), anthocyanins (red pigments), or both (orange pigments), and this depends on the tree species. It’s thought that anthocyanins (found in deciduous trees like oaks and maples) act as a sunscreen or antifreeze to protect the leaves (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1082902/).
When will the fall colors peak here in Colorado? Depending on where you live, it varies from September 16 – 23 (southern Colorado); to September 19 – 25 (central Colorado); to September 20 – 26 (northern Colorado). Severe drought conditions cause leaves to turn color earlier – and often times the colors don’t last as long. Worst case, they skip changing color completely, turn brown instead, and then fall off early – there is total metabolic shutdown. More moderate drought and warmer temperatures can delay the onset of changing colors because the trees aren’t getting the signal that fall is here – the slow-down of metabolic processes gets delayed. In a future with unchecked climate change, fall colors WILL be affected. Just how intensely depends on just how hot and dry it gets. If you have a chance to get out and see the fall colors, do so – it’s a spectacular show put on by nature!