phenology fi-ˈnä-lə-jē n 1 : a branch of science dealing with the relations between climate and periodic biological phenomena (such as bird migration or plant flowering) 2: periodic biological phenomena that are correlated with climatic conditions.
Vine Maple (Acer circinatum)
Photos by www.nwplants.com shared under a Creative Commons Attribution-ShareAlike 3.0 Unported License.
While the forests of the Pacific Northwest are not known for showy fall foliage like those of the Northeast, we do have at least one tree that sports especially vibrant colors in autumn – the vine maple (Acer circinatum). If you’ve recently walked along the Elwha or driven Highway 112 along the Pysht and you noticed a bright pop of red leaves against the yellows and greens, you likely spotted a vine maple.
Unlike the massive and appropriately named big leaf maple (Acer macrophyllum), vine maples are small, graceful trees with leaves no bigger than a few inches wide. Their sprawling vine-like trunks can often resemble a shrub more than a tree. But why do their leaves have the ability to turn red in the fall while big leaf maples don’t? Let’s take a bit of a dive into the science behind leaf color…
You’ve probably already heard of photosynthesis – which is how plants convert sunlight, water, and carbon dioxide into fuel. Photosynthesis and plant growth in spring and summer is driven by a chemical compound called chlorophyll, which is what makes leaves look green. As the nights grow colder and the days grow shorter, photosynthesis shuts down because the tree is preparing for winter. The chlorophyll then dissipates from the leaves and hidden colors like red, yellow, and orange make their appearance.
The red color in maple trees is a result of an antioxidant called anthocyanin (the same stuff that makes red and purple in apples and beets). But vine maples don’t always have red leaves in the fall, sometimes they are bright yellow. You may notice that vine maple growing in open spaces like clearcuts or at the edge of a river tend have red leaves in the fall, but those that stick to the shady understory usually have yellow foliage.
A side by side comparison of a vine maple with red leaves on the edge of a forest versus yellow-leaved vine maple snaking through a shaded forest understory.
The simple answer may be that the trees growing in drier areas with more direct sun and exposure to cold weather want and need more anthocyanin. Working as a natural sunscreen, providing disease and drought tolerant properties, and repairing leaf damage are all traits of anthocyanin that can help a tree better weather those conditions.
This fall, try going for a stroll through your local forest and see if you can find a vine maple! Whether its leaves are red or yellow, or don’t see one, fall is an enchanting time to explore the North Olympic Peninsula.