It’s late autumn in northern New England, and this year the colors are beautiful. I spent last weekend with my family in the White Mountains of New Hampshire – we went for an afternoon walk, and I was amazed by the array of yellows, oranges, purples, reds, and pinks that were on display.
In summertime, leaves are green because they contain chlorophyll, the main light-absorbing pigment for photosynthesis. Leaves start to change color in autumn when short days and cooler weather signal to the tree that it’s time to stop producing new chlorophyll molecules. As the amount of chlorophyll in the leaf drops, yellow xanthophyll and orange carotenoid pigments, which had been previously masked by the dark green chlorophyll, become dominant.
In some species, like maple, the leaves also start to synthesize new pigments, like red and purple anthocyanins, in autumn. In New England, about 70% of our native tree species can produce anthocyanins, which is one of the reasons that this area is so famous for its fall colors.
Here are some pictures from our “leaf peeping” expedition today – I focused on maple, because they seemed to me to be the most interesting, but the oaks (deep purple), aspen (bright yellow), and sumac (scarlet) are all worth mentioning as well. Beech, on the other hand, isn’t yet doing much at all! In fact, most beech leaves are still bright green. It will be interesting to see how much longer they stay like that.
P.S. If you are interested in autumn colors, you may want to take a look at a paper we published a few years ago, which investigated how future climate change might affect the duration and intensity of autumn colors in New England. The Wikipedia article on autumn colors is pretty interesting too.