Why Trees Change Color and How Leaves Support Wildlife

Author: Nicole McAdam

In the month of November, there’s just so much to do - make your voice heard on Election Day, cook, eat, and be thankful on Thanksgiving Day, and don’t forget, National STEAM Day on November 8! November is also a busy time for our beautiful deciduous trees here at Hirundo. You’ve likely noticed the drastic change in the foliage around Hirundo over the past few weeks. In light of this transition into late autumn, do you ever wonder why trees change their color this time of year?

Trees change the color of their leaves when they stop producing chlorophyll, the photosynthetic agent that allows plants to use light as a source of food. Many recognize this transition as a parallel to the change in weather, when we start to feel a cool, brisk air. However, the changing of leaf color is related not to temperature but to the amount of daylight.

As the days grow shorter, trees recognize that their efforts to continue producing chlorophyll (the green, sun-catching pigment) are not energetically worth it, due to the shortening days. In order to conserve as much energy as possible, they choose instead to halt chlorophyll production and drop their leaves. This leaf abscission (or dropping of leaves) allows the plant to focus its efforts throughout the winter on staying alive, keeping water and sugars moving through the phloem and xylem (the straw-like structures that move sugar and water throughout the tree).

Side Note: People can tap into this phloem/xylem highway in some types of tree, to catch a golden and sugary syrup that we use on our pancakes. The first people to tap maple trees were the indigenous Wabanaki tribes of the Northeast, who traditionally used birch bark to collect sap, then boiled it on hot stones. This golden syrup was not only a food source, but an important asset for trading with settlers. Sugar maples, Acer saccharum, are a favorite to most, but they’re not the only ones. Some birch trees can also be tapped! While this process can’t occur until the late winter, when the freezing temperatures begin to briefly rise during the day to resume that flow, we can thank the falling leaves for their contribution to keeping the tree alive during the winter freeze.

Trees losing their leaves in autumn is not only important for the trees’ survival but it is also essential to their environment as a whole. New England’s deciduous trees dropping their leaves contributes to the detritus layer of the forest floor, a home to many invertebrates and fungi. These critters take part in breaking down this dry leaf matter, which is then composted back into the soil throughout the rainy fall and cold winter months, acting as a boundary layer, trapping pockets of warm air beneath the snow in an area called the subnivean, or “below the snow”. Not only invertebrates, but small rodents like mice and voles live beneath this snowy, leafy layer during the winter. So many creatures have beautiful, colorful, autumn leaves to thank for their cozy winter abodes.

To assist small critters this winter, avoid raking the leaves in your yard! Not only will it save you from backaches, but it will also provide a means to keep critters warm during the upcoming winter! As trees respond to the shortening days of fall by dropping their leaves, they’re setting the stage for countless life forms to survive the cold months ahead.

Visit Hirundo this season to see these natural cycles in action and discover how simple choices at home can support the same conservation efforts we are working towards here at the refuge.

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References:

Maine Maple Syrup. The Maine Highlands. (2025, February 27).