Ever wonder why tree leaves change color in the fall? Science and nature have worked hand-in-hand for years painting the fall palette that we have come to enjoy, using light and temperature changes to stimulate vibrant color transitions in our trees. Even the modest changes seen in our indigenous sycamores can provide a visual cue that seasons are changing. Leaf pigment, sunlight, and weather conditions all contribute to the color changes we see. Depending on the species of tree, these changes can range from subtle to vibrant.

The pigment that gives leaves their green color is chlorophyll. Chlorophyll is used in photosynthesis which is the process of turning sunlight into carbohydrates (sugars) that fuel tree growth. During spring and summer, longer days and warm temps keep the process active thus leaves stay green. When days get shorter and temperatures cool, photosynthesis slows down and there is less chlorophyll. As a result, those secondary colors that have always been there begin to emerge, revealing the warm yellows, golds and oranges we associate with fall. Red leaf color is produced in autumns chill as excess sugars combine with water soluble compounds that, once exposed to sunlight, turn to vivid pink, red or purple variations.

Soil moisture can also affect autumn color. Summer drought can delay the onset of fall colors by weeks. Ideal conditions for maximum color display are warm wet springs followed by favorable summer weather and sunny fall days with cool evening temperatures.

To view this science first hand, visit some of Glendale’s many neighborhoods. Our street tree pallet includes several species of trees that provide fall beauty such as Liquidambar styraciflua (American Sweet Gum), Ginkgo biloba (Maidenhair Tree), Sapium sebiferum (Chinese Tallow Tree), and Pistacia chinensis (Chinese Pistache). Bel Aire Drive, on the west side of town has rows of Liquidambar trees, while Pioneer Drive to the south offers the sulfur yellow display common to Ginkgo biloba trees. To view Sapium sebiferum trees, try Stocker Street or California Avenue for displays of red and gold. The east side of town has an abundance of Pistacia chinensis trees, especially in the neighborhoods of Calle Del Pacifico and Calle Simpatico.

Exposure to the elements certainly influences a trees ability to display brilliant color. However, some of winters elements and exposures can harm a trees ability to produce the rewards of spring, such as flowers and fruit. Fortunately, there are a few steps you can take to ensure your trees will remain healthy throughout the winter and bloom heartily when warm weather resumes. Our next article will outline these steps to minimize stress by helping your trees through the cold months.