Phenology Files: November 2023

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.

Fall foliage at Siebert Creek Conservation Area

Experience the magic

Fall is a favorite season for many in the Pacific Northwest, bring with it pumpkin and apple-spice goods, cozy sweaters, cooler weather, and of course the appearance of orange and yellow leaves on trees across the landscape. One of our favorite places to experience these autumn hues is the Siebert Creek Conservation Area in Agnew. Free to visit, this conservation area offers a 0.5 mile mild loop trail through colorful big leaf maple and red alder groves. For those that want to continue further, the Olympic Discovery trail continues just across Old Olympic Highway.

Why do trees shed their leaves in the fall?

Siebert Creek Conservation Area/Courtney Bornsworth

During the autumn season, the leaves of our local deciduous trees undergo a stunning transformation. These vibrant hues not only add beauty to the surroundings but also play a crucial role in the survival of the trees.

Deciduous trees, unlike evergreen trees, are the ones that shed their leaves in the fall. Throughout most of the year, these leaves are green due to the presence of chlorophyll, which helps in the process of photosynthesis. Photosynthesis allows the leaves to absorb energy from sunlight and convert it into sugars that nourish the tree. As the season progresses and temperatures drop, the amount of sunlight decreases, causing the chlorophyll in the leaves to break down. This breakdown reveals the yellow and orange pigments that were already present in the leaves but were masked by the chlorophyll during the warmer months.

Shortly after changing color, leaves fall off. This actually a form of protection that perennial plants, such as trees, use to endure freezing temperatures and winter weather conditions. Their stems, twigs, and buds are designed to withstand extreme cold, allowing them to revive when spring arrives and the growing season begins anew. However, the delicate leaf tissues of deciduous trees are vulnerable to freezing, so shed them to survive the winter.