THE LEAFLET
The Science of the Seasons: Spring Phenology
This article is part of a recurring series in collaboration with Bartlett Tree Experts on the seasonal expressions of phenology – the study of biological cycles and the timing and patterns of events in the natural world.
I have always loved the changing of the seasons in the Mid-Atlantic. Each season, different plants get to show off what makes them unique in the landscape. We often associate the seasons with the stage of the plants that surround us. We notice and even celebrate plant flowering, leaf expansion, fruit setting, and leaf drop throughout the year. The study of the time and duration of these plant stages is known as phenology.
We aren’t the only ones who pay attention to plant phenology, however. Insects, birds, and small mammals are all keen to plant phenology and their life stages are often associated with a specific plant stage.
In the late winter, trees are taking notes on temperature and the length of the daylight hours. These two factors mainly signal trees to start moving resources, stored overwinter in their root systems, up to the canopy. Water, nutrients, and sugars travel through a highway of xylem and phloem cells in the tree trunk to the buds that sit at the twig ends. The buds then swell and open to flowers and leaves, signaling to us that spring is near.
Some deciduous tree species will first break bud and develop leaves, others will start the year with flower development. Early flowering trees are especially important in the landscape as they offer the first chance for pollinators to harvest food and begin to grow their population. Although many DC residents mark the start of spring through the arrival of cherry blossoms around the tidal basin, there are three common native trees that also begin flowering in March: Red Maple, Serviceberry, and Eastern Redbud.
Red maple, Acer rubrum, is a canopy tree known for its vibrant red twigs and fall color. It boasts dense clusters of red flowers that turn into seed structures called samaras. You may know these seeds as “helicopters” that spin down to the ground as they drop. After flowering, leaves emerge with 3-5 pointed lobes and toothed edges, however leaf morphology is dependent on cultivar.
Serviceberry, Amelanchier spp., is a small tree with showy white flowers. The clusters of white flowers develop into blueberry-like fruits. Leaves with finely toothed edges and elliptic shape emerge to photosynthesize and send sugars to the developing fruits, as well as the rest of the tree.
Eastern redbud, Cercis canadensis, is a small tree with purple-pink flowers in March. A member of the pea family, the resemblance is clear when the flowers develop into pods containing seeds. Tiny leaves emerge folded in half, often when flowers are in full bloom, and open to heart shaped leaves with smooth edges.
There are many other trees with spring flowers that can be very small or large and showy and be green, white, pink, purple, red, or yellow in color. The next time you take the dog for a walk or run to the corner store, take a minute to look closely at the ends of the twigs in a tree canopy and you may be delighted by what you find.
