To live in regions with seasonal weather, plants have adapted to deal with weather extremes. During the New England winter, low temperatures can harm plants, but winter drought is a bigger problem. The water in the soil is frozen and unavailable to trees. So, how do trees survive the drought and cold?

Deciduous trees don’t have the adaptations to drought that allow evergreens to be active all year. Deciduous leaves release large amounts of water during photosynthesis. Trees shed their leaves and becomes dormant to survive winter. Dormancy is a series of physical and chemical changes triggered by declining sunlight, temperature, and soil moisture.

As winter approaches, photosynthesis ends. Chlorophyll in leaves begins to break down while sugars in the leaves move into the twigs, trunk, and roots. Then the cells joining the leaf to the tree swell, closing the vessels that bring water into the leaf. The leaf dies and usually severs. Miniature leaves, produced during the growing season, wait inside the buds for spring. Bud scales overlap to protect young leaves from freezing and drying out. Concurrently, the tree’s cell walls strengthen. If water in the cells freezes, the walls rupture and the cells die. Sugars stored in the tree help prevent this – the sugars lower the freezing point of the tree’s tissues.

Once the transition to dormancy is completed, the tree needs a period of cold. Without spending enough time below a certain temperature, it will not flower or leaf out. The chilling requirement keeps trees dormant, protecting it from temperature fluctuations.

In late winter, first the roots return to activity. However, in a warm winter, root activity may not cease. The roots supply the water and carbohydrates needed to grow new leaves and shoots. Water saturated with sugar begins moving in the trees. (Think maple sugar.) Hormones in the buds jump-start the production of new wood (xylem) and inner bark (phloem). Xylem carries water and nutrients from the roots to the leaves. Phloem begins the transport of stored sugars to new growth in the tree. In some species, like oaks or elms, new growth occurs before the buds open. By the time the buds break the tree has been active for several weeks.