The Promise of Winter Buds

In forestry school, one of the primary ways of identifying deciduous trees is by their winter buds. There is a popular field guide that is used entitled “winter twig and bud identification.” In Wisconsin, where I trained, half the year is spent in the bareness of winter. So if you only relied on spring and summer tree identification, you’d be up a creek. What’s amazing about winter buds is that they start to form not long after the leaves have dehisced in the autumn. Behind that leaf scar and in the axils, new growth is signaled. All the promise of the coming spring’s new growth is carried in that minuscule bud. Without them, trees would require a great deal of energy to develop tissue from scratch. 

It's quite an art, delineating one winter tree bud from another. The first thing you look at is the appearance of buds on the branches. Observe how they are arranged: alternate, opposite or whorled around the twig. Then notice if they are single or occur in clusters. Buds can be rounded, pointy, or flattened, and either hairy or smooth. You also need to look at the leaf scar, which is sitting below the bud. Ash trees are easily identified in this way because the scar looks like a smile. Different varieties of ash species are determined by the angle of the smile. Also look at the scales on each bud. The scales are protective sheaths which seal off that delicate primordial tissue from the harsh elements of winter. In another tactic for protecting the promise of next spring’s growth, the tree withdraws water flow from the buds, so they remain in a state of stasis until conducive conditions arrive. Scales can be thick and leathery, or paper-thin. Note the color, shape, and number of them. Tightly overlain scales are more common in harsh northern climates, acting as a barrier to winter extremes. In milder climates some species have “naked” buds with no scales, allowing them to get a head start on bud burst in the spring. 

The buds themselves will change as spring approaches. Barely visible at the end of summer, they pop out a bit in the fall and often sit dormant ‘til spring approaches. As the weather slowly warms and day length increases, trees restart the pumping of water to the buds.  You’ll notice them growing fatter until they burst open to expand those tiny leaves held within. Some trees will extend the terminal shoot before bud burst. For many trees, the buds contain not only tiny leaves, but also the beginning of flowers. While many species have the miniature leaves and flowers within one bud, some have separate buds for leaves and for flowers, and even different ones for male and female flowers. 

The next time you see a tree in winter with all those little nubs on the branches, just think:  winter buds enfold a tiny miracle. Within them lies the promise of a whole new year’s growth.