At this time of year nearly everyone is eagerly waiting for the leaves and flowers to appear. You might not realize this fact, but trees and shrubs prepared for this spring last summer. Even now you can see the buds on the twigs. If they are firm and appear healthy they will certainly be opening up soon. The process is slightly different for coniferous evergreens than it is for deciduous trees and woody shrubs. I will only discuss the deciduous, or leaf-dropping plants, in this article.
Last summer all woody plants developed a very small bud underneath the base of the leaf stalk, or the petiole, where it attaches to the twig. Most people do not see the developing bud because it tends to be hidden by the leaf stalk base. Once the leaf falls from the tree or shrub the presence of the bud is very obvious.
At this time of the year the roots begin to absorb moisture and nutrients in the soil which is directed to the cambial region of cells just inside the outer bark of the twigs, branches and trunks. This is a very critical part of the growth of leaves and twigs in the spring. This moisture and growth hormones, in conjunction with warming days, stimulate those cells to develop into early plant growth rings. The moisture and nutrients move from the soil and produce the specialized cell tissues at the tips of the roots (called meristems) which develop into early annual rings in a region called the cambium.
The cambium is one of nature's amazing miracles. The cambium ring cells closest to the bark produce early bark tissues, and cells (called the phloem) which will eventually transport sugars and starches produced by the green leaves and store them into specialized storage cells throughout the tree or shrub. The cambium ring cells in the inside rings (called the xylem) produce the wood cells as the tree or shrub matures through the summer.
All this happens before the leaves appear on the tree or shrub.
Not long after the development of the first phloem and xylem cells, the buds on the twigs start to open. Within those buds are the very small compacted leaves. They eventually grow into green leaves. Through the process of photosynthesis, atmospheric carbon dioxide and moisture in the presence of sunlight produces the plant's energy food (sugars and starches) in specialized green-leaf cells. The important byproduct of this process is the production of atmospheric oxygen.
Michael Allen M.Sc.F., RPF (ret'd) is a consulting urban forester, tree diagnostician and certified arborist. He owns Viburnum Tree Experts. He can be reached at 204-831-6503 or
204-223-770.
