There is a quick infallible method to gauge the progress of your tree’s growth and its overall health. That is by recognizing the natural divisions between growths of a series of years. This is represented on the branches by the bud scars and the length of growth in between them, called the shoot extension.

Take hold of the end of any branch, depending on the time of year. The bud you find at the terminus will either be complete with bud caps and ready for winter, or if you look some earlier time during the growing season you will see a bud still forming. The finished bud is a very complex group of tissues and takes all growing season to complete. These are next year’s buds, once spring finally arrives the tree is already prepared to leaf out. As the year’s growth proceeds, the shoot extends in the tissue behind the bud, in either one or two growth flushes to complete the year’s growth.

Look at the bottom of the bud; you will find a small ring of wrinkled tissue all the way around the base of the bud. This tissue is called a bud scar. The bud scar is permanent and stays in the same place around the branch through subsequent years of growth until that part of the branch ages to the point where the increasingly rough bark hides the ring of the bud scar.

So starting from the terminal bud proceed back towards the trunk At first you are still in the current year’s growth, but soon enough you will find a bud scar. Shoot extension is not only a good way to see the series of years growth but also a good indication of how much that tree grows each year. If the tree you are inspecting is a Swedish aspen you may have to move back towards the trunk as much as three feet to find the bud scar the demarcates the break between this year’s and last year’s growth.

When I check a tree’s growth rate using bud scars I always check three or four branch tips at random from around all sides of the tree. You will find the shoot extensions longer on the sun side.

Having found the second bud scar, note the subtle change in diameter and in the texture of the bark, As you cross the bud scar into the preceding year’s growth, you will see that the tree has added a growth ring. Past the bus scar we are now into two-year-old wood. Keep following the branch towards the trunk. As you pass small side branches you will come again to the ring of the bud scar, this one showing the difference between the second and third year’s growth. So there is your pattern, repeat at random at several places around the tree.

Now it’s time to analyze what we have seen and learned. By performing this on your tree and perhaps some others of the same species you will be able to gauge the normal shoot extension per year for this type of tree. Knowing what’s average something that you can compare to your own tree.

If the shoot extensions are similar through a several year period, that’s good; its shows regular watering and good growth. Are the shoot extensions very short between the rings of the bud scars? This would show an unhappy struggling tree. Perhaps a newly planted tree, one that was too deeply planted, struggling for air for its roots and in decline. Trees can be so stressed from this, that in the worst cases there are no shoot extensions at all and sometimes not even new buds; that tree is at death’s door.

Bud scar study is fascinating. When I approach a new tree it is almost always the first thing I do. It’s really the human equivalent of saying, “How do you do?” I remember counting 14 years of bud scars/shoot extensions on a burr oak tree at Olds College and once in the mountains on a dry ridge near Head mountain over 40 years of tight inch long extensions on a beautiful ancient limber pine.

Bud scar study will become automatic. It’s the first and best thing you can do to size up the health and life of a tree new to you.

Another set of interesting ideas comes from the area on the branch that we have identified as the shoot extension that is two years old. This shoot extension is where the first side branches of one year old twigs are found on their two year old parent branch or trunk. They will stay in place forever, at least until the day they are either burnt, rot, or cut.

Look closely at the junction of the one year old twig and the two year old parent zoom ahead 48 years. The tree is still here, still healthy, but much larger. If its average leader extension is one foot perhaps the tree is now about 50 feet taller. But the little junction between our one year old twig and its two year old parent branch or trunk is also much changed. The parent branch is now 50 years old and the side twig is also a large branch 49 years old. The trunk will have a much larger diameter but their relationship and relative ages do not change. They are both in the same relative space, just much larger and older.

Branches do not move in position on the trunk, but stay in the same place and get older and larger. The tree grows outward and upward through a long series of both lateral and terminal shoot extensions each year, building always from last year’s growth.

This next idea is important when we come to compartmentalization. The 49 year old side branch growing out of the 50 year old parent branch grows back inside the parent branch for 49 years, back through 49 growth rings. There is tissue common to both inside the 50 year old parent that goes all the way back inside to the original joint where the one was two years old and the other was one year old.

Now come and look at the trunk.We see the 50 year old trunk or major side trunk in this case and the smaller but almost as old 49 year old branch. If we prune off the 49 year old side branch, you could with the right equipment count all of its 49 growth rings. Let’s say this tree was harvested for timber soon after. If the 50 year old trunk was cut through in such a way as to reveal the growth and interaction between the branch and trunk you would see that the branch trace or its core, until now hidden in the trunk, had interacted with the trunk tissue back through each of 49 consecutive growth rings. If this piece of lumber was made into a table top, this darker and distinct branch core would be called a knot, as we have all seen.
No matter how old the tree, any naturally occurring branch (as opposed to a sucker), is one year less in age than the age of the trunk at that height.

These are good things to ponder and a vision inside the working of a living tree is a wonderful thing for the interested student. This subject is dealt with much deeper in Dr. Alex Shigo's New Tree Biology, one of my bibles.

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