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Be thankful for our beautiful fall leaf colours

DON CAMERON Don Cameron Registered professional forester

Last week during a drive toward Tatamagouche, I was treated to a beautifully coloured landscape at every corner. It seems that the autumn leaf colours are near the peak of brilliance, especially when the sun is shining.

We Nova Scotians sometimes take for granted our annual autumn demonstration of incredible fall colours. The unlimited colour pallets that we enjoy here are the envy around the world. Most other areas on the planet do not have the same type of tree species and climate that creates the conditions that make possible this much-anticipated phenomenon.

Every fall we look forward to enjoying the annual fall show of brilliant proportions when our various hardwood (deciduous) leaves change colour. This phenomenon is a common topic of conversation during this season. In fact, during pre-covid times, thousands of people would travel long distances annually and pay a considerable amount of money to witness our awesome fall colour show across the province. Have you ever wondered what causes this colouring of fall leaves?

First of all, plant leaves are green due to the presence of chlorophyll, a complex and unstable molecule produced continually during the growing season. Chlorophyll enables the plant to capture energy from sunlight which is then used to produce starches and sugars from carbon dioxide, water and mineral nutrients which is used by the plant for growth and future development.

The autumn changing of leaf colours is primarily due to two groups of pigments found in the leaf tissue along with the chlorophyll. These are the carotenes - yellow pigment, and the anthocyanins - red pigment.

As the autumn season advances, the average temperature drops, as does the number of daylight hours. When this happens, the growth rate of all plants slows down, as does the production of chlorophyll. As the level of chlorophyll in the foliage drops, the relatively stable carotene pigment becomes dominant which causes the leaves to turn yellow. You can see this in trees such as sugar maple, birches, and poplars (aspens).

Weather conditions and reduced sap flow promote the formation of anthocyanin or red pigment. Warm, sunny autumn days encourage the formation of sugars in the leaves. Since sap flow is slowed down, the sugars become trapped, and anthocyanin is formed.

When cool or frosty nights follow warm days, even more red pigment is formed, and a more intense red colour will result. Red autumn colouring occurs in trees having more acidic sap, such as red oak, red maple, sumac and burning bush. Trees with a more alkaline sap, such as white ash, will display purple, or plum coloured, leaves.

Occasionally you will see a tree that has turned colour much earlier than other trees of the same species, or perhaps only one side or a few limbs of a tree have changed colour.

These signs are quite common and may be due to stresses on the tree or it may simply indicate that the tree is overmature and past its prime. Stress can be the result of many variables such as drought, damage to the root system, trunk or branches, improper use of fertilizer or pesticides, or perhaps by disease or heavy insect feeding. Early leaf colouring is often a sign of overall tree decline.

When you think about it, it is incredible how our plants are able to survive at all in our climate with such wide temperature fluctuations. For most plants, slipping into a dormant stage for the winter is the very key to survival. We are very fortunate that we also benefit in the process as we enjoy the much-anticipated show of fall colours.

Tree Trivia: You may have noticed lately that there are needles on the inner branches of pine trees that are turning yellow and falling off the tree. There is no need to fear, there is nothing wrong with these trees.

This is a perfectly normal effect of the fall as the older needles die and fall from the tree. The newer needles, growing on the outermost part of the branches, will remain green and on the tree.

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2021-10-21T07:00:00.0000000Z

2021-10-21T07:00:00.0000000Z

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