TIME FOR MOTHER NATURE'S PAINTBRUSH 

Thursday October 06, 2011

One of my “other duties as assigned” that I have given myself this fall is sending a twice weekly fall colour report to Ontario Tourism in Barrie. In it, I give percentage of colour and leaf drop and interesting routes to travel to view the developing autumn colours for which parts of Ontario have become famous. This fall, however, reporting has been made more difficult due to recent drought conditions that have seen premature leaf drop. The browns we are seeing right now are actually dead leaves, and they are particularly noticeable on white ash and poplars this fall.

However, a drive through Algonquin Provincial Park right now will see fall colour at its peak. Red, orange and yellow are the predominant colours in the tree canopy, and the best place to view them is in the western portions of the park, dominated by sugar maple. The east part is also good, but since it is dominated by conifers, colours are not as spectacular, but does provide an interesting mix of colour. Right now, the park is at an incredible 100 percent colour change with only 10% leaf fall. Good time to take advantage of any tours being offered by local bus tour companies, or plan on taking the three hour drive to Algonquin yourself and create your own tour.

Fall colour is most intense during years in which a relatively dry sunshiny summer is followed by a rainy period in late August or early September, and then by an autumn with moderately low night temperatures and bright crisp days. Contrary to popular belief, it is not frost that brings on the colour; indeed, a killing frost can turn leaves a dull, dirty brown, causing them to cling to the trees well into winter. Cool temperatures within reason, however, will encourage the formation of the red pigments. All we need to enjoy this spectacular fall show is a bright sunshiny day and that is when we will see the maples and sumacs in an absolute riot of colour.

Leaf colour is caused by the presence of chemicals called pigments. During spring and summer, leaves are green because chlorophyll, which reflects green light, is present in large quantities. Other pigments are there too, but their effects are masked by chlorophyll. But, really,  all this colour we see is sheer waste, in technical terms anyway.  As the days become shorter and the tree begins to tire, sap circulation is sealed off. Production of chlorophyll ceases and disintegrates. The reds and purples appear when the sun has oxidized the sugars and acids abandoned in the leaves.

If you want to be one up, you can refer to these pigments as anthocyanins. They are responsible for the variety of hues from our most brilliant scarlets through a variety of reds, subdued lavenders, purples to deep blue. We are more familiar with these anthocyanins in other forms - apples, violets, grapes, blueberries and beets. These pigments tend to develop in some of our trees during the autumn and it is our maples that put on the best showing. Because pigments are many-hued in different species and since yellow pigments remain after the green pigments have gone, we end up with an explosion of colour in our trees. The red pigments are in the upper surface of the leaf and the yellows throughout the leaf result in all kinds of colour combinations. Some families of trees - the poplar comes to mind - are incapable of producing any of these red pigments, even in the faintest of hues. Thus we are offered only yellow and gold from this species.

The production of the anthocyanins, and therefore the intensity of the reds, is affected by many things - weather during summer and fall, the amount of available light, air and soil temperature, nitrogen supply and soil moisture. Even single leaves may not be evenly coloured if part of the leaf has been shaded by another.

Many of us tend to take the annual fall colour for granted. Not every country, or even every part of North America can boast the complimentary stage show we are treated to each fall. In South America, for example, this colour does not occur - except for a small region in southern Chile. While parts of Europe, China and Japan can also boast the changing colours, it is here, in eastern North America, where the presentation is the most spectacular, for we have the tree species that produce the bright colours that are lacking in other parts of the world.

It is this explosion of colour that compels people to head off each fall to savour the annual spectacle that has made this part of the world famous. My wife and I were at Vanderwater Conservation Area south of Tweed last week for a guided hike, and the colours there, as well as en route were just beginning to take on some interesting blends, including a few interesting purple hues along Highway 37.