Travels back and forth from central Alberta to Southeastern Alberta from mid-September to mid-October present a convincing case that autumn, in the sense both of gorgeous leaf colours and of “fall” (i.e.: leaf fall) is just not happening this year. The majority of deciduous trees remain fully leafed with dry, dull green, or dusty brown leaves.
Here, there, and everywhere, Albertans are asking why, when we had those early frosts, are there few gorgeous fall colours and almost no leaf fall, despite some days of high winds? Little Jack Frost is not just a myth, he’s a fraud. He originates in Viking folklore as Jokul Frosti where he is credited mainly with works in ice, on windows and icicles. But somehow, in translation to our North American children’s fantasies, he skips around daubing bright colours on the leaves in fall. Thus, our little Jack Frost is like so many modern celebrities: all hype and no talent.
The fact is that most of the pigments, certainly the carotenes and xanthophylls that produce the yellow and amber fall colours, are already in the leaves, but are masked by the green of the chlorophyll. Around the time of the fall equinox, as the light wanes and the nights become colder, the natural process starts whereby the plant nutrients flow from the leaves back into the branches, trunk and roots of the tree to be stored for the winter. The tree also ceases manufacturing the green chlorophyll and what remains in the leaves is quickly destroyed by light. Voila! The underlying leaf colours are no longer hidden and the fall colour show that we always enjoy so much goes on.
The pigment responsible for red, orange and purple colouration, anthocyanin, is not generally present in leaves early in the season, but in vintage years can appear in greater amounts depending on weather conditions. If temperatures drop to between zero and seven degrees C., more sugars and tannins remain in the leaves of some plant species, resulting in increased production of anthocyanin and intense orange in some trees and deep reds and purples in some of our underbrush, such as saskatoon, dogwood and gooseberry bushes.
But this year, after a long, late summer and early fall hot spell, suddenly the nights got too cool, with hard, killing frosts.
The natural process never got started before the leaves were killed by being frozen solid. Thus, the nutrients never retreated nor the chlorophyll fade; most of the leaves remain dull, dead green or dusty brown. The odd showy exceptions are genetic oddities in which the process starts earlier than in the majority of a species.
Another mechanism activates in our deciduous and many of our “needled” trees about the time of nutrient retreat and cessation of production of chlorophyll, when a hormone, abscisin, aids in the production by the plant of a layer of corky tissue at the base of the petiole, the leaf stalk of most deciduous trees.
This layer of tissue has a very high proportion of spongy parenchyma cells, and thus contributes to the weakening of the joint between the petiole and the branch.
In normal years the weight of the leaf itself is sufficient eventually to bring the leaf down, but the extra weight of rain or the pressure of wind can hasten the “fall”.
But that process, too, never got started this year, and the joint between leaf and branch remains so strong that several recent high winds have failed to shake many leaves loose.
The dull, drab leaves hang on and on while, in the vintage, high colour autumns, they drop too soon. Leaves hanging late on trees give rise to all manner of dire predictions, not the least of which is broken down trunks and limbs from the weight of wet snows clinging to the leaves.
The best, leaf colour this fall is provided by the tamaracks of our high country or the low country in the swamps of our boreal forests. The tamarack is not an evergreen, but actually a deciduous tree, the only native coniferous tree to shed all its needles in autumn.
My observations over the years show that the natural fall process starts considerably later in the tamaracks than in the aspens, for example. I suspect that somehow those early killing frosts did not stop the natural fall process in the tamaracks before it got started, and there are swamps in the West Country that will take your breath away with the gold glow of the tamaracks made even more brilliant by the counterpoint of green evergreens and this fall’s drab aspens.
So, rather than creating the magic of fall colours in any year, too much of little Jack Frost, in a year like this, has completely stopped the natural process that really conjures up that magic in most years. Is that Bing Crosby I hear in the background, crooning Little Jack Frost, Get Lost, Get Lost . . . ?
Bob Scammell is an award-winning outdoors writer living in Red Deer.