Spring: The Wait n’ Season
Spring is the season when Cape Bretoners go into “Wait and See” mode. Little-league lads ask their dads when spring will come, and they’re told, “Wait and see, son.” We wait for the snow to disappear, and once it’s gone, we wait for that inevitable, final 15-cm dump to come and go. Then we wait for the ground to thaw and turn muddy. We wait for the drift ice to disappear. Then we wait for the air and water to warm up. And finally, once all of these things have happened, we see signs of spring! We see the budding and greening that folks elsewhere have been enjoying for weeks.
Long suffering readers of this column know that “seasonal temperature lag” is the culprit causing all our waiting. It takes a long time, and a whale of a lot of energy, to warm Cape Breton’s surrounding waters each spring. As a result, air temperatures tend to rise sluggishly during the spring (and cool slowly in autumn).
The satellite image shown here illustrates another factor that delays our spring warmup. As ice clears the Gulf of St. Lawrence in April, westerly winds commonly pack it against Cape Breton, providing us with an extra degree of refrigeration. The ice embracing Cape Breton that day (shown in red) was almost the only ice in the entire Gulf.
This spring’s warmup has run into an additional obstacle: a persistent large-scale pattern of air pressure and wind, which has kept spring temperatures down and April snow cover up. So... we wait.
Cape Breton’s plant life is waiting too, biding its time until conditions are right. Each autumn, woody plants go into what’s known as “predictive dormancy”. Sensing that nights are growing longer and temperatures are falling, trees “predict” that winter is coming. They drop their leaves and stop growing, well before the really cold weather sets in. They also form buds on the tips and sides of young shoots, to be ready at the first opportunity next spring. Then they shut down nearly all activity for the winter. Clearly, trees are excellent seasonal weather forecasters! And they have to be: if a tree misses the signs and doesn’t see winter coming, its punishment is nothing less than death!
Just as humans require sleep to function throughout the coming day, our trees need an extended period of dormancy each year. But even while dormant, they are not completely idle; they keep track of the weather in a most remarkable way! Trees count the number of “chill hours”, the hours when the air temperature is between 2 and 7 degrees C. Until a tree has logged a certain number of chill hours, typically in the range of 500 to 1,500, it remains “asleep”, even if jostled by a brief warm spell like the spike to nearly 20C we had this past January. This prevents the tree from beginning its spring growth during a prolonged winter thaw. A cutting brought inside from a tree in December won’t blossom because it won’t have accumulated enough chill hours to free itself from dormancy.
Once a tree has reached its required number of chill hours, it emerges from dormancy and it’s ready to go to work. However, it can’t begin right away; even though “awake”, it must remain quiet until it gets the signal to begin its annual growth. That signal, of course, is the arrival of spring’s warmer temperatures. Normally, the tree must wait around for a number of weeks after leaving dormancy before sensing that it’s warm enough to begin budding out.
During this past winter, Victoria County’s trees have logged over 800 chill hours. They have emerged from dormancy, and surely, they must be eager to grow again. But they’re waiting for warmer temperatures. Just like the rest of us.
NASA’S magnificent false-colour satellite image, taken at noon on April 12, shows drift ice (in red) wrapping around the Highlands. Snow is also depicted in red, bare ground in green, clouds in white and grey.