Spring: The Wait n’ Sea­son

The Victoria Standard - - Environment - BILL DANIELSON

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.

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