Year Without a Winter?

No, of course not. Do not suggest anything like that to Alaskans, or Europeans where hundreds have died, or Inner Mongolians, or Koreans. But, turning the clock back to December and January for the New York City region, it was not apparent that winter would arrive as it ‘normally’ does. Yes, we have had significant snowfall events. While snow in late October is not unusual, Dr. Jeff Masters had to go back to the 1804 snow hurricane to find something similar (BTW, I love the word I learned in Vermont for these events: snow’icane). And, the late January snowstorm was significant, but honestly, I did not bother to shovel. Temperatures were expected to hit the 50’s F two days later. The Sun and warmth rescued my back and melted that snow away in just a couple of days.

And, that is the thing about winter this year in the eastern US: when living with the weather and not the calendar, all the signs of spring were present in December and January. Plants were starting to bud, especially in the Deep South, and there was a warm, wetness in the air more typical of March. We opened windows in late December and early January to exchange the air in our house, which is a spring ritual for me. It has been a freakish winter – it snowed in Libya and a colleague cut a Skype session short with me because of heavy snow in Istanbul. A multitude of temperature records were broken from late December through January (including 875 record highs between late-December and January 6th, 2012). Historical climatologist, Dr. Cary Mock of the University of South Carolina, compared this winter’s warmth to the winter of 1827-1828. There was a rare tropical disturbance in early February 2012. Syracuse basketball fans tailgated prior to a late January game and Oswego, NY, at the leading edge of the Lake Ontario lake effect snowbelt, had to use ‘saved snow’ for its snow festival. I saw some red maple trees in bloom on February 5th. This species typically blooms in mid to late March in the lower Hudson Valley.

All of this gave me pause to wonder if this wasn’t an abstract picture of the future. If so, what would this mean for the trees and forests? While many folks were concerned with the exposed blooms and buds, the potential for real damage of a mild winter is actually hidden away from our senses.

The potential threat to most trees this winter in eastern North America is the one aspect of winter many people are relieved to be without: snow. Snow is important to ecosystem function. Perhaps the most temperature sensitive part of a tree is its root system. Snow is a great insulator for the ‘feet’ of trees.

A study conducted in the White Mountains of New Hampshire found that the lack of snow significantly increased the overwinter mortality of the fine roots of trees. A couple of things amazed me about this study. First, that they had enough money to pay people to shovel snow all winter in the middle of the woods. I imagine some of the conversations during the hiring process went something like this, “For reals?” or “hahahah…what? For reals?” or “I got the job? What do I have to do again? Um thanks, but no thanks.” Second, the years during which this study was conducted were not that cold. The elevated mortality during a warm winter (temperatures were generally around the freezing temperature) made me wonder what would happen during a cold, snowless winter.

I am aware of this study because I was pondering some of my own fresh research at the time the snow & fine roots study was being published. I had created a network of six southern tree species distributed throughout much of the Hudson Valley. Based upon prior work by Ed Cook, Paul Krusic and others, I expected populations of trees at the northern end of the study region, trees closer to their northern range margin, to be more sensitive to winter temperatures. I found the opposite and wasn’t sure what to make of the findings until seeing a lecture about the White Mountain Study. I could only conclude that the regular and persistent snow pack in the northern Hudson Valley made trees less sensitive to winter temperatures than trees closer to New York City and the southern Hudson Valley.

This year’s snow drought and the oncoming cold front could trigger significant damage in living trees. Research by Dr. Colin Beier indicates that yellow-cedar is particularly susceptible to decline in the Pacific Northwest due to a lack of snow and freeze-thaw cycles. Subsequent independent research supports this concept.

And, do you like real maple syrup? Research indicates that sugar maple seems to benefit more from increased snowfall than eastern hemlock of beech. This might not be a good year for maple syrup, eh?

Because we are talking about ecology, however, not all the impacts will be doom and gloom. Nature adapts. Some species in certain areas will likely benefit from warming winters. Almost all of the radial growth of the six species I studied would benefit from warmer temperatures. Like the loblolly pine study mentioned above, conifers will likely benefit more as they as more sensitive to winter temperatures. When the temperature is above freezing, conifers can take advantage of sunlight and conduct low levels of photosynthesis. Over the course of a mild winter, this can result in extra energy for the coming growing season. I suspect that trees in regions with shallow and ephemeral snowpacks will benefit from warmer winters as well since they most likely deal with substantial fine root mortality every year. Warmer temperatures for trees in these regions will likely be a relief to their annual winter stress.

It is truly hard to know exactly what will happen as our winters change. Winter ecology is complex and might not be as well studied as that of other seasons (although there is a textbook on this topic). For now, I am enjoying the unseasonably warm days while my mind quietly ponders if we are seeing an example of the future today.