Is This What We Call Winter?

I n praise of deep snow and cold temperatures

By Dave Anderson

Perhaps you’ve just come inside from shoveling, snow blowing, or sledding? I hope so because until late Januar y, most of New Hampshire still awaited a significant first snowfall Remember? Daily high temperatures remained in the 30s and even 40s during December and Januar y Temperatures spiked into the 60s in November! Regression to average should finally deliver the heavy snow we expect As the temperatures yo-yo, it leaves me thinking about our forests and wildlife and how they might respond to this weather that’s far from normal

Weird Weather

Erratic winter temperature fluctuations impact precipitation and snowpack. Meteorologists coined the term “winter weather whiplash” for the succession of low pressure accompanied by warming temperatures, wind, and rain with marginally frozen precipitation. Rain events are followed by high pressure, colder temperatures, and a hard re-freeze, which create an ice-encrusted snowpack. It’s a whiplash effect that leaves humans and wildlife reeling

Beyond impacts to winter recreation and economic tourism, changing weather patterns can affect trees and wildlife best adapted to cold temperatures and deep snow

Wildlife Woes

In response to shorter day length in autumn, hormonal changes cause snowshoe hares and short-tailed weasels to turn white in winter to better blend into a snowy forest floor. Without snow, these northern species are more visible and more vulnerable to predators.

A deep snowpack provides thermal insulation and concealment for subnivian wildlife, including mice, voles, shrews, and red squirrels, which inhabit underthe-snow burrows linked by a maze of tunnels Bobcats, coyotes, foxes, and owls hunt these animals. Extremely deep snow makes it difficult for some predators to hunt while a low snow year can impact rodent populations Rain on frozen ground will flood rodent burrows drowning mice or driving them indoors. Freeze-thaw cycles form an impenetrable crust on top of the snow, and barred owls are impacted when this crust prevents them from reaching rodents beneath the top layer Foxes and coyotes may experience similar difficulties

The 2022 seed crop was spare with few acorns, beechnuts, and a meager wild apple crop Rodent populations were low following a mediocre mast crop in ‘21. The scarcity ripples across the oak forest food chain. As rodent populations bottom out, predators bobcats or Cooper’s hawks turn their attention to backyard mourning doves, turkeys and gray squirrels All things equal, lower predator birthrates should follow this year.

As for 2023 wildlife “winners,” a lack of snow and prolonged cold improves survival for New Hampshire’s overall deer herd as individual deer conserve heat calories and are spared the exertion of wading in deep snow Turkeys travel readily on bare winter ground and porcupines continue to graze frozen grass nightly in Januar y As for our resident predators coyotes, foxes, and bobcats they may find hunting easier and find available mates and dens more readily during their late Februar y and early March breeding seasons

According to University of Massachusetts Wildlife Biologist Jeff Boettner, whitefooted mice population densities can increase 100 times (from 2 mice to 200 mice per hectare) during winters following heavy acorn crops More mice, more ticks, and fewer spongy moth outbreaks you read that right! This is because during years when there are high densities of mice, these hungr y critters consume all the moth eggs and pupae on trees, particularly when no other foods are available, thus limiting moth reproduction rates. Conversely, fewer mice lowers tick populations and eventually lowers rates of Lyme disease and potentially allows future spongy moth caterpillar eruptions

What’s also interesting is that climaterelated wildlife range expansions may already be underway. Warmer winters are bringing new species of wildlife to the Granite State, including opossum, cardinals, and Carolina wrens. Facultative migrants animals that wander and are found all over their migration route now choose to overwinter in New Hampshire, including bluebirds and robins Wildlife at southern limits of their ranges may shift further north Moose, lynx, snowshoe hare, pine marten, purple finch, and spruce grouse are species adapted to snowy spruce and fir forests of northern New England and comprise a list of potentially departing species

Forest Health

Cold overnight low air temperatures in midwinter limit expansion of forest insect pests, including hemlock wooly adelgid Cold weather is important to forest health. It may be that deep snow is just as important Professors Andrew Reinmann of the City University of New York and Pamela Templer of Boston University are documenting how continued snow cover reduction across the Northeast is causing declines in tree growth and forest carbon storage. At the most basic level, snowpack on the forest floor provides critical insulation for tree roots. Where snow depth is sufficient, soil can remain unfrozen even in temperatures below zero However, Hubbard Brook Experimental Forest researchers documented recent snowpack declines and changes in soil freeze-thaw cycles This could have harmful effects on delicate feeder roots and soil microbes, from bacteria to insects, which require insulation provided by deep snow

In an article the duo published on Boston University’s website, they found “climate and hydrological models show that the area of forests across the northeastern United States that receives insulating midwinter snowpack could decline by 95 percent by the year 2100 Today, 33,000 square miles of forests across northern New York and New England typically have snowpack for several months in winter By the year 2100, this area could shrink to a patch smaller than 2,000 square miles about one-fifth the size of Vermont.”

A companion study of tree growth at Hubbard Brook suggests that sugar maple is a canar y in the coal mine. Researchers used increment borer cores to assess rates of growth of sugar maple stems of trees grown on control plots versus trees where the snowpack was manually removed from the forest floor. The findings “showed a 40 percent decline in sugar maple growth from plots without snowpack Growth rates remained depressed by 40 to 55 percent over the next three years By contrast, there was no growth decline in the sugar maple trees in reference plots where deep snow covered the trees’ roots in midwinter Sugar maples can account for more than half of the annual forest biomass accumulation at Hubbard Brook. Consequently, changes in climate that reduce winter snowpack and increase soil freezing could reduce forest growth rates in the northern hardwood forest region by 20 percent just through their impacts on these trees ” The results are comparable to other tree root mortality studies at Hubbard Brook where Cornell University researchers Geraldine Tierney and Timothy Fahey reported that an increase of soil freeze events alters fine root dynamics and disrupts nutrient uptake.

Above ground, researchers have noted changes in natural albedo, where the lightcolored high-albedo snow surface reflects more sun back to the atmosphere and lowalbedo surfaces, including dark soil and tree bark, absorb more sunlight More erratic cycles of thawing dark tree bark and underlying cambium tissues on warm sunny days and subsequent refreezing subject trees to a greater risk of frost cracking when bitter cold temperatures return events Changes in cold season snowmelt and the amount of winter precipitation falling as rain resulted in transportation of more dissolved and sediment-bound nitrogen and phosphorus that had accumulated in soils

Warming Winters

The 2021 N H Climate Assessment Report states that winter average temperatures are expected to increase an additional 10°F and will lead to earlier snowpack melt by the year 2100

Rain On Snow

Episodes of winter rain runoff from bare frozen ground leads to flooding in small “flashy” watersheds at high landscape positions. Rain on snow is a relatively new phenomenon Historically, winter precipitation arrived gradually and persisted as a long-lasting snowpack gradually released during spring snowmelt in March or April Dormant trees cannot take up and transpire soil moisture back to the atmosphere, and saturated soils freeze and don’t absorb heavy winter water runoff. When meltwater re-freezes in upper soil layers, it creates an impermeable layer of frozen soil, which prevents absorption of water during subsequent rain events and exacerbates future flooding concerns.

Where ice or snowbanks block heavy rain runoff from reaching culverts and drainage features, forest roads, driveways, and local roads are at risk of damage The blocked culverts re-freeze when cold temperatures return

Winter runoff and sediment loads transmit large amounts of dissolved nitrogen and phosphorus formerly bound in soil beneath a stable snowpack. A study led by researchers from the University of Vermont, University of Colorado, University of Kansas, and University of Michigan found climate change poses a significant risk to water resources in New England. The study reported climate change has increased the frequency of rain-on-snow

Climate Central, a nonprofit research organization, released a report that analyzed temperature data from 238 sites across the U.S. to measure how much winters warmed since 1970 At 232 sites (97 percent of those studied), average winter temperatures increased during the past 50 years Two of the top five cities that experienced the largest increase in winter temperatures were in New England: Burlington, Vt (7 1°F), and Concord, N H (6°F).The report showed that winter is the fastest warming season for 75 percent of the locations and warmed more than two degrees Fahrenheit or more in 87 percent of the locations studied

Beyond economic impacts to New Hampshire’s traditional winter tourism economy, largely hidden ecological impacts of erratic fluctuations and warmer temperatures bringing rain are shrinking the traditional five-month winter weather window It’s also true that warm air holds more moisture potentially enabling heavier snow events if it remains cold enough for snow If heavy snow and more consistent cold temperatures return for the second half of winter, appreciating their importance to wildlife and forests makes the weather easier to take.

This winter, outdoor recreation fans and lovers of forests and wildlife grew alarmed by the paltr y snowfall depth at half time. Yet in the third quarter, “team winter” is likely to attempt a comeback. I hope it does