Humans as a species originated in a warm climate; we’re not very well adapted to cold. That tends to make us welcome warmer winter weather. But when temperatures turn frigid, it’s good to remember that, for species and environments adapted to northern regions, cold weather is necessary.
Most gardeners are familiar with one way in which cold is crucial—it breaks seed dormancy. To encourage seeds of some plant species to germinate, gardeners simulate winter through a process called stratification, storing seeds at cold temperatures for several months before planting.
Nature accomplishes stratification naturally via winter. In some northern plant species, seeds are dormant and won’t germinate when they contact soil in autumn. They need an extended cold, moist period to overcome dormancy. Winter exposes seeds to months of cold before spring comes; seeds germinate when weather warms. Many native plants, including Virginia bluebells and Phlox; and herbs, such as lavender and catnip, require cold periods for their seeds to germinate.
Winter cold also helps keep plant-eating insects in check. When winters don’t reach and sustain cold temperatures for long enough, pests of gardens, crops and natural environments can proliferate. Warming climate is responsible for burgeoning numbers of Japanese beetles, which damage our turf grass and garden plants.
But the ongoing die-off of whitebark pine trees in Yellowstone National Park is one of the most serious examples of what can happen without sufficient cold.
Like many places, Yellowstone has had fewer and shorter cold snaps in recent decades. As a result, mountain pine beetles are surviving at elevations once too cold for them. Whitebark pine trees become infested with beetles, lose their needles and die. Some trees that have survived for nearly 1,000 years now are dying because of beetle invasion.
Increasing pine beetle numbers have set in motion a cascade of deadly dominoes, threatening the whole ecosystem, including grizzly bears. Female grizzlies that have plentiful whitebark pine nuts on which to feed are fatter and healthier during hibernation. They also give birth to healthier cubs. But more beetles have lead to swathes of dead pines, fewer pine nuts, and poorer physical condition in grizzlies—adversely affecting reproduction and survival.
In many ways, cold is important to the ecology of northern environments. Milder winters may feel more comfortable, but they have more-than-uncomfortable consequences.