A dose of real winter weather has finally blessed Wintergreen. Single digit temperatures following a blanketing of powdery snow reminds us that winter does exist. While we worry about frozen pipes and heat pumps being frozen, the environment at Wintergreen suffers effects of this polar vortex descending onto the Blue Ridge mountains. This edition of the Nine Minute Naturalist will delve into the consequences that come with severe cold temperatures.

Rhododendron

The most obvious environmental effects of severe cold come from the plant community. Many of these effects can be seen from the comfort of our sofa or gazing out our kitchen windows. I get the opportunity to see plants adjusting to cold weather every morning. Just outside my kitchen window are two large rhododendron bushes. This evergreen can communicate the temperature outside by the shape of its leaves. Rhododendron’s reaction to dropping temperatures is an example of thermotropism, a movement of an organism or part of an organism in response to temperature changes. At 32f, the leaves begin to drupe. At 25f, the drooping leaves begin to curl inward. At 20f, the leaves tightly curl and will officially freeze at 18 degrees. This tight curling protects against rapid rewarming that can damage the cells. This adjustment is consistent with how native plants are adjusted to their climate zones. Rarely will cold weather have long term lasting effects on native plants. Geographic ranges are determined by temperature extremes, not averages. Damage to native plants comes when other factors or stresses make them predisposed to cold weather injury such as shallow soils or insufficient duff layer. Thin barked species such as red maple, apple, birch and cherry are also susceptible to frost cracking. This problem is also known as southwest injury because the cracks often develop on the south or southwest side of the tree. Afternoon sun can warm the phloem and cambial areas causing living cells to become active. If the temperature suddenly drops, the newly active cells can die resulting in a discoloration and vertical cracks.

Non-native plants in our landscape suffer cold weather injury much more frequently than our native species. They most common effect of drastic cold snaps are the killing of flower buds. Generally speaking, flower buds are less hardy than leaf buds. Plants such as forsythia are prone to flower bud kills once we approach the 15f mark. Commonly planted species such as boxwood and Leyland cypress are quick to show the signs of frost damage once the temperatures creep below the 20-degree threshold. These injuries appear as brown or bleached leaves. The best ways to ensure our landscapes at Wintergreen do not suffer winters ill affects is to plant native species and to follow hardiness zones. Here is a link to the USDA hardiness zone map for Virginia: https://efotg.sc.egov.usda.gov/references/public/va/PlantHardiness.pdf.

Junco

When the artic air arrives at Wintergreen, our wildlife has adapted wonderful ways to survive. The most obvious manner to deal with a polar vortex in Virginia is to not be here. Like our human residents that flee south before the cold arrives, large migrations south of birds and bats have predated our current winter cold. Torpor is another excellent strategy to ensure you do not even notice the weather has changed. Many mammals use torpor or hibernation to avoid having to suffer from arctic air blasts. Black bear, groundhogs, chipmunks, and some bats go dormant in warmer insulated spaces. Those left behind have interesting ways to deal with extreme cold. The most fun to look at is the fluff technique. Juncos are a very common year-round resident that just goes about his daily business in a more “fluffy” manner. Birds can manipulate their feathers to rise and allow air pockets to get trapped and help insulate the body. Mammals can also raise the hairs with muscles around the follicle trapping air and keeping them a bit warmer. Many of our mammals have a soft undercoat as well as a thicker overcoat. The undercoat grows thicker in winter in a process triggered by daylength. White-tailed deer have a recognizable difference from summer to winter and effectively insulate even when covered in snow. Once the day length continues to grow, deer shed their unneeded undercoat to allow for the warmth of spring and summer.

Another part of our environment dealing with the consequences of cold are the insects. The vast majority of insects practice freeze avoidance. The mass of Asian ladybugs and brown marmorated stinkbugs piling into your house is freeze avoidance in action. Some insects do not need to seek warm locations and can just prep their bodies to withstand sub-zero temperatures. Freeze tolerant invertebrates can survive being frozen solid. Other species use a special “anti-freeze” to stop themselves from freezing. These techniques make insects some of the most adapted species on the planet.

Just like humans living at Wintergreen that must worry about frozen pipes, there are consequences for severe cold weather at Wintergreen. Plants will suffer freeze cracks, animals and insects will die but the vast majority will tolerate artic air magnificently. Take a moment to find a fluffy junco or the curled leaves of rhododendron next time your thermostat reaches single digits.