How Do Plants Survive In Winter?
You've probably noticed that some animals in our area, like hummingbirds, fly south for the winter. And many animals, like groundhogs hibernate, or sleep, during the winter months. Why? Their food source, flowers and fresh green leaves, aren't available any more. All plants depend on sunlight and water to grow. But during the winter months the shortened day provides less sunlight and freezing temperatures means water is frozen and inaccessible. Freezing temperatures also rupture plant cells. So what's a plant to do?
First, as the days shorten and the cold sets in, many plants become “hardened”. Water is pumped out of plant cells into the roots and any remaining sap, which is a sugary solution, often acts as antifreeze. Broadleaf trees, like maples and oaks, shed their thin, flat leaves each fall to reduce water loss. Evergreen trees and shrubs have waxy, needle-like leaves (pine, spruce, fir) or tough, broad waxy leaves (holly, magnolia) that are more resistant to the cold and moisture loss. Plants can also modify their life cycles, or rate of growth, to deal with the changing seasons and lack of moisture.
Some types of plants only survive for one growing season, dying back at the end of the summer or early fall. But they make lots of seeds that will sprout the next year. These plants are called annuals. If you purchased pansies or marigolds for your garden last summer they are examples of annuals. The whole plant, roots, stems, and leaves die but the seeds endure. In order to germinate next spring, many seeds require a period of cold weather which our area certainly supplies.
Another strategy is to produce low lying leaves that are less susceptible to freezing temperatures – many of these plants are biennials, growing for only two seasons. One local but non-native biennial, Burdock, grows in a circle, or rosette, of low lying leaves its first year. The next growing season the plant sends up long stalks with flowers that turn into the prickly burs (seeds). These burs, which stick to clothes or fur, are carried by unsuspecting wildlife, dogs and people to new places and begin their two-year cycle again the next year.
Other plants, like trees and shrubs, become dormant, or rest in the winter. Tree and shrubs, along with herbaceous (soft-stemmed) plants live for two years or more and are referred to as perennials. They store their food, or sap, in their roots as mentioned above. All of the wildflowers that appear each spring are herbaceous perennials, living off the food stored in their roots so they can sprout again next spring. Poison ivy also belongs in this group but has a woody stem that can be seen in winter, often climbing a tree as a vine or growing on the ground.
We have the change of the seasons to thank for a delicious and familiar tree product – maple syrup. At the end of the winter and beginning of spring, sap starts rising up the tree's trunk to its branches. This sap, the tree's food, provides nourishment for the tree's new leaves, tucked inside a leaf bud, ready to unfurl. On warm sunny days the sap starts its upward journey. Cold, chilly nights slows or temporarily stops the progress of the sap's rise. When you drill a hole in any kind of tree this time of year the sap will drip out. But Sugar Maples have the highest sugar content (2%-3%) and their sap is used to make maple syrup, and sometimes taffy-like candy or granular sugar. Once the sap reaches the leaf buds the taste of the sap, and resulting syrup, changes and is not considered tasty anymore. The “window” for collecting maple sap is short and the process to create syrup is lengthy. Making syrup requires hours of boiling the sap to concentrate the sugar; forty gallons of sap makes only one gallon of syrup. This explains why the cost for 100% pure maple syrup is so high.
Just like animals, plants have developed ingenious ways to adapt to our cold winters. From tiny aquatic plants, called phytoplankton, to towering trees on land, plants are the basis of all food chains, including our own, and essential to life on Earth. To learn more about plant adaptations visit http://www.mbgnet.net/bioplants/adapt.html.
