Deep supercooling is a way to keep a liquid in a liquid state
well below its freezing point. To do this, these plants produce
a special protein to prevent freezing. These are conveniently
known as "antifreeze proteins" or AFPs, and they are pumped
into the spaces between the cells during the fall acclimation
period. AFPs work not by lowering the freezing point, but by
inhibiting the re-formation of ice crystals. They also function
at very low concentrations, which means they do not have the
same issues related to increasing the osmotic pressure as other
methods. Deep supercooling also has its range limits, but will
allow trees such as oak, elm, maple, beech, ash, walnut, hickory,
rose, rhododendron, apple, pear and stone fruits to survive
temps down around negative 40 degrees Fahrenheit. Although
that number seems ridiculously cold to our tropical-loving
bodies, that is still only about half as cold as the Dahurian
larch can endure.
Trees such as paper birch, redtwig dogwood, willow,
quaking aspen, and, of course, the Duhurian larch survive the
damaging crystallization effects of freezing water by trying
to rid themselves of as much water as possible. Rather than
pumping more items into their cells, these plants spend the
autumn pumping the water out of their cells. The water still
freezes, but the crystallization occurs in the cytoplasm within
the intercellular spaces, which has much less damage potential
than freezing inside the cell membranes. Additionally,
removing water from the cell increases the concentration
gradient of solutes within the cell, which, in turn, lowers the
freezing point of the cell, similar to the mechanisms mentioned
earlier. The species that can best perform these tasks are those
that are considered the most cold hardy and come with the
reward of being able to thrive in areas unsuitable for most
other living things.
Even the most cold-hardy species will suffer damage from the
cold if they do not acclimate to it properly. Even though water is
the most damaging thing plants confront once the temps drop,
it is vital to their preparation. Keeping trees well watered up
until the ground freezes is one of the best ways to help them
survive the coming winter. Given the proper care in autumn,
and if the temps do not drop below a tree's minimum comfort
range, they should be able to resume activity in the spring. If
only surviving the winter was as easy for us humans.
Brandon M. Gallagher Watson is creative director at Rainbow
Treecare Scientific Advancements, and is an ISA Certified Arborist
(#MN-4086A).
Water trees even after leaf drop for better hardiness.
Hardy trees withstand freezing temps for months.
28 January/February 2016 Landscape and Irrigation www.landscapeirrigation.com
TREE CARE
LI
"Even the most cold-hardy species will
suffer damage from the cold if they
do not acclimate to it properly."