What do leaves have to do with the seasons? Most people mark the
coming of winter by the trees becomingbare and leaves littering
the ground. The trees themselves, however, begin their winter
preparations long before we do. eciduous trees, those that shed
their leaves, begin to undergo physiological changes as early as
mid-summer, a process known as acclimation. How do trees ‘know’
when to begin preparing for winter? The primary factor involved
is day length. As the nights begin to get longer, growth
inhibiting hormones like abscicic acid build to high levels into
the fall. While the amount of light is the most important factor
for dormancy, it is thought that cool temperatures may be
required to initiate true dormancy. The dormancy period for most
deciduous trees begins in October and ends in March. Dormancy
can be seen in other ways besides the loss of leaves. During the
acclimation period, trees initiate bud dormancy. A dormant bud
consists of an undeveloped shoot and rudimentary leaves, all
enclosed by str