Summing the Seasons of 2005

AMC's mountain tree leaf monitoring results are summarized in the graph below.  Our goal is to document the development of deciduous tree leaves each year from spring bud burst and leaf out on through fall color change and leaf drop.  We will simultaneously monitor temperature and other weather variables to relate climate trends to tree activities year after year.  This is the study of plant phenology. This graph shows average tree development observations at each of our monitoring sites through the season.  As data accumulates in the coming years we will report seasonal patterns for each tree species at our sites.

		Learn More    click on links below
		Interactive tree leaf-out animation! What makes leaves change color? How plants prepare for winter. Kids and Teachers - Check out this Spring and Fall Happenings web site for fun activities related to seasonal changes. Many of the activities can be done in New England.

AMC Naturalists and citizen volunteers are tracking spring bud burst and fall color change and leaf drop at roadside and AMC hut facilities throughout the White Mountain National Forest.

Check back in the spring of 2006 to get involved!

Leaf Color Change and Drop in the Fall

Leaves contain a light sensitive pigment called phytochrome. Phytochrome molecules have two forms; when there is sunlight all the molecules exist in one form. With cooler temperatures and nightfall, the molecules one by one, turn to the “dark” form. Once the “dark” form reaches a certain concentration, it signals a new phase for the plant. No more new leaves are produced, the lengthening of twigs stops. The plant diverts energy to making winter buds. An abscission layer forms at the base of the leaf or petiole. Sun-trapping green chlorophyll is no longer replaced as it is wears out or breaks down. As the existing chlorophyll in the leaves breaks down, pigments from other, more stable, chemicals in the leaves begin to be unmasked. Carotin and xanthophyll, present in most of our trees, are yellow to orange in color. The proteins and sugars are transported to the roots of the plant. The abscission layer deteriorates and the leaf falls from the twig.

Plants preparing for winter

Freezing temperatures are a certainty that all plants in the temperate zones must face each year. Perennial plants, including trees, must have some sort of protection to survive freezing temperatures and other harsh wintertime influences. Stems, twigs, and buds are equipped to survive extreme cold so that they can reawaken when spring heralds the start of another growing season. Tender leaf tissues, however would freeze in winter, so plants either protect their leaves or dispose of them. Evergreen needles are able to survive winter because of adaptations. Their scale-like foliage is covered with a heavy wax coating and the fluid inside their cells contains substances that resist freezing. Thus the foliage of evergreens can safely withstand all but the severest winter conditions, such as those in the Arctic. Evergreen needles survive for some years but eventually fall because of old age. The leaves of broadleaf plants, on the other hand, are tender and vulnerable to damage. These leaves are typically broad and thin and are not protected by any thick coverings. The fluid in cells of these leaves is usually a thin, watery sap that freezes readily. This means that the cells could not survive winter where temperatures fall below freezing. Tissues unable to overwinter must be sealed off and shed to ensure the plant’s continued survival. Thus leaf fall precedes each winter in the temperate zones.