Every fall as the weather gets colder, students begin to settle in for a new year as the leaves begin to turn colors. This is no surprise to natives of New Hampshire, as it is a well- known fact that the northern regions of the state (especially those higher in elevation like the White Mountains) begin changing color in September or even late August. Some folks may have been disappointed last year by the mostly brown leaves. Why did this happen and what is in store for this year?
To answer that question, one must first understand why leaves change colors. During the growing season the leaves are green because of the pigment chlorophyll, which is an important substance in producing food for the tree. Leaves have other pigment colors, but while the tree is producing food, only chlorophyll is the visible.
Approximately two weeks before the leaves start to change, a layer of cells grow at the end of each leaf stem and slowly cuts the leaf off from the tree’s supply of water and nutrients. This causes the flow of nutrients to reverse and instead of the tree supplying the leaves with nutrients, the leaves gives back the nutrients for storage over the winter. As a result, the chlorophyll is no longer renewed and the other leaf pigments become visible. The pigment carotenes produces yellow colors, xanthophylls produces orange, and anthocyanin produce red colors. The colors of the tree depend on what amount of each pigment is present in the leaves. Birches are typically yellow, while maples are often red or orange. “The ideal is to have warm days and cool nights preceding the peak in foliage,” said Dr. Bryon Middlekauff, professor of geography and environmental planning at Plymouth State University. According to Middlekauff, there are several key factors to producing vivid fall foliage. Two of the most important factors are temperature and precipitation. Droughts can cause the leaves to fall early while warm, rainy periods preceding the peak in color make the foliage less vibrant. Early frost causes colors to be more subdued and turn brown faster. Length of daylight also plays a big roll in the changing of the leaves. When the days grow shorter and less sunlight reaches the trees, they begin to turn. This is why even if it remains warm in late August and September the leaves will still change. Last summer the foliage was disappointing to many because the weather was warm and rainy.
This year, the days have been warm and the nights cool. Middlekauff stated, “I think it is going to be an intermediate year compared with other years.” He went on to explain that because of these better conditions, the foliage will still be good despite the rainy summer New Hamphsire experienced.
According to the Weekly Foliage Report from VisitNH.gov, the trees in White Mountains are already “well established in color.” As of September 21, the leaves were about 50-60% turned. On September 25, a new report indicated that the leaves are turning quickly. These regions include Kancamagus Highway, Franconia Notch and the woods around Twin and Jefferson Mountains.
In Plymouth, the leaves are turning slowly. Middlekauff said, “Around here they usually peak around Columbus Day weekend and then it rains a day or two and they’re gone.” After peak, the leaves fall quickly because the tree has nearly completely severed the link with its leaves.