There is evidence that some tree species in the eastern U.S. Without fires recurring once or twice a decade, these species fail to regenerate and ultimately decline, allowing more shade-tolerant, fire-sensitive trees like red maple to invade. This shift began in the 1930s, when federal agencies adopted policies that called for suppressing all wildfires quickly rather than letting some burn. They also produce intense red and yellow displays in the fall. These trees are shade-tolerant and typically grow in conditions that are neither extremely wet nor extremely dry. Notably, eastern forests today have more species such as red maple, black birch, tulip poplar and blackgum than they did in the early 20th century. has changed dramatically over the past century. The types of tree species in a forest are an even bigger factor, and forest composition in the eastern U.S. A changing mix of treesĬlimate isn’t the only thing that affects fall colors. A longer growing season may mean that fall colors emerge later – and it can also make those colors duller. The leaves also produce a third pigment, anthocyanin, which creates red colors. This allows carotenoid (orange) and xanthophyll (yellow) pigments in the leaves to emerge. The trees stop producing chlorophyll, the green pigment in their leaves, which absorbs energy from sunlight. Scientists in western states have even noted this acceleration in bristlecone pines that are over 4,000 years old – the oldest trees in the world.įall colors emerge when the growing season ends and trees stop photosynthesizing. That’s remarkable because old trees’ growth should be slowing down, not speeding up.
This effect is particularly evident in young trees, but we see it in old trees as well. Temperature often limits trees’ growth in cool and cold regions, so the trees usually benefit from slight warming. That’s not surprising given the subtle variations in climate across much of the eastern U.S. have fared quite well in a changing climate. My research in tree physiology and dendrochronology – dating and interpreting past events based on trees’ growth rings – shows that in general, trees in the eastern U.S. In the West, which is becoming both warmer and drier, climate change is having greater physiological effects on trees. This increase in precipitation fuels tree growth and tends to offset stress on the trees from rising temperatures. Since 1980, average temperatures in the Northeast have increased by 0.66 degrees Fahrenheit (0.37 Celsius), andĪverage annual precipitation has increased by 3.4 inches (8.6 centimeters) – about 8%. Longer growing seasonsĬlimate change is clearly making the Northeast warmer and wetter.
But climate change isn’t the only factor at work, and in some areas, human decisions about forest management are the biggest influences. And the persistence of very warm, wet weather in 2021 is reducing color displays in the Northeast and mid-Atlantic. What’s clearest so far is that color changes are occurring later in the season. It’s especially important in the Northeast, where fall colors attract an estimated US$8 billion in tourism revenues to New England every year.Īs a forestry scientist, I’m often asked how climate change is affecting fall foliage displays. Fall foliage season is a calendar highlight in states from Maine south to Georgia and west to the Rocky Mountains.