“In short, for 2020 we can’t expect an extra bright, full-color display everywhere and there might be a less dramatic color peak, unless we get a stretch of sunny days and cold nights in late September and early- to mid-October,” said Collins, who combines her knowledge of forest ecology with observations of weather trends to assess the potential for vibrant leaf colors.
She explained the means behind the methods of her prediction, while acknowledging that, as with any forecast, there are margins for variations. “As we know, local light and temperature conditions vary widely in the mountains over elevation, slope exposure and vegetation type, and there certainly will be areas where colors are brighter or arrive earlier or later,” Collins said. “Sites that typically ‘turn earlier’ are likely to do so again, and colors will progress down the mountain and north to south as they have done in the past.”
Collins said predicted weather patterns can affect fall colors in two ways: First, fall colors may be subdued because there is little stress or cold temperatures to promote abundant yellow, orange and, especially, red pigments. Second, the colors may be spread out or lag over the season and landscape.
“The warm, rainy summer caused little drought or ‘hot sunny day’ stress and promoted a lush, full, green leaf canopy,” Collins said. “This is true even in some species we don’t want around. For example, kudzu seems to be overtaking road signs and covering trees at a faster clip than in years past. The long-term forecast for September and October is for warmer than average temperatures and average precipitation through October; low temperatures around Cullowhee are not predicted to reach the 30s until the last week of October. This suggests our summer weather pattern might hang around longer than normal.”
Collins explained that fall colors are a mixture of yellow, orange and red pigments that are revealed as photosynthesis and chlorophyll production wind down and ultimately stop when the weather turn colder. These pigments – especially the yellow and orange pigments – play a role in photosynthesis and help protect the plant from stresses; for example, when there is drought, when it’s bright and hot, or under high UV conditions. The pigments are always there in the leaf, but may be relatively less abundant when conditions are wet and warm. The red pigments, called anthocyanins, are also produced more in fall when the weather turns cool.