How does climate change affect fallen leaves?
Autumn foliage around the Lamont-Doherty Earth Observatory as photographed by PhenoCam on November 2, 2021
While fall officially begins on September 22, the trees around New York’s Palisades don’t seem to know it yet.at Columbia Climate School Lamont-Doherty Earth ObservatoryA camera is located on the roof Monitor nearby treetops annual.look at it live Indicates that the forest is still covered in green. Pheno
Mukund Raois a postdoctoral research scientist at Lamont who helped install cameras in 2020 to study how trees change with the seasons and climate. We caught up with Rao to find out what he’s learned from PhenoCam over the past few years and how climate change is affecting fall foliage.
behind
PhenoCam observations show that local leaves are starting to change color a few days later 2021 is better than 2020. This is in line with what scientists expected as the climate warms.
The time it takes for the leaves to change from green to a colorful mix depends on two factors: temperature and light.
Cold temperatures tell the tree that it’s time to close for the winter. It stops making chlorophyll, the substance that turns leaves green, so other potential pigments — such as red, yellow and orange — finally have a chance to glow.
Because 2021 is slightly warmer than the year before, Rao believes, the trees don’t receive the signal until later to stop making chlorophyll, so the leaves stay green longer.
Technically speaking: During the summer, trees are constantly making new chlorophyll to replace the decomposed chlorophyll and keep it at a higher level. In autumn, plants stop replacing broken down chlorophyll.
shorter season
Another trend discovered by PhenoCam, and another trend observed by other scientists, is that leaves take less and less time to become bright and colorful and then fall.
“Earlier, the peak of fall color might have lasted a week and a half, and now it’s condensing into shorter and shorter periods,” Rao said. He estimates it will take about 11 minutes for trees to go from brilliant to leafless by 2020. days; in 2021, the transition period appears to be closer to 9 days. However, he noted that there are many differences between individual trees.
Scientists aren’t sure why the colored phases are getting shorter, but Rao offers a possible explanation. In the fall and winter, lower levels of sunlight mean the tree wastes energy making chlorophyll and maintaining leaves which isn’t very beneficial — so it drops them. Warmer temperatures may delay the onset of color change, but since light levels don’t change from year to year, trees lose their leaves at about the same time each year. The time in between is shortened due to the warmer temperatures.
color quality
Stressed trees will not produce as vibrant fall foliage as healthy trees.
In dry years, for example, “fall foliage colors are less vibrant than in wet years, the trees are able to produce a lot of sugar, and they have a good growing season, and they’re very happy.”
Drought can also cause trees to lose their leaves earlier in the season and skip the colorful stage entirely, turning directly to brown before rapidly shedding.
As the planet continues to warm, dry regions are expected to get drier, while wet regions receive more precipitation. In addition to raising concerns about agriculture and water supply, these trends could affect the beauty of fall foliage.
Peak forecast
Combining these weather and climate factors with PhenoCam’s observations, Rao predicts that the peak red leaf fall around Palisades, New York, will occur between October 25 and 30, with fall foliage falling by November 10.
But leaf lovers might not want to get their hopes up—Rao said the leaves may not be very bright this fall due to the summer heatwave and local drought.
